Different efficiencies of the Tag and AlkA DNA glycosylases from Escherichia coli in the removal of 3‐methyladenine from single‐stranded DNA

Escherichia coli possesses two different DNA repair glycosylases, Tag and AlkA, which have similar ability to remove the alkylation product 3-methyladenine from double-stranded DNA. In this study we show that these enzymes have quite different activities for the excision of 3-methyladenine from single-stranded DNA, AlkA being 10-20 times more efficient than Tag. We propose that AlkA and perhaps other glycosylases as well may have an important role in the excision of base damage from single-stranded regions transiently formed in DNA during transcription and replication.