Decrease In Recombination Rate Research Articles

Universal Scaling Law for Polypeptide Backbone Dynamics on the Pico- to Millisecond Time Scale

UV-photolysis of an aromatic disulfide bond which holds a protein or peptide in a non-native conformation has been used to trigger polypeptide backbone relaxation. Geminate recombination of the disulfide bond was used as probe for non-equilibrium backbone dynamics; as the thiyl radicals separate under the influence of backbone motion, their recombination rate decreases, so that observation of the transient thiyl absorbance provides access to backbone dynamics. Unlike fluorescence or triplet quenching experiments, which often are used for the study of polypeptide dynamics, this method observes processes far from equilibrium, and has no intrinsic limitation of the accessible time scale.The encounter probability of the thiyl radicals was found to decay with time following a power law t-0.94 which is incompatible with simple diffusion. Thus, the relative motion of the radicals is affected by the dynamics of the connecting backbone, resulting in an unusual power law for the re-encounter probability which could be described as (fractal) diffusion in a reduced non-integer dimensional space. The scaling law was found to extend over the full experimental time window, covering nine orders of magnitude in time (1 ps to 1 ms), although very different processes govern backbone motion on these different time scales. Furthermore, the same scaling law was observed in a folding protein having secondary and tertiary structure, in simple model peptides forming only secondary structure, and in a protein under unfolding conditions, indicating an intrinsic behaviour of the polypeptide backbone itself.

Consensus features of microsatellite distribution: Microsatellite contents are universally correlated with recombination rates and are preferentially depressed by centromeres in multicellular eukaryotic genomes

Microsatellite DNA is highly polymorphic and informative, which makes its distribution pattern and its associations very valuable for marker applications and genomic research in evolution. Using computational and statistical approaches, based on database technology, we have demonstrated that microsatellite content is consistently and significantly 2 to 5 fold lower than the average chromosomal level in the centromeric and pericentromeric regions of the chromosomes of two plant species, Arabidopsis thaliana and Oryza sativa. We conducted a path coefficient analysis to compare the direct effect of microsatellites (from mono-nucleotide through to penta-nucleotide repeats) on recombination rates. The results revealed that tri- and penta-nucleotide microsatellites significantly influence recombination rates. In the human genome, tri-, tetra- and mono-nucleotide microsatellites, in decreasing order, make significant direct contributions to recombination rates, according to DECODE, GENTHON, and MARSHFIELD averages. Path coefficient analysis in rice and human genomes of the impact of di-nucleotide microsatellites of different motifs on recombination rates indicate that motifs with either A or T have an effect, resulting in increased recombination rates for microsatellites with motifs consisting of 50% A or T, such as AG, TC, CA, TG. Conversely, microsatellites with motifs consisting of only A & T or G & C, such as AT, TA, GC or CG, have decreased recombination rates. The extremely low microsatellite content in centromeric and pericentromeric regions, as well as the quantitative association of microsatellite sequences with the recombination rate at the genome level, suggests that purifying selection in genome evolution creates a balance between genomic polymorphisms and the biological function of sequences in a genome.

Analysis of the segregation and recombination rates at morphological and SSR loci in hybrid combinations of barley substitution lines

The inheritance of nuclear morphological and molecular markers was studied in hybrid reciprocal populations of barley alloplasmic lines. A number of loci displayed a distortion of the Mendelian inheritance and a decrease in recombination rate depending on the cross direction and cytoplasm of parental forms. The segregations shifted towards both the mutant recessive and normal dominant phenotypes. The effect of cytoplasm on transmission and recombination of nuclear loci was shown.

