DNA-binding and dimerization domains of adenosine 3',5'- cyclic monophosphate-responsive protein CREB reside in the carboxyl-terminal 66 amino acids.

The expression of genes in response to cAMP is mediated by one or more trans-activator proteins, CREBs, that bind to cAMP-responsive enhancers (CREs) of the general motif 5'-TGACGTCA-3'. The carboxyl-terminal amino acid sequences of two isoforms of CREB, CREB-327 and CREB-341, deduced from the cDNAs consist of a positively charged (basic) region adjacent to a leucine zipper motif. Three peptides corresponding to the hypothetical DNA-binding and dimerization domains of CREB-327 were synthesized. A peptide that includes both the basic and leucine zipper domains binds to the CRE specifically. Moreover, this peptide readily forms CRE-binding heterodimers with full-length CREB both synthesized by in vitro cell-free translation and isolated from PC-12 cells, but did not heterodimerize with in vitro translated jun or fos. Two other peptides, either partially or totally lacking the basic region, but containing the intact leucine zipper domain, readily form dimers but do not bind to the CRE. We conclude that the carboxy-terminal basic and leucine zipper regions are necessary and sufficient for specific binding of CREB to the CRE as a homodimer. The leucine zipper domain is responsible for the dimerization, and the basic region confers binding specificity for the CRE. Heterodimerization of CREB-327 does not form heterodimers with jun or fos.