Fig. 1. AP-1 complex deletion mutants show fab1-like sorting defects. (A) Aberrant sorting of GFP-CPS in mutants lacking AP-1 complex components. Yeast strains expressing GFP-CPS were inspected by fluorescence and light microscopy as indicated. Wild-type and fab1 strain are included for comparison. Like fab1 cells, apl2, apl4 and aps1 cells clearly fail to sort GFP-CPS to the vacuole lumen. The sorting defect of apm1 and apm2 cells is less transparent than in the other AP-1 component deletion mutants, probably because of the wild-type vacuole morphology of these cells. Similar results were seen with GFP-Phm5p (data not shown). (B) Vacuole morphology of AP-1 complex component deletion mutants. Vacuole morphology of the AP-1 component deletion mutants was visualized by staining with FM4-64 as described in the Materials and Methods, and inspected by fluorescence and light microscopy as indicated. Wild-type and fab1 strains are included for comparison. Both apl2 and apl4 cells have an un-lobed vacuole. The other AP-1 complex component deletion mutants have wild-type vacuole morphology. (C) AP-1 complex component deletion mutants have acidified vacuoles. Yeast cells were stained with quinacrine as described in the Materials and Methods, and inspected by fluorescence and light microscopy as indicated. Wild-type and fab1 strains are included for comparison. Unlike fab1 cells, all AP-1 component mutants retain quinacrine, demonstrating that their vacuoles are acidified correctly.