Yeast DNA repair protein RAD5 that promotes instability of simple repetitive sequences is a DNA-dependent ATPase

The RAD5 gene of Saccharomyces cerevisiae functions in postreplication repair of ultraviolet damaged DNA, and interestingly, it also has a role in increasing the instability of simple repetitive sequences in the genome. In contrast to DNA mismatch repair genes which function in maintaining constant length of repeat sequences, RAD5 promotes alterations in the length of repeat sequences. In this work, we purify the RAD5 protein to near homogeneity from yeast cells and show that it is a single-stranded DNA-dependent ATPase. The possible roles of RAD5 ATPase in postreplication gap filling and in increasing the incidence of length alterations of repeat sequences are discussed.