Control of enzyme synthesis and stability during sporulation in Saccharomyces cerevisiae.

Studies were undertaken to understand the control of synthesis, stability and modification of UDP galactose epimerase and DNA-dependent RNA polymerase during sporulation of Saccharomyces cerevisiae. When a pre-induced culture of an inducible strain (wild type) is transferred to sporulation medium, the epimerase is inactivated to an undetectable level within 16 hours. Surprisingly, the addition of cycloheximide, a protein synthesis inhibitor, during sporulation stabilizes the epimerase activity. However, in a constitutive strain, the epimerase continues to be synthesized de novo during sporulation. Since the enzyme is synthesized during both vegatative growth and sporulation constitutively, the controls for synthesis of epimerase must be similar under these physiologically different conditions. After chromatography on DEAE Sephadex, there is no change observed in the elution patterns of RNA polymerase forms extracted from acetate growth vegetative cells, sporulating cells or from mature asci ; in all cases RNA polymerase consists of three forms, Ib, II and III. However, single spore suspension obtained from asci by treatment with zymolase contains a new form with chromatographic properties similar to those of form Ia. Our data suggests that form Ia may be a modification product of from Ib.