Distinct cAMP response element-binding protein (CREB) domains stimulate different steps in a concerted mechanism of transcription activation

Hormones and neurotransmitters rapidly change patterns of gene expression i n target cells by activating protein kinases that phosphorylate and modify the activity of CREB and other transcription factors. Although CREB was ini tially characterized as mediating the response to cAMP. CREB phosphorylatio n and activation are stimulated by diverse extracellular signals and protei n kinases in essentially all cells and tissues. CREB stimulates transcripti on through a constitutive activation domain (CAD), which interacts with the promoter recognition factor TFIID, and through a kinase-inducible domain ( KID), when Ser-133 is phosphorylated, The present study provides new insigh t into the mechanism of activation by showing that each of the CREB domains contributes to transcription initiation by stimulating sequential steps in the transcription reaction. The CAD effectively assembled a polymerase com plex, as evidenced by constitutive activation in vivo and stimulation of si ngle-round transcription in vitro. In contrast, phosphorylation of the KID in CREB stimulated isomerization of the polymerase complex, as determined b y abortive initiation, and promoter clearance and/or reinitiation. as measu red by multiple rounds of transcription. Our results provide evidence for a new model for CREB-mediated induction through a concerted mechanism involv ing establishment of a polymerase complex by the CAD. followed by stimulati on of isomerization. promoter clearance. and/or reinitiation by phosphoryla ted KID to enhance target gene transcription.