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).