Initial DNA Research Articles

Does Vascular Collapse Occur After Treatment of Hepatocellular Cancer With Stereotactic Body Radiation Therapy?

There is debate about why stereotactic body radiation therapy (SBRT) produces superior control of hepatocellular cancer (HCC) compared to fractionated treatment. Both preclinical and clinical evidence has been presented to support a "classic" biological explanation: the greater BED of SBRT produces more DNA damage and tumor cell kill. More recently, preclinical evidence has supported the concept of a "new biology", particularly radiation-induced vascular collapse, which increases hypoxia and free radical activation. This is hypothesized to cause much greater tumor cell death than was produced by the initial radiation-induced DNA damage to the tumor. We decided to investigate if vascular collapse occurs after standard SBRT for patients with HCC. Eight patients with 10 lesions underwent dynamic contrast enhanced MRI at the time of simulation and either 48 or 96 hours after the first fraction. Only three of 10 tumors showed a decrease in blood flow. These findings suggest that vascular collapse does not typically occur after SBRT for HCC.

In-silico calculations of DNA damage induced by [formula omitted]-particles in the 224Ra DaRT decay chain for a better understanding of the radiobiological effectiveness of this treatment

Diffusing alpha-emitters radiation Therapy (DaRT) is an interstitial brachytherapy technique using 224Ra seeds. For accurate treatment planning a good understanding of the early DNA damage due to α-particles is required. Geant4-DNA was used to calculate the initial DNA damage and radiobiological effectiveness due to α-particles with linear energy transfer (LET) values in the range 57.5–225.9 keV/μm from the 224Ra decay chain. The impact of DNA base pair density on DNA damage has been modelled, as this parameter varies between human cell lines. Results show that the quantity and complexity of DNA damage changes with LET as expected. Indirect damage, due to water radical reactions with the DNA, decreases and becomes less significant at higher LET values as shown in previous studies. As expected, the yield of complex double strand breaks (DSBs), which are harder for a cell to repair, increases approximately linearly with LET. The level of complexity of DSBs and radiobiological effectiveness have been found to increase with LET as expected. The quantity of DNA damage has been shown to increase for increased DNA density in the expected base pair density range of human cells. The change in damage yield as a function of base pair density is largest for higher LET α-particles, an increase of over 50% for individual strand breaks between 62.7 and 127.4 keV/μm. This change in yield shows that the DNA base pair density is an important parameter for modelling DNA damage particularly at higher LET where the DNA damage is greatest and most complex.

Sperm processing methods effectively reduce the DNA fragmentation index in samples with high initial values

The DNA fragmentation index (DFI) in spermatozoa is correlated to in vivo fertility in animals and outcomes in Human Assisted Reproductive Techniques (ARTs). Different sperm selection methods aim to select the most viable sperm population and reduce the DFI after processing. However, it remains unclear which selection method most efficiently reduces DFI and to what extent initial levels in raw semen can be improved to justify the use of these alternative procedures. We hypothesized that sperm selection methods would efficiently reduce the percentage of cells with DNA damage mainly to samples with high initial values. In this study we evaluated frozen-thawed equine spermatozoa from 12 different stallions subjected to four different treatments as follows: i) control / no selection (CN); ii) density gradient centrifugation (DGC); iii) swim up (SU); and iv) a microfluidic chamber (MF). After processing, DFI levels were evaluated based on the percentage of cells outside of the main population (COMPαt) from the Sperm Chromatin Structure Assay (SCSA) as described by Evenson et al., (2013). Levels of COMPαt in the control samples (CN) were used to categorize them as LOW and HIGH based on a median split (Mdn:12.37%). Statistical analysis was performed using R (R Core Team, Vienna, Austria, v3.6.0) to fit a mixed linear regressionmodel. Fixed effects in the model included treatment (CN, DGC, SU and MF) and initial DFI levels (LOW or HIGH). Random effect in the model included stallion (n=12) and effects were retained in the model when p<0.05. There was a significant interaction between treatment and initial DNA fragmentation levels (p<0.00001). In samples with HIGH DFI, COMPαt had a mean of (20.44% ±1.68) for CN and was not significantly different from samples processed by DGC (14.36%±1.68; p=0.07). However, a significant reduction in COMPαt was observed after SU (2.97% ± 1.68; p<0.0001) and MF (1.95% ± 1.68; p<0.0001) in this group. On the other hand, among samples in the LOW DFI group, COMPαt had a mean of (8.32% ±1.68) for CN, which was not significantly different when compared to DGC (7.34%±1.68; p=0.99), SU (3.24%±1.68; p=0.2) or MF (2.07% ±1.68; p=0.059) selection methods. These results demonstrate that SU and MF were the most effective at reducing the percentage of cells with DNA fragmentation (COMPαt) when the initial DFI was considered HIGH. However, in samples with LOW DFI, there was no significant improvement in COMPαt by any selection method. Clinical categorization of initial sperm DFI may be warranted to determine the fecundity of sires and be useful for selecting appropriate sperm selection methods for equine ARTs.

