REPRESSION OF THE AROP GENE OF ESCHERICHIA-COLI INVOLVES ACTIVATION OF A DIVERGENT PROMOTER

The repression of aroP expression which is mediated by the TyrR protei n with phenylalanine, tyrosine, or tryptophan has been shown to be pri marily a direct result of TyrR-mediated activation of a divergent prom oter, P3, which directs the RNA polymerase away from promoter P1. Evid ence which has been presented to support this conclusion is as follows . Repression of P1 does not occur either in vitro or in vivo if wild-t ype TyrR protein is substituted by the activation-negative mutant RQ10 (with an R-to-Q change at position 10). Repression of P1 is greatly d iminished if the P3 promoter is inactivated or if a 5-bp insertion is made between the P3 promoter and the binding sites for TyrR. Repressio n is also abolished if the promoter strength of P1 is increased or a p utative UP element associated, with P3 is altered. Repression of the s econd promoter, P2, still occurs if the wild-type TyrR protein is subs tituted with RQ10 or EQ274. The tryptophan-mediated repression of aroP does not involve the TrpR protein.