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MRN complex
The MRN complex (MRX complex in yeast) is a protein complex consisting of Mre11, Rad50 and Nbs1 (also known as Nibrin 〔(【引用サイトリンク】title=Atlas of Genetics and Cytogenetics in Oncology and Haematology - NBS1 )〕 in humans and as Xrs2 in yeast). In eukaryotes, the MRN/X complex plays an important role in the initial processing of double-strand DNA breaks prior to repair by homologous recombination or non-homologous end joining. The MRN complex binds avidly to double-strand breaks both in vitro and in vivo and may serve to tether broken ends prior to repair by non-homologous end joining or to initiate resection prior to repair by homologous recombination. The MRN complex also participates in activating the checkpoint kinase ATM in response to DNA damage. Production of short single-strand oligonucleotides by Mre11 endonuclease activity has been implicated in ATM activation by the MRN complex.
==Evolutionary ancestry and biologic function==
The MRN complex has been mainly studied in eukaryotes. However, recent work shows that two of the three protein components of this complex, Mre11 and Rad50, are also conserved in extant prokaryotic archaea.〔White MF. (2011). Homologous recombination in the archaea: the means justify the ends. Biochem Soc Trans 39(1):15-9. doi: 10.1042/BST0390015. Review. PMID 21265740〕 This finding suggests that key components of the eukaryotic MRN complex are derived by evolutionary descent from the archaea. In the archaeon ''Sulfolobus acidocaldarius'', the Mre11 protein interacts with the Rad50 protein and appears to have an active role in the repair of DNA damages experimentally introduced by gamma radiation.〔Quaiser A, Constantinesco F, White MF, Forterre P, Elie C. (2008). The Mre11 protein interacts with both Rad50 and the HerA bipolar helicase and is recruited to DNA following gamma irradiation in the archaeon ''Sulfolobus acidocaldarius''. ''BMC Mol Biol'' 9:25. doi: 10.1186/1471-2199-9-25. PMID 18294364〕 Similarly, during meiosis in the eukaryotic protist ''Tetrahymena'' Mre11 is required for repair of DNA damages, in this case double-strand breaks,〔Lukaszewicz A, Howard-Till RA, Novatchkova M, Mochizuki K, Loidl J. (2010). MRE11 and COM1/SAE2 are required for double-strand break repair and efficient chromosome pairing during meiosis of the protist ''Tetrahymena''. ''Chromosoma'' 119(5):505-18. doi: 10.1007/s00412-010-0274-9. PMID 20422424〕 by a process that likely involves homologous recombination.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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