Preliminary Study: DNA Transfer and Persistence on Non-Porous Surfaces Submerged in Spring Water.

Submerged items are often thought to lack evidentiary value. However, previous studies have shown the ability to recover DNA from submerged porous items for upwards of six weeks. The crevices or interweaving fibers in porous items are thought to protect DNA from being washed away. It is hypothesized that, because non-porous surfaces do not have the same traits that might aid in DNA retention, then DNA quantities and the number of donor alleles recovered would decrease over longer submersion periods. Additionally, it is hypothesized that DNA quantity and the number of alleles would be negatively affected by flow conditions. Neat saliva of known DNA quantity was applied to glass slides and exposed to stagnant and flowing spring water to observe the effects on both DNA quantity and STR detection. Results supported that DNA deposited onto glass and subsequently submerged in water experienced a decrease in DNA quantity over time, yet submersion did not have as strong of a negative effect on the detected amplification product. Additionally, an increase in DNA quantity and detected amplification product from designated blank slides (no initial DNA added) could indicate the possibility of DNA transfer.

Germline ATM Mutations Detected by Somatic DNA Sequencing in Lethal Prostate Cancer

BackgroundGermline mutations in the ataxia telangiectasia mutated (ATM) gene occur in 0.5–1% of the overall population and are associated with tumour predisposition. The clinical and pathological features of ATM-mutated prostate cancer (PC) are poorly defined but have been associated with lethal PC. ObjectiveTo report on the clinical characteristics including family history and clinical outcomes of a cohort of patients with advanced metastatic castration-resistant PC (CRPC) who were found to have germline ATM mutations after mutation detection by initial tumour DNA sequencing. Design, setting, and participantsWe acquired germline ATM mutation data by saliva next-generation sequencing from patients with ATM mutations in PC biopsies sequenced between January 2014 and January 2022. Demographics, family history, and clinical data were collected retrospectively. Outcome measurements and statistical analysisOutcome endpoints were based on overall survival (OS) and time from diagnosis to CRPC. Data were analysed using R version 3.6.2 (R Foundation for Statistical Computing, Vienna, Austria). Results and limitationsOverall, seven patients (n = 7/1217; 0.6%) had germline ATM mutations detected, with five of them having a family history of malignancies, including breast, prostate, pancreas, and gastric cancer; leukaemia; and lymphoma. Two patients had concomitant somatic mutations in tumour biopsies in genes other than ATM, while two patients were found to carry more than one ATM pathogenic mutation. Five tumours in germline ATM variant carriers had loss of ATM by immunohistochemistry. The median OS from diagnosis was 7.1 yr (range 2.9–14 yr) and the median OS from CRPC was 5.3 yr (range 2.2–7.3 yr). When comparing these data with PC patients sequenced by The Cancer Genome Atlas, we found that the spatial localisation of mutations was similar, with distribution of alterations occurring on similar positions in the ATM gene. Interestingly, these include a mutation within the FRAP-ATM-TRRAP (FAT) domain, suggesting that this represents a mutational hotspot for ATM. ConclusionsGermline ATM mutations are rare in patients with lethal PC but occur at mutational hotspots; further research is warranted to better characterise the family histories of these men and PC clinical course. Patient summaryIn this report, we studied the clinical and pathological features of advanced prostate cancers associated with germline mutations in the ATM gene. We found that most patients had a strong family history of cancer and that this mutation might predict the course of these prostate cancers, as well as response to specific treatments.

