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:
“The process of writing has something infinite about it. Even though it is interrupted each night, it is one single notation.”
—Elias Canetti (b. 1905)
“The toddler’s wish to please ... is a powerful aid in helping the child to develop a social awareness and, eventually, a moral conscience. The child’s love for the parent is so strong that it causes him to change his behavior: to refrain from hitting and biting, to share toys with a peer, to become toilet trained. This wish for approval is the parent’s most reliable ally in the process of socializing the child.”
—Alicia F. Lieberman (20th century)
“Because her instinct has told her, or because she has been reliably informed, the faded virgin knows that the supreme joys are not for her; she knows by a process of the intellect; but she can feel her deprivation no more than the young mother can feel the hardship of the virgin’s lot.”
—Arnold Bennett (1867–1931)