High levels of recombination induced by homologous P elements in Drosophila melanogaster
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Keywords:
Non-allelic homologous recombination
Ectopic recombination
FLP-FRT recombination
Mitotic crossover
Transposition (logic)
Non-homologous end joining
Gene conversion
DNA Transposable Elements
Site-specific recombination
Abstract In previous studies of the loss of heterozygosity (LOH), we analyzed a hemizygous URA3 marker on chromosome III in S. cerevisiae and showed that homologous recombination is involved in processes that lead to LOH in multiple ways, including allelic recombination, chromosome size alterations, and chromosome loss. To investigate the role of homologous recombination more precisely, we examined LOH events in rad50Δ, rad51Δ, rad52Δ, rad50Δ rad52Δ, and rad51Δ rad52Δ mutants. As compared to Rad+ cells, the frequency of LOH was significantly increased in all mutants, and most events were chromosome loss. Other LOH events were differentially affected in each mutant: the frequencies of all types of recombination were decreased in rad52 mutants and enhanced in rad50 mutants. The rad51 mutation increased the frequency of ectopic but not allelic recombination. Both the rad52 and rad51 mutations increased the frequency of intragenic point mutations ∼25-fold, suggesting that alternative mutagenic pathways partially substitute for homologous recombination. Overall, these results indicate that all of the genes are required for chromosome maintenance and that they most likely function in homologous recombination between sister chromatids. In contrast, other recombination pathways can occur at a substantial level even in the absence of one of the genes and contribute to generating various chromosome rearrangements.
Ectopic recombination
Mitotic crossover
RAD52
Non-allelic homologous recombination
FLP-FRT recombination
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Mitotic crossover
RAD52
Ectopic recombination
FLP-FRT recombination
Non-allelic homologous recombination
Chromosomal crossover
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Citations (7)
Non-allelic homologous recombination
Ectopic recombination
FLP-FRT recombination
Mitotic crossover
Transposition (logic)
Non-homologous end joining
Gene conversion
DNA Transposable Elements
Site-specific recombination
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Citations (35)
Abstract We have examined the role that genomic location plays in mitotic intragenic recombination. Mutant alleles of the LEU2 gene were inserted at five locations in the yeast genome. Diploid and haploid strains containing various combinations of these inserts were used to examine both allelic recombination (between sequences at the same position on parental homologs) and ectopic recombination (between sequences at nonallelic locations). Chromosomal location had little effect on mitotic allelic recombination. The rate of recombination to LEU2 at five different loci varied less than threefold. This finding contrasts with previous observations of strong position effects in meiosis; frequencies of meiotic recombination at the same five loci differ by about a factor of forty. Mitotic recombination between dispersed copies of leu2 displayed strong position effects. Copies of leu2 located approximately 20 kb apart on the same chromosome recombined at rates 6-13-fold higher than those observed for allelic copies of leu2. leu2 sequences located on nonhomologous chromosomes or at distant loci on the same chromosome recombined at rates similar to those observed for allelic copies. We suggest that, during mitosis, parental homologs interact with each other no more frequently than do nonhomologous chromosomes.
Mitotic crossover
Ectopic recombination
Non-allelic homologous recombination
Gene conversion
Chromosomal crossover
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Abstract Allelic and nonallelic (ectopic) recombination events were analyzed in a set of isogenic strains that carry marked Ty elements. We found that allelic recombination between Ty elements occurred at normal frequencies both in meiosis and mitosis. The marked Ty elements were involved in a large variety of different types of ectopic recombination and this variety was greater in mitosis than in meiosis. Allelic and ectopic recombination events occurred at similar frequencies in mitosis, but allelic recombination predominated in meiosis. Some of the types of ectopic mitotic recombination indicated the common occurrence of concerted recombination events. The length of homology represented by a delta element (330 bp) seemed to be sufficient for some types of mitotic and meiotic recombination.
