Family 2.A.39 - The Nucleobase Cation Symporter-1 Family       

Family ID: 52634

The NCS1 family consists of over two dozen currently sequenced proteins derived from Gram-negative and Gram-positive bacteria, archaea, yeast, fungi and plants. The bacterial and yeast proteins are widely divergent and do not cluster closely on the NCS1 family phylogenetic tree. B. subtilis possesses two paralogues of the NCS1 family, and S. cerevisiae has several. Two of the yeast proteins (Dal4 and Fur4) cluster tightly together, and three other S. cerevisiae proteins, one of which is the thiamin permease, Thi10, also cluster tightly together. The latter three proteins are likely to be closely-related thiamin permease isoforms. The bacterial proteins are derived from several Gram-negative and Gram-positive species. These proteins exhibit limited sequence similarity with the xanthine permease, PbuX, of Bacillus subtilis which is a member of the NCS2 family. The two families are therefore probably related.

Proteins of the NCS1 family are 419-635 amino acyl residues long and possess twelve putative transmembrane a-helical spanners (TMSs). At least some of them have been shown to function in uptake by substrate:H+ symport. In these respects, and with respect to substrate specificity, these proteins resemble the symporters of the NCS2 family, providing further evidence that the two families represent distant constituents of a single superfamily. The two families probably arose by an early gene duplication event that occurred long before divergence of the three major kingdoms of life.