Nucleotide binding halts diffusion of the eukaryotic replicative helicase during activation

The eukaryotic replicative helicase CMG centrally orchestrates the replisome and leads the way at the front of replication forks. Understanding the motion of CMG on the DNA is therefore key to our understanding of DNA replication. In vivo, CMG is assembled and activated through a cell-cycle-regulated mechanism involving 36 polypeptides that has been reconstituted from purified proteins in ensemble biochemical studies. Conversely, single-molecule studies of CMG motion have thus far relied on pre-formed CMG assembled through an unknown mechanism upon overexpression of individual constituents. Here, we report the activation of CMG fully reconstituted from purified yeast proteins and the quantification of its motion at the single-molecule level. We observe that CMG can move on DNA in two ways: by unidirectional translocation and by diffusion. We demonstrate that CMG preferentially exhibits unidirectional translocation in the presence of ATP, whereas it preferentially exhibits diffusive motion in the absence of ATP. We also demonstrate that nucleotide binding halts diffusive CMG independently of DNA melting. Taken together, our findings support a mechanism by which nucleotide binding allows newly assembled CMG to engage with the DNA within its central channel, halting its diffusion and facilitating the initial DNA melting required to initiate DNA replication.

Abstract 2819: Genome-wide CRISPR screen identifies NANP as a radio-sensitizing target of GBM by regulating NF-κB pathway

Abstract Glioblastoma multiforme (GBM) are the most malignant primary central nervous system tumors. The standard of care for newly diagnosed GBM patients includes surgery followed by combined radiation therapy (RT) and adjuvant temozolomide (TMZ) therapy. However, one of the therapeutic challenges is the inevitable resistance and recurrence after radiotherapy. Glioblastoma stem cells (GSC) are tumor initiating cells for GBM and plays key roles in radio resistance. Thus, we performed a genome-wide CRISPR screen using a radiation resistant GSC to identify potential RT sensitizing targets. We identified 139 potential RT sensitizing targets with a filter for only those genes associated with a greater than 2-fold reduction in representation with a p&amp;lt;0.05. There were 22 genes with a direct function in key DNA double-strand break repair pathways including 5 genes central to non-homologous end-joining (NHEJ1, XLF, PRKDC, DCLRE1C, XRCC4, LIG4), 6 genes involved in homologous recombination (RAD51D, CYREN, ATM, TONSL, BRCA2, RFWD3), and 7 genes central to initial DNA damage sensing (RNF8, RNF168, TP53BP1, RAD17, FOXM1, RAD9A, RAD1). These results are consistent with the crucial role of DNA repair following radiation exposure and demonstrate the success of the screening. Besides that, one of the top hits is NANP (N-acylneuraminate-9-phosphatase), which is involved in sialic acid synthetic pathway. Knocking down of NANP causes more G2/M arrest followed by apoptosis after radiation. γH2A.X staining and comet assay shows more DNA damage in NANP knock down cells after radiation. Transcriptome analysis reveals NANP inhibition restrain mesenchymal status and NF-κB pathway activation. Furthermore, activation of NF-κB pathway could rescue the RT-induced G2/M arrest of NANP knock down cells. TCGA and CGGA dataset shows NANP is highly expressed in GBM patients and patients with NANP high expression have poorer survival. In conclusion, our study identified NANP as a novel radio-sensitizing target for glioblastoma by regulating NF-κB pathway and mesenchymal status of GSCs. Citation Format: Yingwen Ding, Ze-Yan Zhang, Ravesanker Ezhilarasan, Aram S. Modrek, Jerome Karp, Erik P. Sulman. Genome-wide CRISPR screen identifies NANP as a radio-sensitizing target of GBM by regulating NF-κB pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2819.

The Long and Winding Road: On-Demand DNA Synthesis in High Demand

The Long and Winding Road: On-Demand DNA Synthesis in High Demand

An electrochemical aptasensor for detection of streptomycin based on signal amplification assisted by functionalized gold nanoparticles and hybridization chain reaction.

A ratiometric electrochemical aptasensor based on gold nanoparticles (AuNPs) functionalization and hybridization chain reaction (HCR) assisted signal amplification has been for thefirsttime designed for the detection of streptomycin (STR). The double-stranded DNA (dsDNA) formed by the hybridization of ferrocene (Fc)-labeled STR aptamer (Apt) and capture probe (CP) is first immobilized on the gold electrode (GE) surface via Au-S reaction. The specific binding of the target and Apt results in numerous Fc detachment from the sensing interface. Then, the remaining single-stranded CP is combined with AuNPs modified with initiator DNA (iDNA) by auxiliary DNA (aDNA). Among them, the iDNA triggers HCR between two hairpin probes (H1/H2), thus capturing a large number of methylene blue (MB) electrochemical probe, which generates a strong electrochemical signal of MB and a weak electrochemical signal of Fc. Signals are collected by square wave voltammetry (the potential window ranging from -0.5V to 0.6V, vs.Ag/AgCl ), and the oxidation peak currents at -0.200V (MB) and 0.416V (Fc) are recorded. The use of the ratiometric method has effectively improved the accuracy and reliability of the analysis. The successful application of AuNPs and HCR greatly improves the sensitivity of the sensor, and the detection limit is as low as 0.08pM. It can sensitively determine STR in the range 0.1pM to 10nM. In addition, the designed aptasensor has been successfully applied to the detection of STR in milk and honey samples.

