STRUCTURAL AND FUNCTIONAL-ANALYSIS OF YPT2, AN ESSENTIAL RAS-RELATED GENE IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE ENCODING A SEC4 PROTEIN HOMOLOG

Using the cloned Saccharomyces cerevisiae YPT1 gene as hybridization probe, a gene, designated ypt2, was isolated from the fission yeast Schizosaccharomyces pombe and found to encode a 200 amino acid long protein most closely related to the ypt branch of the ras superfamily. Disruption of the ypt2 gene is lethal. The bacterially produced ypt2 gene product is shown to bind GTP. A region of the ypt2 protein corresponding to but different from the 'effector region' of ras proteins is also different from that of ypt1 proteins of different species but identical to the 'effector loop' of the S. cerevisiae SEC4 gene product, a protein known to be required for vesicular protein transport. The S. pombe ypt2 gene under control of the S. cerevisiae GAL10 promoter is able to suppress the temperature-sensitive phenotype of a S. cerevisiae sec4 mutant, indicating a functional similarity of these GTP-binding proteins from the two very distantly related yeasts.