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Vol. 19, Issue 4, 1282-1294, April 2008
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*Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Department of Medical Genetics, University of British Columbia, Vancouver, BC V5Z 4H4, Canada;
Department of Statistics and Michael Smith Laboratories, University of British Columbia, Vancouver, BC V6T 1Z2, Canada; and
Institute of Molecular Biology, University of Oregon, Eugene, OR 97403-1229
Submitted July 12, 2007;
Revised January 9, 2008;
Accepted January 15, 2008
Monitoring Editor: Sandra Lemmon
Endosomal transport is critical for cellular processes ranging from receptor down-regulation and retroviral budding to the immune response. A full understanding of endosome sorting requires a comprehensive picture of the multiprotein complexes that orchestrate vesicle formation and fusion. Here, we use unsupervised, large-scale phenotypic analysis and a novel computational approach for the global identification of endosomal transport factors. This technique effectively identifies components of known and novel protein assemblies. We report the characterization of a previously undescribed endosome sorting complex that contains two well-conserved proteins with four predicted membrane-spanning domains. Vps55p and Vps68p form a complex that acts with or downstream of ESCRT function to regulate endosomal trafficking. Loss of Vps68p disrupts recycling to the TGN as well as onward trafficking to the vacuole without preventing the formation of lumenal vesicles within the MVB. Our results suggest the Vps55/68 complex mediates a novel, conserved step in the endosomal maturation process.
Address correspondence to: Elizabeth Conibear (conibear{at}cmmt.ubc.ca) or Jennifer Bryan (jenny{at}stat.ubc.ca).
Abbreviations used: CPY, carboxypeptidase Y; ALP, alkaline phosphatase; MVB, multivesicular body; ESCRT, endosomal-sorting complex required for transport.
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