Different Net Effect of TiO2 Sintering Temperature on the Photocatalytic Removal Rates of 4-Chlorophenol, 4-Chlorobenzoic Acid and Dichloroacetic Acid in Water

Our purpose was to show that the sintering temperature of TiO2 can have a different net effect (thought to arise from a decrease in surface area against a decrease in recombination rate of charge carriers) on the photocatalytic removal rate of various organic pollutants in water. For that, we have chosen four chlorinated pollutants, viz. 4-chlorophenol (4-CP), 2,5-dichlorophenol (2,5-DCP), 4-chlorobenzoic acid (4-CBA) and dichloroacetic acid (DCAA). Their photocatalytic removal was studied over four TiO2 samples (from Millennium Chemicals or affiliate) all obtained identically by TiOSO4 thermohydrolysis with subsequent calcination at various temperatures, TiO2 Degussa P25 was used for comparison. At equal TiO2 mass in the slurry photoreactor, the pseudo-first-order removal rate constant k increased with the calcination temperatures for the three aromatic pollutants, whereas it was the opposite for the aliphatic acid. Results obtained with P25 were consistent with the reasoning based on the combined effects of surface area and charge recombination rate. Similar k values for 4-CP and 2,5-DCP, irrespective of the TiO2, further illustrate the importance of the molecular structure. For 4-CBA, the possibility of decarboxylation in addition to an attack on the ring, as well as a much higher extent of adsorption, can explain a higher k with respect to the chlorophenols. The implication of these results is that the hole attack mechanism for carboxylic acids is much more sensitive to surface area variation than would be the (diffusible) OH radical mechanism for aromatics which could react in the near-surface solution-phase.

Kinetic processes in a nonideal Rydberg matter

A kinetic model is developed to describe ultracold nonideal Rydberg plasmas, which allows all stages of the generation and decay of such a plasma to be sequentially traced. The plasma kinetics is considered on the basis of available experimental data corresponding to a nonideality parameter of γ ∼ 1. The results of theoretical analysis are in good agreement with experiment. Calculations show evidence of a significantly decreased recombination rate and, hence, of the possible formation of a metastable structure in the plasma under consideration. The distribution of the number of excited atoms is determined for the plasma with Ne = Ni = 7 × 105 and Ee = 9 K. The observed behavior of the number and density of particles as functions of the time and principal quantum number is explained. It is suggested that the distribution of excited atoms for the given parameters has a maximum for the state with k = 25.

Serial segmental duplications during primate evolution result in complex human genome architecture

The human genome is particularly rich in low-copy repeats (LCRs) or segmental duplications (5%-10%), and this characteristic likely distinguishes us from lower mammals such as rodents. How and why the complex human genome architecture consisting of multiple LCRs has evolved remains an open question. Using molecular and computational analyses of human and primate genomic regions, we analyzed the structure and evolution of LCRs that resulted in complex architectural features of the human genome in proximal 17p. We found that multiple LCRs of different origins are situated adjacent to one another, whereas each LCR changed at different time points between >25 to 3-7 million years ago (Mya) during primate evolution. Evolutionary studies in primates suggested communication between the LCRs by gene conversion. The DNA transposable element MER1-Charlie3 and retroviral ERVL elements were identified at the breakpoint of the t(4;19) chromosome translocation in Gorilla gorilla, suggesting a potential role for transpositions in evolution of the primate genome. Thus, a series of consecutive segmental duplication events during primate evolution resulted in complex genome architecture in proximal 17p. Some of the more recent events led to the formation of novel genes that in human are expressed primarily in the brain. Our observations support the contention that serial segmental duplication events might have orchestrated primate evolution by the generation of novel fusion/fission genes as well as potentially by genomic inversions associated with decreased recombination rates facilitating gene divergence.

Mechanism of surface charge creation due to image forces

The image force is considered to be one of the non-specific sources of surface charge and origin of the double charge layerin the interface between a non-polar liquid dielectric and a polar solid. It is assumed that there is no interaction between phases, neither chemical interaction nor preferential adsorption, due to their specific chemical nature. Two possible physical mechanisms have been investigated. The first takes into account the existence of a potential barrier to the charge movement as it leaves the surface. Therefore, the charges that are in liquid are attracted to the surface. The second is the reduction of dissociation energy of ion pairs close to the interface in comparison with bulk dissociation. Both mechanisms result in a decrease of recombination rate and a sharp increase of dissociation rate. It has been shown that both these mechanisms could lead to the creation and accumulation of an abnormal non-specific surface charge carrier.

