BACKGROUND: We recently found that the Escherichia coli Orf135 protein, a 
MutT-type enzyme, hydrolysed 2-hydroxy-dATP (2-OH-dATP), and less efficiently, 
8-hydroxy-dGTP.
RESULTS: In this study, we examined the effects of the absence of the orf135 
gene. Frequencies of spontaneous and H2O2-induced mutations were two- to 
three-fold higher in the orf135- strain than in the wild-type strain. These 
mutations include various mutations involving a G:C-->T:A transversion, the same 
type of mutation elicited by 2-OH-dATP. Over-expression of the Orf135 protein 
suppressed mutations even in the wild-type strain, as well as in the orf135- 
strain.
CONCLUSIONS: The mutator phenotype of bacteria lacking the Orf135 protein 
suggests that this protein is involved in the suppression of mutations induced 
by oxidized deoxynucleotides in vivo and that various MutT-type enzymes 
contribute to nucleotide pool sanitization.