Protein interactions at DNA lesions. (A) FRET results for reference interacting partners p53 (green) and 53BP1 (red). (B) FRET analysis of UBF1/2 dimerization. FRET analysis of (C) UBF1/2 (red) and γH2AX (green), (D) GFP-UBF1 (green) and 53BP1 (red), and (E) HP1β (green) and UBF1/2 (red). Studies were performed in control and γ-irradiated cells using a Leica TSC SP5 confocal microscope. For each event, 10 nuclei were analyzed in three independent experiments. IF, immunofluorescence; non-irrad., non-irradiated cells.