Part of the ABC transporter complex DrrAB involved in daunorubicin and doxorubicin resistance. Responsible for energy coupling to the transport system. Binds ATP or GTP. The complex is composed of two ATP-binding proteins (DrrA) and two transmembrane proteins (DrrB). Belongs to the ABC transporter superfamily. Drug exporter-1 (DrugE1) (TC 3.A.1.105) family.