Fig. 3. Dynamics of p21 recruitment to DNA-repair sites in living cells. (A) C2C12 myoblasts expressing both p21-GFP and RFP-PCNA were exposed to 405 nm laser microirradiation and fluorescence signals were acquired after the indicated times. Maximum projections of confocal mid sections show the accumulation of p21-GFP and RFP-PCNA fluorescence signals at sites of DNA damage (arrows). (B) Short-term kinetic analysis of p21-GFP and RFP-PCNA fluorescence after 405 nm laser microirradiation. Signals were acquired every 2 seconds and confocal sections are shown of images taken at the indicated times. The arrows indicate the site of irradiation. (C) Plot of the relative fluorescence intensity of p21-GFP (green) and RFP-PCNA (red) at the irradiated spot. Fluorescence intensities acquired every 2 seconds at the irradiated region, were corrected for background, and for total nuclear loss of fluorescence over the time course, and normalised to the pre-irradiation value. Bars, 5 µm (A,B).