Mechanism of initiation and repression of in vitro transcription of the lac operon of Escherichia coli.

A cyclic AMP-binding protein (CAP protein), cyclic AMP, and RNA polymerase holoenzyme are shown to initiate lac transcription at the lac promoter. Lac repressor appears to control transcription by preventing RNA polymerase and/or CAP protein from binding to the lac promoter. Results support the idea that the lac promoter is composed of two sites that interact with CAP protein and RNA polymerase holoenzyme. The promoter can be altered by mutation so that holoenzyme alone can initiate lac transcription correctly.