The Escherichia coli MutT protein hydrolyzes 8-hydroxy-dGTP (8-OH-dGTP) in 
vitro, and mutT gene deficiencies cause increased spontaneous A:T-->C:G 
mutations. However, no direct evidence exists for enhanced mutagenicity of 
8-OH-dGTP in mutT cells. In this study, 8-OH-dGTP was introduced into wild type 
and mutT E. coli cells, and mutations of a chromosomal gene were monitored. 
8-OH-dGTP induced mutations of the rpoB gene, the degree of the mutation 
induction in the mutT strain being approximately 6-fold higher than that in the 
wild type strain. On the other hand, 2-hydroxy-dATP, which is not a substrate of 
the MutT protein, increased the mutation to similar degrees in the two strains. 
These results constitute the first evidence that the MutT protein suppresses 
mutation by 8-OH-dGTP in vivo.