An Essential Subfamily of Drs2p-related P-Type ATPases Is Required for Protein Trafficking between Golgi Complex and Endosomal/Vacuolar System

Abstract

The Saccharomyces cerevisiae genome contains five genes encoding P-type ATPases that are potential aminophospholipid translocases (APTs): DRS2, NEO1, and three uncharacterized open reading frames that we have namedDNF1, DNF2, and DNF3 forDRS2/NEO1 family. NEO1 is the only essential gene in APT family and seems to be functionally distinct from the DRS2/DNF genes. The drs2Δdnf1Δ dnf2Δ dnf3Δ quadruple mutant is inviable, although any one member of this group can maintain viability, indicating that there is a substantial functional overlap between the encoded proteins. We have previously implicated Drs2p in clathrin function at the trans-Golgi network. In this study, we constructed strains carrying all possible viable combinations of null alleles from this group and analyzed them for defects in protein transport. The drs2Δdnf1Δ mutant grows slowly, massively accumulates intracellular membranes, and exhibits a substantial defect in the transport of alkaline phosphatase to the vacuole. Transport of carboxypeptidase Y to the vacuole is also perturbed, but to a lesser extent. In addition, the dnf1Δ dnf2Δdnf3Δ mutant exhibits a defect in recycling of GFP-Snc1p in the early endocytic-late secretory pathways. Drs2p and Dnf3p colocalize with the trans-Golgi network marker Kex2p, whereas Dnf1p and Dnf2p seem to localize to the plasma membrane and late exocytic or early endocytic membranes. We propose that eukaryotes express multiple APT subfamily members to facilitate protein transport in multiple pathways.