Figure 2.

Three paths to the synaptic complex. (A) Docking model. A separate complex, containing a dimer of RAG1 plus associated RAG2 (not pictured), first assembles on each RSS. These then dock with each other, and if the 12/23 rule is satisfied, allow concerted cleavage of both DNA targets. (B) Sequential binding model. The complex of RAG1 and RAG2 binds one DNA first, then must find a second DNA target, which gets incorporated into the same protein complex. The resulting complex would only contain one dimer of RAG1. (C) Cooperative transfer. Complexes first assemble on separate RSSs, but these cooperate to transfer one DNA into the protein complex of the second, resulting in one dimer of RAG1 associated with DNA plus eviction of the second RAG1 dimer. In each case, there would exist intermediates (not shown) prior to the final cleavages.