Abstract

A central unanswered question concerning the initial phases of V(D)J recombination has been at which step the 12/23 rule applies. This rule, which governs which variable (V), diversity (D), and joining (J) segments are able to pair during recombination, could operate at the level of signal sequence synapsis after RAG-HMG1 complex binding, signal nicking, or signal hairpin formation. It has also been unclear whether additional proteins are required to achieve adherence to the 12/23 rule. We developed a novel system for the detailed biochemical analysis of the 12/23 rule by using an oligonucleotide-based substrate that can include two signals. Under physiologic conditions, we found that the complex of RAG1, RAG2, and HMG1 can successfully recapitulate the 12/23 rule with the same specificity as that seen intracellularly and in crude extracts. The cleavage complex can bind and nick 12x12 and 23x23 substrates as well as 12x23 substrates. However, hairpin formation occurs at both of the signals only on 12x23 substrates. Moreover, under physiologic conditions, the presence of a partner 23-bp spacer suppresses single-site hairpin formation at a 12-bp spacer and vice versa. Hence, this study illustrates that synapsis suppresses single-site reactions, thereby explaining the high physiologic ratio of paired versus unpaired V(D)J recombination events in lymphoid cells.

View details for Web of Science ID 000076512900023

View details for PubMedID 9774656

View details for PubMedCentralID PMC109226