Specificity and mechanism of antitermination by Q proteins of bacteriophages lambda and 82

Lambdoid phage late gene operons are positively regulated by genome-specific antiterminator proteins encoded by the Q gene of each phage. In this paper, we compare the activity of phage lambda and phage 82 Q proteins. Q82-mediated antitermination, like that of Q lambda, involves a transcription pause during which the regulator can modify RNA polymerase. We show that the activities of both Q82 and Q lambda are genome-specific in chasing RNA polymerase out of the early pause sites and in mediating antitermination. Finally, we show that the length of the RNA in the paused complex, or the exact position of the pause, affects the efficiency with which Q82 chases RNA polymerase out of the pause.