FIG. 2.

Phosphorylation of murine p53 at Ser23 in ES cells at various times after IR treatment (5 Gy) or UV treatment (60 J/m²). Irradiated and untreated cells were treated with the proteosome inhibitor ALLN for 4 h before harvesting so that samples of all time points would have similar levels of p53 protein. Cell extracts from irradiated cells and untreated controls (0 h) were analyzed by Western blotting with antibodies specific for p53 or p53 phosphorylated at Ser23 (p53-S23p) as described previously (8, 33). The time after irradiation (in hours) is indicated at the top.