Three temperature-sensitive S. cerevisiae RFA1 alleles were found to cause elevated mutation rates. These mutator phenotypes resulted from the accumulation of base substitutions, frameshifts, gross deletions (8 bp-18 kb), and nonreciprocal translocations. A representative rfa1 mutation exhibited a growth defect in conjunction with rad51, rad52, or rad10 mutations, suggesting an accumulation of double-strand breaks. rad10 and rad52 mutations eliminated deletion and translocation formation, whereas a rad51 mutation increased the frequency of these events and revealed a new class of genetic rearrangements - loss of a portion of a chromosome arm combined with telomere addition. The breakpoints of the translocations and deletions were flanked by imperfect direct repeats of 2-20 bp, similar to the breakpoint structures observed at translocations and gross deletions, including LOH events, underlying human cancer and other hereditary diseases.
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We would like to thank Jim Haber and Web Cavenee for helpful discussions, Connie Holm’s laboratory for help with CHEF gel analysis, and John Weger for the DNA sequence analysis. We also thank Web Cavenee, Abhijit Datta, Ruchiria DasGupta, Alex Shoemaker, and Dan Tishkoff for comments on the manuscript. This work was supported by National Institutes of Health grant GM50006 to R. D. K.