Characteristics of the cAMP response unit.

Cyclic AMP (cAMP) mediates the hormonal stimulation of numerous cellular processes by regulating the phosphorylation of critical target proteins. In this report, we review current work suggesting that cAMP regulates transcription of eukaryotic genes through the reversible phosphorylation of a target nuclear protein called CREB. As CREB is currently the only transcription factor that is regulated by a well-defined cytoplasmic kinase-kinase-A, these studies may help to elucidate the general mechanisms underlying signal transduction.