Characterization of a novel DNA damage-inducible gene of Saccharomyces cerevisiae, DIN7, which is a structural homolog of the RAD2 and RAD27 DNA repair genes.

A number of DNA damage-inducible genes (DIN) have been identified in Saccharomyces cerevisiae. In the present study we describe isolation of a novel gene, Din7, the expression of which is induced by exposure of cells to UV light, MMS (methyl methane-sulfonate) or HU (hydoxyurea). The DNA sequence of DIN7 was determined. By comparison of the predicted Din7 amino acid sequence with those in databases we found that it belongs to a family of proteins which includes S. cerevisiae Rad2 and its Schizosaccharomyces pombe and human homologs Rad13 and XPGC; S. cerevisiae Rad27 and its S. pombe homolog Rad2, and S. pombe Exo I. All these proteins are endowed with DNA nuclease activity and are known to play an important function in DNA repair. The strongest homology to Din7 was found with the Dhs1 protein of S. cerevisiae, the function of which is essentially unknown. The expression of the DIN7 gene was studied in detail using a DIN7-lacZ fusion integrated into a chromosome. We show that the expression level of DIN7 rises during meiosis at a time nearly coincident with commitment to recombination. No inducibility of DIN7 was found after treatment with DNA-damaging agents of cells bearing the rad53-21 mutation. Surprisingly, a high basal level of DIN7 expression was found in strains in which the DUN1 gene was inactivated by transposon insertion. We suggest that a form of Dun1 may be a negative regulator of the DIN7 gene expression.