High SSB Research Articles

Sugar-sweetened beverage consumption among pregnant women attending general and teaching hospitals in Ibadan, Nigeria

BackgroundSugar-sweetened beverages (SSBs) have become a global health concern because of their adverse health effects and their association with the obesity pandemic. It has not received much attention in sub-Saharan Africa, including Nigeria, especially among pregnant women. The pattern, frequency and factors associated with SSBs among pregnant women in Ibadan, Nigeria, were investigated.DesignData were from the Ibadan Pregnancy Cohort Study - a prospective cohort study investigating 1745 pregnant women from four comprehensive obstetric facilities in Ibadan. A qualitative food frequency questionnaire (FFQ) was used to assess the pregnant women’s intake of food and drinks over the previous months. Sugar-sweetened beverage variable and scores were also generated using the principal component analysis with varimax rotation. Factors associated with high SSB scores were examined using multivariate logistics regression analyses at a 5% significance level.ResultsThe most commonly consumed SSBs were cocoa-sweetened beverages, soft drinks, malt drinks, and fruit juice. A quarter of the women (75th percentile) consumed SSB more than once weekly. The factors associated with high SSB on multivariate analysis were; being employed (AOR: 1.52, 95% CI 1.02–2.26), maternal obesity (AOR: 0.065, 95% CI 0.47–0.89), high fruit intake (AOR:3.62, 95% CI 2.62–4.99), high green vegetable consumption (AOR:1.99, 95% CI 1.06–3.74), high milk intake (AOR: 2.13, 95% CI 1.65– 2.74), frequent fast food outlet visit (AOR: 2.19, 95% CI 1.53–1.70), all of these remained significant after adjusting for confounding variables.ConclusionSSBs were common among our study population. Factors associated with high SSBs intake are crucial for implementing locally relevant public health interventions.

Consumption of sugar sweetened beverages, artificially sweetened beverages and fruit juices and risk of type 2 diabetes, hypertension, cardiovascular disease, and mortality: A meta-analysis.

Sugar-sweetened beverage (SSB) intake is associated with an increased risk of cardiometabolic diseases. However, evidence regarding associations of artificially sweetened beverages (ASBs) and fruit juices with cardiometabolic diseases is mixed. In this study, we aimed to investigate the association between the SSB, ASB and fruit juice consumption with the incidence of cardiometabolic conditions and mortality. Relevant prospective studies were identified by searching PubMed, Web of Science, Embase, and Cochrane Library until December 2022 without language restrictions. The pooled relative risk (RR) and 95% confidence intervals (CIs) were estimated for the association of SSBs, ASBs, and fruit juices with the risk of type 2 diabetes (T2D), cardiovascular disease (CVD), and mortality by using random-effect models. A total of 72 articles were included in this meta-analysis study. Significantly positive associations were observed between the consumption of individual beverages and T2D risk (RR: 1.27; 95% CI: 1.17, 1.38 for SSBs; RR: 1.32; 95% CI: 1.11, 1.56 for ASBs; and RR:0.98; 95% CI: 0.93, 1.03 for fruit juices). Moreover, our findings showed that intakes of SSBs and ASBs were significantly associated with risk of hypertension, stroke, and all-cause mortality (RR ranging from 1.08 to 1.54; all p < 0.05). A dose-response meta-analysis showed monotonic associations between SSB intake and hypertension, T2D, coronary heart disease (CHD), stroke and mortality, and the linear association was only significant between ASB consumption and hypertension risk. Higher SSB and ASB consumptions were associated with a greater risk of developing cardiometabolic diseases and mortality. Fruit juice intake was associated with a higher risk of T2D. Therefore, our findings suggest that neither ASBs nor fruit juices could be considered as healthier beverages alternative to SSBs for achieving improved health.Systematic Review Registration: [PROSPERO], identifier [No. CRD42022307003].

