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 also examined the distribution of spontaneous recombination events in the exo1 strain YYy34 on the right arm of chromosome IV. The most obvious difference between the wild-type and exo1 strains in this distribution was the absence of the HS3 and HS4 peaks in the exo1 strain (Figure 4). The HS3 and HS4 hotspots in the wild-type strain have two important properties: they are G1 specific and they involve breakage of the W303a-derived homology (St. Charles and Petes 2013). We found that the W303a-derived homolog has an inverted pair of Ty elements spaced ∼50 bp apart at HS4, whereas the YJM789-derived homolog has only a portion of one Ty element at the allelic position (St. Charles and Petes 2013). Since deletion of one of the Ty elements or increasing the distance between the elements results in loss of HS4 activity in the wild-type strain, we suggested that the recombinogenic effect of HS4 likely reflected formation of a secondary structure in unreplicated DNA (St. Charles and Petes 2013). One mechanism for producing a DSB in G1 is to expand a nick on one strand into a gap, allowing for formation of a “hairpin” on the ungapped strand (Figure 5). Cleavage of the unpaired bases at the tip of the hairpin would result in a G1-specific DSB. The role of Exo1p in this process could be in the formation of the gap and/or the processing of the broken ends to allow invasion of the homolog that lacks Ty elements. An interesting feature of the conversion events associated with HS4 in wild-type strains is that median conversion tract length is ∼50 kb, much larger than that observed for other spontaneous G1 gene conversions [14 kb (St. Charles and Petes 2013)].
Affiliation: Department of Molecular Genetics and Microbiology and University Program in Genetics and Genomics, Duke University Medical Center, Durham, North Carolina 27710.