Secretion of cell wall-bound acid phosphatase by Saccharomyces cerevisiae occurs along a restricted portion of the cell surface. Acid phosphatase activity produced during derepressed synthesis on a phosphate-limited growth medium is detected with an enzyme-specific stain and is localized initially to the bud portion of a dividing cell. After two to three generations of phosphate-limited growth, most of the cells can be stained; if further phosphatase synthesis is repressed by growth in excess phosphate, dividing cells are produced in which the parent but not the bud can be stained.

Budding growth is interrupted in α-mating-type cells by a pheromone (α-factor) secreted by the opposite mating type; cell surface growth continues in the presence of α-factor and produces a characteristic cell tip. When acid phosphatase synthesis is initiated during α-factor treatment, only the cell tip can br stained; when phosphate synthesis is repressed during α-factor treatment, the cell body but not the tip can be stained. A mixture of derepressed α cells and phosphatase-negative α cells form zygotes in which mainly one parent cell surface can be stained.

The cell cycle mutant, cdc 24 (Hartwell, L.H. 1971. Exp. Cell Res. 69:265-276), fails to bud and, instead, expands symmetrically as a sphere at a nonpermissive temperature (37 degrees C). This mutant does not form a cell tip during α-factor treatment at 37 degrees C, and although acid phosphatade secretion occurs at this temperature, it is not localized. These results suggest that secretion reflects a polar mode of yeast cell- surface growth, and that this organization requires the cdc 24 gene product.

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