Fig. 8. A model for the regulation of mammalian mRNA turnover by the exosome. (1) Loading of the exosome complex onto mRNAs is promoted by AREs in the 3′-UTR and may be influenced by known ARE-binding proteins such as HuR, AUF-1/hnRNP D, etc. (2) Once loaded, the exosome may help promote mRNA deadenylation. (3) Following deadenylation, the transcript is handed off very efficiently to the exosome that was loaded onto the 3′-UTR, and is degraded rapidly.