Coexpressed MBP-RAG-1 and MBP-RAG-2 (RAG-1/2) was incubated with a radiolabeled intact 23-RSS substrate in the absence or presence of increasing amounts of the following forms of HMGB1 (as indicated above the gel): wild-type or tailless (A), tailless mtA or tailless mtB (B), basic (C), mtB (D), box A or shuffled (E), mtAB or mtA (F), box B′ (G), or box B (H). Protein-DNA complexes were fractionated by EMSA, and visualized from dried gels using a phosphorimager.