Saccharomyces cerevisiae mutants lacking a functional vacuole are defective for aspects of the pheromone response.

The end1 mutant belongs to a group of four vacuolar protein sorting mutants (class C vps) that lack a morphologically distinguishable and functional vacuole. These mutants share several other phenotypes, such as the inability to grow at 37 degrees C or on nonfermentable carbon sources. We show that, as in the case of the end1 mutant, vps16, vps18 and vps33 mutants all internalize but do not degrade alpha-factor. In addition, all four mutants are defective for alpha-factor-induced projection formation to the same extent. A more detailed investigation of pheromone response in the end1 mutant reveals that one aspect of the early response (induction of FUS1) is as defective as late responses (cell cycle arrest and projection formation). In contrast, another measure of the early response (induction of STE2) is normal. These data suggest that the biogenesis of a functional vacuole is necessary for optimal response to pheromone.