Bim1 phosphorylation occurs during anaphase in vivo. (A) Western blot analysis of Bim1 phosphorylation in a WT and in an ipl1-2 background. SDS-PAGE was performed in the presence of 30 µM Mn²⁺ Phos-tag. Note the elimination of the slower migrating form after the shift to the restrictive temperature of an ipl1-2 mutant. (B) Time course of Bim1 phosphorylation in an α factor arrest/release experiment. Note that the slower migrating Bim1 forms are detected after degradation of the yeast securin Pds1p. The circled P represents the phosphorylated form of the protein.