Fig. 4. Pin1 is required for entry into mitosis. A, Mitotic indices of cells transfected with GFP (GFP), GFP-Pin1 (Pin1), and GFP-Pin1 antisense (Pin1-AS). Forty-eight h after transfection, HeLa, 293, and SK-N-AS cells were stained with an antibody directed against phosphorylated histone H3, and the frequency of mitotic events was determined for the transfected cells. B, frequency of mitosis in HeLa cells transiently transfected with GFP, GFP-tagged Pin1, or the indicated mutant proteins. Seventy-two h after transfection, cells were stained with an antibody directed against phosphorylated histone H3, and the nuclei of transfected cells were scored for the frequency of mitosis. Average results from four independent experiments are shown. Bars, SE.