Potassium channel regulatory subunit that modulates the delayed rectifier potassium channel activity of KCNB1 by namely slowing down the deactivation and inactivation time constants (PubMed:10484328). While it does not form functional channel on its own, it can form functional heterotetrameric channels with KCNB1 (PubMed:10484328). . This is the function of Ensembl gene identifier ENSG00000170745 (KCNS3, potassium voltage-gated channel modifier subfamily S member 3).