Transcription Conditions for the lac Operon

Table 12.5 Transcription Conditions for the lac Operon lac Operon Allolactose Transcription Absent CAMP Absent Lactose Absent Glucose Present None Explanation Glucose is present to provide energy. There is no allolactose to bind repres— sor. There is no CAP—CAMP complex to bind CAP site. Present Present Absent Present Basal Glucose is present to provide energy; absence of cAMP prevents positive transcription regulation, but allo- lactose is present and acts as an inducer to allow a small amount of transcription. Absent Absent Present Absent None CAP-CAMP forms, but no allolactose is present to block repressor binding at operator. Present Present Present Absent High lnducer and CAP—CAMP are avail- able to induce and positively regulate transcription.