Regulatory alpha-subunit of the voltage-gated potassium (Kv) channel which, when coassembled with KCNB1 or KCNB2, can modulate their expression and their gating kinetics by acting on deactivation upon repolarization and inactivation during maintained depolarization. Accelerates inactivation but has relatively little effect on deactivation. Coexpression with KCNB1 or KCNB2 markedly slows inactivation. Each modulatory subunit has its own specific properties of regulation, and can lead to extensive inhibitions, to large changes in kinetics, and/or to large shifts in the voltage dependencies of the inactivation process. The gating kinetics depends on the nature and stoichiometry of the associated regulatory sunbunit. Fails to produce a potassium current when expressed alone