RNA Polymerase Structure, Bacterial

Abstract

The multisubunit DNA-dependent RNA polymerase (RNAP) mediates transcription – the first step in gene expression in all cellular organisms. Its basic function is to faithfully synthesize an RNA chain complementary to the transcribed (template) DNA strand in the presence of substrates, ribonucleoside 5′-triphosphates. RNAP structure and function are highly conserved in all three kingdoms of life: bacteria, archaea, and eukaryotes. In bacteria and archaea, a single RNAP enzyme is responsible for the synthesis of all RNAs in the cell, including messenger RNA, ribosomal RNA, transfer RNA, and small noncoding RNA. In eukaryotes, these functions are divided between three related nuclear RNAPs. To orchestrate transcription of ~4000 bacterial genes during cell growth and in response to environmental signals, the enzymatic activity of RNAP is tightly regulated by both intrinsic signals (in DNA template and nascent RNA) and various extrinsic factors (proteins, short peptides, noncoding RNAs, and some small molecules). Extensive genetic, biochemical, and structural studies of RNAP and its regulatory factors conducted in the past 25 years have greatly expanded our knowledge of the organization and function of all major elements of transcription machinery. This article provides a summary of our current understanding of the structure and the mechanisms of action of bacterial RNAPs.