Yeast cells take up inorganic phosphate as a nutrient to support cell growth and metabolism. When starved of phosphate, yeast will induce a gene encoding a broad-specificity phosphatase (an enzyme that hydrolyzes many different organic phosphate esters) and secrete the enzyme into their growth medium, effectively âminingâ their environment for this limiting nutrient. The inorganic phosphate released by the secreted phosphatase enzyme is then taken up and used by the cell for growth. The phosphatase is not induced when there is plenty of inorganic phosphate in the growth medium.
As part of a study on the regulation of the phosphate starvation response, you conduct a genetic screen for mutants with defects in the regulation of phosphatase secretion. You isolate two mutant strains of yeast: One strain fails to induce the secretion of phosphatase into the growth medium upon phosphorus deprivation. The other strain secretes the phosphatase even when there is adequate phosphate in the growth medium. You further show that these mutant strains bear inactivating mutations in different genes, neither of which alter the phosphatase-encoding gene itself.
Propose a plausible model for how the two genes identified in the mutants might act as regulators of the phosphatase gene.
Yeast cells take up inorganic phosphate as a nutrient to support cell growth and metabolism. When starved of phosphate, yeast will induce a gene encoding a broad-specificity phosphatase (an enzyme that hydrolyzes many different organic phosphate esters) and secrete the enzyme into their growth medium, effectively âminingâ their environment for this limiting nutrient. The inorganic phosphate released by the secreted phosphatase enzyme is then taken up and used by the cell for growth. The phosphatase is not induced when there is plenty of inorganic phosphate in the growth medium.
As part of a study on the regulation of the phosphate starvation response, you conduct a genetic screen for mutants with defects in the regulation of phosphatase secretion. You isolate two mutant strains of yeast: One strain fails to induce the secretion of phosphatase into the growth medium upon phosphorus deprivation. The other strain secretes the phosphatase even when there is adequate phosphate in the growth medium. You further show that these mutant strains bear inactivating mutations in different genes, neither of which alter the phosphatase-encoding gene itself.
Propose a plausible model for how the two genes identified in the mutants might act as regulators of the phosphatase gene.