Upregulated SSB Is Involved in Hepatocellular Carcinoma Progression and Metastasis through the Epithelial-Mesenchymal Transition, Antiapoptosis, and Altered ROS Level Pathway.

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors with high morbidity and mortality. Therefore, finding new diagnostic and therapeutic targets is vital for HCC patients. Recent studies have shown that dysregulation of RNA-binding proteins is often associated with cancer progression. Several studies have reported that the RNA-binding protein SSB can promote cancer occurrence and progression and is linked to tumor epithelial-mesenchymal transition (EMT), which could be a new diagnostic marker and therapeutic target. However, the expression and function of SSB in HCC remain to be elucidated. Therefore, this study is aimed at clarifying the expression and biological function of SSB in HCC through bioinformatics analysis combined with in vitro experiments. We found that SSB is highly expressed in HCC and is associated with the poor prognosis of HCC patients, and it can serve as an independent unfavorable prognostic factor. Knockdown of SSB can inhibit the growth of HCC cells in vitro, increase the level of apoptosis and the expression of pro-apoptosis-related proteins, and decrease the expression of antiapoptotic proteins. Meanwhile, SSB knockdown reduced HCC cell invasiveness, and the expression of EMT-related proteins changed significantly. We also found that the gene SSB was associated with the level of oxidative stress in liver cancer cells, and the level of intracellular reactive oxygen species (ROS) increased after knockdown of SSB. The results of bioinformatics analysis also showed that high expression of SSB may affect the effect of checkpoint blockade (ICB) therapy. In conclusion, we found that SSB is highly expressed in HCC and that upregulated SSB can promote the proliferation and metastasis of HCC through antiapoptotic, altered intracellular oxidative stress level, and EMT pathways, which can serve as a new diagnostic marker and therapeutic target, and patients with high SSB expression may not have obvious ICB therapy effect.

Perceptions of sugar-sweetened beverages among adolescents in North Carolina.

IntroductionSugar-sweetened beverage (SSB) consumption among adolescents contributes to diet-related chronic disease including obesity, type 2 diabetes, and poor oral health.ObjectiveTo better understand adolescents' perceptions, attitudes, and consumption behaviors around SSBs by conducting virtual workshop discussions with adolescents in NC.Materials and methodsAdolescents ages 11–17 in communities with a high proportion of Supplemental Nutrition Assistance Program (SNAP) eligible households were selected to participate in a series of virtual group workshops during summer 2021. A semi-structured discussion guide was used by a workshop facilitator. Workshop discussions centered around general health perceptions, SSB perceptions, and consumption behaviors. A thematic analysis was used to summarize knowledge, beliefs, attitudes, and perceptions around SSBs.ResultsApproximately 36 adolescents participated across four group workshops. Parents and caregivers influenced adolescents most when it came to making beverage choices. Positive SSB perceptions included liking the taste and the association with special times and social events. Negative opinions focused on associated health risks (diet-related chronic disease and poor oral health). Some adolescents acknowledged SSBs were not healthy but suggested they could be consumed occasionally. Very few participants mentioned any benefits from SSBs; those that mentioned benefits stated they provided energy, replaced electrolytes, and tasted good.ConclusionFindings provide several key insights that can contribute to the development of messages aimed at curbing SSB consumption among adolescents. For example, messages that focus on catching adolescents' attention and sharing short- and long-term health consequences of high SSB consumption resonated with adolescents, but because occasional SSB intake was not seen as consequential, messages that suggest abstinence from SSBs may not be helpful in reducing consumption.

Association between parental feeding practices and children's dietary intake: a cross-sectional study in the Gardermoen Region, Norway.

