Calcium and SLY genes suppress the temperature-sensitive secretion defect of Saccharomyces cerevisiae uso1 mutant

Saccharomyces cerevisiae uso1-1 mutant stops the transport of secretory proteins from the endoplasmic reticulum to the Golgi apparatus at 37 degrees C. We found that this temperature-sensitive defect was suppressed either by increasing the concentration of calcium ion in the medium or by introducing in the cell the SLY genes which suppress the defect of Ypt1 protein, a small GTP-binding protein. The common phenotype and suppression of the mutants suggest that Uso1 and Ypt1 proteins function in the same process of protein transport, i.e., targeting or fusion of the transport vesicles to the Golgi membrane.