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The lac Promoter

William S. Reznikoff, John N. Abelson


The lac promoter is a region of DNA required for the initiation of transcription of the lac operon (Jacob et al. 1964; Scaife and Beckwith 1967; Miller 1970; Reznikoff 1972; Dickson et al. 1975). The nucleotide sequence of the promoter contains the information necessary for the specific interaction of two proteins with the DNA. These proteins are RNA polymerase and a positive stimulatory protein, the catabolite gene activator protein, CAP (also termed CRP and CGA protein in other chapters of this volume). It is currently believed that transcription initiation occurs by the following general process. CAP in the presence of adenosine 3′,5′-monophosphate (cyclic [c]AMP) binds to a site in the promoter. The binding of the CAP–cAMP complex stimulates the productive interaction of RNA polymerase with the promoter such that, if the four ribonucleoside triphosphates are present, a lac mRNA transcript will be initiated (de Crombrugghe et al. 1971; Eron and Block 1971). This interaction of RNA polymerase with the promoter may be a complex process involving several steps such as the specific loose binding of RNA polymerase to the closed helix (formation of the “closed complex”), the generation of a region of localized denaturation (formation of the “open” or “rapid start complex”), and the initiation of the transcript (Chamberlin 1974).

A complete understanding of the structure of the promoter and an analysis of how specific changes in the structure alter one or more of the reactions mentioned above may yield some insight as to how the various steps...

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