Amber Mutants of Bacteriophage T4 Defective in Deoxycytidine Diphosphatase and Deoxycytidine Triphosphatase

Infectionof Escherichia coli B with T4 amber mutants in gene 56 fails to cause the appearance of either deoxycytidine trkghosphatase or deoxycytidine diphosphatase, and little or no DNA synthesis results.Infection of E. coli B with a 7:3 mixture of a gene 56 amber mutant and wild type T4 results in the appearance of only 30% as much dCTPase activity as normal but gives a 100% yield of mixed phage.This indicates that dCTPase is present in at least a 3-fold excess in the wild type infection.Escherichia coli W4597, shown by others to support 1 J. Flatgaard, personal communication. 2 S. Hattman, personal communication.3 J. S. Wiberg, unpublished experiments.4 These would be double mutants defective in both dCMP hydroxymethylase and dCTPase.6 The abbreviations used are: HMC, 5-hydroxymethylcytosine; dHMP, deoxy-5-hydroxymethylcytidine 5'-monophosphate; T*, T-even phage, the DNA of which lacks the glucose normally attached to HMC groups; am, amber mutants, unable to grow on E. coli B but able to grow on E. coli CR63; ts, temperature-sensitive mutants.6 R. S. Edgar, personal communication.