Mutations in RAD3, MSH2, and RAD52 affect the rate of gene amplification in the yeast Saccharomyces cerevisiae

We report here the use of the ADH4:CUP1 amplification detection system to i dentify five high amplification rate (HAR) strains of Saccharomyces cerevis iae that display 40- to 600-fold higher amplification rates than those of p arental strains. We have identified a mutation in RAD3 DNA repair helicase gene in HAR strain B9-40 that results in a 40-fold increase in amplificatio n rate. RAD3 is the functional homolog of the human XPD gene, suggesting th at this model system will provide important candidates for genes that affec t gene amplification in human cells. Isolation of the HAR strains has allow ed us to test whether RAD52, which is essential for recombinational repair of DNA double-strand breaks, is also essential for amplification. Deletion of RAD52 in MAR strains B3-10 and B11-60 decreases amplification approximat ely 100-fold. In contrast, deletion MSH2, which increases recombination bet ween sequences with limited similarity, increases the amplification rate ab out 10-fold. These results suggest that recombination is an important step in amplification. Environ. Mol. Mutagen. 36.325-334, 2000. (C) 2000 Wiley-l iss, Inc.