The unexpected antitermination of gyrA-directed transcripts is enhanced by DNA relaxation.

We show that transcription originating at the gyrA promoter of Escherichia coli is less subject to termination at the lambda Toop terminator (22% read-through) than is transcription originating from either the galOP (1% read-through) or topA (3% read-through) control regions. Furthermore, termination of the gyrA transcripts decreases (60% read-through) upon relaxation of the template DNA. We believe that events related to stimulation of transcription at the gyrA promoter by DNA relaxation are responsible for the enhanced terminator read-through.