Structural basis of transcriptional regulation by a nascent RNA element, HK022 putRNA

Abstract

HK022 put is an RNA element that inhibits transcription termination without aids from protein factors. Here, authors solved cryo-EM structures of put-associated RNA polymerase and showed the structure of putRNA and its binding to the RNA polymerase. Transcription, in which RNA polymerases (RNAPs) produce RNA from DNA, is the first step of gene expression. As such, it is highly regulated either by trans-elements like protein factors and/or by cis-elements like specific sequences on the DNA. Lambdoid phage HK022 contains a cis-element, put, which suppresses pausing and termination during transcription of the early phage genes. The putRNA transcript solely performs the anti-pausing/termination activities by interacting directly with the E.coli RNAP elongation complex (EC) by an unknown structural mechanism. In this study, we reconstituted putRNA-associated ECs and determined the structures using cryo-electron microscopy. The determined structures of putRNA-associated EC, putRNA-absent EC, and sigma(70)-bound EC suggest that the putRNA interaction with the EC counteracts swiveling, a conformational change previously identified to promote pausing and sigma(70) might modulate putRNA folding via sigma(70)-dependent pausing during elongation.