The collision of cotranscribing E. coli RNA polymerases studied in vitro.

The collision of cotranscribing E. coli ternary complexes was brought about in vitro by forcing the first "leading" complex to stall before first template C, due to the absence of CTP, and then permitting initiation of a second "following" complex. Following collision, the transcript of the leading complex was increased in length by as much as 7 nt., despite the absence of CTP, but did not dissociate. Upon addition of CTP, the leading complex aborted at exactly the positions requiring incorporation of the next Cs', the following complex continued transcription. The observations point to the importance of linking appropriate promoter efficiency with transcriptional pausing times, and the role of transcriptional collisions in termination events.