The FAM114A proteins are adaptors for the recycling of Golgi enzymes

The Golgi apparatus contains many resident enzymes that must remain in place whilst their substrates flow through on their journey from the endoplasmic reticulum to elsewhere in the cell. COPI-coated vesicles bud from the rims of the Golgi stack to recycle Golgi residents to earlier cisternae. Different enzymes are present in different parts of the stack, and at least one COPI adaptor protein, GOLPH3, has been shown to recruit enzymes into vesicles in a specific part of the stack. We have used proximity biotinylation to identify further components of intra-Golgi transport vesicles and found FAM114A2, an uncharacterised cytosolic protein. Affinity chromatography with FAM114A2, and its paralogue FAM114A1 showed that they bind to numerous Golgi resident proteins, with membrane-proximal basic residues in the cytoplasmic tail being sufficient for the interaction. Deletion of both proteins from U2OS cells did not result in substantial defects in Golgi function. However, a Drosophila orthologue of these proteins (CG9590/FAM114A) is also localised to the Golgi and binds directly to COPI. Generation of Drosophila mutants lacking FAM114A revealed defects in glycosylation of glue proteins in the salivary gland. Thus, the FAM114A proteins are COPI vesicle resident proteins that bind to Golgi enzymes and so are candidate adaptors to contribute specificity to COPI vesicle recycling in the Golgi stack.