CLONING OF A 3-METHYLADENINE-DNA GLYCOSYLASE FROM ARABIDOPSIS-THALIANA

We have isolated an Arabidopsis thaliana cDNA that complements the met hyl methanesulfonate sensitive phenotype of an Escherichia coli double mutant deficient in 3-methyladenine glycosylases (DNA-3-methyladenine glycosidases I and II, EC 3.2.2.20 and 3.2.2.21, respectively, encode d by tag and alkA). Expression of the Arabidopsis cDNA enhances the me thyl methanesulfonate resistance of the E. coli double mutant by nearl y four orders of magnitude. The cDNA corresponds to a single-copy, nuc learly encoded sequence which specifies a predicted 28.1-kDa protein w ith a charge of +8 at pH 7.0. Enzymatic analysis of extracts prepared from the transformed mutants indicates that the cDNA encodes a 3-methy ladenine glycosylase. The predicted amino acid sequence of the Arabido psis glycosylase has significant homology to other eukaryotic 3-methyl adenine glycosylases.