The function of KCNE1 (potassium voltage-gated channel subfamily E regulatory subunit 1, Ensembl gene identifier ENSG00000180509) is as follows. 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 (PubMed:19219384, PubMed:20533308, PubMed:9230439). Alters the gating of the delayed rectifier Kv channel containing KCNB1 alpha subunit (PubMed:19219384). Associates with KCNQ1/KVLQT1 alpha subunit to form the slowly activating delayed rectifier cardiac potassium (IKs) channel responsible for ventricular muscle action potential repolarization (PubMed:20533308). The outward current reaches its steady state only after 50 seconds (Probable). Assembly with KCNH2/HERG alpha subunit Kv channel may regulate the rapidly activating component of the delayed rectifying potassium current (IKr) in heart (PubMed:9230439). {ECO:0000269|PubMed:19219384, ECO:0000269|PubMed:20533308, ECO:0000269|PubMed:9230439, ECO:0000305}.