Yck activity is required for accurate bud site selection in haploid and diploid cells. (A) Haploid strains were YCK+, LRB758 (n = 80) and yckts, LRB756 (n = 172). (B) Diploid strains were YCK+, LRB861 (n = 317) and yckts, LRB860 (n = 395). Cells grown at 24°C to a density of 108 cells/ml in rich medium were stained with Calcofluor as in MATERIALS AND METHODS and were observed in 0.1 M potassium phosphate buffer, pH 7. Bar, 2 μm.