TORC1 and TORC2 converge to regulate the SAGA co-activator in response to nutrient availability (2017)
Figure 4

Figure 4. The PP2A phosphatase inhibits differentiation and de-phosphorylates Taf12. (A,B) Expression of ste11+ (A) and mei2+ (B) using quantitative RT-PCR of RNA extracted from cells grown either in rich medium (dark gray) or starved for 4 hours (light grey). Cells of the following genotypes were analyzed: wild-type isogenic controls (WT), ppa2Η, par1Η, pab1Η, tsc1Η, and pab1Η tsc1Η. act1+ served as a control for normalization across samples. Values from a WT strain grown in rich medium were set at 1 to allow comparisons across culture conditions and mutant strains. Each column represents the mean value of 4 independent experiments, overlaid with individual data points and SE. Statistical significance was determined by 2-way ANOVA followed by Bonferroni's multiple comparison tests (n = 4). (C) Cells were grown to mid-log phase either in rich medium or starved for 8 hours. Zygotes and tetrads, which correspond to differentiated cells, were counted under a light microscope. Each value represents the mean percentage and SE of differentiating cells to the total number of cells, averaged from 4 independent experiments. At least 200 cells from the indicated genotypes were counted in each experiment. White arrowheads indicate zygotes. Scale bar, 10 μm. (D) P-Taf12 was followed by anti-FLAG IB of protein extracts from WT and pab1Η strains, grown in rich conditions (R) or starved for 45 minutes (S). An anti-Rpb1 IB is shown as a control for loading. The signal intensities of P-Taf12 and total Taf12 were quantified in each strain and condition. Ratios of P-Taf12 to total Taf12 were calculated from 6 independent experiments and individually plotted in a graph below the IBs, together with the mean and SE. Averaged values from all WT controls grown in rich medium were set at 1 to allow comparisons across culture conditions and strains. Statistical significance was determined by 2-way ANOVA followed by Bonferroni's multiple comparison tests (n = 6; *p < 0.01; #p < 0.05). A short and a long exposure of the FLAG IB are shown to detect total Taf12 and P-Taf12, respectively, within the linear range of the chemi-luminescence signal. (E) FLAG-tagged Taf12 and TAP-tagged Pab1 were affinity purified separately from cells grown in rich conditions (upper panels). TAP-tagged Pab1 was cleaved off from beads using the Tobacco Etch Virus (TEV) protease, releasing a shorter form of Pab1 (CBP-Pab1) in the eluate (E). CBP-Pab1 was then mixed with beads containing FLAG-Taf12 IPs and incubated in a phosphatase buffer, with and without 0.5 µM microcystin. Each reaction was then analyzed by IB and simultaneously probed with anti-FLAG or anti-CBP antibodies (lower panel). (F) Exponentially growing cells were treated for 1 hour with Torin1, which was added at increasing concentrations, 7 and 21 µM, to rich medium. Dimethylsulphoxide (DMSO) was used as the vehicle and added as a negative control. (G) P-Taf12 was followed by anti-FLAG IB of protein extracts from WT and tor2-ts10 strains, grown in rich conditions at 25°C or shifted to 30°C for 4 and 6 hours. (F,G) Anti-tubulin IBs are shown as a control for loading between samples. Shown are IBs that are representative of 3 independent experiments. The star (*) symbol labels unspecific bands detected by the anti-FLAG or anti-CBP antibodies in S. pombe.