Cutting and Pasting DNA to Create our Adaptive Immune System

V(D)J recombination is essential for generating the adaptive immune response and unlimited number of different antibodies and antigen receptors. Encoded by multiple V, D and J gene segments, antigen receptors are assembled by programmed double-stranded DNA cleavage and imprecise re-joining. RAG1/2 recombinase initiates the process by stochastically cleaving DNA at a pair of recombination signal sequences (RSS) bordering the V, D or J gene segments.  DNA double strand cleavage occurs in a single active site in two consecutive steps, hydrolysis and strand transfer, resulting in DNA hairpin on the coding end and DSB on the RSS side. Coding ends processing and joining to complete V, D, and J gene assembly and circularization of RSS end are carried out by the non-homologous end joining process (NHEJ). The DNA-dependent protein kinase (DNA-PK), consisting of the catalytic subunit (DNA-PKcs) and Ku70/80, is the key player in NJEJ by protecting broken DNA ends, promoting DNA hairpin end opening and also coordinating nucleotide removal, addition and DNA end ligation. In this seminar I will report the molecular mechanism of DNA cleavage by RAG1/2 and regulation of NHEJ by autophosphorylation of DNA-PKcs.