Purification and characterization of an endo-exonuclease from Saccharomyces cerevisiae that is influenced by the RAD52 gene.

An endo-exonuclease has been purified from logarithmically growing cells of the yeast Saccharomyces cerevisiae. Identification and purification of this nuclease was facilitated by its being precipitable with an antibody raised against a previously described Neurospora crassa endo-exonuclease (Resnick, M. A., Chow, T. Y.-K. Nitiss, J., and Game, J. C. (1984) Cold Spring Harbor Symp. Quant. Biol. 49, 639-649 and T. Y.-K. Chow and M. A. Resnick (1988) Mol. Gen. Genet., in press). The enzyme which was purified to near homogeneity was composed of a molecular weight 72,000 monomer. The single-strand nuclease activity is endonucleolytic and nonprocessive, whereas the double-strand DNase activity is exonucleolytic and weakly processive. Both nuclease activities have a pH optimum of 7.5, require Mg2+ or Mn2+ but not Zn2+ or Ca2+, are not inhibited by ATP, and exhibit the same kinetics of heat inactivation. Although this protein is not the product of the RAD52 gene, the greatly reduced amounts in rad52 mutants implicate the enzyme in repair and recombination processes in both mitotic and meiotic cells.