title: Multivesicular body sorting: ubiquitin ligase Rsp5 is required for the modification and sorting of carboxypeptidase S.
abstract: The multivesicular body (MVB) sorting pathway provides a mechanism for delivering transmembrane proteins into the lumen of the lysosome/vacuole. Recent studies demonstrated that ubiquitin modification acts in cis as a signal for the sorting of cargoes into this pathway. Here, we present results from a genetic selection designed to identify mutants that missort MVB cargoes. This selection identified a point mutation in ubiquitin ligase Rsp5 (Rsp5-326). At the permissive temperature, this mutant is specifically defective for ubiquitination and sorting of the ubiquitin-dependent MVB cargo precursor carboxypeptidase S (pCPS), but not ligand-induced ubiquitination of Ste2. A previous study implicated Tul1 as the ubiquitin ligase responsible for MVB sorting of pCPS. However, we detected no defect in either the sorting or ubiquitination of pCPS in tul1 mutants. We had previously shown that Fab1 phosphatidylinositol 3-phosphate 5-kinase is also required for MVB sorting of pCPS, but not Ste2. However, our analyses reveal that fab1 mutants do not exhibit a defect in ubiquitination of pCPS. Thus, both Rsp5 and Fab1 play distinct and essential roles in the targeting of biosynthetic MVB cargoes. However, whereas Rsp5 seems to be responsible for cargo ubiquitination, the precise role for Fab1 remains to be elucidated.
authors.affiliation: Department of Cellular and Molecular Medicine, Howard Hughes Medical Institute, University of California, San Diego, School of Medicine, La Jolla, California 92093-0668, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Katzmann
authors.forename: Srimonti
authors.initials: S
authors.lastname: Sarkar
authors.forename: Tony
authors.initials: T
authors.lastname: Chu
authors.forename: Anjon
authors.initials: A
authors.lastname: Audhya
authors.forename: Scott D
authors.initials: SD
authors.lastname: Emr
mesh_terms: D002268:Carboxypeptidases; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D009154:Mutation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D022161:Transport Vesicles / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000235:genetics / Q000378:metabolism*
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D025801:Ubiquitin; D043743:Ubiquitin-Protein Ligase Complexes; C095504:FAB1 protein, S cerevisiae; D017853:Phosphotransferases (Alcohol Group Acceptor); D002268:Carboxypeptidases; C019836:CPS1 protein, S cerevisiae; C469287:RSP5 protein, S cerevisiae