Circular DNA is a product of the immunoglobulin class switch rearrangement

Article Abstract:

There are various classes of immunoglobulins including IgD, IgM, and IgG. The genes coding for these molecules undergo changes so that different parts of the genes are expressed at different times during an immune response. One of the portions of the immunoglobulin gene that changes is the constant region of the heavy chain, a component of the immunoglobulin molecule. A study was conducted with a cell that is a premature B lymphocyte, known as the pre-B-cell. The cell switched from expressing the mu heavy chain to expressing the gamma 2b heavy chain. Occasionally, the gene rearranges so that the deoxyribose nucleic acid (DNA) sequence between the mu and gamma 2b sequences are inverted. For this to happen, the DNA must form a loop, which is then is deleted or removed. This produces a loop or circle of DNA that is free from the rest of the genes. These circular forms of DNA have been isolated and have been found to contain the sequences that are deleted when the heavy chains switch from one class of immunoglobulin to another. Therefore, the mechanism of deletion of DNA segments, which occurs during immunoglobulin class switching, involves the formation of circular loops of DNA. (Consumer Summary produced by Reliance Medical Information, Inc.)

Genetic aspects, Immunoglobulins, Molecular biology, Immunoglobulin G, Immune response, Immunoglobulin M

---

Allelic exclusion model questioned

Article Abstract:

The claim that the targeted disruption of the immunoglobulin class mu heavy chain's membrane exon causes allelic exclusion to fail partially would be better characterized as a case of cellular selection in which the lack of feedback prevents the rearrangement of the immunoglobulin H locus. Moreover, the assertion that the targeted disruption is allelic exclusion lacks a causative mechanism. However, the rebuttal view is that the experimental data invalidates the cellular selection model and favors targeted disruption by membrane-bound antibody heavy chain of class mu.

Models, Molecular genetics, Exon (Molecular genetics), Exons (Molecular genetics)

---

Tussle with a terminator

Article Abstract:

The two ends of a circular bacterial chromosome undergoing replication meet within a restricted terminus region through the intervention of a replication-fork arrest system. Researchers have modeled the structure of the replicator-terminator protein (Tus) linked to a terminus-site DNA of Escherichia coli using X-ray crystallization at a resolution of 27 angstrom. The model provides some possible explanations to the Tus' ability to halt the replication fork coming from only one direction.

Chromosome replication

Similar abstracts:

• Abstracts: Mating ecology of the nonpollinating fig wasps of Ficus ingens. Intersexual sibling interactions and male benevolence in a fig wasp
• Abstracts: Molecular genetic basis of the histo-blood group ABO system. mutY 'directs' mutation?
• Abstracts: Does the eye grow into focus? Stitch in time saves design. Colour is what the eye sees best
• Abstracts: Disruption of a C/EBP binding site in the factor IX promoter is associated with haemophilia B. Parental-origin-specific epigenetic modification of the mouse H19 gene
• Abstracts: Morphological transformation of human keratinocytes expressing the LMP gene of Epstein-Barr virus. Adhesion of epidermal Langerhans cells to keratinocytes mediated by E-cadherin

This website is not affiliated with document authors or copyright owners. This page is provided for informational purposes only. Unintentional errors are possible.