53BP1 protein content decreases upon irradiation is due to protein degradation.

<p><b>A</b>. Before subjection to 10 Gy X-rays, HeLa cells were treated with medium alone (Con; lanes 1, 2), caffeine (10 mM; lane 3, 4) or with MG132 (20 µM; lane 5, 6). 4 h post irradiation, cell lysates were prepared for immunoblots. <b>B</b>. HeLa cells were treated with or without MG132 as in panel A, and immunofluorescence microscopy was applied after 4 h irradiation (10 Gy) as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110522#pone-0110522-g002" target="_blank">Figure 2C</a>. <b>C</b>. Image analysis of cells as shown in panel B was done as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110522#pone-0110522-g002" target="_blank">Figure 2E</a>. The distribution of pixel intensity was plotted for each sample.