Mechanisms and Regulation of Mitotic Recombination in Saccharomyces cerevisiae
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Abstract Homology-dependent exchange of genetic information between DNA molecules has a profound impact on the maintenance of genome integrity by facilitating error-free DNA repair, replication, and chromosome segregation during cell division as well as programmed cell developmental events. This chapter will focus on homologous mitotic recombination in budding yeast Saccharomyces cerevisiae. However, there is an important link between mitotic and meiotic recombination (covered in the forthcoming chapter by Hunter et al. 2015) and many of the functions are evolutionarily conserved. Here we will discuss several models that have been proposed to explain the mechanism of mitotic recombination, the genes and proteins involved in various pathways, the genetic and physical assays used to discover and study these genes, and the roles of many of these proteins inside the cell.Keywords:
Mitotic crossover
FLP-FRT recombination
Effects of the rad52 mutation in Saccharomyces cerevisiae on meiotic, ..gamma..-ray-induced, uv-induced, and spontaneous mitotic recombination were studied. The rad52/rad52 diploids undergo premeiotic DNA synthesis; sporulation occurs but inviable spores are produced. Intra- and intergenic recombination during meiosis were examined in cells transferred from sporulation medium to vegetative medium at different time intervals. No intragenic recombination was observed at the hisl-1/hisl-315 and trp5-2/trp5-48 heteroalleles. Gene-centromere recombination was also not observed in rad52/rad52 diploids. No ..gamma..-ray-induced intragenic mitotic recombination is seen in rad52/rad52 diploids and uv-induced intragenic recombination is greatly reduced. However, spontaneous mitotic recombination is not similarly affected. The RAD52 gene thus functions in recombination in meiosis and in ..gamma..-ray and uv-induced mitotic recombination but not in spontaneous mitotic recombination.
RAD52
Mitotic crossover
Ectopic 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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Mitotic crossover
FLP-FRT recombination
Ectopic recombination
Non-homologous end joining
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Mitotic crossover
FLP-FRT recombination
Gene conversion
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Summary All major recombination pathways in the yeast Saccharomyces cerevisiae require the RAD52 gene product. We have examined the effect of the rad52-1 mutation on spontaneous mitotic recombination between heteroalleles, and found that prototrophs are produced at frequencies significantly above reversion. This residual recombination occurs at a relatively uniform level at all of the loci examined. To help understand the role that RAD52 plays in mitotic recombination, we examined recombination between all pairwise combinations of six mutant alleles of the LYS2 gene. The rad52-1 mutation decreased the variation in amount of recombination between the various pairwise combinations as well as lowering the overall frequency of recombination. The reduced variation results in a different pattern of recombination in rad52-1 cells than in wild type. One interpretation of these results is that the RAD52 gene product, directly or indirectly, plays a role in the formation or the resolution of mismatches in heteroduplex DNA.
Mitotic crossover
RAD52
FLP-FRT recombination
Ectopic recombination
Gene conversion
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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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Mitotic crossover
FLP-FRT recombination
Ectopic recombination
Gene conversion
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This chapter discusses the general features of mitotic recombination in the yeast Saccharomyces cerevisiae. Mitotic recombination was first studied in diploid strains bearing markers heterozygous at several loci. Recombinants are detected as prototrophic segregants that arise primarily from intragenic recombinations, which are gene conversion events. Reciprocal recombination or crossing-over between a gene and the centromere is detected by the homozygosis of a heterozygous marker. Mitotic recombination usually occurs at a site of DNA damage. Because recombination is one of the mechanisms used to repair DNA damage, and more specifically double-strand breaks, mutants that are deficient in the repair of double-strand breaks often show reduced recombination levels. The chapter summarizes the types of mutants identified both in yeast and Escherichia coli that have altered hypo- and hyper-recombination rates. Mitotic hyper-recombination mutants include defects in the functions required for DNA repair systems and functions required for DNA replication. Most of these mutants result in the accumulation of DNA lesions that are recombinogenic.
Mitotic crossover
FLP-FRT recombination
Gene conversion
Ectopic recombination
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A review of research on genetic control of mitotic recombination in the yeast Saccharomyces cerevisiae is presented. The genes controlling different stages of mitotic recombination have been considered. Possible relationship of the recombination and repair functions of these genes is under discussion.
Mitotic crossover
FLP-FRT recombination
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Studies with Saccharomyces cerevisiae, which has been used as a model system for studying the mechanism(s) of genetic recombination, have documented a number of different types of recombination events. In haploid mitotic cells, both intrachromosomal recombination and sister chromatid exchange are known to occur (Szostak and Wu 1980; Jackson and Fink 1981; Klein and Petes 1981), and in diploid mitotic cells, recombination events can also occur between homologous chromosomes (Fogel and Mortimer 1971). Recombination during meiosis occurs at substantially higher frequencies than spontaneous mitotic recombination events (Fogel and Mortimer 1971). Furthermore, the frequency of gene conversion observed at different loci during meiosis is known to vary over a 30-fold range, suggesting that simple sequence homology is not the only requirement at the DNA level for recombination (Fogel et al. 1979). During meiosis, recombination appears to occur at the four-strand stage by a mechanism that yields both gene conversion events and...
Mitotic crossover
Gene conversion
FLP-FRT recombination
Non-allelic homologous recombination
Ectopic recombination
Chromosomal crossover
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