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Related Concept Videos

Homologous Recombination02:31

Homologous Recombination

The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
Gene Conversion02:08

Gene Conversion

Other than maintaining genome stability via DNA repair, homologous recombination plays an important role in diversifying the genome. In fact, the recombination of sequences forms the molecular basis of genomic evolution. Random and non-random permutations of genomic sequences create a library of new amalgamated sequences. These newly formed genomes can determine the fitness and survival of cells. In bacteria, homologous and non-homologous types of recombination lead to the evolution of new...
Conservative Site-specific Recombination and Phase Variation02:53

Conservative Site-specific Recombination and Phase Variation

Because the DNA segments are cut and reorganized in a direction-specific manner, site-specific recombination has emerged as an efficient genetic engineering technique. Flippase and Cyclization recombinases or Flp and Cre, respectively, are two members of the tyrosine recombinase family derived from bacteriophages, that are used to mediate site-specific DNA insertions, deletions, and targeted expression of proteins in mammalian cell lines.
The recognition sites for Cre recombinase called LoxP...
Exon Recombination02:32

Exon Recombination

The evolution of new genes is critical for speciation. Exon recombination, also known as exon shuffling or domain shuffling, is an important means of new gene formation. It is observed across vertebrates, invertebrates, and in some plants such as potatoes and sunflowers. During exon recombination, exons from the same or different genes recombine and produce new exon-intron combinations, which might evolve into new genes. 
Exon shuffling follows “splice frame rules.” Each exon has three reading...
Homologous Recombination02:31

Homologous Recombination

The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
Diversity of Antigen Receptors01:28

Diversity of Antigen Receptors

Antigen receptors are essential components of the immune system crucial in defending the body against foreign invaders. These receptors are present on the surface of B and T cells, enabling them to recognize antigens and mount an appropriate immune response.
Before encountering any antigen, lymphocytes express these receptors. On B cells, the antigen receptor is a membrane-bound antibody molecule called BCR; on T cells, it is a T cell receptor or TCR. B and T cell receptors are composed of two...

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Related Experiment Video

Updated: Jul 22, 2026

Induction and Assessment of Class Switch Recombination in Purified Murine B Cells
09:49

Induction and Assessment of Class Switch Recombination in Purified Murine B Cells

Published on: August 13, 2010

Circular DNA is excised by immunoglobulin class switch recombination.

T Iwasato1, A Shimizu, T Honjo

  • 1Department of Biophysics, Faculty of Science, Kyoto University, Japan.

Cell
|July 13, 1990
PubMed
Summary

Extrachromosomal circular DNA analysis reveals a novel mechanism for immunoglobulin class switching. This process involves the looping out and circularization of DNA, explaining how mu-gamma 1 switching occurs.

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Last Updated: Jul 22, 2026

Induction and Assessment of Class Switch Recombination in Purified Murine B Cells
09:49

Induction and Assessment of Class Switch Recombination in Purified Murine B Cells

Published on: August 13, 2010

Genome-wide Purification of Extrachromosomal Circular DNA from Eukaryotic Cells
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Genome-wide Purification of Extrachromosomal Circular DNA from Eukaryotic Cells

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Analysis of Somatic Hypermutation in the JH4 intron of Germinal Center B cells from Mouse Peyer's Patches
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Analysis of Somatic Hypermutation in the JH4 intron of Germinal Center B cells from Mouse Peyer's Patches

Published on: April 20, 2021

Area of Science:

  • Immunology
  • Molecular Biology
  • Genetics

Background:

  • Immunoglobulin class switching is a critical adaptive immune process.
  • The mechanisms underlying the joining of S mu and S gamma 1 regions during class switching are not fully understood.
  • Extrachromosomal circular DNA (eccDNA) is increasingly recognized for its role in genomic dynamics.

Purpose of the Study:

  • To investigate the role of eccDNA in immunoglobulin heavy chain class switching.
  • To identify the molecular mechanisms of mu-gamma 1 class switching.
  • To characterize the recombination sites involved in S mu and S gamma 1 joining.

Main Methods:

  • Purification of eccDNA from adult mouse spleen cells.
  • Cloning of BamHI fragments from eccDNA into a phage vector.
  • Screening of phage clones using C mu and S gamma 1 probes.
  • Identification and sequencing of recombination breakpoints in S mu-S gamma 1+ clones.

Main Results:

  • 52 S mu+S gamma 1+ clones were identified from 1.4 million screened.
  • Six clones revealed fused S gamma 1 and S mu sequences in a 5' to 3' orientation.
  • Recombination sites were located in the central repetitive sequences of S mu and S gamma 1.
  • The common sequences at recombination sites were at most 2 base pairs long, precluding homologous recombination.

Conclusions:

  • Mu-gamma 1 class switching can occur via looping out and excision of chromosomal DNA, forming a circular intermediate.
  • This mechanism provides direct evidence for a non-homologous recombination pathway in immunoglobulin class switching.
  • eccDNA plays a significant role in facilitating immunoglobulin class switch recombination.