4 Bacteriophage DNA-Dependent RNA Polymerases

Abstract

Infection of a bacterial cell by a bacteriophage leads to a progressive reprogramming of the biosynthetic capabilities of the cell toward the synthesis of bacteriophage components. A fundamental step is the establishment of a regulated transcription program for the bacteriophage genome. This chapter deals with bacteriophage DNA-dependent RNA polymerases, focusing on T7-like RNA polymerases. It also describes RNA polymerases from other phages. T7 RNA polymerase is the most extensively studied polymerase and is generally taken as representative of the general class, although individual phage polymerases may show significant differences. T7 RNA polymerase is usually assayed by incorporation of radioactively labeled nucleotide into acid-insoluble material in the presence of T7 DNA as template. The reaction shows an absolute requirement for the four ribonucleoside triphosphates, Mg 2+ , and T7 DNA. T7 RNA polymerase and related polymerases carry out DNA-directed synthesis of RNA from nucleoside triphosphate substrates. The template specificity of the T7-like phage RNA polymerases is striking as the phage enzymes normally use only their homologous DNA templates at a substantial rate. Other bacteriophage RNA polymerases include bacteriophage PBS2 RNA polymerase and bacteriophage N4 RNA polymerase.