Bacteriophage RNA Polymerases

Abstract

Bacteriophage-encoded RNA polymerase (RNAP) was first discovered in T7 phage infected Escherichia coli cells. It was known that phage infection on host bacterial cells led to redirection of the host gene expression towards generation of progeny phage particles, but a previously uncharacterized "switching event" leading to the expression of late bacteriophage genes was first attributed to a phage-encoded RNAP. This phage RNAP could recognize promoters on the phage genome and express phage genes using a single-polypeptide polymerase of similar to 100 kDa molecular weight, which is similar to 4 times smaller than bacterial RNAPs. This was a substantial simplification from the previously known RNAPs from bacteria (5 subunits) and eukaryotes (more than 12 subunits); nonetheless, the single-unit T7 RNAP is able to recognize promoter DNA and unwind double-stranded (ds) DNA to form open complex, and after abortive initiation, it proceeds to processive RNA elongation. The simplicity of T7 phage RNAP made it an ideal model system to study the transcription mechanism and an ideal tool for protein expression system in bacterial cells. In this chapter, we will review the current state of knowledge of transcription mechanism in single-unit bacteriophage RNAPs from the two deeply studied T7 and the N4 phage RNAPs.