Phage lambda gene Q antiterminator recognizes RNA polymerase near the promoter and accelerates it through a pause site.

The positive regulator encoded by phage lambda gene Q is a transcription antiterminator that affects RNA polymerase initiating at the phage late gene promoter, but not at other promoters. We show that this nucleotide-sequence-specific interaction of Q protein and RNA polymerase can occur while the enzyme is pausing after 16 nucleotides of the late gene transcript have been made. Furthermore, Q protein chases RNA polymerase from this early pause site, so that it both recognizes the enzyme and changes its transcription properties at this site. We suggest that the ability of Q-modified RNA polymerase to escape this pause reflects the change that allows it to go through terminators. We also show that NusA protein is required for efficient Q protein activity in vitro.