Figure 6.

Sfp1 and Sch9 function in parallel pathways. (A) sfp1Δ cells are sensitive to cycloheximide and to decreases in TOR or PKA pathway activity. (Left) Filter disks containing 3 nmole cycloheximide or 15 μg rapamycin were incubated on lawns of the indicated strains for 2 d. (Right) Synthetic proliferation defects between ras2Δ and sfp1Δ. Spore clones were scored after 4 d. (B) Sch9 does not control cell size strictly via Sfp1. Size distributions of an sfp1Δ/Δ strain in the presence or absence of a functionally null heterozygous GAL1–SCH9 (G9/+) allele are shown. Mean cell sizes of the indicated strains in either rich glucose or galactose medium are indicated to the right (n = 4). (C) An sfp1^ER allele is modulated by β-estradiol (E2). Size distributions of log phase sfp1^ER cultures with or without 250 nM E2 (left) or in the presence of various E2 concentrations (right). (D) Progressively compromised SCH9 and SFP1 activity reveals synergistic proliferation defects. An sch9^as sfp1^ER strain was inoculated into varying concentrations of 1NM-PP1 and E2 in synthetic glucose medium. Doubling times (t_d) were determined for each culture and the increase relative to cultures proliferating in 6.25 nM 1NM-PP1 and 125 nM E2 (concentrations at which Sch9^as and Sfp1^ER were fully active) was calculated. (Top) The increase in doubling time (Δt_d) resulting from individually increasing 1NM-PP1 or decreasing E2 was used to calculate the predicted additive effects. Actual increases in doubling time (middle) and the difference (bottom) are plotted.