A search for candidates for a functional homologue of Escherichia coli MutT in 
yeast Saccharomyces cerevisiae was made in the NCBI-BLAST database using the 
Nudix box, a short amino acid sequence conserved among E.coli MutT, Pseudomonoas 
vulgaris MutT, and human, rat and mouse MTH1. Among five candidates, we focused 
on the open reading frame YLR151c, because it had a region with approximately 
76% similarity to the N-terminal half of MutT including the Nudix box. We thus 
evaluated the ability of YLR151c as a functional homologue of E.coli MutT in 
S.cerevisiae. Expression of YLR151c was able to suppress the transversion from 
A:T to C:G caused by misincorporation of the oxidized nucleotide 8-oxo-dGTP in 
the E.coli mutT-deficient strain. The disruption of the YLR151c in yeast strain 
caused approximately 14-fold increase in the frequency of spontaneous mutation 
compared to the wild type. Additionally, biochemical analysis indicated that 
GST-YLR151c fusion protein possessed pyrophosphatase activity for both 
7,8-dihydro-8-oxo-2'-deoxyguanosine triphosphate (8-oxo-dGTP) and 
1,2-dihydro-2-hydroxy-2'-deoxyadenosine triphosphate (2-OH-dATP). The specific 
activity of GST-YLR151c for 8-oxo-dGTP was 5.6 x 10(-3) microM(-1) s(-1), which 
was similar to that of RibA, a backup enzyme for MutT in E.coli, but was 
150-fold lower than that of hMTH1. From these results, we conclude that YLR151c 
has an ability to prevent spontaneous mutagenesis via sanitization of oxidized 
nucleotides, and that it may be the functional homologue of E.coli MutT in 
S.cerevisiae.