The phage lambda gene Q transcription antiterminator binds DNA in the late gene promoter as it modifies RNA polymerase.

The bacteriophage lambda gene Q transcription antiterminator modifies RNA polymerase during an extended pause in elongation at nt +16 and +17 of the phage late gene promoter transcript. We show here that Q binds a specific DNA site between the -10 and -35 elements of the promoter as it interacts with the enzyme. We show that the pause must reflect a specialized elongation structure that is receptive to modification by Q, because Q does not bind to RNA polymerase stopped artificially after transcribing 16 nt of mutant DNA that does not encode the natural pause. Footprinting shows that RNA polymerase in the paused complex makes distinctive interactions with DNA in the region where Q binds; binding of Q, in turn, changes the footprint both at the Q-binding site and in the transcription bubble. Binding of Q to the paused transcription complex is stabilized by the transcription factor NusA, as expected from the dependence of lambda Q-mediated antitermination on NusA.