Required for normal Golgi function. Plays a role in SNARE-pin assembly and Golgi-to-ER retrograde transport via its interaction with SCFD1. Monomer. Component of the conserved oligomeric Golgi (COG) complex which is composed of eight different subunits and is required for normal Golgi morphology and localization. Mediates interaction of SCFD1 with the COG complex. Interacts with STX5. Belongs to the COG4 family.