HMGA1a counteracts the repressive role of histone H1 with respect to Ligase IV/XRCC4 activity.

<p>A. DNA ligation was assayed using fixed amount of Ligase IV/XRCC4 (1.2 pmoles) and increasing quantities of histone H1 (0.1, 0.2, 0.4, 0.8, 1.2, and 2.4 pmoles, lanes 3–8). The unligated DNA substrate is shown in lane 1 and the activity of Ligase IV/XRCC4 alone is shown in lane 10. B. DNA ligation was assayed using fixed amount of Ligase IV/XRCC4 and histone H1 (1.2 and 2.4 pmoles, respectively) and increasing amounts of HMGA1a (0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 2.4, and 4.8 pmoles, lanes 5–12). The unligated DNA substrate is shown in lane 1, the Ligase IV/XRCC4 activity in the presence of histone H1 (2.4 pmoles) is shown in lane 3, and the Ligase IV/XRCC4 alone is shown in lane 10. The figure shows representative ligation assays.