2-Hydroxyadenine in DNA is a Very Poor Substrate of the Escherichia coli MutY Protein

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To test the possibility that the Escherichia coli MutY or MutM protein acts as a 2-hydroxyadenine (2- OH-Ade) glycosylase, we treated double-stranded oligodeoxyribonucleotides containing 2-OH-Ade with the E. coli MutY or MutM protein in vitro. We found that a strand with 2-OH-Ade was a very poor substrate of MutY, irrespective of the base in the complementary strand. Moreover, a strand containing adenine or guanine opposite 2-OH-Ade was also rarely cleaved by MutY. The cleavage of oligonucleotides with 2-OH-Ade by MutM was not observed. These results indicate that neither MutY nor MutM plays an important role in the removal of 2-OH-Ade from DNA. INTRODUCTION The proteins that prevent the effects of oxidative stress are of great interest1,2). Of these, Escherichia coli MutY and MutM proteins are thought to be important because they suppress mutagenesis caused by 8-hydroxyguanine (8-OH-Gua) in vivo3,4). The MutY protein is a DNA glycosylase that removes A residues opposite G or C5); another substrate for MutY is A paired with 8-OH-Gua6). The MutM protein is identical to Fapy (formamidopyrimidine) DNA glycosylase and 8-OH-Gua endonuclease, and removes oxidized purines as 8-OH-Gua, Fapy- Gua, and Fapy-Ade7-9). The E. coli mutY and mutM genes were found to be mutator genes of a G.C→T.A transversion10,11).