CXCR4, the receptor for stromal cell-derived factor (SDF)-1, was expressed inSaccharomyces cerevisiaecoupled to the pheromone response pathway via a chimeric Gα subunit. Engagement of CXCR4 by SDF-1 resulted in expression of reporter genes,HIS3orlacZunder the transcriptional control of aFUS1promoter, which is pheromoneresponsive. CXCR4 mutants with constitutive signaling activity were generated by random mutagenesis of receptor coding sequences and selection for complementation of histidine auxotrophy in the yeast strain by autonomous expression of theFUS1-HIS3reporter gene. Linkage of CXCR4 to the pheromone response pathway in yeast provides a system that lends itself to screening of receptor antagonists. The use of constitutively active mutants to screen for inhibitors of the weak partial agonist and inverse agonist pharmacologic types offers a sensitive, efficient approach that is independent of ligand.
