Among the different families of transporter, only two occur ubiquitously in all classifications of organisms. These are the ATP-Binding Cassette (ABC) superfamily and the Major Facilitator Superfamily (MFS). The MFS transporters are single-polypeptide secondary carriers capable only of transporting small solutes in response to chemiosmotic ion gradients [<cite idref="PUB00007278"/>, <cite idref="PUB00007279"/>].<p>This entry represents the uncharacterised major facilitator superfamily protein YcaD.</p> Major facilitator superfamily, YcaD