The cAMP response element binding protein, CREB, is a potent inhibitor of diverse transcriptional activators.

Cyclic AMP response element binding protein (CREB) activates transcription of cAMP response element (CRE)-containing promoters following an elevation of intracellular cAMP. Here we show that CREB and the highly related protein ATF-1 are also potent transcription inhibitors. Strikingly, CREB inhibits transcription of multiple activators, whose DNA-binding domains and activation regions are unrelated to one another. Inhibition requires that the CREB dimerization and DNA-binding domains are intact. However, inhibition is not dependent upon the presence of a CRE in the promoter, and does not involve heterodimer formation between CREB and the activator. The ability of an activator protein to inhibit transcription in such a promiscuous fashion has not been previously reported.