Characterization of yeast sar1 temperature-sensitive mutants, which are defective in protein transport from the endoplasmic reticulum.

SAR1 encodes a low molecular weight GTPase that is essential in the early process of vesicular transport in the secretory pathway. By random and site-directed mutagenesis of the SAR1 gene, we have obtained three temperature-sensitive mutants, N132I, E112K, and D32G. They all show a defect in transport from the endoplasmic reticulum to the Golgi apparatus, and accumulate endoplasmic reticulum membranes at the restrictive temperature. This is consistent with our previous observations in vivo on a galactose-shutoff mutant as well as the in vitro results, and provides powerful tools for further genetic analyses.