A complex for the transport of metabolites out of the cell, consisting of 4 domains: two ATP-binding domains and two membrane spanning domains. In some cases, all 4 domains are contained on 1 polypeptide, while in others one ATP-binding domain and one membrane spanning domain are together on one polypeptide in what is called a "half transporter". Two "half-transporters" come together to form a functional transporter. Transport of the substrate across the membrane is driven by the hydrolysis of ATP.