When cells divide, organelles must be segregated between the mother and daughter cells. The yeast vacuole segregates in a cell cycle dependent manner and precedes nuclear segregation. vac7-1 is defective both in vacuole segregation and vacuole morphology. In the original isolate, about 60% of medium sized buds inherit little to no vacuole material from the mother. Roughly 25% have a vacuole that traverses both the mother and bud and contains an open gap at the neck of the two cells. When wild-type vacuoles are swollen to the size of vac7-1 vacuoles, neither of these phenotypes are observed. This suggests that the vacuole segregation defect of vac7-1 is not an indirect effect due to the size of its vacuoles. It appears that Vac7p is involved in the vesiculation of the vacuole which is required for normal segregation. VAC7 encodes a putative 1165 amino acid protein with no known sequence homologies. Deletion of the gene causes a phenotype similar to that of vac7-1. By Western analysis, a 139 kDa protein has been identified in the soluble (S100) fraction. Several other mutants exhibit a vac7-1 like phenotype. These mutants are distinct from vac7-1, suggesting that several genes are involved in this process. One such mutant, fab1-2 (Yamamoto et al. 1995 Molec. Biol. Cell 6: 525-539) represents a PI4(P) 5 kinase. Lipids play an important role in membrane fusion events, thus a defect in a PI(4)P 5 kinase may have a direct affect on vacuole membrane vesiculation.