CBR antimicrobials alter coupling between the bridge helix and the ? subunit in RNA polymerase.

ABSTRACT: Bacterial RNA polymerase (RNAP) is a validated target for antibacterial drugs. CBR703 series antimicrobials allosterically inhibit transcription by binding to a conserved ? helix (?' bridge helix, BH) that interconnects the two largest RNAP subunits. Here we show that disruption of the BH-? subunit contacts by amino-acid substitutions invariably results in accelerated catalysis, slowed-down forward translocation and insensitivity to regulatory pauses. CBR703 partially reverses these effects in CBR-resistant RNAPs while inhibiting catalysis and promoting pausing in CBR-sensitive RNAPs. The differential response of variant RNAPs to CBR703 suggests that the inhibitor binds in a cavity walled by the BH, the ?' F-loop and the ? fork loop. Collectively, our data are consistent with a model in which the ? subunit fine tunes RNAP elongation activities by altering the BH conformation, whereas CBRs deregulate transcription by increasing coupling between the BH and the ? subunit.

SUBMITTER: Malinen AM 

PROVIDER: S-EPMC3959191 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature