Histone H1 inhibits the ability of HMGB1 to bend DNA.

<p><b>A</b>, formation of DNA circles by HMGB1 is inhibited by the full-length histone H1 (DNA circularization assay). The 5´-end ³²P-labeled 123-bp DNA fragment (~1 nM) was pre-incubated with 5 nM HMGB1, followed by titration with increasing concentrations of H1 (0.2–15 nM, <i>left</i> to <i>right</i>) and ligation by T4 DNA ligase. Deproteinised DNA samples were separated by electrophoresis on 5% non-denaturing polyacrylamide gels in 0.5x TBE buffer. Panels <b>B</b>-<b>E</b>, DNA circularization assays in the presence of the full-length histone H1(fl) or peptides H1Δ24, H1Δ48 and H1Δ72. The percentage of DNA circles by reduced or oxidized HMGB1 or HMGB1ΔC (50 nM) in the presence of increasing concentrations of H1 or H1 peptides (1–15 nM, <i>left</i> to <i>right</i>) is indicated. The percentage of the minicircles formed by HMGB1 or HMGB1ΔC in the absence of H1 or peptides was arbitrary set to 100%. Oxidized HMGB1 or HMGB1ΔC proteins are indicated in red.