The Escherichia coli catabolite gene activator protein (CAP) is a DNA binding protein involved with the transcription of several genes, including those that code for enzymes involved in the metabolism of certain sugars (i.e. lactose, maltose, and arabinose.) <u>Basically, CAP is responsible for the global regulation of carbon utilization.</u> Upon binding cAMP, CAP binds to a conserved DNA sequence from which it can either activate or repress transcription initiation from various promoters. In some cases clusters of several promoters are all controlled by a single cAMP-CAP complex bound to the DNA.
Once CAP has bound cAMP, the protein exhibits a higher affinity for a specific conserved DNA sequence. When the intracellular level of cAMP increases, the second messenger is bound by CAP and the cAMP-CAP complex binds to the DNA. Once bound, it is able to stimulate the transcription of the aforementioned genes. DNA bound by the CAP-cAMP complex is bent by ~90 degrees. This DNA bend, coupled with a protein-protein interaction between CAP and RNA polymerase is thought to be the mechanism by which CAP regluates transcription initiation on the chromosome.
