A new member of the endonuclease III family of DNA repair enzymes that removes methylated purines from DNA

DNA is constantly exposed to endogenous and exogenous alkylating agents tha t can modify its bases, resulting in mutagenesis in the absence of DNA repa ir [1,2], Alkylation damage is removed by the action of DNA glycosylases, w hich initiate the base excision repair pathway and protect the sequence inf ormation of the genome [3-5], We have identified a new class of methylpurin e DNA glycosylase, designated MpgII, that is a member of the endonuclease I II family of DNA repair enzymes. We expressed and purified MpgII from Therm otoga maritima and found that the enzyme releases both 7-methylguanine and 3-methyladenine from DNA. We cloned the MpgII genes from T. maritima and fr om Aquifex aeolicus and found that both genes could restore methylmethanesu lfonate (MMS) resistance to Escherichia coli alkA tagA double mutants, whic h are deficient in the repair of alkylated bases. Analogous genes are found in other Bacteria and Archaea and appear to be the only genes coding for m ethylpurine DNA glycosylase activity in these organisms. MpgII is the fifth member of the endonuclease III family of DNA repair enzymes, suggesting th at the endonuclease III protein scaffold has been modified during evolution to recognize and repair a variety of DNA damage. (C) Elsevier Science Lid ISSN 0960-9822.