title: Novel Ist1-Did2 complex functions at a late step in multivesicular body sorting.
abstract: In Saccharomyces cerevisiae, integral plasma membrane proteins destined for degradation and certain vacuolar membrane proteins are sorted into the lumen of the vacuole via the multivesicular body (MVB) sorting pathway, which depends on the sequential action of three endosomal sorting complexes required for transport. Here, we report the characterization of a new positive modulator of MVB sorting, Ist1. We show that endosomal recruitment of Ist1 depends on ESCRT-III. Deletion of IST1 alone does not cause cargo-sorting defects. However, synthetic genetic analysis of double mutants of IST1 and positive modulators of MVB sorting showed that ist1Delta is synthetic with vta1Delta and vps60Delta, indicating that Ist1 is also a positive component of the MVB-sorting pathway. Moreover, this approach revealed that Ist1-Did2 and Vta1-Vps60 compose two functional units. Ist1-Did2 and Vta1-Vps60 form specific physical complexes, and, like Did2 and Vta1, Ist1 binds to the AAA-ATPase Vps4. We provide evidence that the ist1Delta mutation exhibits a synthetic interaction with mutations in VPS2 (DID4) that compromise the Vps2-Vps4 interaction. We propose a model in which the Ist1-Did2 and Vta1-Vps60 complexes independently modulate late steps in the MVB-sorting pathway.
authors.affiliation: Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Rue
authors.forename: Sara
authors.initials: S
authors.lastname: Mattei
authors.forename: Suraj
authors.initials: S
authors.lastname: Saksena
authors.forename: Scott D
authors.initials: SD
authors.lastname: Emr
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; C511158:DID2 protein, S cerevisiae; D056827:Endosomal Sorting Complexes Required for Transport; C532818:Ist1 protein, S cerevisiae; D046912:Multiprotein Complexes; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D049452:Green Fluorescent Proteins