BackgroundParental feeding practices may be important determinants for children’s diets. In Norway, few studies have assessed this association and to our knowledge, no studies have included fish as an outcome.ObjectiveThe purpose of this study was to explore the association between multiple parental feeding practices and children’s food intake.DesignParents (n = 111) of preschool children aged 1–5 years in the Gardermoen Region in Norway were recruited. The parents completed a web–based questionnaire regarding the use of 12 feeding practices measured by the Comprehensive Feeding Practices Questionnaire (CFPQ). Children’s weekly food intake was measured using a food frequency questionnaire (FFQ). The association between parental feeding practices and food intake was assessed by logistic regression.ResultsThe feeding practices involvement and environment increased the likelihood of children having a higher intake of fruit and berries (OR = 1.99, 95% CI = 1.15, 3.44 and OR = 2.10, 95% CI = 1.17, 3.78, respectively) when controlling for potential confounders. A positive association was found between the feeding practice environment and the children’s intake of vegetables (OR = 2.94, CI = 1.55, 5.55), and between modeling and intake of vegetables (OR = 2.14, CI = 1.26, 3.63). Also, the feeding practice encourage balance and variety increased the likelihood of a higher consumption of vegetables (OR = 5.18, CI = 1.63, 16.5). Parents who more frequently encouraged the child to eat balanced and varied were more likely to have children with a higher consumption of fish (OR = 5.03, CI = 1.62, 15.7). If parents used more restriction for weight, the child was less likely to have a high SSB consumption (OR = 0.43, CI = 0.22, 0.83).ConclusionFindings suggest that children’s intake of the favorite food item groups, fruit and berries, vegetables and fish, was associated with the use of positive feeding practices, such as involvement, environment, modeling and encouragement. For unfavorable food groups, only restriction for weight was negatively associated with SSB consumption. Findings should be interpreted carefully due to the relatively small sample size.

Clustering of Physical Activity, Diet and Sedentary Behavior among Youth from Low-, Middle-, and High-Income Countries: A Scoping Review.

Background: The interaction between physical activity (PA), diet, and sedentary behavior (SB) plays an important role on health-related outcomes. This scoping review (Prospero CRD42018094826) aims to identify and appraise clusters of PA, diet, and SB among youth (0–19 years) according to country income. Methods: Five databases were searched. Fifty-seven articles met the inclusion criteria. Results: Fifty-five cluster types were identified, with greater variety in high-income than lower income countries. The most prevalent profiles were “High SB and consumption of sugar, salt, and beverages (SSB)” (n = 17) and “High PA” (n = 13–5), both of which presented in all income countries. The healthiest profile, “High PA and fruit and vegetables (F&V); Low SB and SSB” (n = 12), was present in upper-middle and high-income countries, while the unhealthiest “Low PA and F&V; High SB and SSB” (n = 6) was present only in high-income countries. Conclusions: High SB and unhealthy diet (SSB) were more prevalent in clusters, mainly in high-income countries. The results support the need for multi-component actions targeting more than one behavior at the same time.

Association between intake of sweetened beverages with all-cause and cause-specific mortality: a systematic review and meta-analysis.

Conclusions remain controversial between the consumption of sugar and artificially sweetened beverages (SSBs and ASBs) and mortality. We systematically searched the PubMed, Embase, Cochrane Library and Web of Science databases from their inception date to 1st January 2020, prospective cohort studies researching the mortality risk and SSBs or ASBs consumption were included. Random effects meta-analyses and dose-response analyses were performed to measure the association. Subgroup analyses and sensitivity analyses were further performed to explore the source of heterogeneity. Publication bias was assessed by Funnel plots and Egger's regression test. Across all 15 cohorts, 1211470 participants were included. High SSB consumption was associated with a higher risk of all-cause mortality (hazard ratio [HR], 1.12; 95% confidence interval [CI], 1.06-1.19, P<0.001; and cardiovascular disease [CVD] mortality [HR 1.20, 95% CI, 1.05-1.38, P<0.001]), and high ASBs consumption showed similar result (HR 1.12, 95% CI, 1.04-1.21, P=0.001 for all-cause mortality and HR 1.23, 95% CI, 1.00-1.50, P=0.049 for CVD mortality), both showed a linear dose-response relationship. High consumption of both ASBs and SSBs showed significant associations with a higher risk of CVD mortality and all-cause mortality. This information may provide ideas for decreasing the global burden of diseases by reducing sweetened beverage intake.

