Molecular Characterization of VAC1, a Gene Required for Vacuole Inheritance and Vacuole Protein Sorting

Cell division requires an accurate partitioning of cytoplasmic organelles. The segregation of vacuoles in the budding yeast Saccharomyces cerevisaie occurs at a specific time in the cell cycle and is spatially targeted to the small bud. Several yeast vac mutants have been isolated which are defective in this process. We have now cloned the VAC1 gene, corresponding to the first of these mutants, vac1-1. This gene encodes a protein of 515 amino acids, without homolog in the current data bases. It contains neither long hydrophobic stretches nor a classical leader peptide. The most notable aspect of the sequence is the presence of three zinc fingers. Yeast in which the VAC1 gene has been entirely deleted are viable. However, they grow more slowly than wild-type cells and only form microcolonies when grown on glycerol at 37 degrees C. These yeast are defective in vacuole segregation at both the permissive and nonpermissive temperatures. The vac1 mutant was previously shown to mislocalize carboxypeptidase Y to the cell surface, suggesting that Vac1p is involved in more than one vesicular traffic pathway.