RNA editing in eag potassium channels: Biophysical consequences of editing a conserved S6 residue

RNA editing at four sites in eag, a Drosophila voltage-gated potassium channel, results in the substitution of amino acids into the final protein product that are not encoded by the genome. These sites and the editing alterations introduced are K467R (Site 1, top of the S6 segment), Y548C, N567D and K699R (sites 2–4, within the cytoplasmic C-terminal domain). We mutated these residues individually and expressed the channels in Xenopus oocytes. A fully edited construct (all four sites) has the slowest activation kinetics and a paucity of inactivation, whereas the fully unedited channel exhibits the fastest activation and most dramatic inactivation. Editing Site 1 inhibits steady-state inactivation. Mutating Site 1 to the neutral residues resulted in intermediate inactivation phenotypes and a leftward shift of the peak current-voltage relationship. Activation kinetics display a Cole-Moore shift that is enhanced by RNA editing. Normalized open probability relationships for 467Q, 467R and 467K are superimposa...