1994 Volume 116 Issue 2 Pages 243-247
SAR1 encodes a 21-kDa GTPase, which is required for vesicle formation from the endoplasmic reticulum in yeast. Although it belongs to the expanding small GTPase superfamily, there are interesting structural features that are unique to the Sari protein. We performed a site-directed mutational study to identify the amino acid residues that are essential for the Sarlp function. Among seven mutants we constructed, four are functionless by themselves, while two confer temperature sensitivity to cells. When the mutant proteins are overproduced in wild-type cells, all of these six show a dominant negative effect on cell growth. The replacement by serine of the only cysteine residue present in Sarlp caused no significant change in the growth phenotype. These findings are not only important for analyzing the mechanism of the Sarlp action in yeast, but will also be very useful for studying the function of Sarlp counterparts in higher eukaryotes.
