Interaction of RNA polymerase and rho in transcription termination: coupled ATPase

We have previously described temperature sensitive rho mutants of Escherichia coli (e.g., rho15) that are defective in transcription termination at various signals, including an IS2 DNA insertion in the gal operon [Das, A., Court, D. & Adhya, S. (1976) Proc. Natl. Acad. Sci. USA, 73, 1959-1963]. In this paper, we report the isolation of mutants altered in the beta subunit of RNA polymerase (a class of Rifampicin-resistant mutants), which restore gal IS2 polarity in the rho 15 strain. It has been shown that one of these suppressor RNA polymerases (rpoB101) requires rho to terminate transcription of phage lambda mRNA. In contrast to the wild type RNA polymerase, the suppressor RNA polymerase also terminates lambda mRNA transcription in the presence of rho15 protein. We have isolated new rho mutants (e.g., rho112) that are defective in transcription termination in the rpoB101 strain. These results strongly support the notion that rho and RNA polymerase interact functionally during transcription termination. We have shown that rho15 catalyzes ATP hydrolysis during transcription with rpoB101 RNA polymerase, but not with wild-type RNA polymerase. Because rho 15 protein hydrolyzes ATP in the presence of free RNA, we suggest that rho may recognize the 3'-OH end of RNA. During transcription, this recognition involves an interaction with RNA polymerase, resulting in the displacement of the polymerase and the release of the nascent mRNA.