Abstract
BackgroundCellular RNA polymerases (RNAPs) are complex molecular machines that combine catalysis with concerted conformational changes in the active center. Previous work showed that kinking of a hinge region near the C-terminus of the Bridge Helix (BH-HC) plays a critical role in controlling the catalytic rate.ResultsHere, new evidence for the existence of an additional hinge region in the amino-terminal portion of the Bridge Helix domain (BH-HN) is presented. The nanomechanical properties of BH-HN emerge as a direct consequence of the highly conserved primary amino acid sequence. Mutations that are predicted to influence its flexibility cause corresponding changes in the rate of the nucleotide addition cycle (NAC). BH-HN displays functional properties that are distinct from BH-HC, suggesting that conformational changes in the Bridge Helix control the NAC via two independent mechanisms.ConclusionsThe properties of two distinct molecular hinges in the Bridge Helix of RNAP determine the functional contribution of this domain to key stages of the NAC by coordinating conformational changes in surrounding domains.
Highlights
Cellular RNA polymerases (RNAPs) are complex molecular machines that combine catalysis with concerted conformational changes in the active center
The results show that this region contains a highly localized molecular hinge, and that the conformation of this site has a substantial influence on the rate of the nucleotide addition cycle (NAC)
The mutants were assayed in robotic promoter-independent transcription assays, which provide a consistent measure of the synthetic rate of the NAC and correlate directly with results obtained from a variety of promoter-dependent, abortive- and elongation transcription assays
Summary
Cellular RNA polymerases (RNAPs) are complex molecular machines that combine catalysis with concerted conformational changes in the active center. Models of the fundamental reaction catalyzed by RNAPs, the nucleotide addition cycle (NAC), have predominantly been derived from a series of crystal structures that contain RNAPs as apoenzymes (for example [5,6,7,8,9]), or complexed with various substrates and inhibitors (for example [10,11,12,13,14,15]) Such structures, revealing (among other features) pre- and posttranslocation states of RNAPs, have provided the basis for various hypotheses concerning the molecular mechanism of the NAC [1,2,3,4,16,17]. It is likely that an awareness of the existence and functional significance of such intermediates will be required to develop a deeper understanding of the mechanisms operating within molecular machines
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
