Dual promoter control of the escherichia coli lactose operon

The control of transcription initiation at the lactose operon promoter was investigated in vitro. We found that an upstream promoter (termed lac P 2) interfered with RNA polymerase binding at the principal promoter (termed lac P 1). The start site for lac P 2 was located at base pair position −22 relative to the P 1 start site. The addition of cAMP receptor protein and cAMP was shown to repress lac P 2 and to activate lac P 1. Abortive initiation reactions for both promoters were used to investigate the coordinate repression-activation elicited by CRP-cAMP. The effects of lac promoter mutations (L8, P 8, and UV5) were consistent with an important RNA polymerase positioning role for CRP-cAMP in the activation of lac operon expression.