FUNCTIONAL EXPRESSION OF A VERTEBRATE INWARDLY RECTIFYING K+ CHANNEL IN YEAST

We describe the expression of gpIRK1, an inwardly rectifying K+ channe l obtained from guinea pig cardiac cDNA. gpIRK1 is a homologue of the mouse IRK1 channel identified in macrophage cells. Expression of gpIRK 1 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 cerev isiae. Several observations suggest that gpIRK1 forms functional ion c hannels when expressed in yeast. gpIRK1 complements a trk1 Delta trk2 Delta strain, which is defective in potassium uptake. Expression of gp IRK1 in this mutant restores growth on low potassium media. Growth dep endent on gpIRK1 is inhibited by external Cst The strain expressing gp IRK1 provides a versatile genetic system for studying the assembly and composition of inwardly rectifying Kt channels.