Ribonuclease bound to transfer RNA. Computer model showing the molecular structure of a bacterial ribonuclease III (RNase III) enzyme (upper left and lower right) bound to a double-stranded RNA (ribonucleic acid) molecule (red, upper right and lower left). RNase is a type of nuclease that catalyses the degradation of RNA into smaller components. Bacterial RNase III is an enzyme that digests double-stranded RNA and is involved in the processing of ribosomal RNA precursors and of some mRNAs (messenger RNAs).