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.