The proposed studies apply classical phage genetic approaches to the screening of massive combinatorial primary structure libraries related to the leucine zipper of yeast transcription factor GCN4. The object of these studies is to define sequences which can form heterodimers with wild type GCN4 leucine zippers, and to characterize primary sequence requirements for heterodimerization. %%% The roles of amino acid side chains in protein dimerization processes will be evaluated by altering the primary sequence randomly of a simple leucine zipper structural motif. The functional significance of each new structure (there will be millions of such structures) will be screened, in a genetics based system, in terms of ability to dimerize. Two types of populations will be sequenced: (1) those molecules which can form heterodimers with the wild-type GCN4 leucine zipper, and (2) those molecules which form stable homodimers, but not heterodimers (with the wild- type leucine zipper). Such studies will shed considerable insight into the structural constraints involved in peptide-peptide, protein-protein interactions.