Sperm selection during ICSI treatments reduces single- but not double-strand DNA break values compared to the semen sample.

To detect a possible bias in sperm DNA fragmentation (SDF) testing when performed on semen samples or on those few spermatozoa selected for Intracytoplasmic Sperm Injection (ICSI) treatments. A multimethodological analysis of Single- and Double-Strand DNA Breaks (SSB and DSB, respectively) was performed through the Neutral Comet, the Alkaline Comet, the Sperm Chromatin Dispersion (SCD) and the Terminal deoxynucleotidyl transferase dUTP Nick End Labelling (TUNEL) assays. SDF was evaluated in (i) semen samples from 23 infertile patients (not achieving pregnancy or suffering recurrent miscarriage); (ii) samples after a Swim-up and (iii) spermatozoa microselected for ICSI (ICSI-S). The analysis of 3217 ICSI-S revealed a significant reduction of SSB values compared to the Ejaculate and the Swim-up samples. On the contrary, DSB values were not reduced after any sperm selection method. The No-pregnancy group presented poorer semen parameters and higher SSB values. The Recurrent miscarriage group presented better semen parameters but also higher DSB values. The analysis of SDF on semen samples may not be fully representative of those few spermatozoa selected for ICSI. Since oxidative stress impairs sperm motility and causes SSB, selecting a motile sperm may intrinsically imply choosing a sperm not affected by this damage. DSB have an enzymatic origin which does not affect motility, making it difficult to select a sperm without this damage. Therefore, ICSI treatments could be effective in patients presenting high SSB values. Patients presenting high DSB values should expect bad ICSI results if this damage is not reduced through other specific methods.

Using nutritional survey data to inform the design of sugar-sweetened beverage taxes in low-resource contexts: a cross-sectional analysis based on data from an adult Caribbean population

ObjectiveSugar-sweetened beverage (SSB) taxes have been implemented widely. We aimed to use a pre-existing nutritional survey data to inform SSB tax design by assessing: (1) baseline consumption of SSBs and...

Sugar-sweetened beverage consumption is associated with visceral fat in children.

Sugar-sweetened beverage (SSB) consumption has been associated with visceral fat partitioning in adults; however, the underlying mechanisms in childhood remain unclear and warrant exploration. This cross-sectional study aimed to investigate the association between SSB consumption and body fat in children aged 9-13 years and the potential modifying effect of children's sex and serum cortisol levels. A sample of 2665 Greek schoolchildren participated in the 'Healthy Growth Study', and anthropometric, body composition, dietary intake and serum cortisol data were assessed. SSB consumption was defined as low (<1 serving/d), medium (1-2 servings/d) or high (>2 servings/d). We used linear regression models to assess the association between SSB consumption and measures of adiposity and to assess effect modification; models were stratified by sex and tertiles of morning serum cortisol. A significant positive association was observed between high SSB consumption and visceral adipose tissue (VAT) (β = 1·4, 95 % CI 0·4, 2·3, P = 0·01) but not BMI or BMI z-score. When stratified by sex, the association was observed in boys (β = 1·8, 95 % CI 0·3, 3·4, P = 0·02) but not in girls. When stratified by cortisol levels, SSB consumption was associated with VAT in children with cortisol levels in the lowest tertile (β = 2·8, 95 % CI 1·0, 4·6, P < 0·01). These results indicate that increased SSB consumption is associated with visceral adiposity in schoolchildren and this association may be modified by sex and morning serum cortisol. To prevent VAT accumulation and concomitant disease risk, dietary interventions should target SSB consumption during childhood.

Energy balance and occupational activity as predictors of obesity risk in women.

