Table 1. Fraction of the yeast and mammalian genomes involved in each DNA double‐stranded break
(1)DNA content (Mbp) (known)176,600
(2)γ‐H2A(X)/total H2A(X) (%) (experimental)425
(3)Gy (experimental)2,00025
(5)γ‐H2A(X)/DSB (%) ((row 2)/[(row 3) × (row 4)])0.020.03
(6)Focus size (Mbp) ((row 1) × (row 5))0.0042
(7)H2A(X) × 106 molecules per cell (experimental)0.176
(8)Molecules of γ‐H2A(X) per DSB ((row 1) × (row 5))341,800
  • The experiment was performed as described in the legend to Table II of Rogakou et al. (1998). Briefly, yeast cultures were exposed to 2,000 Gy and IMR90 cultures to 25 Gy (row 3). The histones were extracted and analysed by two‐dimensional gel electrophoresis. Densitometry analysis of Coomassie‐blue‐stained gels gave relative values for H2A(X) and γ‐H2A(X) for yeast (Saccharomyces cereviseae, Sc) and normal human (Homo sapiens, Hs) fibroblasts (row 2). Using known values for DNA content (row 1) and double‐strand breaks (DSBs) per Gy per genome (row 4), the fraction of phosphorylated H2A(X) per DSB was calculated (row 5), as was focus size (row 6). Knowing the number of H2A(X) molecules per cell (row 7) gives the number of γ‐H2A(X) molecules per DSB (row 8). Mbp, megabase pairs.