The novel protein Ccz1p required for vacuolar assembly in Saccharomyces cerevisiae functions in the same transport pathway as Ypt7p

CCZ1 was previously identified by the sensitivity of ccz1 Delta mutants to high concentrations of Caffeine and the divalent ions Ca2+ and Zn2+. In this paper we show that deletion of CCZ1 leads to aberrant vacuole morphology, similar to the one reported for the family of vacuolar protein sorting (vps) mutants of class B, The ccz1 Delta cells display severe vacuolar protein sorting defects for both the soluble carboxipeptidase Y and the membrane-bound alkaline phosphatase, which are delivered to the vacuole by distinct routes. Ccz1p is a membranous protein and the vast majority of Ccz1p resides in late endosomes. These results, along with a functional linkage found between the CCZ1 and YPT7 genes, indicate that the site of Ccz1p function is at the last step of fusion of multiple transport intermediates with the vacuole.