A novel cold-sensitive allele of the rate-limiting enzyme of fatty acid synthesis, acetyl coenzyme A carboxylase, affects the morphology of the yeastvacuole through acylation of Vac8p

The yeast vacuole functions both as a degradative organelle and as a storag e depot for small molecules and ions. Vacuoles are dynamic reticular struct ures that appear to alternately fuse and fragment as a function of growth s tage and environment. Vac8p, an armadillo repeat-containing protein, has pr eviously been shown to function both in vacuolar inheritance and in protein targeting from the cytoplasm to the vacuole, Both myristoylation and palmi toylation of Vac8p are required for its efficient localization to the vacuo lar membrane (Y.-X. Wang, N. L. Catlett, and L. S. Weisman, J. Cell Biol. 1 40:1063-1074, 1998). We report that mutants with conditional defects in the rate-limiting enzyme of fatty acid synthesis, acetyl coenzyme. A carboxyla se (ACC1), display unusually multilobed vacuoles, similar to those observed in vac8 mutant cells. This vacuolar phenotype of acc1 mutant cells was sho wn biochemically to be accompanied by a reduced acylation of Vac8p which wa s alleviated by fatty acid supplementation. Consistent with the proposed de fect of acc1 mutant cells in acylation of Vac8p, vacuolar membrane localiza tion of Vac8p aas impaired upon shifting acc1 mutant cells to nonpermissive condition. The function of Vac8p in protein targeting, an the other hand, was not affected under these conditions. These observations link fatty acid synthesis and availability to direct morphological alterations of an organ ellar membrane.