Angew. Chem. Int. Ed. Engl., published online 17 September 2012; doi:10.1002/anie.201204109

Natural product biosynthetic clusters often include efflux pumps or other enzymes that provide resistance to these frequently toxic compounds. The gene cluster for the DNA-alkylating agent yatakemycin contains five genes, ytkR2–ytkR6, that could have a role in resistance: whereas YtkR6 is homologous to drug-resistance transporters, YtkR2–YtkR5 are homologous to enzymes involved in base-excision repair, whereby damaged DNA bases are first cleaved by DNA glycosylases to reveal an abasic site and then further repaired to regenerate the parent DNA sequence. To test whether this mechanism might be operative in bacteria synthesizing yatakemycin, Xu et al. focused on YtkR2, the putative DNA glycosyltransferase. Inactivation of this gene in Streptomyces sp. TP-A0356 resulted in decreased production of the natural product, whereas overexpression of the gene increased production, supporting a functional role for the enzyme in protecting cells from yatakemycin. The enzyme was also able to protect Escherichia coli cells from yatakemycin as well as another alkyating agent. In vitro assays confirmed that the purified enzyme yielded an adenine-modified yatakemycin, with mutation of residues known to be important for glycosyltransferase function as well as those proposed to be involved in yatakemycin recognition reducing YtkR2 activity. These results highlight a new self-resistance mechanism and raise new questions regarding DNA glycosylase substrate specificity.