The soo1-1 (for suppressor of osmo-sensitivity) mutation results in a temperature-dependent osmo-sensitive phenotype at non-permissive temperature (37 degrees C), makes yeast cells more susceptible to Zymolyase and affects in vitro beta1,3-glucan synthase activity level. Transformation of soo1-1 mutant by SOO1 gene reverses these effects. Nucleotide sequencing of SOO1 revealed that this gene is identical to the recently reported alpha-COP that is involved in the intracellular protein translocation from endoplasmic reticulum to Golgi and vice versa. Although the soo1-1 mutant strain showed osmotically remediable growth at 37 degrees C, SOO1 disruptants could not grow in any culture conditions. Analysis of cell wall fractions revealed that the soo1-1 mutation causes a decrease in in vitro beta1,3-glucan synthase activity, and, thus, a subsequent alteration of the cell wall composition.