Population genetic perspectives on the evolution of recombination.

Optimality arguments and modifier theory are reviewed as paradigms for the study of the evolution of recombination. Optimality criteria (such as maximization of mean fitness) may agree with results from models developed in terms of the evolution of recombination at modifier loci. Modifier models demonstrate, however, that equilibrium mean fitness can decrease during the evolution of recombination rates and is not always maximized. Therefore, optimality arguments do not successfully predict the conditions under which increased or decreased recombination will evolve. The results from modifier models indicate that decreased recombination rates are usually favored when the population is initially near a polymorphic equilibrium with linkage disequilibrium. When the population is subject to directional selection or to deleterious mutations, increased recombination may be favored under certain conditions, provided that there is negative epistasis among alleles.

In vivo assay of p53 function in homologous recombination between simian virus 40 chromosomes.

To investigate a possible role of p53 in DNA exchange mechanisms, we have developed a model system which allows us to quantify homologous recombination rates in eukaryotic cells. We generated two types of simian virus 40 (SV40) whose genomes were mutated in such a way that upon double infection of monkey cells, virus particles can be released only after interchromosomal exchange of genetic material. This test system allowed us to determine recombination rates in the order of 10(-4) to 10(-6) for chromatin-associated SV40 genomes. To study the role of p53-T-antigen (T-Ag) complexes in this process, we designed viral test genomes with an additional mutation leading to a single amino acid exchange in T-Ag (D402H) and specifically blocking T-Ag-p53 interactions. Analysis of primary rhesus monkey cells endogenously expressing wild-type p53 showed a decreased recombination rate upon loss of efficient T-Ag-p53 complex formation. However, cells expressing mutant p53 (LLC-MK2 cells), the introduction of mutant T-Ag did not affect the DNA exchange rates. Our data are interpreted to indicate an inhibitory role of wild-type p53 in recombination. In agreement with this hypothesis, p53-T-Ag complex formation alleviates the inhibitory effect of wild-type p53.

In situ measurements of the recombination at the crystalline silicon/amorphous silicon heterointerface by time resolved microwave conductivity measurements during low temperature annealing and silane plasma exposure

The decay of optically generated excess charge carriers at the heterointerface between crystalline silicon and amorphous silicon has been monitored in situ during plasma deposition of the amorphous layer. A dramatic increase in the interface recombination rate is seen instantly when the silane plasma is ignited. In a later stage of amorphous layer deposition, the recombination rate decreases. This interface passivation depends strongly on the substrate temperature and is more efficient at higher temperature and in the presence of silane plasma. The effect is not due to a change in the band bending at the heterointerface.

Variation for genetic recombination among tomato plants regenerated from three tissue culture systems

Shoot morphogenesis was compared among two tomato inbred lines, two mutant lines, and their eight reciprocal F1 hybrids in three tissue culture systems. The number of shoots per explant was greatest on tomato pedicel explants, intermediate on cotyledon calli, and poor on micropropagated shoot tips. Genetic recombination rates of F1 hybrid plants regenerated from three tissue culture systems were analyzed by backcrossing the regenerated plants with mutant parents and comparing the observed crossover frequencies with those expected based on control plants raised from seed. Increased recombination rates and map distance were observed among plants from micropropagated shoot tips (18.8%), cotyledon calli (17.3%), and pedicel explants (13.5%) between the markers sunny (sy) and baby leaf syndrome (bls), which flank the centromere on chromosome 3. Conversely, decreased recombination rates and map distance were observed between bls and the locus solanifolia (sf), which is more distal to the centromere on the same arm of chromosome 3 as bls. Increased recombination rates and map distance among plants from micropropagated shoot tips, cotyledon calli, and pedicel explants were also observed between the loci white virescence (wv) and anthocyanin reduced (are) on chromosome 2.Key words: genetic recombination, tomato, Lycopersicon esculentum, pedicel explants, micropropagation, callus culture, plant regeneration.

