The Nucleobase:Cation Symporter-1 (NCS1) Family (TC 2.A.39) The NCS1 family consists of bacterial and yeast transporters for nucleobases including purines and pyrimidines. Members of this family possess twelve putative transmembrane a-helical spanners (TMSs). At least some of them have been shown to function in uptake by substrate:H+ symport mechanism. [Transport and binding proteins, Nucleosides, purines and pyrimidines]