Nonhomologous DNA End Joining in Cell-Free Extracts
Figure 1
Double-strand breaks (DSBs) are generated exogenously by ionizing radiation, or endogenously by free radicals or during V(D)J recombination in pre-B (bone marrow) and pre-T cells (thymus) by RAG complex or also during class switch recombination in activated B cells (in the peripheral lymphoid tissues such as spleen, lymph nodes, and Peyer’s patches). NHEJ involves the binding of Ku70 and Ku80 heterodimeric complex to the DNA ends, and DNA-PKcs in association with ARTEMIS. ARTEMIS is a - exonuclease in an unphosphorylated form while it is an endonuclease in a phosphorylated form. Artemis protein acts as an exonuclease and helps in resection of the ends. Polymerase family members are then recruited for DNA synthesis, which includes both template dependent and independent DNA synthesis. The resulting DNA ends are ligated by a specific DNA LIGASE IV with stimulatory factors (XRCC4-LIGASE IV-XLF complex) that restores the integrity of DNA.
