The role of Exo1p exonuclease in DNA end resection to generate gene conversion tracts in Saccharomyces cerevisiae.
Bottom Line: In accordance with this expectation, gene conversion tract lengths associated with spontaneous crossovers in exo1 strains were reduced about twofold relative to wild type.For UV-induced events, conversion tract lengths associated with crossovers were also shorter for the exo1 strain than for the wild-type strain (3.2 and 7.6 kb, respectively).Unexpectedly, however, the lengths of conversion tracts that were unassociated with crossovers were longer in the exo1 strain than in the wild-type strain (6.2 and 4.8 kb, respectively).
Affiliation: Department of Molecular Genetics and Microbiology and University Program in Genetics and Genomics, Duke University Medical Center, Durham, North Carolina 27710.Show MeSH
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Mentions: We propose two new models to explain our data (Figure 7). Both require the assumption that the conversion events associated with crossovers are fundamentally different from those unassociated with crossovers. We suggest that the conversion events associated with crossovers are limited by the length of the resection tract, consistent with the observation that the conversion events associated with crossovers in wild type are significantly longer than those observed in the exo1 strain. In contrast, for the models shown in Figure 7, the lengths of the conversion tracts that are unassociated with crossovers are not limited by resection. In the first model (Figure 7A, wild type; and Figure 7B, exo1), the invading strand synthesizes a region of DNA longer than the gap resulting from end processing. When the invading strand is displaced by SDSA, the displaced end reinvades the processed black chromosome, producing a displaced 5′ end. This end could be removed by Rad27p or a related flap-processing enzyme. By this model, the conversion events unassociated with crossovers can be longer than conversions associated with crossovers (Figure 7B). The processing of a 5′ flap was previously proposed as a step in meiotic recombination (Osman et al. 2003), although in this model, the flap was generated during resolution of a recombination intermediate into a crossover rather than as a step in producing a conversion event unassociated with a crossover.
Affiliation: Department of Molecular Genetics and Microbiology and University Program in Genetics and Genomics, Duke University Medical Center, Durham, North Carolina 27710.