The highways and byways of mRNA decay

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Abstract
Changes in mRNA-decay rates account for a large proportion of regulated gene expression. The predominant pathway initiates with deadenylation. Subsequently, the mRNA can either undergo decapping and 5′→3′ decay, or 3′→5′ decay. Many of the enzymes and regulatory factors for these processes have now been described. Recently, cytoplasmic structures, known as P bodies, which are sites of mRNA decay, have been identified. There are minor pathways of decay for certain mRNAs. These include pathways initiated by deadenylation-independent decapping and endoribonucleolytic cleavage. There are several surveillance mechanisms to degrade aberrant and unwanted mRNAs. These include nonsense-mediated decay, non-stop decay and no-go decay. Turnover of mRNAs is a highly regulated process that responds to cellular signals. Sequences within the mRNA, such as AU-rich elements, can determine the rate of decay under various conditions. RNA-binding proteins recognize sequence elements and modulate the rate of decay, some by recruiting the decay machinery, others by remodelling the conformation of messenger ribonucleoprotein. The process of mRNA decay is just one aspect of mRNA metabolism, but it is intimately linked with other processes, including translation, transcription and mRNA localization.