Rag mutations reveal robust alternative end joining

In the process of generating antibody diversity, DNA in the V(D)J locus undergoes programmed double-strand breaks that are made by the Rag1–Rag 2 complex. These breaks are repaired by the non-homologous end-joining (NHEJ) pathway. Cells deficient in NHEJ factors show very low levels of recombinants, so it was believed there might be another repair pathway. But this paper shows that an alternative NHEJ pathway exists, and that it functions at low levels even in wild-type cells.