Substitution of 2 base pairs (1 base pair per DNA half-site) within the Escherichia coli lac promoter DNA site for catabolite gene activator protein places the lac promoter in the FNR regulon.

The consensus DNA site for Escherichia coli catabolite gene activator protein (CAP) is 5'-AAATGTGATCTAGATCACATTT-3'. The proposed consensus DNA site for E. coli FNR is 5'-AAATTTGATATATATCAAATTT-3'. In this report, we show that substitution of 2 base pairs (1 base pair per DNA half-site) within the E. coli lac DNA site for CAP suffices to remove the lac promoter from the CAP regulon and to place the lac promoter in the FNR regulon. FNR stimulates transcription of the derivative of the lac promoter having G:C----T:A substitutions at base pair 5 each DNA half-site (13-fold stimulation). FNR does not stimulate transcription of the wild-type lac promoter, or of derivatives of the lac promoter having G:C----A:T or G:C----C:G substitutions at base pair 5 of each DNA half-site. Stimulation of transcription is strictly dependent on anaerobiosis. FNR-stimulated transcription initiates at the same base pair as does CAP-dependent transcription of the wild-type lac promoter.