ER exit sites (ERES) and ER–mitochondria encounter structures (ERMES) often localize proximally

Abstract

To understand the potential interplay between vesicular trafficking and direct membrane contact sites-mediated transport, we selected the endoplasmic reticulum (ER), which participates in both modes of inter-organelle transport. ER–mitochondria encounter structures (ERMES) are direct membrane contact junctions that mediate macromolecule exchange, while the secretory pathway originates at ER exit sites (ERES). Using the budding yeast Pichia pastoris, we documented that ERMES resident proteins are often juxtaposed with ERES markers. We further demonstrated that ERES form de novo almost always near a pre-existing ERMES. Disruption of either ERES or ERMES affects the other. Djp1, a chaperone reported to mediate mitochondrial import of ER-resident proteins, localizes at the ERES–ERMES proximal region. Our results indicate a potential functional link between ERES–ERMES proximity and mitochondrial protein import.