The structural gene for deoxyribonucleic acid polymerase in bacteriophages T4 and T5.

Genetic studies by Epstein, Edgar, and their colleagues1-3 with conditional lethal (amber and temperature-sensitive) mutants of bacteriophage T4 have led to the construction of a genetic map for this phage, containing approximately 70 different genes of which 20 are believed to function in DNA synthesis. Thus far, only one of these genes has been identified with a specific enzymatic function. Wiberg et al.4 investigated seven amber mutants; five of these, representing genes 39, 41, 42, 44, and 46, were defective in DNA synthesis. Of these, mutants in gene 42 were found incapable of inducing the enzyme deoxycytidylate hydroxymethylase in the restrictive host (Escherichia coli B). Subsequent work by Dirksen et al.5 suggested that gene 42 is the structural gene for this enzyme. Mutants of gene 43 were not investigated in these studies. Dr. Edgar generously made available to us a series of amber and temperaturesensitive mutants of bacteriophage T4 and we have examined them for their ability to induce the T4 DNA polymerase.6 These studies have led to the identification of gene 43 as the structural gene for the phage-induced polymerase. After this work was completed, Dr. H. R. Warner, of the Department of Biochemistry of the University of Minnesota, informed us that he had independently identified gene 43 with the T4 DNA polymerase. We have also examined four temperature-sensitive mutants of bacteriophage T5,7 kindly provided by Dr. Frank Lanni, for their ability to induce the T5 DNA polymerase.8 One of these was found to induce the synthesis of a DNA polymerase of significantly greater heat-lability than that induced by the wild-type phage. The cistron bearing this mutation would therefore appear to be the structural gene for the T5-induced DNA polymerase.