Fig. 4. DSB repair response to Hoechst 33342 + 405 nm damage. (A) YFP-MDC1(BRCT) expressing cells were incubated with Hoechst 33342 and irradiated in an area of approximately 5 µm² (white box) with 405 nm laser-light and the fluorescence redistribution was followed in time. YFP-MDC1(BRCT) accumulates in a non-focal/homogenous pattern at the damaged area (right panel). (B) Ku-GFP expressing cells were incubated with Hoechst 33342 and irradiated with 405 nm light in a big (top cell) or small (lower cell) area in the nucleus (white boxes). The accumulation of Ku-GFP was followed in time (right panel). (C) PKcs does not accumulate at Hoechst 33342 + 405 nm treated sites (line in the nucleus indicated by arrowhead). The bright spots in the PKcs channel are described in Fig. 2A and are also found in cells that were not damaged. (D) Rad54-GFP expressing cells were treated with Hoechst 33342 and 405 nm irradiation (white boxes) and fluorescence redistribution was followed in time (right panel). Rad54-GFP accumulates in very low numbers at locally damaged areas in a non-focal/homogenous pattern. The bar graph indicates the fluorescence intensity in the nucleus (1) and at the locally damaged area (2).