title: Ric1p and the Ypt6p GTPase function in a common pathway required for localization of trans-Golgi network membrane proteins.
abstract: In Saccharomyces cerevisiae, clathrin is necessary for localization of trans-Golgi network (TGN) membrane proteins, a process that involves cycling of TGN proteins between the TGN and endosomes. To characterize further TGN protein localization, we applied a screen for mutations that cause severe growth defects in combination with a temperature-sensitive clathrin heavy chain. This screen yielded a mutant allele of RIC1. Cells carrying a deletion of RIC1 (ric1Delta) mislocalize TGN membrane proteins Kex2p and Vps10p to the vacuole. Delivery to the vacuole occurs in ric1Delta cells also harboring end3Delta to block endocytosis, indicative of a defect in retrieval to the TGN rather than sorting to endosomes. SYS1, originally discovered as a multicopy suppressor of defects caused by the absence of the Rab GTPase YPT6, was identified as a multicopy suppressor of ric1Delta. Further comparison of ric1Delta and ypt6Delta cells demonstrated identical phenotypes. Multicopy plasmids expressing v-SNAREs Gos1p or Ykt6p, but not other v- and t-SNAREs, partially suppressed phenotypes of ric1Delta and ypt6Delta cells. SLY1-20, a dominant activator of the cis-Golgi network t-SNARE Sed5p, also functioned as a multicopy suppressor. Because Gos1p and Ykt6p interact with Sed5p, these results raise the possibility that TGN membrane protein localization requires Ric1p- and Ypt6p-dependent retrieval to the cis-Golgi network.
authors.affiliation: Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, California 90095-3717, USA.
authors.forename: E S
authors.initials: ES
authors.lastname: Bensen
authors.forename: B G
authors.initials: BG
authors.lastname: Yeung
authors.forename: G S
authors.initials: GS
authors.lastname: Payne
mesh_terms: D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors; D007425:Intracellular Membranes / Q000737:chemistry; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D010641:Phenotype; D021381:Protein Transport / Q000187:drug effects; D050766:Qb-SNARE Proteins; D050600:SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000737:chemistry; D029701:Saccharomyces cerevisiae Proteins; D013489:Suppression, Genetic / Q000187:drug effects; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic; D033921:Vesicular Transport Proteins; D021601:trans-Golgi Network / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; C490973:GOS1 protein, S cerevisiae; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D050766:Qb-SNARE Proteins; C105592:RIC1 protein, S cerevisiae; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D033921:Vesicular Transport Proteins; D020558:GTP Phosphohydrolases; D020559:Monomeric GTP-Binding Proteins; C499307:YPT6 protein, S cerevisiae