Of Activation Induced Cytidine
Activation-induced cytidine deaminase (AID) expressed by germinal center B cells is a central regulator of somatic hypermutation (SHM) and class switch recombination.
6 6 F1 Start 122,553,801 End 122,564,180 pattern Molecular function. Cellular component. Biological process. Sources: / Orthologs Species Human Mouse RefSeq (mRNA) RefSeq (protein) Location (UCSC) search Activation-induced cytidine deaminase, also known as AICDA and AID, is a 24 which in humans is encoded by the AICDA. It creates mutations in by of base, which turns it into (which is recognized as a ). In other words, it changes a C:G base pair into a U:G mismatch. The cell's machinery recognizes the U as a T, and hence C:G is converted to a T:A base pair.
During development of, AID also generates other types of mutations, such as C:G to A:T. The mechanism by which these other mutations are created is not well understood. In B cells in the, AID causes mutations that produce antibody diversity, but that same mutation process leads to. Contents.
Function This gene encodes a DNA-editing deaminase that is a member of the family. The protein is involved in somatic hypermutation, gene conversion, and class-switch recombination of immunoglobulin genes in B cells of the immune system.
AID is currently thought to be the master regulator of secondary diversification. It is involved in the initiation of three separate immunoglobulin (Ig) diversification processes:. (SHM), in which the antibody genes are minimally mutated to generate a library of antibody variants, some of which with higher affinity for a particular antigen and any of its close variants. (CSR), in which B cells change their expression from IgM to IgG or other immune types. (GC) a process that causes mutations in antibody genes of chickens, pigs and some other vertebrates. AID has been shown to be active on single-strand DNA, and has been shown to require active in order to exert its deaminating activity.
Activation Induced Cytidine Deaminase Ips
The involvement of -regulatory factors is suspected as AID activity is several orders of magnitude higher in the immunoglobulin 'variable' region than other regions of the genome that are known to be subject to AID activity. This is also true of artificial reporter constructs and that have been integrated into the. A recent publication suggests that high AID activity at a few non-immunoglobulin targets is achieved when transcription on opposite DNA strands converges due to activity. Recently, AICDA has been implicated in active DNA demethylation. AICDA can deaminate 5-methylcytosine, which can then be replaced with cytosine by base excision repair.
Mechanism AID is believed to initiate SHM in a multi-step mechanism. AID deaminates cytosine in the target DNA. Cytosines located within hotspot motifs are preferentially deaminated (WRCY motifs W=adenine or thymine, R=purine, C=cytosine, Y=pyrimidine, or the inverse RGYW G=guanine). The resultant U:G (U= uracil) mismatch is then subject to one of a number of fates. The U:G mismatch is replicated across creating two daughter species, one that remains unmutated and one that undergoes a C = T transition mutation.
(U is analogous to T in DNA and is treated as such when replicated). The uracil may be excised by (UNG), resulting in an abasic site. This abasic site (or AP, /) may be copied by a translesion synthesis DNA polymerase such as, resulting in random incorporation of any of the four, i.e. A, G, C, or T. Also, this abasic site may be cleaved by apurinic (APE), creating a break in the backbone.
This break can then lead to normal DNA repair, or, if two such breaks occur, one on either strand a staggered double-strand break can be formed (DSB). It is thought that the formation of these DSBs in either the switch regions or the Ig variable region can lead to CSR or GC, respectively. The U:G mismatch may also be recognized by the (MMR) machinery, to be specific by the MutSα(alpha) complex. MutSα is a consisting of and. This heterodimer is able to recognize mostly single-base distortions in the DNA backbone, consistent with U:G DNA mismatches.
The recognition of U:G mistmatches by the MMR proteins is thought to lead to processing of the DNA through exonucleolytic activity to expose a single-strand region of DNA, followed by error prone DNA polymerase activity to fill in the gap. These error-prone polymerases are thought to introduce additional mutations randomly across the DNA gap. This allows the generation of mutations at AT base pairs. The level of AID activity in B cells is tightly controlled by modulating AID expression. AID is induced by transcription factors E47, HoxC4, Irf8 and Pax5, and inhibited by Blimp1 and Id2. At the post-transcriptional level of regulation, AID expression is silenced by mir-155, a small non-coding microRNA controlled by IL-10 cytokine B cell signalling. Clinical significance Defects in this gene are associated with.
In certain haematological malignancies such as persistent AID expression has been linked to lymphomagenesis. References. ^ -, May 2017. ^ -, May 2017.
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