ABSTRACT
Saccharomyces cerevisiae was transformed with a high-copy-number plasmid carrying either the WT gene PHO5 or two modified genes with a deletion spanning or immediately adjacent to the signal peptide cleavage site. The enzyme is secreted by yeast protoplasts, provided they have been prepared from log-phase cells and are incubated in low-phosphate medium containing glucose. Acid phosphatase is actively synthesized by yeast cells grown on a low-phosphate medium but is usually not secreted into the medium. Cells expressing PHO5-lacZ hybrids did not secrete β-galactosidase, and, on cell fractionation, the hybrids were found associated with the membrane fraction. The acid proteases activity was measured in intact cells with p-nitrophenylphosphate which has free access to the cell wall and periplasmic space. Most PHO5 cells showed no intracellular labeling, but some gold particles were found between the two nuclear membranes and in small vesicles located close to the plasma membrane.
