VprBP binds full-length RAG1 and is required for B-cell development and V(D)J recombination fidelity

Abstract

The N‐terminus of full‐length RAG1, though dispensable for RAG1/2 cleavage activity, is required for efficient V(D)J recombination. This region supports RING E3 ubiquitin ligase activity in vitro, but whether full‐length RAG1 functions as a single subunit or a multi‐subunit E3 ligase in vivo is unclear. We show the multi‐subunit cullin RING E3 ligase complex VprBP/DDB1/Cul4A/Roc1 associates with full‐length RAG1 through VprBP. This complex is assembled into RAG protein–DNA complexes, and supports in‐vitro ubiquitylation activity that is insensitive to RAG1 RING domain mutations. Conditional B lineage‐specific VprBP disruption arrests B‐cell development at the pro‐B‐to‐pre‐B cell transition, but this block is bypassed by expressing rearranged immunoglobulin transgenes. Mice with a conditional VprBP disruption show modest reduction of D–J_H rearrangement, whereas V_H–DJ_H and V_κ–J_κ rearrangements are severely impaired. D–J_H coding joints from VprBP‐insufficent mice show longer junctional nucleotide insertions and a higher mutation frequency in D and J segments than normal. These data suggest full‐length RAG1 recruits a cullin RING E3 ligase complex to ubiquitylate an unknown protein(s) to limit error‐prone repair during V(D)J recombination.