Structural basis of the transcription termination factor Rho engagement with transcribing RNA polymerase

Transcription termination is an essential step in transcription by RNA polymerase (RNAP) and crucial for gene regulation. For many bacterial genes, transcription termination is mediated by the ATP-dependent RNA translocase/helicase Rho, which causes the dissociation of RNA/DNA from RNAP elongation complex (EC). However, structural basis of the interplay between Rho and RNAP remains obscure. Here we report the cryo-electron microscopy structure of the Rho-engaged EC. The Rho hexamer binds RNAP through the C-terminal domains, which surround the RNA-exit site of RNAP, directing the nascent RNA seamlessly from the RNA exit to the Rho central channel. The β-flap tip at the RNA exit is critical to the Rho-dependent RNA release, and its deletion causes an alternative Rho-RNAP binding mode, which is irrelevant to termination. The Rho-binding site overlaps with the binding sites of other macromolecules, such as ribosomes, providing a general basis of gene regulation. Teaser Cryo-EM captures the structure of an RNA polymerase elongation complex engaged with the termination factor Rho.