It is now clear that such ncRNA plays an important role in regulating the expression of protein-coding DNA, especially in the human species (Mattick, 2007). One type of non-coding RNA has been known for 30 years. Embedded in protein-coding genes are DNA sequences called introns that are transcribed into RNA but are spliced out before messenger RNA leaves the nucleus. The remaining parts of genes are spliced back together and are called exons. Exons exit the nucleus and are translated into amino acid sequences. Exons usually consist of only a few hundred base pairs, but introns vary greatly, from 50 to over 1,000,000 base pairs, and some genes have hundreds of introns. Only exons are translated into amino acid sequences that make up proteins. However, introns are not ‘junk’. In many cases ncRNAs embedded in the introns of protein-coding genes regulate the transcription of the gene in which they reside and in some cases they also regulate other genes (Rodriguez, Griffiths-Jones, Ashurst, & Bradley, 2004).