AbstractReduced occupational energy expenditure and increased energy intake are important contributors to the increasing prevalence of obesity. The aim of this study was to examine whether sedentary occupations, and specific indicators of energy intake and expenditure are associated with obesity risk in Australian women. Data were from 3,444 participants in the Australian Longitudinal Study on Women's Health, who reported their weight, dietary intake, physical activity and occupation in 2009 (at age 31–36), and weight in 2012. Participants were categorised as having a ‘less sedentary’ or ‘sedentary work’, based on occupation and activity patterns at work. Multivariate models were conducted to examine the odds of being obese (&gt; 30 body-mass index) and risk of obesity in the two occupational groups based on energy balance factors (diet and physical activity). Models were adjusted for major confounders (smoking, education, income, number of children).There was no significant difference in the prevalence of obesity between groups (20.3% less sedentary vs 22.7% sedentary work, p = 0.11) at baseline. Being in the highest total energy intake tertile, saturated fat intake &gt; 35g/d and drinking 3 or more sugar-sweetened beverages per week increased the odds of being obese in both groups. But to a higher extent in ‘less sedentary work’ (OR 2.11 95%CI 1.41–3.19; OR 3.04 95%CI 2.09–4.45; 2.07 95%CI 1.45–2.97, respectively). High physical activity (&gt; 1000MET.min/week) was consistently associated with lower odds of being obese (OR 0.64 95%CI 0.43–0.97 ‘less sedentary’; OR 0.58 95%CI 0.36–0.93 ‘sedentary work’) but lower incidence of obesity only in ‘less sedentary work’ group (IRR 0.52 95%CI 0.30–0.88, absolute risk 14%). High sugar-sweetened beverages increased the incidence of obesity only in this group (IRR 1.72 95%CI 1.08–2.73, absolute risk 23%). Having a sedentary work per se did not play a major role in obesity prevalence and risk in women. Instead, high saturated fat and SSB intake, and physical inactivity remained the major contributors to obesity prevalence and risk, particularly for those in less sedentary jobs.

Fluid intake of Latin American adults: results of four 2016 Liq.In7 national cross-sectional surveys

PurposeTo report total fluid intake (TFI) and the intake of different fluid types in adults (≥ 18 years old) from Mexico, Argentina, Brazil and Uruguay. To compare intakes between countries and with recommended adequate intake (AI) of water from fluids.MethodsCross-sectional data were collected using a validated liquid intake 7-day record (Liq.In7) in populations from Argentina (n = 1089), Brazil (n = 477), Mexico (n = 1677) and Uruguay (n = 554). Population characteristics, including age, gender, body mass index and socioeconomic level were recorded. Mean TFI was compared with the AI of water from fluids set by the USA Institute of Medicine.ResultsThe lowest TFI was recorded in Mexican women (1748 mL/day) and the highest in Argentinean men (2318 mL/day). Median daily TFI was significantly different between countries; Uruguay and Argentina had higher values than Mexico and Brazil. In the former, plain water contributed to only 25% of TFI, the remainder being predominantly from hot beverages. Approximately, a third of adults did not drink enough fluid to meet the recommended AI. High SSB consumption was reported, which was significantly different between countries (p < 0.05), the highest being in Mexico (median 25–75th percentiles): 531 (300–895 mL/day.ConclusionsThis survey highlights the need to increase water consumption and reduce SSB intake in this region to avoid potential associated health risks. These findings may be useful information in monitoring public health policy strategies.

Association of sugar-sweetened beverage intake frequency and asthma among U.S. adults, 2013

