The OAD family is comprised of systems involved in ion channel regulation, ion channel formation and efflux of organic anions across cellular membranes in eukaryotes. Some systems are linked to resistance to cytotoxic drugs but in contrast with DPL family systems, drug resistance is achieved by the efflux of drugs conjugated or associated with anionic molecules such as gluthatione or glucuronide derivatives. The phylogenetic tree shows three main branches corresponding to three subfamilies corresponding to systems respectively homologous to the CFTR (cystic fibrosis transmembrane conductance regulator), the MRP proteins (involved in conjugate drug export and the SUR (sulphonyl-urea receptor) proteins involved in the regulation of inwardly rectified potassium channels.