Mechanisms of σ54-Dependent Transcription Initiation and Regulation

Cellular RNA polymerase is a multi-subunit macromolecular assembly responsible for gene transcription, a highly regulated process conserved from bacteria to humans. In bacteria, sigma factors are employed to mediate gene-specific expression in response to a variety of environmental conditions. The major variant a factor, am, has a specific role in stress responses. Unlike sigma(70)-dependent transcription, which often can spontaneously proceed to initiation, sigma(54)-dependent transcription requires an additional ATPase protein for activation. As a result, structures of a number of distinct functional states during the dynamic process of transcription initiation have been captured using the sigma(54) system with both x-ray crystallography and cryo electron microscopy, furthering our understanding of sigma(54)-dependent transcription initiation and DNA opening. Comparisons with sigma(70) and eukaryotic polymerases reveal unique and common features during transcription initiation. (C) 2019 The Authors. Published by Elsevier Ltd.