CBXs and BMI1 are components of PRC1 complexes which keep the memory of cell identity by maintaining the repression of numerous target genes. In human U2OS cells, they accumulate into nuclear foci of different sizes and intensities called Polycomb bodies. Fluorescence recovery after photobleaching analysis reveals that PcG dynamics outside foci is governed by diffusion as complexes and transient binding to target genes. Recovery curves inside foci are substantially slower, and exhibit larger variability. On the cover page, representative pre-bleach and post-bleach recovery images are shown for BMI1-GFP in foci containing either CBX4-mcherry (row 1-3) or CBX8-mcherry (row 4 and 5). Images of mcherry tagged CBXs, pre-bleach images, images acquired 0.5s, 10s and 350s after the bleach are arranged respectively in columns 1, 2, 3, 4 and 5.