Molecular characterization of the USO1 gene product which is essential for vesicular transport in Saccharomyces cerevisiae.

We have previously shown that USO1 gene required in the protein transport from the endoplasmic reticulum (ER) to the Golgi apparatus encodes a hydrophilic protein of 1790 amino acids. The sequence of carboxyl-terminal 1010 amino acids was predicted to have an alpha-helical structure characteristic of the coiled-coil rod region of the cytoskeleton-related proteins. Antibodies raised against partial sequences of the Uso1 polypeptide reacted with a 200 kDa protein in Western blots of the wild-type yeast proteins. The Uso1 protein was found predominantly in the soluble fraction and displayed a molecular mass of 800-900 kDa in gel filtration when globular protein were used as molecular mass standards. In sucrose density gradient centrifugation, however, the Uso1 protein cosedimented with a globular 6S marker protein, horseradish peroxidase (44 kDa). These results suggest that, in its native state, the Uso1 protein forms a nonglobular oligomer.