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A non-coding RNA (ncRNA) is an RNA molecule that is not translated into a protein. Less-frequently used synonyms are non-protein-coding RNA (npcRNA), non-messenger RNA (nmRNA) and functional RNA (fRNA). The DNA sequence from which a functional non-coding RNA is transcribed is often called an RNA gene. Non-coding RNA genes include highly abundant and functionally important RNAs such as transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), as well as RNAs such as snoRNAs, microRNAs, siRNAs, snRNAs, exRNAs, piRNAs and scaRNAs and the long ncRNAs that include examples such as Xist and HOTAIR (see here for a more complete list of ncRNAs). The number of ncRNAs encoded within the human genome is unknown; however, recent transcriptomic and bioinformatic studies suggest the existence of thousands of ncRNAs., but see Since many of the newly identified ncRNAs have not been validated for their function, it is possible that many are non-functional. It is also likely that many ncRNAs are non functional (sometimes referred to as Junk RNA), and are the product of spurious transcription. ==History and discovery== Nucleic acids were first discovered in 1868 by Friedrich Miescher and by 1939 RNA had been implicated in protein synthesis. Two decades later, Francis Crick predicted a functional RNA component which mediated translation; he reasoned that RNA is better suited to base-pair with an mRNA transcript than a pure polypeptide. The first non-coding RNA to be characterised was an alanine tRNA found in baker's yeast, its structure was published in 1965. To produce a purified alanine tRNA sample, Robert W. Holley ''et al.'' used 140kg of commercial baker's yeast to give just 1g of purified tRNAAla for analysis.〔(【引用サイトリンク】 The Nobel Prize in Physiology or Medicine 1968 )〕 The 80 nucleotide tRNA was sequenced by first being digested with Pancreatic ribonuclease (producing fragments ending in Cytosine or Uridine) and then with takadiastase ribonuclease Tl (producing fragments which finished with Guanosine). Chromatography and identification of the 5' and 3' ends then helped arrange the fragments to establish the RNA sequence.〔 Of the three structures originally proposed for this tRNA,〔 the 'cloverleaf' structure was independently proposed in several following publications. The cloverleaf secondary structure was finalised following X-ray crystallography analysis performed by two independent research groups in 1974. Ribosomal RNA was next to be discovered, followed by URNA in the early 1980s. Since then, the discovery of new non-coding RNAs has continued with snoRNAs, Xist, CRISPR and many more. Recent notable additions include riboswitches and miRNA; the discovery of the RNAi mechanism associated with the latter earned Craig C. Mello and Andrew Fire the 2006 Nobel Prize in Physiology or Medicine. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Non-coding RNA」の詳細全文を読む スポンサード リンク
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