The yeast gene PBS2 encodes a presumed protein kinase. The gene is essential for manifestation of resistance to the antibiotic polymyxin B. Deletion of PBS2 enables a ras2-530 null mutant to grow on nonfermentable carbon sources; overexpression of PBS2+ enhances viability of a RAS2Val19 mutant. Overexpression of PBS2+ also diminishes cellular response to mating pheromone MF alpha. These results suggest that the PBS2 and RAS2 genes affect a common pathway that may communicate with the pheromone response pathway. In addition, disruption of PBS2 renders cells sensitive to high osmolarity: exposure to 0.9 M-NaCl causes growth arrest, appearance of bizarre morphological forms, and eventual death. A mutation suppressing pbs2 deletion has been found. That mutation restores full polymyxin B resistance but only partially corrects the osmotic sensitivity defect. These observations indicate that PBS2 is involved in diverse physiological pathways in yeast.