CREB is a DNA-binding protein that stimulates gene transcription upon activation of the cAMP signaling pathway. The mammalian CREB protein consists of an amino-terminal transcriptional activation domain and a carboxy-terminal DNA-binding domain comprised of a basic region and a leucine zipper. Recent studies have shown that the mammalian CREB is one of many transcription factors that can bind to the cAMP regulated enhancer (CRE) sequence. Consequently, a complete understanding of regulation through the CRE sequence requires the elucidation of how the various CRE-binding proteins interact with each other. To accomplish this goal, we have begun to characterize the family of CRE-binding proteins in a system that is amenable to genetic manipulations, Drosophila melanogaster. We have previously cloned a protein designated dCREB-A from a Drosophila embryonic cDNA library. Here, we describe an additional member of the Drosophila CREB gene family, isolated by screening a lambda gt11 library of adult Drosophila head cDNAs with a multimerized CRE sequence. This protein, dCREB-B, contains 285 amino acids and is remarkably similar within the basic/zipper region to the corresponding portion of mammalian CREB. In contrast, the dCREB-B and mammalian CREB zipper domains differ considerably from the dCREB-A zipper in both length and composition. However, the putative DNA binding domains for all three proteins are highly conserved. The activator region of dCREB-B is completely different from that of both mammalian CREB and dCREB-A. Northern blot analysis shows that multiple transcripts of the dCREB-B gene are expressed in embryonic and adult tissues and that these transcripts arise from both strands of the DNA.(ABSTRACT TRUNCATED AT 250 WORDS)