DNA is constantly exposed to endogenous andexogenous alkylating agents that can 
modify its bases,resulting in mutagenesis in the absence of DNA repair [1,2]. 
Alkylation damage is removed by the action of DNA glycosylases, which initiate 
the base excision repair pathway and protect the sequence information of the 
genome [3-5]. We have identified a new class of methylpurine DNA glycosylase, 
designated MpgII, that is a member of the endonuclease III family of DNA repair 
enzymes. We expressed and purified MpgII from Thermotoga maritima and found that 
the enzyme releases both 7-methylguanine and 3-methyladenine from DNA. We cloned 
the MpgII genes from T. maritima and from Aquifex aeolicus and found that both 
genes could restore methylmethanesulfonate (MMS) resistance to Escherichia coli 
alkA tagA double mutants, which 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 methylpurine DNA glycosylase activity in these organisms. 
MpgII is the fifth member of the endonuclease III family of DNA repair enzymes, 
suggesting that the endonuclease III protein scaffold has been modified during 
evolution to recognize and repair a variety of DNA damage.