Potassium channel ancillary subunit that is essential for generation of some native K(+) currents by virtue of formation of heteromeric ion channel complex with voltage-gated potassium (Kv) channel pore-forming alpha subunits. Functions as an inhibitory beta-subunit of the repolarizing cardiac potassium ion channel KCNQ1. Interacts with KCNQ1; impairs KCNQ1 localization in lipid rafts and only conducts current upon strong and continued depolarization. Highly expressed in heart, skeletal muscle, brain, spinal cord and placenta. The gene represented in this entry may be involved in disease pathogenesis. Belongs to the potassium channel KCNE family.