A common mechanism of action for the N-glycosylase activity of DNA N-glycosylase/AP lyases from E. coli and T4

Abstract

Duplex oligonucleotides containing the base lesion analogs, O-methylhydroxylamine- and O-benzylhydroxyIamine-modified abasic (AP) sites, were substrates for the DNA N-glycosylases endonuclease III, formamidopyrimidine DNA N-glycosylase and T4 endonuclease V. These N-glycosylases are known to have associated AP lyase activities. In contrast, uracil DNA N-glycosylase, a simple N-glycosylase which does not have an associated AP lyase activity, was unable to recognize the modified AP sites. Endonuclease III, formamidopyrimidine DNA N-glycosylase and T4 endonuclease V recognized the base lesion analogs as N-glycosylases generating intermediary AP sites which were subsequently cleaved by the enzyme-associated AP lyase activities. Kinetic measurements showed that O-alkoxyamine-modified AP sites were poorer substrates than the presumed physiological substrates. For endonuclease III, DNA containing O-methylhydroxylamine or O-benzylhydroxylamine was recognized at 12 and 9% of the rate of DNA containing thymine glycol, respectively, under subsaturating substrate concentrations (as determined by relative V(max)/K(m)). Similarly, with formamidopyrimidine DNA N-glycosylase and T4 endonuclease V, DNA containing O-methylhydroxylamine or O-benzylhydroxylamine was recognized at 4-9% of the efficiency of DNA containing N7-methyl formamidopyrimidine or pyrimidine cyclobutane dimers, respectively. Based on the known structures of these base lesion analogs and the substrate specificities of the N-glycosylases, a common mechanism of action is proposed for DNA N-glycosylases with an associated AP lyase activity.