The mutY gene of Escherichia coli, which codes for an adenine glycosylase that excises the adenine of a G-A mispair, has been cloned and sequenced. The mutY gene codes for a protein of 350 amino acids (Mr = 39,123) and the clone genetically complements the mutY strain. The protein shows significant sequence homology to E. coli endonuclease III, an enzyme that has previously been shown to have glycosylase activity on damaged base pairs. Sequence analysis suggests that, like endonuclease III, MutY is an iron-sulfur protein with a [4Fe-4S]2+ cluster.
We have cloned chromosomal DNA bordering an insert that inactivates mutM. Sequencing of this clone has revealed that the insertion element is located between the promoter and structural gene for formamidopyrimidine-DNA glycosylase (Fapy-DNA glycosylase). An overproducing clone of Fapy-DNA glycosylase complements the original mutM strain that had been isolated after EMS mutagenesis. Thus, we conclude that MutM is actually Fapy-DNA glycosylase. mutM has previously been characterized as a mutator strain that leads specifically to G.C----T.A transversions. This in vivo characterization correlates well with the mutagenic potential of one of the lesions Fapy-DNA glycosylase removes, 8-oxo-7,8-dihydro-2'-deoxyguanine (8-OxodG).
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