PathwayStep2967 PathwayStep2966 PathwayStep2969 PathwayStep2968 PathwayStep2972 PathwayStep2974 PathwayStep2973 Processing of DNA ends prior to end rejoining Nonhomologous End-joining (NHEJ) Authored: Lees-Miller, S, 2003-07-14 15:03:25 Edited: Joshi-Tope, G, 0000-00-00 00:00:00 GENE ONTOLOGYGO:0006303 Pubmed10207111 Pubmed10908332 Pubmed11030616 Pubmed11376007 Pubmed12016139 Pubmed12379113 Pubmed14506474 Pubmed8621537 Pubmed9826654 Reactome Database ID Release 4373889 Reactome, http://www.reactome.org ReactomeREACT_1022 Reviewed: West, SC, 0000-00-00 00:00:00 The NHEJ pathway is initiated in response to the formation of a DNA double-strand break (DSB) induced by a DNA-damaging agent such as ionizing radiation. First, the Ku70/80 heterodimer binds to the ends of the DSB. The catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs) is then recruited to DNA-bound Ku to form the DNA-PK holoenzyme. The ends of the break are brought together as two molecules of DNA-PK (one at each end of the break) are joined in a synaptic complex. Other factors, such as polynucleotide kinase (PNK), Artemis, the MRE complex, hTdp1 or the Werner Syndrome protein (WRN) may be required for processing of the DNA ends prior to end rejoining, but exactly when processing takes place is not known. Following the formation of the synaptic complex, the XRCC4/DNA ligase IV complex is recruited. Prior to end rejoining, protein factors must be removed from the DNA. This may involve DNA-PK autophosphorylation (Chan and Lees-Miller, 1996; Douglas et al., 2001; 2002; Merkle et al., 2002). After removal of the repair factors, the DNA ends are ligated and the DNA is repaired. Both Mg-ATP and the protein kinase activity of DNA-PKcs are required for NHEJ (Kurimasa et al.,1999; Kienker et al, 2000; Baumann and West, 1998), probably through phosphorylation of DNA-PKcs and/or other proteins. In addition, inositol hexaphosphate (IP6) stimulates end joining in vitro (Hanakahi et al., 2000) and binds to Ku, but its precise role in NHEJ is unknown. Association of Ku heterodimer with ends of DNA double-strand break Association of DNA-PKcs with Ku-bound ends of DNA double-strand breaks Removal of repair proteins and ligation of the processed ends of the DNA double-strand break Association of the XRCC4:DNA ligase IV complex with the DNA-PK:DNA synaptic complex Synapsis, or interaction between two DNA-PK:DNA complexes at opposing ends of DNA DSB Autophosphorylation of DNA-PKcs