Functional expression of a vertebrate inwardly rectifying K⁺ channel in yeast

We describe the expression of gpIRK1, an inwardly rectifying K⁺ channel obtained from guinea pig cardiac cDNA. gpIRK1 is a homologue of the mouse IRK1 channel identified in macrophage cells. Expression of gpIRK1 in Xenopus oocytes produces inwardly rectifying K⁺ current, similar to the cardiac inward rectifier current I(K1). This current is blocked by external Ba²⁺ and Cs⁺. Plasmids containing the gpIRK1 coding region under the transcriptional control of constitutive (PGK) or inducible (GAL) promoters were constructed for expression in Saccharomyces cerevisiae. Several observations suggest that gpIRK1 forms functional ion channels when expressed in yeast. gpIRK1 complements a trk1Δ trk2Δ strain, which is defective in potassium uptake. Expression of gpIRK1 in this mutant restores growth on low potassium media. Growth dependent on gpIRK1 is inhibited by external Cs⁺. The strain expressing gpIRK1 provides a versatile genetic system for studying the assembly and composition of inwardly rectifying K⁺ channels.