YKC1 ENCODES THE DEPOLARIZATION-ACTIVATED K-MEMBRANE OF YEAST( CHANNEL IN THE PLASMA)

Our previous patch-clamp studies showed that depolarization activates a K+-specific current in the plasma membrane of the budding yeast, Sac charomyces cerevisiae [Gustin et al, (1986) Science 233, 1195-1197]. T he Yeast Genome Sequencing Project has now uncovered on the left arm o f chromosome X an open reading frame (ORF) that predicts a 77-kDa prot ein reminiscent of a shaker-like alpha subunit with 6 membrane spans f ollowed by a subunit with 2 spans. We found that deleting this ORF rem oves the yeast K+ current. Furnishing the ORF from plasmids restores o r even greatly amplifies this current. These manipulations have no eff ects on the 40-pS mechanosensitive conductance also native to this mem brane. 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 ind uce in frog oocytes a K+ current. Its activation is coupled to E(K)+ a nd its outward rectification depends on external divalent cations. We found the YKC1 channel in its native membrane activates at low voltage s largely independent of E(K)+ and it remains so despite removal of di valents by chelation.