STRUCTURAL DETERMINANTS OUTSIDE OF THE LEUCINE ZIPPER INFLUENCE THE INTERACTIONS OF CREB AND ATF-2 - INTERACTION OF CREB WITH ATF-2 BLOCKS E1A ATF-2 COMPLEX-FORMATION

Dimerization of leucine zipper-containing proteins has been associated characteristically with the formation of a coiled-coil structure betw een two compatible leucine zipper motifs. In the present study we demo nstrate the association of the leucine zipper of cAMP response element -binding protein (CREB) with a zinc finger motif of ATF-2. The associa tion of the CREB leucine zipper with the ATF-2 zinc finger is stabiliz ed if the ATF-2 leucine zipper is intact, implying that the preferred interactive structure of ATF-2 juxtaposes the amino-terminal zinc fing er motif of this protein with the carboxy-terminal leucine zipper of t his same protein. Furthermore, we demonstrate that the association of the CREB leucine zipper with the ATF-2 zinc finger in vitro blocks the association of the adenoviral E1a protein with ATF-2. Similarly, over expression of full-length CREB, or a truncated version of this protein corresponding to the carboxy-terminal 74 amino acids that make up the DNA-binding and dimerization domains, can block the ATF-2-mediated tr anscriptional stimulation by E1a in vivo. Mutation of the ATF-2 zinc f inger motif stimulates DNA binding of this protein, and abolishes inte ractions with E1a and CREB proteins. These results demonstrate that th e structural conformation of ATF-2 is critical for DNA binding and pro tein-protein interactions and, further, that leucine zippers can media te protein-protein interactions with structural motifs other than leuc ine zippers.