Fig. 3. Monophasic activation of PARP by UVC. (A) Time course of PARP activation in UVC-irradiated cells. Cells were exposed to 0.01 kJ/m² UVC or 100 µM H₂O₂ for 10 minutes. The pADPr-modified proteins were detected by immunoblotting with polyclonal LP96-10 or monoclonal 10H antibodies. Blots were reprobed with PARP antibody C-2-10. (B) Immediate activation of PARP at the site of local UVC irradiation. Cells were exposed directly or through a polycarbonate filter to 0.1 kJ/m² UVC. Samples were fixed using the TCA protocol at times ranging from 15 seconds to 2 hours after irradiation. The signals for T-T (FITC green) or pADPr (Texas red) were detected by indirect immunofluorescence; where the signals co-localized, a yellow colour was present in the merged images. Nuclear DNA was stained with DAPI. Images shown are representative of four experiments with identical results.