Rho-dependent transcription termination: mechanisms and roles in bacterial fitness and adaptation to environmental changes.

The bacterial transcription termination factor Rho is a rare example of an RNA helicase that functions as a ring-shaped ATP-powered six-subunit motor. Recent studies have linked Rho's distinctive architecture to a variety of regulatory mechanisms that shape the bacterial transcriptome at the global scale and control the transcription of individual genes in a context-dependent manner. In this review, we provide a comprehensive overview of the molecular mechanisms by which Rho triggers transcription termination. We examine the two prevailing modes of Rho's action: the "catch-up" mode, where Rho actively translocates along RNA and collides with the RNA polymerase to terminate transcription, and the "stand-by" mode where Rho, recruited by transcription elongation factor NusG, remains poised to engage RNA polymerase at specific sites or under particular constraints. Additionally, we highlight Rho's interplay with nucleoid-structuring protein H-NS in the regulation of bacterial chromatin transcription, as well as the crucial role played by Rho in the conditional regulation of specific genomic loci. We discuss how these mechanisms contribute to the fine-tuning of gene activity and integrate into broader regulatory networks, supporting bacterial adaptation to environmental changes and resilience to external challenges.