Transcripts that increase the processivity and elongation rate of RNA polymerase

Abstract

Transcripts encoded by the cis-acting antitermination sites (put sites) of lambdoid phage HK022 promote readthrough of downstream transcription terminators. Proper conformation of the transcripts is essential for activity, since put mutations that prevent the formation of predicted RNA stems prevented antitermination, and suppressor mutations that restore the stems restored antitermination. Antitermination does not appear to require proteins other than RNA polymerase, since put-dependent readthrough of multiple sequential terminators was observed in a purified transcription system consisting of template, polymerase, substrates, and buffer. Transcription of put also increased the elongation rate of polymerase, very likely by suppressing pausing. A mutation that alters the zinc-finger region of the β' subunit of polymerase specifically prevented the put-dependent increases in terminator readthrough and elongation rate. The simplicity of HK022 antitermination contrasts with that of other known antitermination pathways. We propose that the central effector is a transcript that directly alters the elongation properties of RNA polymerase.