Structural basis for transcription inhibition by E. coli SspA.

ABSTRACT: Stringent starvation protein A (SspA) is an RNA polymerase (RNAP)-associated protein involved in nucleotide metabolism, acid tolerance and virulence of bacteria. Despite extensive biochemical and genetic analyses, the precise regulatory role of SspA in transcription is still unknown, in part, because of a lack of structural information for bacterial RNAP in complex with SspA. Here, we report a 3.68 Å cryo-EM structure of an Escherichia coli RNAP-promoter open complex (RPo) with SspA. Unexpectedly, the structure reveals that SspA binds to the E. coli ?70-RNAP holoenzyme as a homodimer, interacting with ?70 region 4 and the zinc binding domain of EcoRNAP ?' subunit simultaneously. Results from fluorescent polarization assays indicate the specific interactions between SspA and ?70 region 4 confer its ? selectivity, thereby avoiding its interactions with ?s or other alternative ? factors. In addition, results from in vitro transcription assays verify that SspA inhibits transcription probably through suppressing promoter escape. Together, the results here provide a foundation for understanding the unique physiological function of SspA in transcription regulation in bacteria.

SUBMITTER: Wang F 

PROVIDER: S-EPMC7515715 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature