FIGURE 4. Loss of yeast PP2A activity increases c-Myc Ser-62 phosphorylation and c-Myc half-life.

A, c-Myc^WT expression was induced at 30 °C for 1 h in the BY4741 or Δpph21 yeast strains. After the addition of glucose, cells were harvested and lysed in SDS sample buffer. Equal cell numbers were visualized by Western blot analysis with the indicated antibodies and quantitated as described in Fig. 1A. Ratios of phosphorylated c-Myc^WT to total c-Myc^WT were calculated. -Fold change of ratios in the Δpph21 strain compared with the BY4741 strain are shown. B, c-Myc^WT expression was induced for 1 h at 30 °C in the BY4741, Δpph21, or Δrts1 yeast strain. After the addition of glucose, cells were harvested at the indicated time points and lysed in SDS sample buffer. Western blot analysis and quantitation were performed as described in Fig. 1B. Experiments were repeated three or more times, and representative data are shown. Mean half-lives ± S.D. are indicated in bold. αPS62, α-Ser(P)-62; αPT58, α-Thr(P)-58.