YKC1 encodes the depolarization‐activated K+ channel in the plasma membrane of yeast

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Abstract
Our previous patch‐clamp studies showed that depolarization activates a K+‐specific current in the plasma membrane of the binding yeast, Saccharomyces cerevisiae [Gustin et al. (1986) Science 233, 1195–1197]. The yeast Genome Sequencing Project has now uncovered on the left arm of chromosome X an open reading frame (ORF) that predicts a 77‐kDa protein reminiscent of a shaker‐like α subunit with 6 membrane spans followed by a subunit with 2 spans. We found that deleting this ORF removes the yeast K+ current. Furnishing the ORF from plasmids restores or even greatly amplifies this current. These manipulations have no effects on the 40‐pS mechanosensitive conductance also native to this membrane. Thus, this ORF, named YKC1 here, likely encodes a structure for the K+‐specific channel of the yeast plasma membrane. This and other K+ channel subunits are compared and the possible uses of this gene in research are discussed. YKC1 has recently been shown by others to induce in frog oocytes a K+ current. Its activation is coupled to E K+ and its outward rectification depends on external divalent cations. We found the YKC1 channel in its native membrane activates at low voltages largely independent of E K+ and it remains so despite removal of divalents by chelation.