Macromolecular Crystallography Laboratory, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA. jix@ncifcrf.gov
Ribonuclease III (RNase III) represents a highly conserved family of double-stranded (ds) RNA-specific endoribonucleases, exemplified by bacterial RNase III and eukaryotic Rnt1p, Drosha and Dicer. Bacterial RNase III, containing an endonuclease domain followed by a dsRNA-binding domain, is the most extensively studied member of the family. It can affect RNA structure and gene expression in either of two ways: as a processing enzyme that cleaves dsRNA or as a binding protein that binds but does not cleave dsRNA. The available biochemical and structural data support the existence of two distinct forms of the RNase III-dsRNA complex which reflect the dual activities of the protein. The information revealed by the structures of bacterial RNase III provides insight into the mechanism of dsRNA processing by all members of the family.