Messenger RNA decay in mammalian cells: the exonuclease perspective.

The majority of messenger RNA (mRNA) decay in mammalian cells appears to be the work of a series of RNA exoribonucleases. A set of multiple poly(A)-specific deadenylases has been identified, some, if not most, of which are likely to play a role in the key first step of mRNA turnover--the regulated shortening of the poly(A) tail. After deadenylation, the transcript likely gets degraded by either a 5'-to-3' or a 3'-to-5' exonucleolytic pathway. Interestingly, multiple exonucleases have been identified for both of these pathways that appear to form multicomponent complexes with diverse roles in cellular biology. Therefore these enzymes appear not only to be important components of the mRNA turnover machinery, but also may function in a networked fashion in the post-transcriptional control of gene expression.