Studies on the mutator gene, mutT of Escherichia coli. Molecular cloning of the gene, purification of the gene product, and identification of a novel nucleoside triphosphatase.

The mutator gene, mutT, has been cloned into an expression vector and overproduced in Escherichia coli. The gene product has been purified to over 90% homogeneity as judged by gel electrophoresis and amino acid analysis. The amino acid composition of the protein and the sequence of the 20 amino acids of the N-terminal region agree well with the nucleotide sequence of the gene reported by Akiyama et al. (Akiyama, M., Horiuchi, T., and Sekiguchi, M. (1987) Mol. Gen. Genet. 206, 9-16) and indicate that the first of the potential initiation codons (position 164) of the open reading frame in the PvuII fragment carrying the mutT gene is the site of initiation of translation of the 15,000-Da polypeptide. A novel nucleoside triphosphatase activity which has a preference for dGTP is associated with the purified protein, and preliminary experiments are consistent with the notion that the mutT gene product is the enzyme responsible for this activity.