Termination of transcription in vitro in the Escherichia coli tryptophan operon leader region
Lee, F.; Squires, C.L.; Squires, C.; Yanofsky, C.
Journal of Molecular Biology 103(2): 383-393
ISSN/ISBN: 0022-2836 PMID: 781272 DOI: 10.1016/0022-2836(76)90318-1
Transcription of the wild-type tryptophan (trp) operon of Escherichia coli was examined in vitro. Virtually all Rna polymerase molecules which initiate transcription at the trp promoter cease transcription within the leader region of the operon after synthesizing about 145 nucleotides of leader RNA, and thus rarely transcribe the structural genes of the operon. Transcription stops with approximately equal frequency at either of two adjacent nucleotide pairs within an A + T-rich region, giving rise to transcripts with U-rich 3′ termini. The site of transcription termination is in a segment of the leader region proposed on the basis of genetic and biochemical evidence to contain a new regulatory element, a transcription attenuator, which functions in controlling the maximum level of expression of the operon.