RAG1 and RAG2 cooperate in specific binding to the recombination signal sequence in vitro.

An essential step in the development of the vertebrate immune system is the DNA level rearrangement of the antigen receptor genes. This process, termed "V(D)J recombination," begins with DNA cleavage at the appropriate sites mediated by the two proteins RAG1 and RAG2. We report here that the two proteins cooperate to bind DNA with significantly higher specificity than either protein alone. Gel purification of the triple complex is performed in the absence of any cross-linking agents. Both proteins remain present in the complex, and UV cross-linking using iodouridine-containing probes shows that RAG1 makes close contacts in both the heptamer and nonamer motifs. The two proteins are also shown to associate with each other in the absence of any DNA. These findings refine our understanding of the protein-DNA interactions that accompany cleavage at the recombination signals.