Acts as essential component of the peripheral membrane COG complex that is involved in intra-Golgi protein trafficking. COG is located at the cis-Golgi, and regulates tethering of retrograde intra-Golgi vesicles and possibly a number of other membrane trafficking events (By similarity). Component of the conserved oligomeric Golgi (COG) complex which consists of eight different proteins cog1-cog8. Belongs to the COG1 family.