ASSEMBLY OF A 12 23 PAIRED SIGNAL COMPLEX - A CRITICAL CONTROL POINT IN V(D)J RECOMBINATION/

The 12/23 rule requires that V(D)J recombination only occurs between r ecombination signals with 12 and 23 base pair spacers. We show that th e 12/23 rule is established prior to DNA cleavage, by the formation of a synaptic complex containing both 12-spacer and 23-spacer signals. T he RAG1 and RAG2 proteins, as well as the DNA bending protein HMG1, ar e needed for efficient formation of this complex. We show further that the synaptic complex is the functional complex for coupled cleavage. After cleavage, all four broken DNA ends remain associated with the RA G proteins in a postcleavage synaptic complex, whose existence helps t o explain the known role of RAG1 and RAG2 in the subsequent end-joinin g events that complete V(D)J recombination.