scholarly journals The interpretation of gene conversion data from ordered eight-spored asci

1980 ◽  
Vol 35 (2) ◽  
pp. 179-194 ◽  
Author(s):  
J. R. S. Fincham ◽  
W. G. Hill ◽  
E. C. R. Reeve
Keyword(s):  
Gene Conversion ◽  
Wild Type ◽  
Heteroduplex Dna ◽  
Heterozygous Site ◽  
Restricted Model ◽  
Sordaria Fimicola ◽  
Heteroduplex Formation

SUMMARYCurrently favoured models postulate that gene conversion is due to the correction of mis-matches in heteroduplex DNA. If heteroduplex is formed reciprocally on both chromatids participating in recombination, the mis-matches due to a heterozygous site will be different on the two chromatids, and there will be four correction probabilities to be taken into account. It is shown that, given the frequencies of the five different kinds of aberrant ascus ratios, it is possible to calculate four alternative sets of values for the four correction probabilities and the total number of asci in which heteroduplex is formed. These four solutions reduce in effect to two when there are no other markers distinguishing the two chromatids. With the aid of flanking markers and the assumption that heteroduplex formation is chemically polarized, it is possible, in principle, to choose one best solution.The method has been applied to the five one-point crosses in Sordaria fimicola from which most data are available. The data from four different mutants crossed to wild type are compatible with a restricted model in which the correction frequencies, from mutant to wild and from wild to mutant, are the same on both chromatids. In the case of the fifth mutant the data are not consistent with this restricted model, and indicate different correction frequencies in the two chromatids.

scholarly journals Polarity of gene conversion and post-meiotic segregation at the buff locus in Sordaria brevicollis

1973 ◽  
Vol 22 (3) ◽  
pp. 279-289 ◽  
Author(s):  
D. J. Bond
Keyword(s):  
Gene Conversion ◽  
Meiotic Segregation ◽  
Wild Type ◽  
Heteroduplex Dna ◽  
Dna Models ◽  
Hybrid Dna

SUMMARYThe flanking markers of wild-type recombinant spores originating from crosses of spore colour mutants in Sordaria brevicollis were analysed. Recombinant asci were of two main types – either with one or with two wild-type spores. In most crosses the behaviour of flanking markers was significantly different for these two types of recombinant asci. The main differences were in the polarity of gene conversion (as inferred from parental outside marker combinations) and in the frequency of recombinant outside markers. These differences were interpreted in terms of hybrid DNA models of recombination and correction of heteroduplex DNA.

scholarly journals Effect of the Molecular Nature of Mutation on the Efficiency of Intrachromosomal Gene Conversion in Mouse Cells

Genetics ◽  
1987 ◽  
Vol 117 (4) ◽  
pp. 759-769
Author(s):  
Anthea Letsou ◽  
R Michael Liskay
Keyword(s):  
Gene Conversion ◽  
Mammalian Cells ◽  
Directed Path ◽  
Wild Type ◽  
Heteroduplex Dna ◽  
Single Base ◽  
Conversion Rates ◽  
Mouse Cells ◽  
Single Base Pair ◽  
Molecular Nature

ABSTRACT With the intent of further exploring the nature of gene conversion in mammalian cells, we systematically addressed the effects of the molecular nature of mutation on the efficiency of intrachromosomal gene conversion in cultured mouse cells. Comparison of conversion rates revealed that all mutations studied were suitable substrates for gene conversion; however, we observed that the rates at which different mutations converted to wild-type could differ by two orders of magnitude. Differences in conversion rates were correlated with the molecular nature of the mutations. In general, rates of conversion decreased with increasing size of the molecular lesions. In comparisons of conversion rates for single base pair insertions and deletions we detected a genotype-directed path for conversion, by which an insertion was converted to wild-type three to four times more efficiently than was a deletion which maps to the same site. The data are discussed in relation to current theories of gene conversion, and are consistent with the idea that gene conversion in mammalian cells can result from repair of heteroduplex DNA (hDNA) intermediates.

scholarly journals The Extent of Migration of the Holliday Junction Is a Crucial Factor for Gene Conversion in Rhizobium etli

