Fig. 5. Phosphorylation mimic and phosphorylation site removal at T198 affects the localization of mSTI1-EGFP under G1/S-phase arrest. (A) NIH3T3 fibroblasts were stably transfected with pB-mSTI1-EGFP, derivative plasmids pB-mSTI1(T198E)-EGFP or with pB-mSTI1(T198A)-EGFP. Cells were treated with hydroxyurea (10 mM) for 10 hours and fixed in 3.7% paraformaldehyde before mounting and visualization by confocal laser fluorescence microscopy. Scale bars, 10 µm. (B) Cells were transfected as above, and cells demonstrating cytoplasmic fluorescence or nuclear and cytoplasmic fluorescence were quantified. The error bars represent standard deviations.