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ADAR
Double-stranded RNA-specific adenosine deaminase is an enzyme that in humans is encoded by the ''ADAR'' gene (which stands for ''adenosine deaminase acting on RNA'').〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=103 )〕
Adenosine deaminases acting on RNA (ADAR) are enzymes responsible for binding to double stranded RNA (dsRNA) and converting adenosine (A) to inosine (I) by deamination. ADAR protein is a RNA-binding protein, which functions in RNA-editing through post-transcriptional modification of mRNA transcripts by changing the nucleotide content of the RNA.〔 The conversion from A to I in the RNA disrupt the normal A:U pairing which makes the RNA unstable. Inosine is structurally similar to that of guanine (G) which leads to I to cytosine (C) binding. In RNA I functions the same as G in both translation and replication. Codon changes can arise from editing which may lead to changes in the coding sequences for proteins and their functions.〔 Most editing site are found in noncoding regions of RNA such as untranslated regions (UTRs), Alu elements and long interspersed nuclear element (LINEs). Mutations in this gene have been associated with dyschromatosis symmetrica hereditaria, as well as Aicardi–Goutières syndrome. Alternate transcriptional splice variants, encoding different isoforms, have been characterized.〔(【引用サイトリンク】website=NBCI )〕
==Discovery==
Adenosine Deaminase Acting on RNA (ADAR) and its gene were first discovered accidentally in 1987 as a result of research by Brenda Bass and Harold Weintraub. These researchers were using antisense RNA inhibition to determine which genes play a key role in the development of Xenopus leavis embryos. Previous research on Xenopus oocytes had been successful. However, when Bass and Weintraub applied identical protocols to Xenopus embryos, they were unable to determine the embryo’s developmental genes. In an attempt to understand why the method was unsuccessful, they began comparing duplex RNA in both oocytes and embryos. This lead them to discover that a developmentally regulated activity denatures RNA:RNA hybrids in embryos.
In 1988, Richard Wagner et al. further studied the activity occurring on Xenopus embryos. They determined that a protein was responsible for the unwinding of RNA due to the absence of activity after proteinase treatment. It was also shown that this protein is specific for double stranded RNA, or dsRNA, and does not require ATP. Additionally, it became evident that the protein’s activity on dsRNA modifies it beyond a point of rehybridization, but does not fully denature it. Finally, the researchers determined that this unwinding is due to the deamination of adenosine residues to inosine. This modification results in mismatched base-pairing between inosine and uridine, leading to the destabilization and unwinding of dsRNA.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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