The control of enzymes and other proteins is of central metabolic import to nutrition.
The relationship between DNA, RNA and protein is no longer as simple as once thought – that specific genomic sequences are transcribed into messenger RNAs, which are then translated into proteins. It is now apparent that there is large and growing family of non-proteincoding RNAs (ncRNAs), with different mechanisms of their transcription and their role in regulating gene expression.
These single-stranded molecules are unstable. RNA I liable to chemical degradation and enzymatic cleavage, as well as to incomplete conversion back to DNA. The identification of ncRNAs in the past has often been dismissed as an artefacts. High-throughput genomics approaches, however, have begun to chart consistent patterns that are unlikely to be artefacts, and show several specific mechanisms for ncRNA biogenesis and processing.
The mechanisms by which ncRNAs are generated seem to be similar to those that operate during mRNA transcription and processing. Normally, the enzyme RNA polymerase II (Pol II) binds to the promoter sequence of a given gene to generate mRNA from the downstream genomic region. In a few cases, the 5′ ends of genes on opposite DNA strands are located close together and so share the same promoter, which – when bound to Pol II bidirectionally triggers their transcription. These mRNAs, which are generally long, are also often translated into proteins. The latest studies report the widespread existence of ncRNAs in yeast, and mammalian cells, and show that these sequences originate from known promoters and can be transcribed in the opposite orientation to known genes.
Carninci P 2009 The long and short of RNAs Nature vol 457 , 974-5
- Martin Eastwood