Template properties of bacteriophage T4 vegetative DNA. II. Effect of maturation and DNA-arrest mutations

Abstract

The DNA in gently lysates of T4-infected Escherichia coli cells sediments in sucrose gradients as two major components; the slower sedimenting component is designated as the S-5 fraction and the faster sedimenting component as the pad fraction. The distribution of these fractions in lysates of cells infected with T4 maturation-defective and DNA-arrest mutants was determined, and their template activities were compared in a DNA-dependent amino acid-incorporating system. The S-5 DNA template was found to be completely absent in E. coli B cells infected with a T4 maturation-defective mutant (gene 55). On the other hand, DNA sedimenting as the S-5 component is greatly increased, while that sedimenting as the pad component is virtually absent in nonpermissive cells infected with a DNA-arrest mutant (gene 46). The S-5 fractions prepared from cells infected with a DNA ligase mutant (gene 30) and a gene 30 gene 46 double mutant are reduced in their ability to stimulate amino acid incorporation compared to similar preparations from cells infected with wild type T4 or a gene 46 mutant. Moreover, the template activity of partially purified replicative DNA prepared from cells infected with phage-carrying mutations either on gene 30 or in both genes 46 and 56 (dCTPase) is lower than that of DNA obtained from cells infected with wild type phage. The polypeptide products of reaction mixtures programmed with several of the mutant DNAs were found to be qualitatively different from polypeptides synthesized in response to either mature DNA or replicative DNA prepared from cells infected with wild type phage. These data suggest that the expression of phage DNA may be significantly influenced by physical changes in the DNA arising from abnormal replication.