Osmotic Remedial Response in a Galactose-negative Mutant of Saccharomyces cerevisiae

We investigated an osmotic remedial mutant of Saccharomyces which was deficient in galactose-1-phosphate uridyl transferase. Both the rate of growth and the transferase activity of the mutant culture were dependent on the osmotic activity of the growth medium. Organic and ionic solutes proved to be equally effective in inducing the osmotic remedial response. The galactose pathway enzymes were separable by ultracentrifugation, indicating that a stable interenzyme complex was not formed. The results were consistent with the hypothesis that the corrective effect occurs at the tertiary or quaternary level of organization in an environmentally sensitive protein. The possibility that the osmotic remedial response represents an effect of translation is discussed.