- RNA polymerase attaches to promoter site and then transcription proceeds in 5’ to 3’ direction beginning with operator site (O).
- The regulator site regulates the synthesis of 3 enzymes and produces a repressor protein of 360 AA residue.
- In absence of lactose, repressor protein binds to wild operator (O+) and prevents attachment of RNA polymerase to promoter. Hence, transcription is prevented.
- In Presence of lactose, RNA polymerase binds to repressor and hence preventing it from binding to operator and hence all 3 genes are transcribed.
- Finally, transcription is imitated in the operator site.
- Turning on of lactose operon is done by catabolite receptor protein (CRP) bind to molecules of cyclic adenosine monophosphate (CAMP).
- This enhances RNA polymerase binding and consequent transcription of the lac operon.
- Presence of glucose interferes the production of CAMP and hence halts transcription of the lac operon.
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