ObjectivesSugar-sweetened beverage (SSB) intake among U.S. adults is associated with obesity and type 2 diabetes. An association between SSB intake and asthma has been shown among U.S. children and Australian adults, but scant published information exists for U.S. adults. We examined associations between SSB intake and current asthma among U.S. adults, and the role of obesity in this association. MethodsWe analyzed 2013 Behavioral Risk Factor Surveillance System data for 146,990 adults (≥18years) from 23 states and the District of Columbia. We used multivariable logistic regression to estimate associations between current asthma and frequency (none, <1 time/day, once/day, ≥2 times/day) of SSB intake (soda, fruit drink, sweet tea, and sports/energy drink). SSB intake was measured using two questions. Covariates included age, sex, race/ethnicity, education, and smoking. Obesity, based on self-reported height and weight, was assessed as an effect modifier. ResultsOverall, 9.1% of adults reported current asthma: 8.5% of adults who did not consume SSBs had current asthma vs 12.1% of adults who consumed SSBs ≥2 times/day. There was no difference in asthma prevalence with SSB intake <1 time/day (8.7%) or once/day (8.7%). Among non-obese adults, the odds of having current asthma were higher among those who consumed SSBs ≥2 times/day (aOR=1.66, 95%CI=1.39, 1.99) than non-SSB consumers. However, SSB intake frequency was not associated with asthma among obese adults. ConclusionsFrequent SSB consumption was associated with asthma among non-obese adults. Research on asthma prevention should further consider the potential adverse effects of high SSB intake among U.S. adults.

The impact of sugar sweetened beverage intake on hunger and satiety in minority adolescents

Limited research has examined the effects of habitual SSB consumption on hunger/fullness ratings and gut hormones. This study hypothesized that high versus low intakes of habitual SSBs would result in greater hunger, decreased fullness, and a blunted gut hormone response, however the high versus low fiber group would exhibit decreased hunger and increased fullness. This was a randomized crossover feeding trial with 47 African American and Hispanic adolescents. The experiment included three 24-hour recalls to assess habitual dietary intake. During the test meal phase, subjects were served breakfast and lunch. During the ad libitum meal phase, subjects were fed an ad libitum dinner. During the test meal phase, blood was drawn every 30 minutes for 3 hours. During the ad libitum meal phase, hunger and fullness visual analogue scales were completed. For this analysis, subjects were grouped into the following habitual SSB categories: low SSB (≤1 SSB serv/day), medium SSB (>1 - <2 serv/day), and high SSB (≥2 serv/day). Fiber categories were created based on quartiles of intake. Mixed modeling was used to explore how SSB and fiber categories predicted ghrelin/PYY values and hunger/fullness ratings across time within and between test meals. The following a priori covariates included: sex, ethnicity, age, and obesity status. The low SSB group had higher fullness ratings over the ad libitum meal compared to the high SSB group (β =-0.49, CI=(-0.89, -0.08), p=0.02) and higher ghrelin concentrations than the medium and high SSB group over the test meal phase (β =-1.86, CI=(-2.81, -0.92), p<0.01). Habitual SSB intake appears to play a key role in moderating fullness responses possibly via ghrelin.

Sedentary behavior, depressed affect, and indicators of mental well-being in adolescence: Does the screen only matter for girls?

The study investigated the effects of sedentary behavior (SB) on mental well-being and examined differences between screen-based (sSB) and non-screen-based sedentary behaviors (nSB) separately by gender. In a total sample of 1296 students (609 girls) aged 12–17 (m = 13.7, SD = 0.67), SB, depressed affect, self-esteem, physical self-concept, general self-efficacy and physical activity were assessed through self-administered questionnaires. Among girls, lower scores in self-esteem, physical self-concept as well as general self-efficacy were associated with higher sSB but not nSB. Among boys higher levels of sSB related to higher self-esteem, nSB but not sSB predicted higher scores in depressed affect, and there was a u-shaped association between sSB and general self-efficacy. Results replicate the inverse association between SB and mental well-being, and suggest a distinction between nSB and sSB especially among girls. Additional studies will be necessary to replicate, and further examine mediating mechanisms.

