InterPro domain: IPR011907

This family consists of ribonuclease III (RNase III). This ubiquitous enzyme specifically cleaves double-stranded rRNA and is found in all bacteria and eukaryotes [ 1 ]. In bacteria its main role is the processing of pre-rRNAs, where the large precursor ribosomal RNA molecules are at cleaved at specific sites to produce the immediate precursors of the functional molecules. RNase III also functions in the maturation and degradation of mRNAs, and the maturaton of tRNAs. In some organisms (eg. Escherichia coli) cells are viable without this enzyme, though they are impeded in growth, but in others (eg. B. subtilis and M. genitalium) this enzyme is essential.

The bacterial RNase III enzymes so far characterised are homodimers with a molecular mass of ~50kDa [ 2 , 3 ]. The endonuclease domain is located within the N-terminal two-thirds of the protein, containing several alpha helices, but no beta strands. The double-stranded RNA binding domain is found at the C-terminal third of the protein, forming the alpha-beta(3)-alpha fold common to dsRNA-binding proteins. A signature box of 11 conserved amino acids found in the N-terminal region of RNase III may contain the active site, though this has not been proven.

1. Ribonuclease III: new sense from nuisance. Int. J. Biochem. Cell Biol. 34, 116-29
2. Structure of the nuclease domain of ribonuclease III from M. tuberculosis at 2.1 A. Protein Sci. 14, 2744-50
3. Crystallographic and modeling studies of RNase III suggest a mechanism for double-stranded RNA cleavage. Structure 9, 1225-36