Uracil DNA glycosylase activity is dispensable for immunoglobulin class switch

Science. 2004 Aug 20;305(5687):1160-3. doi: 10.1126/science.1098444.


Activation-induced cytidine deaminase (AID) is required for the DNA cleavage step in immunoglobulin class switch recombination (CSR). AID is proposed to deaminate cytosine to generate uracil (U) in either mRNA or DNA. In the second instance, DNA cleavage depends on uracil DNA glycosylase (UNG) for removal of U. Using phosphorylated histone gamma-H2AX focus formation as a marker of DNA cleavage, we found that the UNG inhibitor Ugi did not inhibit DNA cleavage in immunoglobulin heavy chain (IgH) locus during CSR, even though Ugi blocked UNG binding to DNA and strongly inhibited CSR. Strikingly, UNG mutants that had lost the capability of removing U rescued CSR in UNG-/- B cells. These results indicate that UNG is involved in the repair step of CSR yet by an unknown mechanism. The dispensability of U removal in the DNA cleavage step of CSR requires a reconsideration of the model of DNA deamination by AID.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • B-Lymphocytes / enzymology
  • B-Lymphocytes / immunology
  • B-Lymphocytes / physiology*
  • Cell Line, Tumor
  • Cytidine Deaminase / metabolism
  • DNA / metabolism*
  • DNA Glycosylases / antagonists & inhibitors
  • DNA Glycosylases / genetics
  • DNA Glycosylases / metabolism*
  • DNA Repair
  • Genes, Immunoglobulin*
  • Immunoglobulin Class Switching*
  • Immunoglobulin Heavy Chains / genetics
  • Immunoglobulin Switch Region
  • Mice
  • Mutation
  • Precipitin Tests
  • Recombination, Genetic
  • Transfection
  • Uracil / metabolism
  • Uracil-DNA Glycosidase
  • Viral Proteins / metabolism


  • Immunoglobulin Heavy Chains
  • Viral Proteins
  • uracil-DNA glycosylase inhibitor protein, B. subtilis bacteriophage
  • Uracil
  • DNA
  • DNA Glycosylases
  • Uracil-DNA Glycosidase
  • AICDA (activation-induced cytidine deaminase)
  • Cytidine Deaminase