The Mechanism of Early Transcription Termination by Rho026

We previously found thatnusD-type mutations inEscherichia colitranscription termination factor Rho enhancein vitrotranscription termination at four points within the λcrogene. Here we show that the early termination points are part of one Rho-dependent termination site, tRE, with properties like those of previously characterized Rho-dependent sites λ tR1 andtrpt′. The early termination points are all RNA polymerase pause sites, and by deletion analysis and oligonucleotide blocking experiments, a common 5′ Rho entry site for the early termination points (rutE) is identified. We show that both Rho026 and Rho+can userutEas an entry point for termination, but that Rho026 is more efficient in releasing the nascent RNA at tRE. The RNA-dependent ATPase activities of wild-type and mutant Rhos are similar, as are their abilities to bind free RNA and to use (rC)10oligomers for ATPase activation. We therefore suggest that Rho-RNA polymerase interactions that define the site of RNA 3′ end formation are altered in NusD Rho mutants.