VAC8P, A VACUOLAR PROTEIN WITH ARMADILLO REPEATS, FUNCTIONS IN BOTH VACUOLE INHERITANCE AND PROTEIN TARGETING FROM THE CYTOPLASM TO VACUOLE

During each cell cycle, the yeast vacuole actively partitions between mother and daughter cells, This process requires actin, profilin, an u nconventional myosin (Myo2p), and Vac8p, A mutant yeast strain, vac8, is defective in vacuole inheritance, specifically, in early vacuole mi gration. Vac8p is a 64-kD protein found on the vacuole membrane, a sit e consistent with its role in vacuole inheritance. Both myristoylation and palmitoylation are required for complete Vac8p localization. Inte restingly, whereas myristoylation of Vac8p is not required for vacuole inheritance, palmitoylation is essential, Thus, palmitoylation appear s to play a more direct role in vacuole inheritance. Most of the VAC8 sequence encodes 11 armadillo (Arm) repeats. Arm repeats are thought t o mediate protein-protein interactions, and many Arm proteins have mul tiple functions. This is also true for Vac8p. In addition to its role in early vacuole inheritance, Vac8p is required to target aminopeptida se I from the cytoplasm to the vacuole. Mutant analysis demonstrates t hat Vac8p functions separately in these two processes. Vac8p cosedimen ts with actin filaments. Vac8p is related to beta-catenin and plakoglo bin, which connect a specific region of the plasma membrane to the act in cytoskeleton. In analogy, Vac8p may link the vacuole to actin durin g vacuole partitioning.