2009 ◽  
Vol 191 (15) ◽  
pp. 4987-4995 ◽  
Author(s):  
Mildred Castellanos ◽  
David Romero
Keyword(s):  
Homologous Recombination ◽  
Gene Conversion ◽  
Holliday Junction ◽  
Relative Role ◽  
Rhizobium Etli ◽  
Wild Type ◽  
Migration Activity ◽  
Efficient System ◽  
In The Wild ◽  
Heteroduplex Formation

ABSTRACT Gene conversion, defined as the nonreciprocal transfer of DNA, is one result of homologous recombination. Three steps in recombination could give rise to gene conversion: (i) DNA synthesis for repair of the degraded segment, (ii) Holliday junction migration, leading to heteroduplex formation, and (iii) repair of mismatches in the heteroduplex. There are at least three proteins (RuvAB, RecG, and RadA) that participate in the second step. Their roles have been studied for homologous recombination, but evidence of their relative role in gene conversion is lacking. In this work, we showed the effect on gene conversion of mutations in ruvB, recG, and radA in Rhizobium etli, either alone or in combination, using a cointegration strategy previously developed in our laboratory. The results indicate that the RuvAB system is highly efficient for gene conversion, since its absence provokes smaller gene conversion segments than those in the wild type as well as a shift in the preferred position of conversion tracts. The RecG system possesses a dual role for gene conversion. Inactivation of recG leads to longer gene conversion tracts than those in the wild type, indicating that its activity may hinder heteroduplex extension. However, under circumstances where it is the only migration activity present (as in the ruvB radA double mutant), conversion segments can still be seen, indicating that RecG can also promote gene conversion. RadA is the least efficient system in R. etli but is still needed for the production of detectable gene conversion tracts.

A general method for identifying correct solutions in the quantitative analysis of gene conversion data

1986 ◽  
Vol 28 (5) ◽  
pp. 701-711 ◽  
Author(s):  
Bernard C. Lamb
Keyword(s):  
Quantitative Analysis ◽  
Gene Conversion ◽  
Simulated Data ◽  
Not Given ◽  
Heterozygous Site ◽  
Simplifying Assumptions ◽  
Sordaria Fimicola ◽  
Recombination Gene ◽  
General Method ◽  
Hybrid Dna

Past attempts to obtain values for meiotic parameters relating to hybrid DNA formation and the correction of mismatched bases in hybrid DNA have not given unique solutions unless various simplifying assumptions were made. A method is given for identifying correct sets of solutions after calculating the frequency of hybrid DNA formation at a heterozygous site and using the fact that closely linked sites within a locus have very similar hybrid DNA formation frequencies. The method is illustrated with simulated data and Sordaria fimicola data; it can also show up incorrect assumptions in analysis. A method is suggested for assessing the importance of double-strand gaps in producing conversions.Key words: recombination, gene conversion, quantitative analysis.

scholarly journals Interaction between mismatch repair and genetic recombination in Saccharomyces cerevisiae.

Genetics ◽  
1994 ◽  
Vol 137 (1) ◽  
pp. 19-39 ◽  
Author(s):  
E Alani ◽  
R A Reenan ◽  
R D Kolodner
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Gene Conversion ◽  
Mismatch Repair ◽  
Base Pair ◽  
Genetic Recombination ◽  
Sequence Similarity ◽  
Amino Acid Sequence Similarity ◽  
Wild Type ◽  
Yeast Saccharomyces Cerevisiae ◽  
Heteroduplex Dna

