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:
“Thinking is seeing.... Every human science is based on deduction, which is a slow process of seeing by which we work up from the effect to the cause; or, in a wider sense, all poetry like every work of art proceeds from a swift vision of things.”
—Honoré De Balzac (1799–1850)
“A designer who is not also a couturier, who hasn’t learned the most refined mysteries of physically creating his models, is like a sculptor who gives his drawings to another man, an artisan, to accomplish. For him the truncated process of creating will always be an interrupted act of love, and his style will bear the shame of it, the impoverishment.”
—Yves Saint Laurent (b. 1936)
“Consumer wants can have bizarre, frivolous, or even immoral origins, and an admirable case can still be made for a society that seeks to satisfy them. But the case cannot stand if it is the process of satisfying wants that creates the wants.”
—John Kenneth Galbraith (b. 1908)