Subunit stoichiometry of a mammalian K+ channel determined by construction of multimeric cDNAs.

The subunit stoichiometry of the mammalian K+ channel KV1.1 (RCK1) was examined by linking together the coding sequences of 2-5 K+ channel subunits in a single open reading frame and tagging the expression of individual subunits with a mutation (Y379K or Y379R) that altered the sensitivity of the channel to block by external tetraethylammonium ion. Two lines of evidence argue that these constructs lead to K+ channel expression only through the formation of functional tetramers. First, currents expressed by tetrameric constructs containing a single mutant subunit have a sensitivity to tetraethylammonium that is well fitted by a single site binding isotherm. Second, a mutant subunit (Y379K) that expresses only as part of a heteromultimer contributes to the expression of functional channels when coexpressed with a trimeric construct but not a tetrameric construct.