The Ccz1 protein interacts with Ypt7 GTPase during fusion of multiple transport intermediates with the vacuole in S-cerevisiae

Previously we have shown that the Saccharomyces cerevisiae CCZ1 (YBR131w) g ene encodes a protein involved in protein trafficking. Deletion of this gen e leads to fragmentation of the vacuole typical of the class B vps mutants. Genetic and biochemical data indicated that Ccz1p is required for fusion o f various transport intermediates with the vacuole. Here we present data in dicating that CCZ1 is a close partner of the YPT7 gene, which encodes Rab G TPase and is required for fusion of transport vesicles to vacuole and homot ypic vacuole fusion. We isolated extragenic suppressors of CCZ1 deletion. A ll these suppressors belong to one complementation group and correspond to mutated alleles of the YPT7 gene. The mutated residues are located in two Y pt7p domains responsible for guanine binding. These data suggest that Ccz1p and Ypt7p interact physically. Coimmunoprecipitation experiments provide d irect evidence that this indeed is the case. A possible mechanism of Ccz1p action is discussed.