ERCs (ERC1 and ERC2) also referred to as ELKS and CAST are related proteins which share an identical C-terminal sequence. They interact with the conserved RIM PDZ domain via an unusual PDZ binding motif. ERC2/CAST 1 is only expressed as a single RIM binding variant. All ERCs have been shown to interact with Rab6, a protein involved in membrane trafficking at the Golgi complex. The function of these proteins has not been determined yet. They may link Rab6 mediated non-neuronal membrane traffic at the Golgi complex to neuronal membrane traffic at the active zone executed via RIMs.