Ancillary protein that functions as a regulatory subunit of the voltage-gated potassium (Kv) channel complex composed of pore-forming and potassium-conducting alpha subunits and of regulatory beta subunits. KCNE1 beta subunit modulates the gating kinetics and enhances stability of the channel complex. Alters the gating of the delayed rectifier Kv channel containing KCNB1 alpha subunit. Associates with KCNQ1/KVLQT1 alpha subunit to form the slowly activating delayed rectifier cardiac potassium (IKs) channel responsible for ventricular muscle action potential repolarization. The outward current reaches its steady state only after 50 seconds. Assembly with KCNH2/HERG alpha subunit Kv channel may regulate the rapidly activating component of the delayed rectifying potassium current (IKr) in heart