Noncoding RNA

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), or 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} Many of the newly identified ncRNAs have not been validated for their function. It is also likely that many ncRNAs are non functional (sometimes referred to as Junk RNA), and are the product of spurious transcription.

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.

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