Articles written in Journal of Biosciences
Volume 34 Issue 3 September 2009 pp 445-463 Review
Cyclic adenosine 5′-phosphate (cAMP) is a global regulator of gene expression in
In carbon-limited cultures (including cultures limited by glucose), cAMP is at near-saturation levels with respect to expression of several catabolic promoters (including
The cAMP levels in carbon-excess cultures are substantially lower than those observed in carbon-limited cultures. Under these conditions, the expression of catabolic promoters is very sensitive to variation of cAMP levels.
cAMP · CRP invariably activates the expression of catabolic promoters, but it appears to inhibit the expression of anabolic promoters.
These results suggest that the physiological function of cAMP is to maintain homeostatic energy levels.
In carbon-limited cultures, growth is limited by the supply of energy; the cAMP levels therefore increase to enhance energy accumulation by activating the catabolic promoters and inhibiting the anabolic promoters. Conversely, in carbon-excess cultures, characterized by the availability of excess energy, the cAMP levels decrease in order to depress energy accumulation by inhibiting the catabolic promoters and activating the anabolic promoters.