Analyses of DNA double-strand break repair pathways in tandem arrays of HXT genes of Saccharomyces cerevisiae.

Abstract

Eukaryotic genomes contain numerous homologous repeat sequences including redundant genes with divergent homology that can be potential recombination targets. Recombination between divergent sequences is rare but poses a substantial threat to genome stability. The hexose transporter (HXT) gene family shares high sequence similarities at both protein and DNA levels, and some members are placed close together in tandem arrays. In this study, we show that spontaneous interstitial deletions occur at significantly high rates in HXT gene clusters, resulting in chimeric HXT sequences that contain a single junction point. We also observed that DNA double-strand breaks created between HXT genes produce primarily interstitial deletions, whereas internal cleavage of the HXT gene resulted in gene conversions as well as deletion products. Interestingly, interstitial deletions were less constrained by sequence divergence than gene conversion. Moreover, recombination-defective mutations differentially affected the survival frequency. Mutations that impair single-strand annealing (SSA) pathway greatly reduced the survival frequency by 10-1,000-fold, whereas disruption of Rad51-dependent homologous recombination exhibited only modest reduction. Our results indicate that recombination in the tandemly repeated HXT genes occurs primarily via SSA pathway.