Activating transcription factor / cyclic-AMP response element-binding protein (ATF/CREB) has been implicated as a key regulator in the transcriptional control of many genes. In this study, we isolated and characterized a full-length cDNA that encodes a CRE-binding protein 2 (CREB2) called ATF4 in Xenopus embryos. Like other CREB 2 transcription factors, the 342-amino acid ATF4 protein contains a carboxyl terminal leucine-zipper motif, an adjacent basic domain, and an amino terminal leucine-zipper motif. Unlike other CREB2 (ATF4) proteins, the ATF4 isolated from the gonads of Xenopus embryos contains a consensus phosphorylation site for protein kinase A (PKA). In a gel shift analysis, ATF4 bound to a CLS sequence in the promoter of Xenopus aromatase.