Mitotic crossover
Ectopic recombination
Chromosomal crossover
Non-allelic homologous recombination
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Abstract Chromosomal rearrangements can result from crossing over during ectopic homologous recombination between dispersed repetitive DNA. We have previously shown that meiotic ectopic recombination between artificially dispersed ade6 heteroalleles in the fission yeast Schizosaccharomyces pombe frequently results in chromosomal rearrangements. The same recombination substrates have been studied in mitotic recombination. Ectopic recombination rates in haploids were ∼1-4 × 10-6 recombinants per cell generation, similar to allelic recombination rates in diploids. In contrast, ectopic recombination rates in heterozygous diploids were 2.5-70 times lower than allelic recombination or ectopic recombination in haploids. These results suggest that diploid-specific factors inhibit ectopic recombination. Very few crossovers occurred in ade6 mitotic recombination, either allelic or ectopic. Allelic intragenic recombination was associated with 2% crossing over, and ectopic recombination between multiple different pairing partners showed 1-7% crossing over. These results contrast sharply with the 35-65% crossovers associated with meiotic ade6 recombination and suggest either differential control of resolution of recombination intermediates or alternative pathways of recombination in mitosis and meiosis.
Ectopic recombination
Mitotic crossover
FLP-FRT recombination
Non-allelic homologous recombination
Chromosomal crossover
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Abstract Homologous recombination is increased during meiosis between DNA sequences at the same chromosomal position (allelic recombination) and at different chromosomal positions (ectopic recombination). Recombination hotspots are important elements in controlling meiotic allelic recombination. We have used artificially dispersed copies of the ade6 gene in Schizosaccharomyces pombe to study hotspot activity in meiotic ectopic recombination. Ectopic recombination was reduced 10–1000-fold relative to allelic recombination, and was similar to the low frequency of ectopic recombination between naturally repeated sequences in S. pombe. The M26 hotspot was active in ectopic recombination in some, but not all, integration sites, with the same pattern of activity and inactivity in ectopic and allelic recombination. Crossing over in ectopic recombination, resulting in chromosomal rearrangements, was associated with 35–60% of recombination events and was stimulated 12-fold by M26. These results suggest overlap in the mechanisms of ectopic and allelic recombination and indicate that hotspots can stimulate chromosomal rearrangements.
Ectopic recombination
Mitotic crossover
FLP-FRT recombination
Non-allelic homologous recombination
Ectopic expression
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Summary The eukaryotic DNA mismatch repair (MMR) system contributes to maintaining genome integrity and DNA sequence fidelity in at least two important ways: by correcting errors arising during DNA replication, and also by preventing recombination events between divergent sequences. This study aimed to investigate the role of one key MMR gene in recombination. We obtained a mutant line in which the AtMLH1 gene has been disrupted by the insertion of a T‐DNA within the coding region. Transcript analysis indicated that no full‐length transcript was produced in mutant plants. The loss of a functional AtMLH1 gene led to a significant reduction in fertility in both homozygotes and heterozygotes, and we observed a strong bias against transmission of the mutant allele. To investigate the role of AtMLH1 in mitotic recombination, the mutant was crossed to a series of recombination reporter lines. A strong decrease (72%) in the frequency of homologous recombination was observed in the mutant. However, the decline in recombination due to homeology was less severe in the Atmlh1 mutant than in a wild‐type control. These data demonstrate a dual role for AtMLH1 in recombination: it is both required for recombination and acts to limit recombination between diverged sequences.
Mitotic crossover
Ectopic recombination
Non-allelic homologous recombination
FLP-FRT recombination
Gene conversion
Gene targeting
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Three recombination events, reciprocal recombination, sister-chromatid recombination, and gene conversion, were studied using substrates designed in vitro. Each type of recombination event can be monitored at any chromosomal location. We have shown that sister-chromatid recombination is induced mitotically by DNA damaging agents, such as methyl methanesulfonate and gamma-rays, but is decreased mitotically in strains defective in rad52. Reciprocal recombination by which circular plasmids integrate into the genome is unaffected by rad52 defective alleles and occurs by a different recombination pathway. Mechanisms are suggested by which gene conversion between sister chromatids can generate chromosome rearrangements.
Non-allelic homologous recombination
FLP-FRT recombination
Site-specific recombination
Ectopic recombination
Gene conversion
Mitotic crossover
Cre-Lox recombination
RAD52
Non-homologous end joining
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Citations (104)