USO1 PROTEIN IS A DIMER WITH 2 GLOBULAR HEADS AND A LONG COILED-COIL TAIL

USO1 is one of the essential genes in Saccharomyces cerevisiae whose g ene products participate in protein transport from the endoplasmic ret iculum to the Golgi apparatus, This product was purified to homogeneit y, Electron microscopic study revealed that it has a single or do-cabl e globular domain with a long tail and that the molecule is a dimer, A peak position of the distribution of rod length was 154.5 nm, in agre ement with the secondary structure prediction that it has a long alpha -helix at the carboxyl terminus. Probability of coiled-coil formation was also predicted from the primary structure of the product, which as serts that if, has a long cu-helical coiled-coil at the carboxyl-termi nal region with some interruptions. Certainly, the electron microscopi c image of this molecule had same hinges within the rod region. The di stance was measured between the globular domain and the hinges, Two pe aks of the distribution of the hinge position exist at 23.1 and 85.5 n m from the globular domain, This is consistent with the predicted posi tions of interruption, These results give new experimental evidence th at Uso1 protein is a dimer and has an alpha-helical coiled-coil tail w ith two globular heads. (C) 1996 Academic Press, Inc.