This project focuses on the transport pathway from the endoplasmic reticulum to the lysosomal membrane. A family of recently characterized lysosomal membrane glycoproteins ("lgp's") and their cDNAs will be used to study the molecular requirements for transport to, and maintenance in, the limiting membranes of these terminal degradative compartments. Site-directed mutagenesis and expression of the cDNAs in cultured cells will be used to define targeting features of lgp's, while antisense RNA expression will be used to explore functions. The apparent mistargeting of overexpressed lgp's will be studied to further elucidate the regulation of this pathway. Additional components of the lysosomal membrane will be characterized to search for common targeting features, as well as to further define and understand this dynamic organelle. Membranes of eukaryotic cells define a diverse set of intracellular compartments that are functionally and biochemically distinct. Proteins that span or cross membranes are transported from their points of synthesis to their appropriate sites of action, often traversing multiple organellar compartments along the way. Proteins must therefore possess features that are not only essential for their functions, but also essential for transport and targeting to their final destinations. To date, few of the latter features have been defined. The results of this project will increase our understanding in this fundamental area of cell biology.