Modelling fishers' response to discard prevention strategies: the case of the North Sea saithe fishery

Abstract Designing effective management plans requires understanding fishers' behaviour under that plan, because fishers change their behaviour in response to economic and management incentives, which in turn will lead to different fishery outcomes. This study presents a modelling framework for management strategy evaluations which takes into account the response of fishers to management schemes. Based on the upcoming discard ban, two discard prevention strategies were tested for the North Sea saithe fishery, where fleet segments have either no or a generally low quota for cod. Costs and benefits were assessed under the current management, a non-flexible system, where fleet segments had to stop fishing once the cod quota was reached and a flexible system where quota of saithe could be used to cover over-quota catch of cod at a ratio 1:5. The flexible scenario was beneficial both in protecting the North Sea saithe and cod stock and in increasing net profits of fleet segments in the long term. The avoidance behaviour of fleet segments to over-quota catch led to a high SSB level of saithe and cod in the long term, ensuring high long-term catches and profits. A non-flexible scenario had a negative impact on the saithe stock, because mainly juvenile saithe before spawning were caught reducing the spawning-stock biomass in the longer term. A non-flexible scenario was costly in terms of up to 29% lower net profits for individual fleet segments generating little economic incentive to be compliant.

Mechanism of Interaction between Single-Stranded DNA Binding Protein and DNA

A single-stranded DNA binding protein (SSB), labeled with a fluorophore, interacts with single-stranded DNA (ssDNA), giving a 6-fold increase in fluorescence. The labeled protein is the adduct of the G26C mutant of the homotetrameric SSB from Escherichia coli and a diethylaminocoumarin {N-[2-(iodoacetamido)ethyl]-7-diethylaminocoumarin-3-carboxamide}. This adduct can be used to assay production of ssDNA during separation of double-stranded DNA by helicases. To use this probe effectively, as well as to investigate the interaction between ssDNA and SSB, the fluorescent SSB has been used to develop the kinetic mechanism by which the protein and ssDNA associate and dissociate. Under conditions where ∼70 base lengths of ssDNA wrap around the tetramer, initial association is relatively simple and rapid, possibly diffusion-controlled. The kinetics are similar for a 70-base length of ssDNA, which binds one tetramer, and poly(dT), which could bind several. Under some conditions (high SSB and/or low ionic strength), a second tetramer binds to each 70-base length, but at a rate 2 orders of magnitude slower than the rate of binding of the first tetramer. Dissociation kinetics are complex and greatly accelerated by the presence of free wild-type SSB. The main route of dissociation of the fluorescent SSB·ssDNA complex is via association first with an additional SSB and then dissociation. Comparison of binding data with different lengths of ssDNA gave no evidence of cooperativity between tetramers. Analytical ultracentrifugation was used to determine the dissociation constant for labeled SSB2·dT70 to be 1.1 μM at a high ionic strength (200 mM NaCl). Shorter lengths of ssDNA were tested for binding: only when the length is reduced to 20 bases is the affinity significantly reduced.

RecFOR proteins are essential for Pol V-mediated translesion synthesis and mutagenesis

When the replication fork moves through the template DNA containing lesions, daughter-strand gaps are formed opposite lesion sites. These gaps are subsequently filled-in either by translesion synthesis (TLS) or by homologous recombination. RecA filaments formed within these gaps are key intermediates for both of the gap-filling pathways. For instance, Pol V, the major lesion bypass polymerase in Escherichia coli, requires a functional interaction with the tip of the RecA filament. Here, we show that all three recombination mediator proteins RecFOR are needed to build a functionally competent RecA filament that supports efficient Pol V-mediated TLS in the presence of ssDNA-binding protein (SSB). A positive contribution of RecF protein to Pol V lesion bypass is demonstrated. When Pol III and Pol V are both present, Pol III imparts a negative effect on Pol V-mediated lesion bypass that is counteracted by the combined action of RecFOR and SSB. Mutations in recF, recO or recR gene abolish induced mutagenesis in E. coli.

