New insights into the mechanism of RNA degradation by ribonuclease II: identification of the residue responsible for setting the RNase II end product.

RNase II is a key exoribonuclease involved in the maturation, turnover, and quality control of RNA. RNase II homologues are components of the exosome, a complex of exoribonucleases. The structure of RNase II unraveled crucial aspects of the mechanism of RNA degradation. Here we show that mutations in highly conserved residues at the active site affect the activity of the enzyme. Moreover, we have identified the residue that is responsible for setting the end product of RNase II. In addition, we present for the first time the models of two members of the RNase II family, RNase R from Escherichia coli and human Rrp44, also called Dis3. Our findings improve the present model for RNA degradation by the RNase II family of enzymes.