Thanks to the new technological advances in genome and transcriptome sequencing, we know that a major portion of the genome is being transcribed but only a small portion of this transcriptome contains the protein-coding sequences. The remainder can be split (at approximately 100 nucleotide length) into two major categories: small non-coding RNA (including microRNA) and long non-coding RNA, both of which have been shown to exert regulatory control over protein production/expression.
Interestingly, these two types of non-coding RNA exert their control by very different mechanisms. Small RNAs regulate gene expression predominantly through reduction of mRNA levels and subsequent reduced protein output1 (negative regulation), while long non-coding RNAs increase the synthesis of nearby proteins2 (positive regulation).
- Guo H, Ingolia NT, Weissman JS, Bartel DP. (2010) Mammalian microRNAs predominantly act to decrease target mRNA levels. Nature 466(7308), 835-40. [abstract]
- Orom UA, Derrien T, Beringer M, Gumireddy K, Gardini A, Bussotti G, Lai F, Zytnicki M, Notredame C, Huang Q, Guigo R, Shiekhattar R. (2010) Long Noncoding RNAs with Enhancer-like Function in Human Cells. Cell143(1), 46-58. [abstract]