SUBUNIT COMPOSITION OF MINK POTASSIUM CHANNELS

Expression of minK protein in Xenopus oocytes induces a slowly activating, voltage-dependent, potassium-selective current. Point mutations in mink that alter current gating kinetics, ion selectivity, pharmacology, and response to protein kinase C all support the notion that mink is a structural protein for a channel-type transporter. Yet, minK has just 130 amino acids and a single transmembrane domain. Though larger cloned potassium channels form functional channels through tetrameric subunit association, the subunit composition of minK is unknown. Subunit stoichiometry was determined by coexpression of wild-type minK and a dominant lethal point mutant of mink, which reaches the plasma membrane but passes no current. The results support a model for complete mink potassium channels in which just two mink monomers are present, with other, as yet unidentified, non-mink subunits.