Structures and mechanism of transcription initiation by bacterial ECF factors.

ABSTRACT: Bacterial RNA polymerase (RNAP) forms distinct holoenzymes with extra-cytoplasmic function (ECF) ? factors to initiate specific gene expression programs. In this study, we report a cryo-EM structure at 4.0 Å of Escherichia coli transcription initiation complex comprising ?E-the most-studied bacterial ECF ? factor (Ec ?E-RPo), and a crystal structure at 3.1 Å of Mycobacterium tuberculosis transcription initiation complex with a chimeric ?H/E (Mtb ?H/E-RPo). The structure of Ec ?E-RPo reveals key interactions essential for assembly of E. coli ?E-RNAP holoenzyme and for promoter recognition and unwinding by E. coli ?E. Moreover, both structures show that the non-conserved linkers (?2/?4 linker) of the two ECF ? factors are inserted into the active-center cleft and exit through the RNA-exit channel. We performed secondary-structure prediction of 27,670 ECF ? factors and find that their non-conserved linkers probably reach into and exit from RNAP active-center cleft in a similar manner. Further biochemical results suggest that such ?2/?4 linker plays an important role in RPo formation, abortive production and promoter escape during ECF ? factors-mediated transcription initiation.

SUBMITTER: Fang C 

PROVIDER: S-EPMC6648896 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature