MutT-related proteins degrade 8-oxo-7,8-dihydrodeoxyguanosine triphosphate 
(8-oxo-dGTP), a mutagenic substrate for DNA synthesis, in the nucleotide pool, 
thereby preventing DNA replication errors. During a search of GenBank EST 
database, we found a new member of MutT-related protein, MTH2, which possesses 
the 23-amino acid MutT module. The cloned mouse MTH2 (mMTH2) cDNA was expressed 
in Escherichia coli mutT(-) cells and the protein was purified. mMTH2 protein 
hydrolyzes 8-oxo-dGTP to 8-oxo-dGMP, with Km of 32 microM. Expression of cDNA 
for mMTH2 reduced significantly the elevated level of spontaneous mutation 
frequency of E. coli mutT(-) cells. Thus, MTH2 has a potential to protect the 
genetic material from the untoward effects of endogenous oxygen radicals. MTH2 
could act as an MTH1 redundancy factor.