Transcription-translation coupling status determines transcription termination

Abstract

Abstract In Escherichia coli, transcription is terminated by two mechanisms: Rho-independent termination (RIT) and Rho-dependent termination (RDT). Transcription of the galactose operon is terminated by two tandem terminators, RIT and RDT. In this work, we investigated whether RNA polymerase is terminated randomly at the RIT and RDT sites or is predetermined. Our results show that the transcription and translation complexes have different coupling statuses upon reaching the terminator, of which 50% were loosely coupled and 50% were closely coupled. RIT terminates transcripts that are loosely coupled to translation, and closely coupled transcripts that cannot be terminated by RIT are terminated by the downstream RDT. Thus, RIT and RDT are predetermined events that depend on the coupling status. This rule also holds for the 850 operons in E. coli. Our study reveals an important rule that E. coli has evolved different transcription termination systems at the ends of operons to adapt to different transcription-translation coupling statuses.