A Transcription Antiterminator Constructs a NusA-Dependent Shield to the Emerging Transcript

SummaryThe universal bacterial transcription elongation factor NusA mediates elongation activities of RNA polymerase. By itself, NusA induces transcription pausing and facilitates intrinsic termination, but NusA also is a cofactor of antiterminators that antagonize pausing and prevent termination. We show that NusA is required for λ-related phage 82 antiterminator Q82 to construct a stable complex in which RNA-based termination mechanisms have restricted access to the emerging transcript; this result suggests a locale for both Q82 and NusA near the β flap domain of RNA polymerase. Furthermore, as NusA is not required for the antipausing activity of Q82 in vitro, we distinguish two distinct activities of antiterminators, namely antipausing and RNA occlusion, and discuss their roles in Q82 function.