REGULATION OF TRANSCRIPTION TERMINATION IN LEADER REGION OF TRYPTOPHAN OPERON OF ESCHERICHIA-COLI INVOLVES TRYPTOPHAN OR ITS METABOLIC PRODUCT

In cultures of E. coli grown with excess tryptophan about 7 of every 8 RNA polymerase molecules that initiate transcription on the trp operon terminate in the leader region (Bertrand et al., 1976). Tryptophan starvation relieves this termination, allowing a greater fraction of initiating RNA polymerase molecules to proceed beyond the termination site into the structural genes of the operon. Isoleucine starvation does not have a similar effect. These findings suggest that tryptophan or a metabolic product of tryptophan functions as an effector in regulation at the termination site. None of the 5 major polypeptides specified by the operon appears to regulate termination of transcription in the leader region; the polypeptides are neither required for termination nor do they influence the relief of termination observed during tryptophan starvation.