Figure 4.

Phase 2 of recombination, DNA joining. (A) NHEJ example between a V (green) segment and J (yellow) segment after RAG mediated DNA cleavage. Ku70/80 (purple/red) is recruited to the double stranded break. Hereafter, DNA-PKcs (blue) is recruited, and trans/auto-phosphorylated. DNA-PKcs activates Artemis (light blue), which in turn opens the hairpins at both coding ends (cleavage location indicated by the black arrows) generating P nucleotides. TdT (cyan) then introduces N nucleotides to the P nucleotides. Strands are paired and unpaired nucleotides are removed by exonucleases. The DNA is then synthesised by either Pol µ or Pol λ and is then further ligated by DNA ligase IV (purple), supported by XRCC4 (yellow), XLF (dark purple) and PAXX (cyan). (B) Overview of the starting germline DNA to the end of the DNA cleavage and joining phases of recombination of a V and J segment. ATM, ataxia-telangiectasia mutated; DNA-PKcs, DNA-dependent protein kinase catalytic subunit; TdT, terminal deoxynucleotide transferase; XRCC4, X-ray repair cross-complementing protein 4; XLF, XRCC4-like factor; RAG, recombination-activating gene(complex); HMGB1/2, high mobility group box 1/2. Created with BioRender.com.