The role of Trs65 in the Ypt/Rab GEF function of the TRAPPII complex

The conserved modular-complex TRAPP is a nucleotide exchanger, GEF, for the yeast Golgi Ypt-GTPase gatekeepers. TRAPPI and TRAPPII 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 TRAPPII-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 TRAPPII function is unclear. Here, we provide genetic, biochemical and cellular evidence for the role of Trs65 in TRAPPII 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 are defective in the GEF activity of TRAPPII and the intracellular distribution of Ypt1 and Ypt31/32. Together, these results show that Trs65 plays a role in the Ypt GEF activity of TRAPPII in concert with the two other TRAPPII-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.