Abstract
The protein-coding region of the essential Saccharomyces cerevisiae YPT1 gene coding for a ras-related, guanine-nucleotide-binding protein was exchanged in chromosome VI by the protein-coding segment of either the mouse ypt1 gene or the v-Ki-ras gene, and different chimeric YPT1-v-Ki-ras genes. The mouse ypt1 protein with 71% of identical residues compared with the yeast Ypt1 protein could functionally fully replace its yeast homologue as long as the mouse gene was overexpressed under transcriptional control of the inducible GAL10 promoter. In contrast, neither the viral Ki-ras nor the hybrid proteins were able to substitute for the loss of YPT1 gene function. This study suggests that different parts of the yeast Ypt1 protein are required for the interaction with cellular targets and that these essential parts are conserved in the mammalian ypt1 protein.