title: MutSalpha binds to and promotes synapsis of transcriptionally activated immunoglobulin switch regions.
abstract: Immunoglobulin class switch recombination joins a new constant (C) region to the rearranged and expressed heavy chain variable (VDJ) region in antigen-activated B cells (Figure 1A) (reviewed in [1, 2]). Switch recombination is activated by transcription of intronic, G-rich and repetitive switch (S) regions and produces junctions that are heterogeneous in sequence and position in the S regions. Switch recombination depends upon the B cell-specific cytidine deaminase, AID, and conserved DNA repair factors, including the mismatch repair heterodimer, MutSalpha (MSH2/MSH6). In mice, ablation of Msh2 or Msh6, but not Msh3, decreases levels of switch recombination and diminishes heterogeneity of switch junctions [3-7]. Here, we demonstrate that MSH2 associates with transcribed S regions in primary murine B cells activated for switch recombination. Electron microscopic imaging reveals that MutSalpha binds in vitro to DNA structures formed within transcribed S regions and mediates their synapsis. MutSalpha binds with high affinity to G4 DNA formed upon transcription of the S regions and also binds to U.G mismatches, initial products of DNA deamination by AID. These results suggest that MutSalpha interacts with the S regions in switching B cells to promote DNA synapsis and recombination.
authors.affiliation: Department of Immunology, Molecular and Cellular Biology Graduate Program, University of Washington School of Medicine, 1959 N.E. Pacific Street, Box 357650, Seattle, WA 98195, USA. edlarson@u.washington.edu
authors.forename: Erik D
authors.initials: ED
authors.lastname: Larson
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Duquette
authors.forename: W Jason
authors.initials: WJ
authors.lastname: Cummings
authors.forename: Raphael J
authors.initials: RJ
authors.lastname: Streiff
authors.forename: Nancy
authors.initials: N
authors.lastname: Maizels
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism* / Q000648:ultrastructure; D020137:Base Pair Mismatch; D002843:Chromatin / Q000378:metabolism; D023902:Chromosome Pairing / Q000502:physiology*; D043525:Cytosine Deaminase / Q000378:metabolism; D017931:DNA Primers; D045643:DNA Repair Enzymes / Q000378:metabolism / Q000502:physiology; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology; D004591:Electrophoresis, Polyacrylamide Gel; D024202:Electrophoretic Mobility Shift Assay; D017578:Immunoglobulin Class Switching / Q000502:physiology*; D007134:Immunoglobulin Switch Region / Q000502:physiology*; D047468:Immunoprecipitation; D051379:Mice; D008854:Microscopy, Electron; D051718:MutS Homolog 2 Protein; D009841:Oligonucleotides; D011518:Proto-Oncogene Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology
chemical_list: D002843:Chromatin; D017931:DNA Primers; D004268:DNA-Binding Proteins; D009841:Oligonucleotides; D011518:Proto-Oncogene Proteins; D043525:Cytosine Deaminase; C497173:Msh2 protein, mouse; D051718:MutS Homolog 2 Protein; D045643:DNA Repair Enzymes