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. Assembled with KCNB1 modulates the gating characteristics of the delayed rectifier voltage-dependent potassium channel KCNB1 (PubMed:19219384). Assembled with KCNQ1/KVLQT1 is proposed to form the slowly activating delayed rectifier cardiac potassium (IKs) channel. The outward current reaches its steady state only after 50 seconds. Assembled with KCNH2/HERG may modulate the rapidly activating component of the delayed rectifying potassium current in heart (IKr) (By similarity). Interacts with KCNB1 (PubMed:19219384). Interacts with KCNC2 (PubMed:14679187). Associates with KCNH2/HERG (By similarity). Interacts with KCNQ1; targets the complex KCNQ1-KCNE1 to the membrane raft (By similarity). Colocalizes with KCNB1 at the plasma membrane. Restrictively localized in the apical membrane portion of epithelial cells. Targets to the membrane raft when associated with KCNQ1 (By similarity). Expressed in the heart (PubMed:2183220, PubMed:19219384). Expressed in kidney (PubMed:2344412). Expressed in estrogen-induced uterus (PubMed:2344412). By estrogen. Phosphorylation inhibits the potassium current. N-glycosylation at Asn-26 occurs post-translationally, and requires prior cotranslational glycosylation at Asn-5. Mutagenesis experiments were carried out by expressing in Xenopus oocytes the mutant Asn-77 either individually (homomultimers) or in combination with wild-type KCNE1 (heteromultimers) in a 1:1 ratio (PubMed:7605639). Belongs to the potassium channel KCNE family.