Bro1-domain proteins such as yeast Bro1 and mammalian AIP1/Alix are well-established participants in endosome metabolism. The Bro1-domain interacts with endosomal surface protein Snf7/Vps32 in yeast, a subunit of the ESCRT complex. Yeast Bro1-domain protein Rim20 has no role in endosome function, but is required for alkaline pH-stimulated cleavage of transcription factor Rim101. Rim20-GFP is cytoplasmic under acidic conditions but concentrated in punctate foci under alkaline conditions. Bro1-GFP also accumulates in foci, but they are more numerous under acidic than alkaline conditions. Colocalization experiments indicate that some Rim20-GFP foci correspond to Bro1-RFP foci, whereas others do not. Rim8, Rim9, Rim21, Dfg16, Snf7, Vps20, Vps23, and Vps25, which are required for Rim101 cleavage, are required for appearance of Rim20-GFP foci. ESCRT complexes accumulate on endosome-derived compartments in cells that lack the AAA-ATPase Vps4. We find that Rim20-GFP foci accumulate in a vps4 mutant background independently of external pH, Rim101 pathway-specific genes, and most ESCRT subunit genes except for SNF7. Rim20-GFP foci seem to represent endosomes, because they colocalize with Snf7-RFP and because they correspond to a perivacuolar compartment in the vps4 strain. We propose that alkaline growth conditions alter the endosomal surface to favor Rim20-Snf7 interaction and Rim101 cleavage. Our findings raise the possibility that Bro1-domain proteins may be differentially regulated in the same cell, thereby coupling endosome metabolism to signaling.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Reference||Annotation Extension|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Conditions||Strain||Source||Reference|