Complete Inhibition of Streptococcus pneumoniae RecA Protein-catalyzed ATP Hydrolysis by Single-stranded DNA-binding Protein (SSB Protein): IMPLICATIONS FOR THE MECHANISM OF SSB PROTEIN-STIMULATED DNA STRAND EXCHANGE

The ATP-dependent three-strand exchange activity of the Streptococcus pneumoniae RecA protein (RecA(Sp)), like that of the Escherichia coli RecA protein (RecA(Ec)), is strongly stimulated by the single-stranded DNA-binding protein (SSB) from either E. coli (SSB(Ec)) or S. pneumoniae (SSB(Sp)). The RecA(Sp) protein differs from the RecA(Ec) protein, however, in that its ssDNA-dependent ATP hydrolysis activity is completely inhibited by SSB(Ec) or SSB(Sp) protein, apparently because these proteins displace RecA(Sp) protein from ssDNA. These results indicate that in contrast to the mechanism that has been established for the RecA(Ec) protein, SSB protein does not stimulate the RecA(Sp) protein-promoted strand exchange reaction by facilitating the formation of a presynaptic complex between the RecA(Sp) protein and the ssDNA substrate. In addition to acting presynaptically, however, it has been proposed that SSB(Ec) protein also stimulates the RecA(Ec) protein strand exchange reaction postsynaptically, by binding to the displaced single strand that is generated when the ssDNA substrate invades the homologous linear dsDNA. In the RecA(Sp) protein-promoted reaction, the stimulatory effect of SSB protein may be due entirely to this postsynaptic mechanism. The competing displacement of RecA(Sp) protein from the ssDNA substrate by SSB protein, however, appears to limit the efficiency of the strand exchange reaction (especially at high SSB protein concentrations or when SSB protein is added to the ssDNA before RecA(Sp) protein) relative to that observed under the same conditions with the RecA(Ec) protein.

Co-operative Binding of Escherichia coli SSB Tetramers to Single-stranded DNA in the (SSB) 35 Binding Mode

Escherichia coli SSB tetramers can bind to single stranded (ss) DNA in several binding modes. At 25°C, ph 8·1, SSB can form at least three distinct binding modes, (SSB) n, where the number of nucleotides occluded per tetramer ( n) can have values of 35, 56 or 65. Stability of the different modes is modulated by solution conditions, primarily the salt concentration and type, as well as the free SSB concentration. At least two different types of positive co-operative binding of SSB to ssDNA have also been observed, which appear to be correlated with different SSB binding modes. The (SSB) 65 mode, which dominates at monovalent salt concentrations >0·2 M, displays only moderate, "limited" co-operative binding in which clustering of SSB is limited to the formation of dimers of tetramers (octamers). However, at lower salt concentrations, "unlimited" co-operative binding is observed in which long SSB clusters can form, similar to the behavior observed for the phage T4 gene 32 protein. It has been proposed that unlimited co-operativity is linked to the (SSB) 35 binding mode; however, this has not been verified since quantitative estimates of the co-operativity in this binding mode are difficult on long ssDNA. To estimate the nearest-neighbor co-operativity parameter in the (SSB) 35 mode, we have examined the equilibrium binding of SSB to the oligodeoxynucleotide, dA(pA) 69. Under certain conditions, 1:1 complexes, in which all four SSB subunits interact with the dA(pA) 69, can form at low SSB binding densities, whereas 2:1 complexes, in which both SSB tetramers bind to DNA using only two subunits, can form at high SSB binding densities. These 2:1 complexes serve as a model for co-operative binding in the (SSB) 35 binding mode. We show that SSB tetramers bind in this mode with a minimum nearest-neighbor co-operativity parameter of ω35 = 1·0 × 10 5 (0·125 M NaCl, pH 8·1, 25°C). This indicates that the nearest-neighbor co-operativities for SSB tetramers bound to ssDNA in the (SSB) 35 versus the (SSB) 65 mode differ qualitatively and quantitatively and suggests that the (SSB) 35 mode is responsible for the ability of SSB protein to form long clusters on ssDNA. If the ability of helix destabilizing proteins to form uninterrupted protein clusters on ssDNA is important in DNA replication, then it is likely that SSB uses its (SSB) 35 mode to function in this capacity.