Abstract The yeast Saccharomyces cerevisiae encodes a set of genes that show strong amino acid sequence similarity to MutS and MutL, proteins required for mismatch repair in Escherichia coli. We examined the role of MSH2 and PMS1, yeast homologs of mutS and mutL, respectively, in the repair of base pair mismatches formed during meiotic recombination. By using specifically marked HIS4 and ARG4 alleles, we showed that msh2 mutants displayed a severe defect in the repair of all base pair mismatches as well as 1-, 2- and 4-bp insertion/deletion mispairs. The msh2 and pms1 phenotypes were indistinguishable, suggesting that the wild-type gene products act in the same repair pathway. A comparison of gene conversion events in wild-type and msh2 mutants indicated that mismatch repair plays an important role in genetic recombination. (1) Tetrad analysis at five different loci revealed that, in msh2 mutants, the majority of aberrant segregants displayed a sectored phenotype, consistent with a failure to repair mismatches created during heteroduplex formation. In wild type, base pair mismatches were almost exclusively repaired toward conversion rather than restoration. (2) In msh2 strains 10-19% of the aberrant tetrads were Ab4:4. (3) Polarity gradients at HIS4 and ARG4 were nearly abolished in msh2 mutants. The frequency of gene conversion at the 3' end of these genes was increased and was nearly the frequency observed at the 5' end. (4) Co-conversion studies were consistent with mismatch repair acting to regulate heteroduplex DNA tract length. We favor a model proposing that recombination events occur through the formation and resolution of heteroduplex intermediates and that mismatch repair proteins specifically interact with recombination enzymes to regulate the length of symmetric heteroduplex DNA.

scholarly journals Rad51-Independent Interchromosomal Double-Strand Break Repair by Gene Conversion Requires Rad52 but Not Rad55, Rad57, or Dmc1

2007 ◽  
Vol 28 (3) ◽  
pp. 897-906 ◽  
Author(s):  
Thomas J. Pohl ◽  
Jac A. Nickoloff
Keyword(s):  
Gene Conversion ◽  
Strand Break ◽  
Double Strand Break ◽  
Single Strand ◽  
Homology Search ◽  
Wild Type ◽  
Dsb Repair ◽  
Single Strand Annealing ◽  
In The Wild ◽  
Break Induced Replication

ABSTRACT Homologous recombination (HR) is critical for DNA double-strand break (DSB) repair and genome stabilization. In yeast, HR is catalyzed by the Rad51 strand transferase and its “mediators,” including the Rad52 single-strand DNA-annealing protein, two Rad51 paralogs (Rad55 and Rad57), and Rad54. A Rad51 homolog, Dmc1, is important for meiotic HR. In wild-type cells, most DSB repair results in gene conversion, a conservative HR outcome. Because Rad51 plays a central role in the homology search and strand invasion steps, DSBs either are not repaired or are repaired by nonconservative single-strand annealing or break-induced replication mechanisms in rad51Δ mutants. Although DSB repair by gene conversion in the absence of Rad51 has been reported for ectopic HR events (e.g., inverted repeats or between plasmids), Rad51 has been thought to be essential for DSB repair by conservative interchromosomal (allelic) gene conversion. Here, we demonstrate that DSBs stimulate gene conversion between homologous chromosomes (allelic conversion) by >30-fold in a rad51Δ mutant. We show that Rad51-independent allelic conversion and break-induced replication occur independently of Rad55, Rad57, and Dmc1 but require Rad52. Unlike DSB-induced events, spontaneous allelic conversion was detected in both rad51Δ and rad52Δ mutants, but not in a rad51Δ rad52Δ double mutant. The frequencies of crossovers associated with DSB-induced gene conversion were similar in the wild type and the rad51Δ mutant, but discontinuous conversion tracts were fivefold more frequent and tract lengths were more widely distributed in the rad51Δ mutant, indicating that heteroduplex DNA has an altered structure, or is processed differently, in the absence of Rad51.

scholarly journals Inherited Differences in Crossing Over and Gene Conversion Frequencies Between Wild Strains of Sordaria fimicola From “Evolution Canyon”

Genetics ◽  
2001 ◽  
Vol 159 (4) ◽  
pp. 1573-1593
Author(s):  
Muhammad Saleem ◽  
Bernard C Lamb ◽  
Eviatar Nevo
Keyword(s):  
Genetic Variation ◽  
Gene Conversion ◽  
Spontaneous Mutation ◽  
Crossing Over ◽  
Natural Genetic Variation ◽  
Evolution Canyon ◽  
Wild Strains ◽  
Sordaria Fimicola ◽  
First And Second Generation ◽  
Consistent Direction

