Ancillary protein that assembles as a beta subunit with a voltage-gated potassium channel complex of pore-forming alpha subunits. Modulates the gating kinetics and enhances stability of the channel complex. May associate with KCNQ1/KVLTQ1 and inhibit potassium current. Interacts with KCNQ1; impairs KCNQ1 localization in lipid rafts and inhibits voltage-gated potassium channel activity. Predominantly expressed in embryo and adult uterus. Low expression found in kidney, small intestine, lung and heart. Belongs to the potassium channel KCNE family. Truncated N-terminus. Truncated N-terminus.