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Published online 16 October 2000. doi:10.1083/jcb.151.2.289
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© The Rockefeller University Press, 0021-9525/2000//289 $5.00
The Journal of Cell Biology, Volume 151, Number 2, , 2000 289-296

Original Article

Trapp Stimulates Guanine Nucleotide Exchange on Ypt1p



Wei Wanga, Michael Sachera, and Susan Ferro-Novicka

a Howard Hughes Medical Institute and the Department of Cell Biology Yale University School of Medicine, New Haven, Connecticut 06519-1418
Howard Hughes Medical Institute, Yale University School of Medicine, Department of Cell Biology, Boyer Center for Molecular Medicine, 295 Congress Avenue, BCMM 254B, New Haven, CT 06519-1418.(203) 737-5746(203) 737-5207

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.

Key Words: exchange factor • small GTPase • secretion • ER-to-Golgi • tethering factor

© 2000 The Rockefeller University Press

Abbreviations used in this paper: GEF, guanine nucleotide exchange factor; GST, glutathione-S-transferase; His6, six histidine tag; ts, temperature-sensitive.


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