BRCA2-GFP diffusion in a live Brca2GFP/GFP ES cell. An individual Brca2GFP/GFP nucleus was imaged by oblique illumination using a TIRF setup (Eclipse Ti-E microscope; Nikon). Most BRCA2-GFP particles display only very short-lived transient interactions while diffusing in the nucleus; at time point 5.55 s, two particles are subject to longer-lasting interactions until they diffuse away at time points of 6.2 and 6.6 s. The population of BRCA2-GFP is bleached to a large extent during the 10-s image acquisition period. Spontaneous foci that usually contain tens of proteins and appear stationary were not detected in this field of view. The laser beam passing into the sample had a 75° angle with respect to the objective optical axis. Frames were continuously collected for 10 s using a frame acquisition time of 50 ms. The display rate is 7 frames per second. Compare Fig. 2 (A–C) and Fig. 4 A. Bar, 5 µm.
