title: MRE11/RAD50 cleaves DNA in the AID/UNG-dependent pathway of immunoglobulin gene diversification.
abstract: MRE11/RAD50/NBS1 (MRN) is a ubiquitous complex that participates in the response to DNA damage and in immunoglobulin (Ig) gene diversification. Ig gene diversification is initiated by deamination of cytosine to uracil, followed by removal of uracil to create an abasic (AP) site. We find that MRE11 associates specifically with rearranged Ig genes in hypermutating B cells, whereas APE1, the major AP-endonuclease in faithful base excision repair, does not. We show that purified, recombinant MRE11/RAD50 can cleave DNA at AP sites and that this AP-lyase activity is conserved from humans to Archaea. MRE11/RAD50 cleaves at AP sites within single-stranded regions of DNA, suggesting that at transcribed Ig genes, cleavage may be coordinated with deamination by AID and deglycosylation by UNG2 to produce single-strand breaks (SSBs) that undergo subsequent mutagenic repair and recombination. These results identify MRN with DNA cleavage in the AID-initiated pathway of Ig gene diversification.
authors.affiliation: Department of Immunology, University of Washington Medical School, 1959 Northeast Pacific Street, Seattle, Washington 98195, USA.
authors.forename: Erik D
authors.initials: ED
authors.lastname: Larson
authors.forename: W Jason
authors.initials: WJ
authors.lastname: Cummings
authors.forename: David W
authors.initials: DW
authors.lastname: Bednarski
authors.forename: Nancy
authors.initials: N
authors.lastname: Maizels
mesh_terms: D017766:Acid Anhydride Hydrolases; D001402:B-Lymphocytes / Q000378:metabolism*; D002478:Cells, Cultured; D045647:DNA Glycosylases / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000235:genetics / Q000378:metabolism*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007074:Immunoglobulin G / Q000235:genetics / Q000378:metabolism; D000076228:MRE11 Homologue Protein; D027041:Somatic Hypermutation, Immunoglobulin / Q000502:physiology*
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D007074:Immunoglobulin G; C121766:MRE11 protein, human; D000076228:MRE11 Homologue Protein; C492570:CCNO protein, human; D045647:DNA Glycosylases; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D045643:DNA Repair Enzymes