The aromatic acid:H+ symporter family (AAHS) is classified as family 15 of the major facilitator superfamily (MFS) [<cite idref="PUB00007278"/>]. Members of the AAHS family show fairly uniform sizes (418 to 460 residues). They transport a variety of aromatic acids as well as cis,cis-muconate [<cite idref="PUB00019527"/>]. 4-hydroxybenzoate transporter (PcaK Ppu), a member of this family, has been implicated in chemotaxis, allowing the bacteria to swim up concentration gradients of its substrates [<cite idref="PUB00018323"/>]. This is the only documented case where an MFS protein apparently serves as a chemoreceptor. One of the AAHS proteins (BenK Aca) transports benzoate [<cite idref="PUB00055026"/>]. Under the transporter classification (TC) system [<cite idref="PUB00055028"/>], this family is classified as TC number 2.A.1.15. Major facilitator superfamily, aromatic acid:H+ symporter family