This proposal is aimed at delineating the structural and functional relationships of nucleic acid- and protein-protein interactive domains of bacteriophage T4 gene 32 protein. 32 protein is an elegant and accessible system for structure-function studies, and the investigators believe this work will lead to insights relevant to protein-nucleic acid interactions in general. They are concerned with the details of protein structure responsible for specificity for single-stranded nucleic acid structure, binding cooperativity, homologous protein-protein interaction, nucleic acid helix-destabilizing and renaturing activities, as well as the relationship of these properties to the protein's physiological roles. The investigators will continue their studies on the structural basis of this protein's binding cooperativity. In this respect, they will utilize in vitro mutagenesis and chemical modification methods to better understand what they term the LAST ([Lys/Arg]3[Ser/Thr]2 motif, which forms the basis of a model in which there is a functional relationship between the protein-interactive and nucleic acid-interactive domains of this protein. The nucleic acid binding surface of the protein will be explored via chemical modification methods, with the assistance of modern mass spectroscopic techniques, and by in vitro mutagenesis experiments. Having shown that the binding of peptides containing the N-terminal LAST sequence to the core domain of 32 protein is an excellent model for homotypic protein-protein interactions in this system, they will determine the binding affinities of core domain with peptides of wild-type and altered sequences. The investigators propose several genetic approaches for localizing the segment of the protein's core domain responsible for nucleic acid binding cooperativity. The mechanism by which a truncated variant of 32 protein, *I, brings about DNA helix-destabilization will be probed by kinetic and binding assays. They will use fluorescence measurements to determine if a conformational change occurs in the protein upon binding nucleic acid. Finally, in collaboration with crystallography and NMR groups, they will attempt to obtain structural data for 32 protein containing an intact C-terminal domain.
