A cluster of phosphorylation sites on the cyclic AMP-regulated nuclear factor CREB predicted by its sequence

Cyclic AMP regulates the expression of a number of genes through a conserved promoter element, the CRE¹. Moreover, transcrip-tional induction by cAMP requires the activation of cAMP-dependent protein kinase (protein kinase A)^1,2. We have previously characterized the cAMP response element binding protein (CREB) in PC 12 cells and brain tissue as a nuclear factor, of relative molecular mass 43,000, whose transcriptional efficacy is regulated by protein kinase A phosphorylation^3,4. CREB stimulates transcription on binding to the CRE as a dimer. Experiments suggesting that the dimerization and transcriptional efficacy of CREB are each stimulated by phosphorylation at distinct sites prompted us to suggest that CREB is regulated by multiple kinases in vivo ⁴. We now report the isolation of a cDNA clone for rat CREB using amino-acid sequence information from purified CREB protein. Sequence analysis of this CREB cDNA predicts a cluster of protein kinase A, protein kinase C and casein kinase II consensus recognition sites near the N terminus of the protein. The proximity of these potential phosphorylation sites to one another indicates that they may interact either positively or negatively to regulate CREB bioactivity.