Detection of Hepatitis C virus RNA using a novel hybridization chain reaction method that competitively dampens cascade amplification.

The hybridization chain reaction (HCR) is widely used for biosensing. However, HCR does not provide the required sensitivity. In this study, we reported a method to improve the sensitivity of HCR by dampening the cascade amplification. First, we designed a biosensor based on HCR, and an initiator DNA was used to trigger the cascade amplification. Optimization of the reaction was then performed, and the results showed that the limit of detection (LOD) for the initiator DNA was about 2.5 nM. Second, we designed a series of inhibitory DNAs to dampen the HCR cascade amplification, and DNA dampeners (50 nM) were applied in the presence of the DNA initiator (50 nM). One of the DNA dampeners (D5) showed the best inhibitory efficiency of greater than 80%. This was further applied at concentrations ranging from 0 nM to 10 nM to prohibit the HCR amplification caused by a 2.5 nM initiator DNA (the limit of detection for this initiator DNA). The results showed that 0.156 nM of D5 could significantly inhibit the signal amplification (p<0.05). Additionally, the limit of detection for the dampener D5 was 16 times lower than that for the initiator DNA. Based on this detection method, we achieved a detection limit as low as 0.625 nM for HCV-RNAs. In summary, we developed a novel method with improved sensitivity to detect the target designed to prohibit the HCR cascade. Overall, this method could be used to qualitatively detect the presence of single-stranded DNA/RNA.

Inflammatory mediator-induced bystander effects and genomic instability: role of tissue-specificity

Much evidence showed that radiation-induced inflammation can cause cellular damage in direct irradiated and bystander cells, which are in vicinity of irradiated cells underlying radiation-induced bystander effects (BE). As well as radiation-induced genomic instability (GI) is observed within the progeny of irradiated and bystander cells as a delayed damage responses. This study tried to mimic the effects of radiation-induced GI and BE by exploring the inflammatory effect of lipopolysaccharide (LPS) on human primary fibroblast (HF 19) and umbilical vein endothelial (HUVEC) cells. To prove the principles of LPS can cause DNA damage in HF 19; cells were treated with 1 μg/ml LPS, and BE was induced by media transfer. Comet assay was used to estimate DNA damage in the direct treated and bystander cells. The early DNA damage result was significantly observed in the direct treated and bystander HF 19 cells. However, these cells did not show a significant delayed DNA damage within their progeny. Comet data showed that LPS frequently induced only initial DNA damage in HF 19 cells. The experiment was repeated utilising HF 19 and HUVEC cells, in order to investigate whether LPS could be involved in the induction of GI in a tissue-specificity manner. Both HF 19 and HUVEC cells were treated with 1 μg/ml LPS. BE was also induced by media transfer. Chromosomal analysis was used for early and late chromosomal damage estimation. Data showed that LPS treatment could significantly cause early chromosomal aberrations in the direct treated and bystander HF 19 and HUVEC cells. However, delayed chromosomal instability was observed only in the direct treated HUVEC cells. Our finding suggested that LPS frequently induced BE in HF 19 and HUVEC cells, which could be mediated by pro-inflammatory cytokines that stimulated by LPS treatment. Moreover, LPS could be involved in the GI induction in a tissue-specificity manner.Keywords:

An Ultrasensitive Colorimetric Foodborne Pathogenic Detection Method Using a CRISPR/Cas12a Mediated Strand Displacement/Hybridization Chain Reaction.

