B-ATF: a novel human bZIP protein that associates with members of the AP-1 transcription factor family.

A new member of the ATF/CREB family of transcription factors, called B-ATF, has been isolated from a cDNA library prepared from Epstein-Barr virus stimulated human B cells. B-ATF is a 125 amino acid nuclear protein possessing a basic leucine zipper domain that is most similar to the basic leucine zipper of ATF-3. Northern blot analysis of polyadenylated mRNA isolated from a variety of human tissues and established cell lines indicates that the 1.0 kilobase B-ATF mRNA is expressed differentially, with the strongest hybridization detected in lung and in Raji Burkitt's lymphoma. Efficient homodimerization of the B-ATF protein cannot be detected using the yeast two hybrid system or using in vitro binding assays with glutathione-s-transferase-B-ATF and maltose binding protein-B-ATF fusion proteins produced in E. coli. However, a yeast two hybrid library screen has identified the human oncoprotein JunB as a specific binding partner for B-ATF. Glutathione-s-transferase-B-ATF heterodimerizes efficiently with in vitro translated JunB, c-Jun, and JunD, but only weakly associates with c-Fos. In addition, electrophoretic mobility shift assays demonstrate that a B-ATF/c-Jun protein complex can interact with DNA containing a consensus binding site for AP-1, suggesting that B-ATF functions as a tissue-specific modulator of the AP-1 transcription complex in human cells.