Non-coding RNA

A non-coding RNA (ncRNA) is a functional RNA molecule that is not translated into a protein. The DNA sequence from which a functional non-coding RNA is transcribed is often called a non-coding gene or an RNA gene. Abundant and functionally important types of non-coding RNAs include transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), as well as small RNAs such as microRNAs, siRNAs, piRNAs, snoRNAs, snRNAs, exRNAs, scaRNAs and the long ncRNAs such as Xist, HOTAIR, and MALAT1.

The number of non-coding RNAs within the human genome is unknown; however, recent transcriptomic and bioinformatic studies suggest that there are thousands of non-coding transcripts.

Many of the newly identified ncRNAs have unknown functions, if any.

There is no consensus on how much of non-coding transcription is functional: some believe most ncRNAs to be non-functional "junk RNA", spurious transcriptions, while others expect that many non-coding transcripts have functions to be discovered.

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.