Characterization of the ORF YBR264c in Saccharomyces cerevisiae, which encodes a new yeast Ypt that is degraded by a proteasome dependent mechanism

We identified the ORF YBR264c during the systematic sequencing of the Sacch aromyces cerevisiae genome. It encodes a putative protein of 218 amino acid s. We demonstrate here that the gene is indeed expressed and encodes a new Ypt in yeast. This protein specifically binds guanine nucleotides and inter acts via its C-terninal end with the unique Rab GDP Dissociation Inhibitor (RabGDI). In accordance with a recent proposal, the gene is now designated YPT10. No mutant phenotype could be associated with inactivation of the gen e. However, overexpression of YPT10 resulted in defects in growth; microsco pic examination of such cells revealed an overabundance of vesicular and tu bular structures, suggesting some alteration in the function of the Golgi a pparatus. In addition, degradation of the Ypt10 protein, which possesses a PEST sequence, is shown to be dependent on proteasome activity.