Figure 3.

Identification of phospho-Ser-388. NIH 3T3 cells were transfected with 2 μg of pRc/CMV-FLAG-UBF1, pRc/CMV-FLAG-UBF1/S388G, or pRc/CMV-FLAG-UBF1/S388D, and labeled for 8 h with 0.5 mCi/ml [³²P]orthophosphate; UBF was immunoprecipitated and analyzed by tryptic phosphopeptide mapping. Two synthetic peptides (Q-A-T-^PS-P-A-S-K and S-L-^PS-P-Q-D-R) were added before electrophoresis. The position of the synthetic peptides was visualized by fluorescamine staining (dashed circles). A schematic illustration of UBF indicating the positions of phosphopeptides a, b, and c is shown above.