DNA-SYNTHESIS ERRORS ASSOCIATED WITH DOUBLE-STRAND-BREAK REPAIR

Repair of a site-specific double-strand DNA break (DSB) resulted in in creased reversion frequency for a nearby allele. Site-specific DSBs we re introduced into the genome of Saccharomyces cerevisiae by the endon uclease encoded by the HO gene. Expression of the HO gene from a galac tose-inducible promoter allowed efficient DNA cleavage at a single sit e in large populations of cells. To determine whether the DNA synthesi s associated with repair of DSBs has a higher error rate than that ass ociated with genome duplication, HO-induced DSBs were generated 0.3 kb from revertible alleles of trp1. The reversion rate of the trp1 allel es was similar to 100-fold higher among cells that had experienced an HO cut than among uninduced cells. The reverted allele was found predo minantly on the chromosome that experienced the DNA cleavage.