This proposal is designed to explore the role of immunoglobulin heavy chain binding protein(BiP) in regulating protein transport through the secretory pathway. We will use immunoglobulin (ig) synthesis as a model system for monitoring B1) association with secretory pathway proteins. Initial experiments will determine whether proteins that combine with BiP can be released and continue along the secretory pathway of whether the binding of BiP to proteins ins irreversible and signals their intracellular degradation. The site of degradation of proteins that remain bound to BiP and the role of Bip, if any, in their degradation will be determined. The role of post-translational modifications in regulating the function of BiP will be explored. Initial experiments indicate that two modifications of BiP, phosphorylation and ADP- ribosylation, are differentially segregated between free and bound pools of BiP and that these pools may be interconvertible. Therefore, we will focus on these modifications in the association, dissociation and degradation of ig heavy chains. finally, we will attempt to produce BiP conditional cellular mutants to more directly assess the role of BiP in monitoring protein transport along the secretory pathway. The experiments described in this proposal will use a combination of biochemical and genetic approaches to elucidate the function of BiP.
