Structural insights into NusG regulating transcription elongation

摘要

NusG is an essential transcription factor that plays multiple key regulatory roles in transcription elongation, termination and coupling translation and transcription. The core role of NusG is to enhance transcription elongation and RNA polymerase processivity. Here, we present the structure of Escherichia coli RNA polymerase complexed with NusG. The structure shows that the NusG N-terminal domain (NGN) binds at the central cleft of RNA polymerase surrounded by the beta clamp helices, the beta protrusion, and the beta lobe domains to close the promoter DNA binding channel and constrain the beta clamp domain, but with an orientation that is different from the one observed in the archaeal beta clamp-Spt4/5 complex. The structure also allows us to construct a reliable model of the complete NusG-associated transcription elongation complex, suggesting that the NGN domain binds at the upstream fork junction of the transcription elongation complex, similar to sigma 2 in the transcription initiation complex, to stabilize the junction, and therefore enhances transcription processivity.