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Vol. 18, Issue 7, 2533-2541, July 2007

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The Role of Trs65 in the Ypt/Rab Guanine Nucleotide Exchange Factor Function of the TRAPP II Complex

Yongheng Liang^*, Nadya Morozova^*, Andrei A. Tokarev^*, Jonathan W. Mulholland, and Nava Segev^*

*Department of Biological Sciences, Laboratory for Molecular Biology, University of Illinois at Chicago, IL 60607; and Cell Sciences Imaging Facility, Beckman Center, Stanford University School of Medicine, Stanford, CA 94305

Submitted March 8, 2007; Revised April 17, 2007; Accepted April 20, 2007
Monitoring Editor: Vivek Malhotra

The conserved modular complex TRAPP is a guanine nucleotide exchanger (GEF) for the yeast Golgi Ypt-GTPase gatekeepers. TRAPP I and TRAPP II share seven subunits and act as GEFs for Ypt1 and Ypt31/32, respectively, which in turn regulate transport into and out of the Golgi. Trs65/Kre11 is one of three TRAPP II-specific subunits. Unlike the other two subunits, Trs120 and Trs130, Trs65 is not essential for viability, is conserved only among some fungi, and its contribution to TRAPP II function is unclear. Here, we provide genetic, biochemical, and cellular evidence for the role of Trs65 in TRAPP II function. First, like Trs130, Trs65 localizes to the trans-Golgi. Second, TRS65 interacts genetically with TRS120 and TRS130. Third, Trs65 interacts physically with Trs120 and Trs130. Finally, trs65 mutant cells have low levels of Trs130 protein, and they are defective in the GEF activity of TRAPP II and the intracellular distribution of Ypt1 and Ypt31/32. Together, these results show that Trs65 plays a role in the Ypt GEF activity of TRAPP II in concert with the two other TRAPP II-specific subunits. Elucidation of the role played by Trs65 in intracellular trafficking is important for understanding how this process is coordinated with two other processes in which Trs65 is implicated: cell wall biogenesis and stress response.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Address correspondence to: Nava Segev (nava{at}uic.edu)

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