Non-coding RNA: a new frontier in regulatory biology

A striking finding in the past decade is the production of numerous non-coding RNAs (ncRNAs) from mammalian genomes. While it is entirely possible that many of those ncRNAs are transcription noises or by-products of RNA processing, increasing evidence suggests that a large fraction of them are functional and provide various regulatory activities in the cell. Thus, functional genomics and proteomics are incomplete without understanding functional ribonomics. As has been long suggested by the 'RNA world' hypothesis, many ncRNAs have the capacity to act like proteins in diverse biochemical processes. The enormous amount of information residing in the primary sequences and secondary structures of ncRNAs makes them particularly suited to function as scaffolds for molecular interactions. In addition, their functions appear to be stringently controlled by default via abundant nucleases when not engaged in specific interactions. This review focuses on the functional properties of regulatory ncRNAs in comparison with proteins and emphasizes both the opportunities and challenges in future ncRNA research.