An Escherichia coli homologue of eukaryotic potassium channel proteins.

A DNA sequence in Escherichia coli K-12 contains an evident gene, kch, which predicts a protein 417 residues long with extensive similarity to a group of eukaryotic potassium channel proteins in amino acid sequence, in the presence of six apparent transmembrane (S) regions, and in the potassium-specific P (or H5) "pore" region found between S5 and S6. Most of the kch gene, including all of these regions and the 5' flanking region, have been sequenced in 38 wild reference (ECOR) strains as well; variation is conservative, indicating the protein's importance to the species, possibly as a defense against osmotic shock. Since the major family of eukaryotic potassium channel proteins is thought to have evolved from a common ancestor, the evolutionary position of this evident bacterial homologue is of interest, particularly since its function may have changed less than those of eukaryotic channels in the last billion years. While cases of probable importation of eukaryotic genes into bacteria are known, there is no evidence that kch has been imported. The relevant properties of the Kch protein and further ways to investigate its evolutionary position are discussed.