UMMS Affiliation

Department of Molecular Genetics and Microbiology

Publication Date


Document Type



Animals; B-Lymphocytes; Cytidine Deaminase; DNA; DNA Glycosylases; Gene Expression Regulation; Gene Rearrangement, B-Lymphocyte; Immunoglobulin Constant Regions; Immunoglobulin mu-Chains; Mice; Mice, Mutant Strains; Recombination, Genetic; Somatic Hypermutation, Immunoglobulin; Spleen; Uracil-DNA Glycosidase


Life Sciences | Medicine and Health Sciences | Women's Studies


Class switch recombination (CSR) occurs by an intrachromosomal deletion whereby the IgM constant region gene (Cmu) is replaced by a downstream constant region gene. This unique recombination event involves formation of double-strand breaks (DSBs) in immunoglobulin switch (S) regions, and requires activation-induced cytidine deaminase (AID), which converts cytosines to uracils. Repair of the uracils is proposed to lead to DNA breaks required for recombination. Uracil DNA glycosylase (UNG) is required for most CSR activity although its role is disputed. Here we use ligation-mediated PCR to detect DSBs in S regions in splenic B cells undergoing CSR. We find that the kinetics of DSB induction corresponds with AID expression, and that DSBs are AID- and UNG-dependent and occur preferentially at G:C basepairs in WRC/GYW AID hotspots. Our results indicate that AID attacks cytosines on both DNA strands, and staggered breaks are processed to blunt DSBs at the initiating ss break sites. We propose a model to explain the types of end-processing events observed.

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DOI of Published Version



J Exp Med. 2005 Aug 15;202(4):561-8. Link to article on publisher's site

Journal/Book/Conference Title

The Journal of experimental medicine

Related Resources

Link to article in PubMed

PubMed ID


Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.