Mechanisms of Rad52-independent spontaneous and UV-induced mitotic recombination in Saccharomyces cerevisiae

In wild type diploid cells, heteroallelic recombination between his4A and his4C alleles leads mostly to His+ gene conversions that have a parental configuration of flanking markers, but about 22% of recombinants had associated reciprocal crossovers. In rad52 strains, gene conversion is reduced 75-fold and the majority of His+ recombinants were crossover-associated, with the largest class being half-crossovers in which the other participating chromatid was lost. We report that UV-irradiating rad52 cells results in an increase in overall recombination frequency, comparable to increases induced in WT cells, and surprisingly results in a pattern of recombination products quite similar to RAD52 cells: gene conversion without exchange is favored, and the number of 2n-1 events is markedly reduced. Both spontaneous and UV-induced RAD52-independent recombination depends strongly on Rad50, whereas rad50 has no effect in cells restored to RAD52. The high level of noncrossover gene conversion outcomes in UV-induced rad52 cells depends on Rad51, but not on Rad59. Those outcomes also rely on the UV-inducible kinase Dun1 and Dun's target, the repressor Crt1, whereas gene conversions events arising spontaneously depend on Rad59 and Crt1. Thus, there are at least two Rad52-independent recombination pathways in budding yeast.

Key Words: RAD52-independent recombination, UV-induced recombination, gene conversion, half-crossovers

Online ISS 1091-6490
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