Uso1 Protein Is a Dimer with Two Globular Heads and a Long Coiled-Coil Tail

USO1is one of the essential genes inSaccharomyces cerevisiaewhose gene products participate in protein transport from the endoplasmic reticulum to the Golgi apparatus. This product was purified to homogeneity. Electron microscopic study revealed that it has a single or double 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 agreement with the secondary structure prediction that it has a long α-helix at the carboxyl terminus. Probability of coiled-coil formation was also predicted from the primary structure of the product, which asserts that it has a long α-helical coiled-coil at the carboxyl-terminal region with some interruptions. Certainly, the electron microscopic image of this molecule had some hinges within the rod region. The distance was measured between the globular domain and the hinges. Two peaks of the distribution of the hinge position exist at 23.1 and 85.5 nm from the globular domain. This is consistent with the predicted positions of interruption. These results give new experimental evidence that Uso1 protein is a dimer and has an α-helical coiled-coil tail with two globular heads.