4.8 Article

TRAPPII subunits are required for the specificity switch of a Ypt-Rab GEF

Journal

NATURE CELL BIOLOGY
Volume 8, Issue 11, Pages 1263-U44

Publisher

NATURE PUBLISHING GROUP
DOI: 10.1038/ncb1489

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Funding

  1. NIGMS NIH HHS [GM-45444] Funding Source: Medline

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Ypt-Rab GTPases are key regulators of the various steps of intracellular trafficking. Guanine nucleotide-exchange factors (GEFs) regulate the conversion of Ypt-Rabs to the GTP-bound state, in which they interact with effectors that mediate all the known aspects of vesicular transport(1-3). An interesting possibility is that Ypt-Rabs coordinate separate steps of the transport pathways(4). The conserved modular complex TRAPP is a GEF for the Golgi gatekeepers Ypt1 and Ypt31/32 (refs 5-7). However, it is not known how Golgi entry and exit are coordinated. TRAPP comes in two configurations: the seven-subunit TRAPPI is required for endoplasmic reticulum-to-Golgi transport, whereas the ten-subunit TRAPPII functions in late Golgi(8-10). The two essential TRAPPII-specific subunits Trs120 and Trs130 have been identified as Ypt31/32 genetic interactors(11-13). Here, we show that they are required for switching the GEF specificity of TRAPP from Ypt1 to Ypt31. Moreover, a trs 130ts mutation confers opposite effects on the intracellular localization of these GTPases. We suggest that the Trs120-Trs130 subcomplex joins TRAPP in the late Golgi to switch its GEF activity from Ypt1 to Ypt31/32. Such a 'switchable' GEF could ensure sequential activation of these Ypts, thereby coordinating Golgi entry and exit.

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