Process
Junctional diversity concludes the process of somatic recombination or V(D)J recombination, during which the different variable gene segments (those segments involved in antigen recognition) of TCRs and immunoglobulins are rearranged and unused segments removed. This introduces double-strand breaks between the required segments. These ends form hairpin loops and must be joined together to form a single strand (summarised in diagram, right). This joining is a very inaccurate process which results in the variable addition or subtraction of nucleotides and thus generates junctional diversity.
Generation of junctional diversity starts as the proteins, recombination activating gene-1 and -2 (RAG1 and RAG2), along with DNA repair proteins, such as Artemis, are responsible for single-stranded cleavage of the hairpin loops and addition of a series of palindromic, 'P' nucleotides. Subsequently the enzyme, terminal deoxynucleotidyl transferase (TdT), adds further random ‘N’ nucleotides. The newly synthesised strands anneal to one another, but mismatches are common. Exonucleases remove these unpaired nucleotides and the gaps are filled by DNA synthesis and repair machinery. Exonucleases may also cause shortening of this junction, however this process is still poorly understood.
Junctional diversity is liable to cause frame-shift mutations and thus production of non-functional proteins. Therefore there is considerable waste involved in this process.
Read more about this topic: Junctional Diversity
Famous quotes containing the word process:
“Science and art are only too often a superior kind of dope, possessing this advantage over booze and morphia: that they can be indulged in with a good conscience and with the conviction that, in the process of indulging, one is leading the “higher life.””
—Aldous Huxley (1894–1963)
“The invention of photography provided a radically new picture-making process—a process based not on synthesis but on selection. The difference was a basic one. Paintings were made—constructed from a storehouse of traditional schemes and skills and attitudes—but photographs, as the man on the street put, were taken.”
—Jean Szarkowski (b. 1925)
“Experiences in order to be educative must lead out into an expanding world of subject matter, a subject matter of facts or information and of ideas. This condition is satisfied only as the educator views teaching and learning as a continuous process of reconstruction of experience.”
—John Dewey (1859–1952)