Accurate, rapid, and sensitive pathogenic detections play an important role in food safety. Herein, we developed a novel CRISPR/Cas12a mediated strand displacement/hybridization chain reaction (CSDHCR) nucleic acid assay for foodborne pathogenic colorimetric detection. A biotinylated DNA toehold is coupled on avidin magnetic beads and acts as an initiator strand to trigger the SDHCR. The SDHCR amplification allowed the formation of long hemin/G-quadruplex-based DNAzyme products to catalyze the TMB-H2O2 reaction. In the presence of the DNA targets, the trans-cleavage activity of CRISPR/Cas12a was activated to cleave the initiator DNA, resulting in the failure of SDHCR and no color change. Under optimal conditions, the CSDHCR has a satisfactory linear detection of DNA targets with a regression equation Y = 0.0531*X - 0.0091 (R2 = 0.9903) in the range of 10 fM to 1 nM, and the limit of detection was determined as 4.54 fM. In addition, Vibrio vulnificus, one foodborne pathogen, was used to verify the practical application of the method, and it showed satisfactory specificity and sensitivity with a limit of detection at 1.0 × 100 CFU/mL coupling with recombinase polymerase amplification. Our proposed CSDHCR biosensor could be a promising alternative method for ultrasensitive and visual detection of nucleic acids and the practical application of foodborne pathogens.

Self-powered DNA nanomachines for fluorescence detection of lead.

A versatile DNA nanomachine detection system has been developedvia the combination ofDNAzyme with catalytic hairpin assembly (CHA) technology for achieving accurate and sensitive detection of lead ions (Pb2+). In the presence of target Pb2+, capture DNA nanomachine formed by AuNP and DNAzyme recognized and reacted with Pb2+, which yielded an "active" DNAzyme, that induced the cleavage of substrate strand, and then released the initiator DNA (TT) for CHA. With the help of the initiator DNA TT, self-powered CHA was activated to achieve the signal amplification reaction in the detection of DNA nanomachine. Meanwhile, the initiator DNA TT was released and hybridized with the other H1 strand to initiate another CHA, replacement, and turnovers, producing enhanced fluorescence signal of fluorophore FAM (excitation 490nm/emission 520nm) for sensitive determination of Pb2+. Under the optimized conditions, the DNA nanomachine detection system revealed high selectivity toward Pb2+ in the concentration range 50-600pM, with the limit of detection (LOD) of 31pM. Recovery tests demonstrated that the DNA nanomachine detection system has excellent detection capability in real samples. Therefore, the proposed strategy can be extended and act as a basic platform for highly accurate and sensitive detection of various heavy metal ions.

Comparative quantitation of DNA water tracers using OptiQ, Qubit, and Nanodrop

AbstractWe have recently developed new synthetic DNA tracers for tracking sources and pathways of contamination in surface water and groundwater. The use of DNA tracers in natural water systems results in substantial and rapid dilutions, thus accurate quantitation of initial DNA tracer concentrations applied is crucial to ensure their successful downstream detections. We compared the sensitivity and accuracy of three portable analytical techniques for quantitation of these DNA tracers: Nanodrop, Qubit, and OptiQ. All three methods were about equally effective when measuring high concentrations of DNA tracers (e.g., for c‐amine DNA tracer 1.54 × 105, 1.37 × 105, and 1.77 × 105 ng/mL for Nanodrop, Qubit, and OptiQ, respectively). However, the fluorescent methods of Qubit and OptiQ were significantly more sensitive at detecting lower concentrations of DNA tracers with limits of detection in the range 0.1–2 ng/mL, compared to 5 × 103 ng/mL for Nanodrop. The results of this work will facilitate the practical deployment of DNA tracers for tracking water contamination, and improving freshwater quality.

Laboratory protocol is important to improve the correlation between target copies and metabarcoding read numbers of seed DNA in ground beetle regurgitates

DNA metabarcoding is increasingly important for studying feeding interactions, yet it remains unresolved whether reporting read counts or occurrences is to be preferred. To address this issue for gut content samples, basic experimental data on the relationship between read numbers and initial prey DNA amounts and how both change over digestion time is needed. Using regurgitates of the carabid Pseudoophonus rufipes the digestion of Taraxacum officinale seeds was documented for 128 h post-feeding to determine how the number of (1) seed DNA copies and (2) metabarcoding reads change over digestion time, and (3) how they correlate to each other. Additionally, we tested (4) whether PCR cycle-numbers during library preparation affect this correlation. The number of copies and reads both decreased with digestion time, but variation between samples was high. Read and copy numbers correlated when using a library preparation protocol with 35 cycles (R2 = 42.0%), yet a reduction to 30 cycles might significantly improve this correlation, as indicated by additional PCR testing. Our findings show that protocol optimization is important to reduce technical distortions of read numbers in metabarcoding analysis. However, high inter-sample variation, likely due to variable digestive efficiency of individual consumers, can blur the relationship between the amount of food consumed and metabarcoding read numbers.

