Determinants of DNA Binding by Plant Homologs of 3-Methyladenine–DNA Glycosylase

Tag proteins, widespread among prokaryotes, are DNA glycosylases that participate in the repair of alkylated DNA excising 3-methyladenine. Among eukaryotes, Tag homologs are found only in plants, but they have not yet been characterized. Here, we report the first study of a plant Tag homolog, BvTAG1 from sugar beet (Beta vulgaris). Unlike bacterial Tags, BvTAG1 lacks activity towards alkylated DNA, which can be explained by the mutation of the critical catalytic Glu residue to Ser. At the same time, BvTAG1 exhibits a high affinity for undamaged DNA, mediated by a long N-terminal tail characteristic of all plant Tag homologs. This binding further increases in the presence of free 3-methyladenine. Our results suggest that plant Tag homologs may be required for regulating the plant response to genotoxic stress, rather than for DNA repair.