Requirements for Host Gene Products in Replication of Single-stranded Phage DNA In Vivo

Abstract

The identification of those proteins required for host-cell DNA synthesis that are essential for replication of the DNA of the small, single-stranded DNA phages has closely paralleled the genetic dissection of the DNA-synthesis apparatus of the host cell itself. Conditionally lethal mutants of the host cell marked in those genes whose products are required for host DNA synthesis have been used to determine which bacterial proteins are also essential for synthesis of viral DNA. The genes identified by temperature-sensitive mutations are designated dna genes. To a lesser extent, highly specific drug inhibitors of host proteins have been used in similar analyses.

Those genes pertinent to this discussion, as well as the role played by each gene’s product in DNA replication in Escherichia coli, are listed in Table 1. Some of these gene products play crucial roles in the initiation of DNA synthesis, either at the origin of replication or in the initiation of the synthesis of Okazaki fragments. Others play important roles in chain elongation and fork migration or in termination reactions, including gap filling, primer excision, and fragment ligation.

The specific inhibitors of E. coli DNA synthesis that are pertinent to this discussion include rifampicin, nalidixic acid, novobiocin, and coumermycin. Rifampicin inhibits DNA-dependent RNA polymerase, which plays an essential role in the initiation of DNA synthesis at the origin of replication (Table 1). Novobiocin and coumermycin hinder DNA synthesis (Smith and Davis 1967; Ryan 1976) by inhibiting specifically DNA gyrase (Gellert et al. 1976). Nalidixic acid inhibits DNA synthesis...