IMG00210

Positiye confrol also QCCWr£jnJlLgJ^gaSŁ&Il-

Positive control occurs when lactose is E. s sole carbon soutct.

(but not if glucose also is present).

.CatafrgUte actiyator protein (CAP) binds cAMP, activates, and binds to a CAP recognition site upstream of the promoter (cAMP is greatly reduced In prescnccof glucose).

CAP changes the conformation of DNA and facilitates binding of RNA polymerase and transcription.

When glucose and lactose are present, E. coli prcfercntially uses glucose due to Iow levels of active CAP (Iow cAMP).

Adding cAMP to cells restore transcription of the la opcron even when glucose is still present.