Prokaryotic ribonuclease III (EC 3.1.26.3) (gene rnc) [1] is an enzyme that digests double-stranded RNA. It is involved in the processing of ribosomal RNA precursors and of some mRNAs. RNase III is evolutionary related [2] to the following proteins:

• Fission yeast pac1, a ribonuclease that probably inhibits mating and meiosis by degrading a specific mRNA required for sexual development.
• Yeast ribonuclease III (gene RNT1), a dsRNA-specific nuclease that cleaves eukaryotic preribosomal RNA at various sites.
• Caenorhabditis elegans hypothetical protein F26E4.13.
• Paramecium bursaria chlorella virus 1 protein A464R.
• Synechocystis strain PCC 6803 hypothetical protein slr0346.
• Fission yeast hypothetical protein SpAC8A4.08c, a protein with a N-terminal helicase domain and a C-terminal RNase III domain.
• Caenorhabditis elegans hypothetical protein K12H4.8, a protein with the same structure as SpAC8A4.08c.

These proteins share regions of sequence similarity; one of which is a highly conserved stretch of 9 residues which we use as a signature pattern.