Activating transcription factor-2 (ATF-2) is a member of the CREB (cyclic AMP response element binding protein)/ATF family of transcription factors. Though it is present ubiquitously in mammalian tissues, the role of ATF-2 in normal cellular function is not known. Experiments suggest that ATF-2 has a cell cycle-related role: a) ATF-2 is translocated to the nucleus in Gl and G2/M phase cells, and b) similar nuclear translocation of ATF-2 is seen in response to stimulation with mitogenic growth factors, including epidermal growth factor. Though it has been shown to mediate - transcriptional activation by adenoviral E1a protein, an endogenous cellular regulator of ATF-2 function has not been identified. Adenoviral Ela protein does not directly bind DNA; it is able to activate gene transcription by interacting with DNA-bound ATF-2. We postulate that ATF- 2 interacts with endogenous cellular proteins in a similar fashion to form transcriptional complexes which regulate cell cycle-dependent gene expression. The goal of the experiments described in this proposal is the identification of mammalian proteins that interact with ATF-2 to form transcriptional complexes which transduce positive or negative signals to RNA-polymerase to effect expression of specific genes. This will be accomplished by screening for proteins, expressed by a mouse embryo cDNA library, which interact with ATF-2 in the yeast two-hybrid system. Proteins which interact with ATF-2 will be expressed, purified and sequenced. The tissue specificities, DNA-binding capabilities and transcriptional activation potential of these proteins will be characterized. The CREB/ATF family of transcription factors function in cellular signal transduction and in the regulation of cell growth and differentiation. Experiments based on the structure/function characteristics of CREB and ATF-2 will have implications for guiding future protocols of cancer therapy. Delineation of the role of protein- protein interactions in transcriptional activation is important for understanding the mechanisms involved in the normal and abnormal regulation of gene expression, cell growth, cell differentiation and oncogenesis.