Fig. 6. pRb is present at hundreds of sites scattered throughout mammalian nuclei. An asynchronous culture of WI38 cells was pulse-labeled for 5 minutes with 30 µg/ml BrdU, fixed with freshly prepared formaldehyde and stained with pRb-specific rabbit polyclonal antibodies (A,D,G) and a nuclease/anti-BrdU labeling cocktail (B,E). DNA was stained with DAPI. (H) pRb foci (red) density is higher within nuclear regions with lower density of DNA (blue).