This is a family of K+ potassium transporters that are conserved across phyla, having both bacterial (KUP) Swiss:P30016 [3], yeast (HAK) Swiss:P50505 [2], and plant (AtKT) Swiss:O22397 [1] sequences as members.

1: A new family of K+ transporters from Arabidopsis that are conserved across phyla. Quintero FJ, Blatt MR; FEBS Lett 1997;415:206-211. PMID:9350997

2: A potassium transporter of the yeast Schwanniomyces occidentalis homologous to the Kup system of Escherichia coli has a high concentrative capacity. Banuelos MA, Klein RD, Alexander-Bowman SJ, Rodriguez-Navarro A; EMBO J 1995;14:3021-3027. PMID:7621817

3: Nucleotide sequence and 3'-end deletion studies indicate that the K(+)-uptake protein kup from Escherichia coli is composed of a hydrophobic core linked to a large and partially essential hydrophilic C terminus. Schleyer M, Bakker EP; J Bacteriol 1993;175:6925-6931. PMID:8226635