IMPORTANT ROLES OF THE C-TERMINAL PORTION OF HPC-1 SYNTAXIN 1A IN MEMBRANE ANCHORING AND INTRACELLULAR-LOCALIZATION/

HPC-1/syntaxin 1A (HPC-1), which plays an important role in vesicular transport to the plasma membrane, possesses a hydrophobic sequence at its C terminus. When expressed from cDNA in COS cells, wild-type HPC-1 was localized in the Golgi complex and the plasma membrane. Truncatio n of the hydrophobic domain resulted in the cytoplasmic localization o f the mutant, thus indicating that the domain indeed functions as a me mbrane anchor. A fusion protein with the C-terminal glycosylation site s was glycosylated in transfected cells, providing evidence that HPC-1 has a transmembrane structure, and that the protein is first inserted into the endoplasmic reticulum and then transported to the plasma mem brane. A chimeric protein consisting of Escherichia coli maltose-bindi ng protein with the last 24 amino acids of HPC-1 was inserted into the endoplasmic reticulum in a transmembrane topology and localized along the exocytic pathway of transfected cells similar to HPC-1, These res ults indicate that the portion is important for intracellular localiza tion of HPC-1.