ABSTRACT
GTP-binding proteins of the Ypt family are members of the ras superfamily of proteins. The first example of a YPT gene, YPT1, was cloned and sequenced as part of the actin-β-tubulin gene cluster in the yeast Saccharomyces cerevisiae and the homology of the Ypt1 protein (Ypt1p) with ras proteins was immediately noted. 1 The subsequent identification by cDNA cloning of mammalian proteins that are strikingly similar in primary structure to the yeast Ypt1p 2 , 3 suggested the existence of a larger family of evolutionarily conserved proteins distinct from ras gene products. In fact, multiple members of the Ypt family have been found in the evolutionarily distant yeasts S. cerevisiae and Schizosaccharomyces pombe. 1 , 4 - 7 The existence in mammals of 20 or more Ypt-related proteins, designated Rab, 2 , 3 , 8 - 10 signifies the importance of this still-growing family.