Abstract Recombination generates new combinations of existing genetic variation and therefore may be important in adaptation and evolution. We investigated whether there was natural genetic variation for recombination frequencies and whether any such variation was environment related and possibly adaptive. Crossing over and gene conversion frequencies often differed significantly in a consistent direction between wild strains of the fungus Sordaria fimicola isolated from a harsher or a milder microscale environment in “Evolution Canyon,” Israel. First- and second-generation descendants from selfing the original strains from the harsher, more variable, south-facing slope had higher frequencies of crossing over in locus-centromere intervals and of gene conversion than those from the lusher north-facing slopes. There were some significant differences between strains within slopes, but these were less marked than between slopes. Such inherited variation could provide a basis for natural selection for optimum recombination frequencies in each environment. There were no significant differences in meiotic hybrid DNA correction frequencies between strains from the different slopes. The conversion analysis was made using only conversions to wild type, because estimations of conversion to mutant were affected by a high frequency of spontaneous mutation. There was no polarized segregation of chromosomes at meiosis I or of chromatids at meiosis II.

The Effect of Mismatch Repair and Heteroduplex Formation on Sexual Isolation in Bacillus

Genetics ◽  
1998 ◽  
Vol 148 (1) ◽  
pp. 13-18 ◽  
Author(s):  
Jacek Majewski ◽  
Frederick M Cohan
Keyword(s):  
Mismatch Repair ◽  
Wild Type Strain ◽  
Resistance Mechanism ◽  
Sequence Divergence ◽  
Sexual Isolation ◽  
Wild Type ◽  
Exponential Relationship ◽  
Dna Strands ◽  
The Relationship ◽  
Heteroduplex Formation

AbstractIn Bacillus transformation, sexual isolation is known to be an exponential function of the sequence divergence between donor and recipient. Here, we have investigated the mechanism under which sequence divergence results in sexual isolation. We tested the effect of mismatch repair by comparing a wild-type strain and an isogenic mismatch-repair mutant for the relationship between sexual isolation and sequence divergence. Mismatch repair was shown to contribute to sexual isolation but was responsible for only a small fraction of the sexual isolation observed. Another possible mechanism of sexual isolation is that more divergent recipient and donor DNA strands have greater difficulty forming a heteroduplex because a region of perfect identity between donor and recipient is required for initiation of the heteroduplex. A mathematical model showed that this heteroduplex-resistance mechanism yields an exponential relationship between sexual isolation and sequence divergence. Moreover, this model yields an estimate of the size of the region of perfect identity that is comparable to independent estimates for Escherichia coli. For these reasons, and because all other mechanisms of sexual isolation may be ruled out, we conclude that resistance to heteroduplex formation is predominantly responsible for the exponential relationship between sexual isolation and sequence divergence in Bacillus transformation.

scholarly journals Mechanisms of Recombination between Diverged Sequences in Wild-Type and BLM-Deficient Mouse and Human Cells

2010 ◽  
Vol 30 (8) ◽  
pp. 1887-1897 ◽  
Author(s):  
Jeannine R. LaRocque ◽  
Maria Jasin
Keyword(s):  
Gene Conversion ◽  
Mammalian Cells ◽  
Sequence Divergence ◽  
Dna Lesions ◽  
Human Cells ◽  
Deficient Mouse ◽  
Wild Type ◽  
Strand Breaks ◽  
Major Mechanism ◽  
Homeologous Recombination

ABSTRACT Double-strand breaks (DSBs) are particularly deleterious DNA lesions for which cells have developed multiple mechanisms of repair. One major mechanism of DSB repair in mammalian cells is homologous recombination (HR), whereby a homologous donor sequence is used as a template for repair. For this reason, HR repair of DSBs is also being exploited for gene modification in possible therapeutic approaches. HR is sensitive to sequence divergence, such that the cell has developed ways to suppress recombination between diverged (“homeologous”) sequences. In this report, we have examined several aspects of HR between homeologous sequences in mouse and human cells. We found that gene conversion tracts are similar for mouse and human cells and are generally ≤100 bp, even in Msh2 − / − cells which fail to suppress homeologous recombination. Gene conversion tracts are mostly unidirectional, with no observed mutations. Additionally, no alterations were observed in the donor sequences. While both mouse and human cells suppress homeologous recombination, the suppression is substantially less in the transformed human cells, despite similarities in the gene conversion tracts. BLM-deficient mouse and human cells suppress homeologous recombination to a similar extent as wild-type cells, unlike Sgs1-deficient Saccharomyces cerevisiae.

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