Structural basis of Rho-dependent transcription termination.

Abstract

Rho is a ring-shaped hexameric ATP-dependent molecular motor. Together with the transcription elongation factor NusG, Rho mediates factor-dependent transcription termination and transcription-translation-coupling quality control in Escherichia coli1-4. Here we report the preparation of complexes that arefunctional in factor-dependent transcription termination from Rho, NusG, RNA polymerase (RNAP), and synthetic nucleic acid scaffolds, and we report cryogenic electron microscopystructures of thecomplexes. The structures show that functional factor-dependent pre-termination complexes contain a closed-ring Rho hexamer;have RNA threaded through the central channel of Rho;have 60 nucleotidesof RNA interacting sequence-specifically with the exterior of Rho and 6 nucleotidesof RNA interacting sequence-specifically with the central channel of Rho;have Rho oriented relative to RNAP such that ATP-dependent translocation by Rho exerts mechanical force on RNAP;and have NusG bridging Rho and RNAP. The results explain five decades of research on Rho and provide a foundation for understanding Rho's function.