Nitrogen regulation of Saccharomyces cerevisiae invertase

Abstract

The regulation of extracellular enzymes is of great biotechnological interest. We studied the regulatory role of the URE 2 gene on the periplasmic invertase of Saccharomyces cerevisiae, because its periplasmic asparaginase is regulated by the URE2/GLN3 system. Enzymatic activity was measured in the isogenic strains P40-1B, the ure2 mutant P40-3C, and the P40-3C strain transformed with the pIC-CS plasmid carrying the URE2 gene. The assays were performed using midlog and stationary phase cells and nitrogen-starved cells from these growth phases. During exponential growth, the level of invertase in both wild-type and ure 2 mutant cells was comparable. However, the invertase activity in ure2 mutant cells from stationary phase was sixfold lower than in the wild-type cells. When P40-3C cells were transformed with the pIC-CS plasmid, the wild-type phenotype was restored. On nitrogen starvation in the presence of sucrose, the invertase activity in wild-type cells from midlog phase decreased three times, whereas in stationary cells, the activity decreased eight times. However, invertase activity doubled in ure 2 mutant cells from both phases. When these cells were trans-formed with the aforementioned plasmid, the wild-type phenotype was restored, although a significant invertase decrease in stationary cells was not observed. These results suggested that the URE2 protein plays a role in invertase activity.