Deoxythymidylate Phosphohydrolase Induced by Bacteriophage PBS2 during Infection of Bacillus

The deoxythymidylate phosphohydrolase (dTMPase) induced by Bacillus subtilis bacteriophage PBS2 (whose DNA contains uracil instead of thymine) has been partially purified and shown to possess deoxyuridylate phosphohydrolase (dUMPase) activity. The similarities of induction period, pH dependence, heat and trypsin inactivation, sulfhydryl reagent and fluoride inhibition, metal ion effects, kinetic constants for substrates and products, and apparent molecular weight suggest that a single enzyme catalyzes both dTMPase and dUMPase reactions. Although the PBS2 phosphohydrolase is active on many different deoxyribonucleotide derivatives of 4-hydroxypyrimidine and 6-hydroxypurine, it displays a strong preference for dTMP (apparent Km of 10m6 M uersus lOua M for dUMP). This phage-induced phosphohydrolase may be responsible for the exclusion of thymine from PBS2 DNA during PBS2 phage infection, by eliminating the substrate (dUMP) and the product (dTMP) of the B. su btilis thymidylate synthetase.