Molecular characterization of Richter syndrome identifies de novo diffuse large B-cell lymphomas with poor prognosis

Richter syndrome (RS) is the transformation of chronic lymphocytic leukemia (CLL) into aggressive lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL). We characterize 58 primary human RS samples by genome-wide DNA methylation and whole-transcriptome profiling. Our comprehensive approach determines RS DNA methylation profile and unravels a CLL epigenetic imprint, allowing CLL-RS clonal relationship assessment without the need of the initial CLL tumor DNA. DNA methylation- and transcriptomic-based classifiers were developed, and testing on landmark DLBCL datasets identifies a poor-prognosis, activated B-cell-like DLBCL subset in 111/1772 samples. The classification robustly identifies phenotypes very similar to RS with a specific genomic profile, accounting for 4.3-8.3% of de novo DLBCLs. In this work, RS multi-omics characterization determines oncogenic mechanisms, establishes a surrogate marker for CLL-RS clonal relationship, and provides a clinically relevant classifier for a subset of primary “RS-type DLBCL” with unfavorable prognosis.

Corrigendum for PM 7/149 (1) Anoplophora glabripennis and Anoplophora chinensis

Corrigendum for <scp>PM</scp> 7/149 (1) <i>Anoplophora glabripennis</i> and <i>Anoplophora chinensis</i>

Calculation of Radiation-induced DNA Damage Efficiency. Analysis of Uncertainties

Computer simulations of the DNA damage are widely used due to their large application area. The computational methods to predict DNA breaks are based on molecular concepts about the formation of breaks, the geometric structure of DNA, as well as information about the distribution of absorbed energy in a DNA mo-lecule. Since the calculations use different postulates and algorithms, it is often difficult to make intercompa-rison between theoretical results in the literature. Due to the spread of experimental data on DNA breaks, the determination of parameters of DNA lesion models from the data is not straightforward. In this paper, a comparative analysis of two basic models of DNA structure, molecular and enlarged subvolume, various schemes for the formation of single- and double-strand DNA breaks, as well as different classifications of the break complexity after irradiation with protons and α-particles is performed. Numerical results on initial radiation-induced DNA damage due to direct and quasi-direct action demonstrate the dependence on variation of model parameters. The parameter values where the two models agree or differ are discussed.

Phytogenotoxicity of thymol and semisynthetic thymoxyacetic acid in pre/post emergence of model plants and weeds.

Herbicides are commonly used to control weed. However, some plants are resistant to such products. To identify less harmful herbicides, it is crucial to search for different mechanisms of action. Thymol is an easily acquired allelopathic compound, capable of producing its respective semisynthetic derivative, thymoxyacetic acid. The aim of this study was to determine the effects of thymol and thymoxyacetic acid molecules as bioherbicides in greenhouse at the concentration of 3mmol L-1 in pre- and postemergence applications in five species: Amaranthus viridis L., Cucumis sativus L., Lactuca sativa L., Eleusine indica L., and Sorghum bicolor L. The initial seedling development and DNA changes were analyzed. These molecules were contrasting with the solvent, in the negative control, and with the glyphosate, in the positive control, promoting phytogenotoxic activities. The toxic effect of thymoxyacetic acid was more effective in preemergence and thymol's in postemergence. We also observed a reduction in the germination speed index and root growth with a negative correlation to the increase in potassium leaching. Damage to the root and shoot of the seedlings was verified at the DNA level, and the phytotoxicity of the plants treated with the herbicide glyphosate was similar to the plants treated with the natural molecules tested. The bioherbicidal effect of thymol and thymoxyacetic acid exacerbates the reduction of the environmental impact caused by the disordered and increased use of residual pesticides.

Role of helicity in the nonenzymatic template-directed primer extension of DNA.

Complexing a DNA primer with an RNA template showed improved nonenzymatic template-directed primer extension, attributed to a shift in the DNA helicity from a B-type towards an A-type helix. A 2-fold (deoxyadenosine) and 4.5-fold (deoxycytidine) increase in conversion from initial DNA primer to a primer + 1 nucleotide product was observed.