Figure 1.—

Characterization of bck2Δ swi6-ts mutants. (A and B) Thermosensitivity of bck2Δ swi6-4 and bck2Δ swi6-12 mutants. bck2 swi6-4 (A) or bck2 swi6-12 (B) with either control plasmid (Yep24) or YCp SWI6 plasmid were grown to log phase in −URA medium at 25°. Cells were counted and 10-fold serial dilutions with a starting dilution of ∼5000 cells were spotted onto −URA plates and incubated at the temperatures indicated for 2–3 days. (C) Swi6 protein is thermolabile in swi6-ts mutant. Cells were grown to log phase and then split and either grown at permissive temperature or shifted to 37° for 6 hr. After separation on a 10% SDS gel and Western blotting, Swi6 was detected with a polyclonal anti-Swi6 antibody. Cdc28 is shown as loading control. (D) Cell size of bck2 and swi6 mutants. Strains carrying the indicated SWI6 and BCK2 alleles were grown at 25° in YEPD and then either left untreated or shifted to 37° for 3 hr. Approximately 1.5 × 10⁵ cells were sonicated and diluted into 20 ml of physiological saline solution and the mean cell volume in femtoliters was determined with a Coulter Z2 Channelyzer. Cell number in each size class is presented as a percentage of the total population. (E) Morphology of bck2 and swi6 mutants. Cells carrying the indicated BCK2 and SWI6 alleles were grown to log phase at 25° in YEPD and then either left untreated or shifted to 37° for 3 hr. Cells were imaged by phase-contrast microscopy on an Axiostar plus microscope (Zeiss) with a ×40 objective.