Rapid accumulation of MRE11 and NBS1 at DSB sites requires the nuclear enzyme PARP1. a, live cell imaging of wild-type cells (C3H10T½) expressing either YFP-MRE11 or GFP-NBS1. After microirradiation, YFP-MRE11 and GFP-NBS1 rapidly accumulate at sites of DNA damage. Bar, 5 μm. b, live cell imaging of fluorescently tagged MRE11 and NBS1 proteins after laser-generated DSB in PARP1-deficient cells (A1) shows differences in recruitment of YFP-MRE11 and GFP-NBS1 to DSB sites compared with wild-type cells show in a. Confocal images were captured at 500-ms intervals for 120 s after microirradiation. The arrows indicate nuclear regions containing laser-induced DSB. Fluorescently tagged proteins and times elapsed after microirradiation are indicated. c, the kinetics of MRE11 association with DSB from both wild-type and PARP1-deficient cells were plotted. d, graph reviews the real time measurements of NBS1 accumulation at DSB sites from both wild-type and PARP1-deficient cells. Quantitative measurements of YFP-MRE11 and GFP-NBS1 accumulation in regions of laser-induced DSB represent the average fluorescence ± S.E. from more than 10 individual cells.
