IDENTIFICATION OF RAB12 AS A SECRETORY GRANULE-ASSOCIATED SMALL GTP-BINDING PROTEIN IN ATRIAL MYOCYTES

A subfamily of small GTP-binding proteins, rab, has been shown to be i nvolved in regulation of vesicular traffic in eukaryotic cells. The go al of this study was to identify the rab proteins associated with atri al secretory granules. A [P-32]GTP-overlay assay showed the presence o f multiple small GTP-binding proteins on the atrial granules. By bioch emical analysis, we have demonstrated that one of the small GTP-bindin g proteins associated with the atrial granules is a rab12 protein (rab 12p), one of the rab proteins that are most closely related to a Sec4 protein of yeast. Association of rab12p with the atrial granules was c onfirmed by immunogold electron microscopy. Immunoprecipitation follow ed by immunoblot analysis with anti-rab12 antibody showed that in addi tion to atria, rab12p was expressed in multiple other organs and cell lines. These results suggest that rab12p may function in vesicular tra ffic in multiple diverse types of cells.