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:
“... geometry became a symbol for human relations, except that it was better, because in geometry things never go bad. If certain things occur, if certain lines meet, an angle is born. You cannot fail. It’s not going to fail; it is eternal. I found in rules of mathematics a peace and a trust that I could not place in human beings. This sublimation was total and remained total. Thus, I’m able to avoid or manipulate or process pain.”
—Louise Bourgeois (b. 1911)
“It haunts me, the passage of time. I think time is a merciless thing. I think life is a process of burning oneself out and time is the fire that burns you. But I think the spirit of man is a good adversary.”
—Tennessee Williams (1914–1983)
“I wish to see, in process of disappearing, that only thing which ever could bring this nation to civil war.”
—Abraham Lincoln (1809–1865)