Identification and characterization of a new transcriptional termination factor from Escherichia coli.

We have identified and partially purified an activity from Escherichia coli that enhances transcription termination at the bacteriophage T7 early terminator when cloned on the plasmid pAR1707. The factor also causes the transcript to be terminated at a site several nucleotides earlier than in its absence. The resulting 3' OH ends of the transcripts are identical to those found in vivo by S1 nuclease mapping. From this we conclude that the factor we have identified is probably responsible for determination of the 3' OH ends of T7 RNA transcripts in vivo. This factor does not act by processing a preformed RNA transcript, nor is it replaced by rho protein or nusA or nusB proteins. Therefore, it appears to be a new transcription termination factor, and we have designated it "tau factor." Elucidation of its role in transcription in E. coli will depend on its purification to homogeneity and further studies of its properties.