Abstract
Gene 1.7 of bacteriophage T7 confers sensitivity of phage T7 to dideoxythymidine (ddT). We have purified the product of gene 1.7 (gp1.7). It exists in two molecular weight forms. Only the C‐terminal half of the protein is required for ddT sensitivity. We show that gp1.7 catalyzes the phosphorylation of dTMP to dTDP with dTTP or dGTP as the phosphate donor. The Km of 70 μM and Vmax of 4.3 M‐1S‐1 are similar to those found for E. coli thymidylate kinase. However, unlike the host enzyme, gp1.7 efficiently catalyzes the conversion of the chain terminating dideoxythymidylate (ddTMP) to ddTDP, thus explaining the sensitivity of phage T7 but not E. coli to exogenous ddT. Gp1.7 has no sequence homology to any known nucleotide kinase, no identifiable nucleotide‐binding motif, and its activity is not dependent on added metal ion. When coupled with nucleoside diphosphosphate kinase, dTMP is exponentially converted to dTTP.
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