TRAPP stimulates guanine nucleotide exchange on Ypt1p.
TRAPP, a novel complex that resides on early Golgi, mediates the targeting of ER-to-Golgi vesicles to the Golgi apparatus. Previous studies have shown that YPT1, which encodes the small GTP-binding protein that regulates membrane traffic at this stage of the secretory pathway, interacts genetically with BET3 and BET5. Bet3p and Bet5p are 2 of the 10 identified subunits of TRAPP. Here we show that TRAPP preferentially binds to the nucleotide-free form of Ypt1p. Mutants with defects in several TRAPP subunits are temperature-sensitive in their ability to displace GDP from Ypt1p. Furthermore, the purified TRAPP complex accelerates nucleotide exchange on Ypt1p. Our findings imply that Ypt1p, which is present on ER-to-Golgi transport vesicles, is activated at the Golgi once it interacts with TRAPP.
Wang
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W
Howard Hughes Medical Institute and the Department of Cell Biology Yale University School of Medicine, New Haven, Connecticut 06519-1418, USA.
Sacher
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M
Ferro-Novick
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S
D002352:Carrier Proteins / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D021381:Protein Transport; D029701:Saccharomyces cerevisiae Proteins; D022161:Transport Vesicles / Q000378:metabolism; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
C098389:BET3 protein, S cerevisiae; C114038:BET5 protein, S cerevisiae; D002352:Carrier Proteins; D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; D006150:Guanine Nucleotides; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; C406327:transport protein particle, TRAPP; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; C060755:YPT1 protein, S cerevisiae; D020691:rab GTP-Binding Proteins