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© The Rockefeller University Press,
0021-9525/2000//551 $5.00
The Journal of Cell Biology, Volume 151, Number 3,
, 2000 551-562
Original Article |
New Component of the Vacuolar Class C-Vps Complex Couples Nucleotide Exchange on the Ypt7 Gtpase to Snare-Dependent Docking and Fusion
The class C subset of vacuolar protein sorting (Vps) proteins (Vps11, Vps18, Vps16 and Vps33) assembles into a vacuole/prevacuole-associated complex. Here we demonstrate that the class C-Vps complex contains two additional proteins, Vps39 and Vps41. The COOH-terminal 148 amino acids of Vps39 direct its association with the class C-Vps complex by binding to Vps11. A previous study has shown that a large protein complex containing Vps39 and Vps41 functions as a downstream effector of the active, GTP-bound form of Ypt7, a rab GTPase required for the fusion of vesicular intermediates with the vacuole (Price, A., D. Seals, W. Wickner, and C. Ungermann. 2000. J. Cell Biol. 148:1231–1238). Here we present data that indicate that this complex also functions to stimulate nucleotide exchange on Ypt7. We show that Vps39 directly binds the GDP-bound and nucleotide-free forms of Ypt7 and that purified Vps39 stimulates nucleotide exchange on Ypt7. We propose that the class C-Vps complex both promotes Vps39-dependent nucleotide exchange on Ypt7 and, based on the work of Price et al., acts as a Ypt7 effector that tethers transport vesicles to the vacuole. Thus, the class C-Vps complex directs multiple reactions during the docking and fusion of vesicles with the vacuole, each of which contributes to the overall specificity and efficiency of this transport process.
Key Words: Vps39/Vam6 • endosome • Vps41/Vam2 • rab • Vps11
© 2000 The Rockefeller University Press
Abbreviations used in this paper: ALP, alkaline phosphatase; API, aminopeptidase I; CHCR, clathrin heavy chain repeat; CPY, carboxypeptidase Y; EEA1, early endosome antigen 1; GAP, GTPase activating protein; GST, glutathione S-transferase; NSF, N-ethylmaleimide-sensitive fusion protein; ORF, open reading fame; SNAP, soluble NSF attachment protein; SNARE, SNAP receptor; TRAPP, transport protein particle; Vps, vacuolar protein sorting.
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