CLONING AND CHARACTERIZATION OF A CDNA-ENCODING A 3-METHYLADENINE DNAGLYCOSYLASE FROM THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

We have begun to develop the fission yeast, Schizosaccharomyces pombe, as a eukaryotic model for cellular defenses against alkylating agents . Here we describe the cloning and characterization of a cDNA, designa ted mag1, encoding a S. pombe 3-methyladenine (3MeA) DNA glycosylase. 3MeA DNA glycosylases in Escherichia coli are encoded by alkA and tag. S. pombe mag1 was cloned by its ability to reverse the alkylation-sen sitive phenotype of an alkA tag E. coli double mutant. The expression of S. pombe mag1 in E. coli confers partial resistance to alkylating a gents that produce methyl, ethyl and propyl lesions, and Mag1 producti on produces 3MeA DNA glycosylase activity. In contrast to the E. coli alkA and Saccharomyces cerevisiae MAG genes, expression of S. pombe ma g1 was not appreciably induced by alkylating agents. The mag1 cDNA enc odes a protein of 228 amino acids (aa) that shares similarity with 3Me A DNA glycosylases from E. coli (AlkA), Bacillus subtilis (BsAlkA) and S. cerevisiae (MAG). A consensus sequence of 9 aa common to these mic robial 3MeA DNA glycosylases is discussed.