Radiofrequency detector for gas chromatography

A radiofrequency detector is described that is designed as a parallel-plate 63Ni electron-capture detector working with pure argon as carrier gas and with a radiofrequency voltage superimposed on a d.c. voltage. The principle of operation is that the radiofrequency voltage increases the mean electron energy within the detector, decreases the drift velocity and, owing to an increase in the recombination rate, the ionization current drops. In the presence of sample molecules the reverse process takes place: the drift velocity increases, the recombination rate decreases and the ionization current increases. Positive substance peaks occur. Detection limits down to 0.1 ppm for organic substances and 1.0 ppm for inorganic gases (carbon dioxide) are obtainable.

Variability for Recombination Frequencies in the AP12 Soybean Population

Repeated intermating in a plant‐breeding procedure increases the number of meiotic cycles and the opportunities to break genetic linkages, but it also increases the number of generations required to complete a round of the procedure. Because a 50% increase in recombination over the normal level in an F1 generation would be as effective in breaking linkages as one generation of intermating of F2 individuals, genetic control of recombination might be usable in place of repeated intermating. The objectives of this study were to determine if variability in recombination frequency exists in the API2 soybean [Glycine max (L.) Merr.] population and to isolate genotypes with increased or decreased recombination rates. Recombination frequencies were measured in F2 populations of 50 AP12 individuals crossed with each of three ‘Clark’ near isolines containing the respective linkage groups P1r, lnp2, and dt1L1. For each of the three linkage groups, significant (P ≤ 0.05) variability for recombination frequency existed among individuals in the AP12 population, and the recombination frequencies were normal|y distributed. As in many other organisms, recombination frequency of soybean appears to be under polygenic control. Correlation coefficients of recombination frequencies among individuals across the three linkage groups were nonsignificant (P > 0.05). Although genotypes were present with recombination frequencies above or below the population mean for all the linkage groups, a genotype that generally enhances or represses recombination was not isolated.

Pulsed-laser conductivity study of recombination kinetics of proton and hydroxide in alcohol water/liquid mixtures

The kinetics of the self-ionization of water have been studied in water-rich alcohol/water mixtures (ethanol, methanol, and 1-propanol). A pulsed laser excites overtones of the O-H vibrations, leading to the dissociative ionization of water and formation of excess hydronium and hydroxide ions. The relaxation back to equilibrium concentrations is analyzed for the recombination and dissociation rates at 25/sup 0/C as a function of solvent composition. The recombination rate for ethanol/water mixtures is constant within experimental error between 0 and 4.5 mol% ethanol, and then decreases monotonically as the concentration of ethanol increases to 25 mol%. Methanol and 1-propanol mixtures show an almost identical decrease in recombination rate with mol% alcohol. Dissociation rate constants also decrease with increasing alcoholic content; however, the rate of decrease depends upon the particular alcohol. 23 references, 5 figures, 2 tables.

Molecular models for recombination and disproportionation of radicals

The modified Gorin model of recombination as a long range interaction of weakly bound radicals, constrained only by steric forces, is rederived to give a collision impact parameter 11% larger than rmax, the separation at the centrifugal maximum. This larger impact parameter resolves some of the earlier difficulties with secondary and tertiary radicals. By imposing a new constraint, that the orientation of the radicals be such as to permit exchange forces to act, a new model is developed in which kr = 1/4 Zr α, where a represents the product of fractions of active surface areas of each radical available for bonding. Excellent agreement is obtained in estimating values of kr.Analysis of disproportionation is made to show that it cannot be described by the tight transition state but must also be governed by similar, long range exchange forces between the bond being attacked and the same "active surface" of the abstracting radical. Using an ad hoc radius for [Formula: see text]equal to 4 Å it is possible to reproduce the data on alkyl radical disproportionation to within ± 10%.The model predicts a small decrease in rate of recombination with increasing temperature. This decrease is more pronounced for bulkier radicals and at higher temperatures (> 900 K).

