8-Oxo-dGTP (8-oxo-7,8-dihydrodeoxyguanosine triphosphate) is a potent mutagenic 
substrate for DNA synthesis. The accumulation of 8-oxo-dGTP in the nucleotide 
pool induces G:C-->T:A transversion as well as A:T-->C:G transversion, and 
Escherichia coli cells possess mechanisms for preventing such mutations. The 
mutT gene product specifically hydrolyzes 8-oxo-dGTP to the monophosphate form 
while the mutM and the mutY gene products function to correct mispairs caused by 
incorporation of 8-oxoguanine into DNA. From analyses of forward mutations 
induced in cells lacking 8-oxo-dGTPase (MutT protein) and/or repair enzymes that 
suppress mutations caused by 8-oxoguanine in DNA (MutM and MutY proteins), 
cooperative functions of these proteins in control of the spontaneous 
mutagenesis became evident. In mutator strains lacking MutT and/or MutM 
proteins, 8-oxoguanine of DNA increased to a concentration expected from the 
increased rate of mutation.