The coatomer is a cytosolic protein complex that binds to dilysine motifs and reversibly associates with Golgi non-clathrin-coated vesicles, which further mediate biosynthetic protein transport from the ER, via the Golgi up to the trans Golgi network. Coatomer complex is required for budding from Golgi membranes, and is essential for the retrograde Golgi-to-ER transport of dilysine-tagged proteins (By similarity). Oligomeric complex. Binds to CDC42. Interacts with JAGN1. Interacts with TMED10 (via cytoplasmic domain). The coatomer is cytoplasmic or polymerized on the cytoplasmic side of the Golgi, as well as on the vesicles/buds originating from it (By similarity). Over 60% of the COPG1-containing coatomers are found in the trans-Golgi apparatus and less than 40% in the cis-Golgi. Belongs to the COPG family.