Homologues are present in many Gram-negative and Gram-positive bacteria, with at least one member classified from archaea (TC# 2.A.42.1.7, Thermococcus barophilus).
Proteins of the HAAAP family possess 403-443 amino acyl residues and exhibit eleven putative or established TransMembrane α-helical Spanners (TMSs).
These proteins exhibit topological features common to the eukaryotic amino acid/auxin permease (AAAP) family (TC# 2.A.18).
The aromatic amino acid/H+ symport permeases are: The two hydroxy amino acid permeases are: Thus[clarification needed], FhuA (TC# 1.B.14.1.4) transports phage T5 DNA while BtuB (TC# 1.B.14.3.1) transports phage C1 DNA (Samsonov et al., 2002).
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