The Nucleobase cation symporter-2 (NCS2) family, also called the Nucleobase ascorbate transporter (NAT) family,[1] consists of over 1000 sequenced proteins derived from gram-negative and gram-positive bacteria, archaea, fungi, plants and animals.
[3] Many functionally characterized members are specific for nucleobases including both purines and pyrimidines, but others are purine-specific.
[5] E. coli possesses four distantly related paralogous members of the NCS2 family.
[6] Proteins of the NCS2 family are 414–650 amino acyl residues in length and probably possess 14 TMSs.
Lu et al. (2011) have concluded from x-ray crystallography that UraA (2.A.40.1.1) has 14 TMSs with two 7 TMS inverted repeats.