Figure 4.

Formation of repair centers in yeast and human cells. The mobility of double-strand breaks (DSBs) induced by ionizing radiation (IR) is confined within the nucleus to a volume having a diameter of 1–2 µm. Because the yeast nucleus is approximately 2 µm in diameter, most DSBs except centromeric and telomeric are essentially free to roam the nucleus and coalesce into repair centers that can be visualize by green fluorescent protein (GFP) tagging of late-acting nuclear recombination proteins (green). The same principle of spatial confinement applies to subregions of mammalian nuclei indicated by dashed circles 2 µm in diameter. Yeast and mammalian cells are illustrated approximately at the same scale.