The phage lambda Q gene product: activity of a transcription antiterminator in vitro.

Phage lambda gene Q encodes a positive regulator of phage late gene expression. We show that purified Q gene protein functions as a transcription antiterminator in vitro. It acts at the terminator for lambda 6S RNA, a small constitutive transcript that precedes the late genes, thus opening transcription into the entire late gene region. It is active in a purified transcription system consisting otherwise of only RNA polymerase, L factor and DNA containing the region encoding the 6S RNA. Q protein thus acts directly on the transcription complex to alter its response to transcription terminators.