Circular DNA is excised by immunoglobulin class switch recombination

Cell. 1990 Jul 13;62(1):143-9. doi: 10.1016/0092-8674(90)90248-d.


We have purified extrachromosomal circular DNAs from adult mouse spleen cells, and cloned into a phage vector the BamHl fragments hybridizing with C mu and S gamma 1 probes. We obtained 52 S mu+S gamma 1+ clones by screening 1.4 million phage clones derived from spleen cells stimulated with bacterial lipopolysaccharide and interleukin 4. We have identified the breakpoints of six clones that contain S gamma 1 and S mu sequences fused in the 5' to 3' orientation. All these switch recombination sites were assigned to the central repetitive sequences of the S mu and S gamma 1 regions. Since the common S mu-S gamma 1 sequences at the recombination sites are at most 2 bases long, typical homologous recombination cannot account for their joining. These findings provide direct evidence that mu-gamma 1 class switching can occur by the looping out and excision of chromosomal DNA, with formation of a circle.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • B-Lymphocytes / immunology
  • Base Sequence
  • Cloning, Molecular
  • DNA, Circular / genetics*
  • Female
  • Gene Library
  • Genes, Immunoglobulin*
  • Genes, Regulator*
  • Genes, Switch*
  • Genetic Vectors
  • Mice
  • Mice, Inbred BALB C
  • Molecular Sequence Data
  • Nucleic Acid Hybridization
  • Oligonucleotide Probes
  • Plasmids
  • Recombination, Genetic
  • Restriction Mapping
  • Spleen / immunology


  • DNA, Circular
  • Oligonucleotide Probes

Associated data

  • GENBANK/M38077
  • GENBANK/M38078
  • GENBANK/M38079
  • GENBANK/M60757
  • GENBANK/M60758
  • GENBANK/M60759
  • GENBANK/M60760