Essential and perilous: V(D)J recombination and DNA damage checkpoints in lymphocyte precursors

V(D)J recombination generates a diverse array of antigen-binding specificities, but breakage and re-joining of DNA segments have grave implications for the maintenance of genomic stability and oncogenic risk. Exposure of eukaryotic cells to genotoxic agents activates a DNA damage checkpoint that induces cell-cycle arrest and DNA repair, or apoptosis. We discuss several lines of evidence implicating DNA-dependent protein kinase (DNA-PK), and the gene mutated in ataxia telangiectasia (ATM), two mammalian homologues of yeast DNA damage-checkpoint genes, in regulating the response to intrinsic DNA damage that occurs during V(D)J recombination.