Activation and repression at the Escherichia coli ynfEFGHI operon promoter.

Induction of the Escherichia coli K-12 ynfEFGHI operon in response to anaerobiosis is repressed by nitrate ions. We show that the global transcription factor FNR is a Class II activator at the ynfEFGHI promoter and that NarL represses activation by binding to a single target that overlaps the promoter -10 element. Electromobility shift assays show that NarL does not prevent RNA polymerase binding and suggest that repression may involve a quaternary NarL-FNR-RNA polymerase-promoter complex.