RNA recognition by 3′-to-5′ exonucleases: The substrate perspective

The 3′-to-5′ exonucleolytic decay and processing of a variety of RNAs is an essential feature of RNA metabolism in all cells. The 3′-5′ exonucleases, and in particular the exosome, are involved in a large number of pathways from 3′ processing of rRNA, snRNA and snoRNA, to decay of mRNAs and mRNA surveillance. The potent enzymes performing these reactions are regulated to prevent processing of inappropriate substrates whilst mature RNA molecules exhibit several attributes that enable them to evade 3′-5′ attack. How does an enzyme perform such selective activities on different substrates? The goal of this review is to provide an overview and perspective of available data on the underlying principles for the recognition of RNA substrates by 3′-to-5′ exonucleases.