Failure of Translation Initiation of the Next Gene Decouples Transcription at Intercistronic Sites and the Resultant mRNA Generation

Transcription of operons is initiated at the promoter of the first gene in the operon, continues through cistron junctions, and terminates at the end of the operon, generating a full-length mRNA. Here, we show that Rho-dependent termination of transcription occurs stochastically at a cistron junction, generating a stable mRNA that is shorter than the full-length mRNA. In Escherichia coli, transcription is coupled with translation. The polar gal operon is transcribed galE-galT-galK-galM; however, about 10% of transcription terminates at the end of galE because of Rho-dependent termination (RDT). When galE translation is complete, galT translation should begin immediately. It is unclear whether RDT at the end of galE is due to decoupling of translation termination and transcription at the cistron junction. In this study, we show that RDT at the galE/galT cistron junction is linked to the failure of translation initiation at the start of galT, rather than translation termination at the end of galE. We also show that transcription pauses 130 nucleotides downstream from the site of galE translation termination, and this pause is required for RDT. IMPORTANCE Transcription of operons is initiated at the promoter of the first gene in the operon, continues through cistron junctions, and terminates at the end of the operon, generating a full-length mRNA. Here, we show that Rho-dependent termination of transcription occurs stochastically at a cistron junction, generating a stable mRNA that is shorter than the full-length mRNA. We further show that stochastic failure in translation initiation of the next gene, rather than the failure of translation termination of the preceding gene, causes the Rho-dependent termination. Thus, stochastic failure in translation initiation at the cistron junction causes the promoter-proximal gene to be transcribed more than promoter-distal genes within the operon.