Semiconductor Electrodes: XLI . Improvement of Performance of Electrodes by Electrochemical Polymerization of o‐Phenylenediamine at Surface Imperfections

The dark electrochemical polymerization of o‐phenylenediamine (OPD) at and single crystal electrodes (surface ⊥ C axis exposed) was investigated. The results indicate that polymerization occurs only at surface imperfections (edges, steps) in the otherwise smooth van der Waal's surface. The photoelectrochemical response, in aqueous solutions containing and , of electrodes subjected to this polymerization is improved compared to the untreated electrodes. The results are consistent with a decrease in recombination rate due to blocking of surface states by OPD polymerization. The characteristics of several PEC cells before and after OPD polymerization are also described. Increases in the solar‐to‐electrical power efficiency, η, range from 30–300% after surface pretreatment.

GENETIC MODIFICATION OF RECOMBINATION RATE IN TRIBOLIUM CASTANEUM

Asymmetrical responses were obtained in a replicated study of 15 generations of two-way selection for recombination rate between the ruby (rb) and jet (j) loci in Tribolium castaneum. Recombination rates in the two replicate high lines increased from an average of 0.22 in the base populations to an average of 0.42 at generation 15. Recombination rate pooled over the 15 generations of selection in each low line was significantly less than the control but there was no clear downward trend in response to selection for decreased recombination rate. The realized heritabilities were 0.16 +/- 0.03 and 0.17 +/- 0.02 in the two high lines, and were not significantly different from zero in the two low lines. Selection was based on crossing over in cis females only; however, rates measured in cis males after 12 generations showed the same response patterns as female rates. Similar response patterns were also determined for recombination measured in trans males and females at generation 18 following three generations of relaxed selection. The distribution of recombination rates measured in backcross beetles [(H X L) X H and (H X L) X L] at generation 12 indicated polygenic control with those genes decreasing recombination rate being dominant. Detailed analysis of recombination rates in F1's produced by interline crosses at generation 15 confirmed the directional dominance findings. Under a polygenic model of recombination modifiers in which low recombination is dominant to high, average recombination rates will increase as inbreeding progresses, thus providing a mechanism for the production of new gene combinations in small populations.

Effect of temperature and physical state on the inhibition by additives of radiation‐induced degradation of poly(methyl methacrylate)

AbstractIt has been reported in earlier papers that aromatic additives can reduce the rate of radiation‐induced degradation of poly(methyl methacrylate) (PMMA), depending on the concentration, the distribution, and the resonance of the aromatic system. In the present work, the temperature dependence is studied, together with the influence of molecular mobility, which is determined by the physical state of the system. For this purpose, PMMA containing benzene, biphenyl, naphthalene, anthracene, phenanthrene, pyrene, or benz[a]anthracene, was γ‐irradiated at room temperature and also, except with naphthalene and biphenyl, in the temperature range −80 to 160°C. The changes in degradation rate were related to the first excited singlet state and to the resonance energy of the additives. The results suggest that at low temperatures both electron scavenging and transfer of excitation energy occur. At temperatures between the γ transition and the glass transition, the significance of energy transfer compared with electron scavenging increases, whereas the inhibitory effect decreases. Above the glass transition temperature the inhibition decreases more rapidly. This is related to scavenging of radical chain fragments, due to increasing molecular mobility, which causes a decrease in recombination rate. This sensitization of degradation competes with the inhibition by energy transfer and electron scavening, and may prevail at temperatures above 185°C. The opposing effects of these mechanisms can be clearly shown with the system PMMA–benzene. In viscous mixtures, sensitization prevails even at room temperature.

Angular momentum role in oxygen recombination

The dependence on the atomic oxygen ground state total angular momentum quantum number J of the three body recombination rate to form the ground molecular state X 3Σg- is calculated. An adiabatic approach of the atoms is assumed. For a thermal equilibrium distribution of the atoms in the 3PJ states, a 20% decrease in recombination rate as the temperature increases from 100 to 1000°K is found. The dependence is too small to warrent inclusion in the modified phase-space theory of reaction rates of Keck and co-workers.