Cex1 is a new component of the COPI Golgi-to-vacuole intracellular trafficking machinery

Abstract

During translational elongation, aminoacylated tRNA are supplied to the ribosome by RNA-interacting proteins. Cex1, a HEAT-containing protein, has been shown to participate to this tRNA channeling by interacting with aminoacylated tRNA during their export from the nucleus. Here, we show that Cex1 is a component of COPI (coatomer complex I) coated vesicles involved in the Golgi-to-vacuole trafficking pathway in Saccharomyces cerevisiae. Cex1 interacts with key components of the COPI coat Sec27, Sec28 and Sec33 proteins. Moreover, fluorescent microscopy indicates that Cex1 is not localized at the nuclear periphery as expected for an effector of nuclear tRNA channeling, but is observed on endosomal trans-Golgi network (TGN) positive structures. This localization relies on the vacuolar protein sorting receptor Vps10. Our data not only resolve the functional ambiguity regarding Cex1 homologues across species, but also point to the possibility to develop yeast-based models to study neurodegenerative disorders linked to the Human Cex1 homologue SCYL1.