Yeast translation elongation factor-1A binds vacuole-localized Rho1p to facilitate membrane integrity through F-actin remodeling.

Abstract Rho GTPases are molecular switches that modulate a variety of cellular processes, most notably those involving actin dynamics. We have previously shown that yeast vacuole membrane fusion requires re-organization of actin filaments mediated by two Rho GTPases, Rho1p and Cdc42p. Cdc42p initiates actin polymerization to facilitate membrane tethering; Rho1p has a role in the late stages of vacuole fusion, but its mode of action is unknown. Here we identified eEF1A as a vacuolar Rho1p-interacting protein. eEF1A (encoded by the TEF1 and TEF2 genes in yeast) is an aminoacyl-tRNA transferase needed during protein translation. eEF1A also has a second function that is independent of translation; it binds and organizes actin filaments into ordered cable structures. Here we report that eEF1A interacts with Rho1p via a C-terminal sub-domain. This interaction, occurs predominantly when both proteins are in the GDP-bound state. Therefore, eEF1A is an atypical downstream effector of Rho1p. eEF1A does not promote vacuole fusion however, overexpression of the Rho1p interacting sub-domain affects vacuole morphology. Vacuoles were destabilized and prone to leakage when treated with the eEF1A inhibitor narciclasine. We propose a model whereby eEF1A binds to Rho1p-GDP on the vacuole membrane; it is released upon Rho1p activation and then bundles actin filaments to stabilize fused vacuoles. Therefore, the Rho1p-eEF1A complex acts to spatially localize a pool of eEF1A to vacuoles were it can readily organize F-actin.