Correlation between the Phosphohydrolase Activity of the Escherichia coli Orf135 (NudG) Protein and Mutation Suppression

Abstract

The Escherichia coli Orf135 (NudG) protein, a MutT-type enzyme, catalyzes the hydrolysis of 2-hydroxy-dATP and 8-hydroxy-dGTP, and its deficiency causes an increase in the mutation frequency. In this study, Orf135 proteins with substitutions at the Gly-36, Gly-37, Lys-38, Glu-43, Arg-51, Glu-52, Leu-53, Glu-55, and Glu-56 residues, which are conserved in three MutT-type proteins (Orf135, MutT, and MTH1), were each expressed in the orf135- strain, and the rpoB mutant frequency upon H2O2 treatment was examined. The in vivo mutation suppression abilities and the in vitro enzymatic activities obtained in a previous study were compared. The expression of the enzymatically active Orf135 mutants in the orf135- strain tended to reduce the rpoB mutant frequency induced by H2O2. This result suggests the importance of the phosphohydrolase activity in the suppression of mutations by the Orf135 protein