Fig. 3. RUNX proteins localize to sites of active transcription. SaOS-2 cells were transiently transfected with (A) EGFP-RUNX1 and (B) EGFP-RUNX2. Nascent transcripts were labeled with BrUTP for 30 minutes. Confocal microscopy was used to capture images of the intrinsic green fluorescence of EGFP and BrUTP labeling using a rat -BrdU antibody (red). Merged images show, in NMIF preparations, colocalization of EGFP-RUNX1 or EGFP-RUNX2 with BrUTP incorporation (yellow) in a significant subset of foci. The images shown are 3D projections (top) and a center section (bottom). The scale bars equal 10 µm. Line scans below the images show the extent of colocalization across the center of the nucleus indicated by the white lines of the merged 3D projections in panels A and B.