An Autoregulatory Mechanism Imposes Allosteric Control on the V(D)J Recombinase by Histone H3 Methylation

• V(D)J recombination is stimulated by binding of H3K4me3 to RAG-2
• An autoinhibitory domain in RAG-2 confers responsiveness to H3K4me3
• Disruption of this domain mimics stimulation of wild-type RAG by H3K4me3
• Active chromatin allosterically stimulates RAG through relief of autoinhibition

SummaryV(D)J recombination is initiated by a specialized transposase consisting of the subunits RAG-1 and RAG-2. The susceptibility of gene segments to DNA cleavage by the V(D)J recombinase is correlated with epigenetic modifications characteristic of active chromatin, including trimethylation of histone H3 on lysine 4 (H3K4me3). Engagement of H3K4me3 by a plant homeodomain (PHD) in RAG-2 promotes recombination in vivo and stimulates DNA cleavage by RAG in vitro. We now show that H3K4me3 acts allosterically at the PHD finger to relieve autoinhibition imposed by a separate domain within RAG-2. Disruption of this autoinhibitory domain was associated with constitutive increases in recombination frequency, DNA cleavage activity, substrate binding affinity, and catalytic rate, thus mimicking the stimulatory effects of H3K4me3. Our observations support a model in which allosteric control of RAG is enforced by an autoinhibitory domain whose action is relieved by engagement of active chromatin.

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