Simultaneous initiation of synthesis of bacteriophage T4 DNA and of deoxyribonucleotides.

In earlier reports we have suggested that bacteriophate T4 DNA replication occurs in a complex composed of the proteins required for polymerization and the system of enzymes synthesizing the deoxyribonucleoside triphosphate precursors of DNA. T4-induced dCMP hydroxymethylase and dTMP synthetase, though demonstrable in extracts soon after infection, are not active in vivo until about 5 min. The in vivo activities increase exponentially for approximately 15 min and then become constant. We have suggested that the exponential period represents the formation of the complexes. This paper shows that the initiation of DNA synthesis and of the two deoxyribonucleotide-synthesizing activities occurs simultaneously and with coinciding exponential kinetics. The in vivo activities of the two enzymes were tested after infection by a number of T4 amber Dna- mutants. Their activities were essentially unchanged compared to the wild-type phage, except on infection by mutants of gene 43 (T4 DNA nucleotidyltransferase or DNA polymerase). With these mutants the rate of increase of dTMP synthetase and dCMP hydroxymethylase activities was always substantially lower than after infection by wild-type phage. It is proposed that an intimate interaction occurs between T4-induced DNA polymerase and the complex of enzymes forming 5-hydroxymethyl-dCMP and dTMP.