RNase III enzymes specifically bind to and cleave double-stranded RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 (dsRNA). There are three subdivisions, known as Class 1, 2, and 3.

Prokaryotic ribonuclease III (gene rnc) is an enzyme that digests double-stranded RNA. It is involved in the processing of ribosomal RNA precursors and of some mRNAs.

• Class 1 RNases III are largely found in bacteria
  Bacteria
  Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
  
  , bacteriophage
  Bacteriophage
  A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...
  
  , and some fungi. Among the RNases III in the class are the rnc from E. coli, Pac1p from S. pombe, and Rnt1p from S. cerevisiae. Class 1 RNases III process precursors to ribosomal RNA
  Ribosomal RNA
  Ribosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...
  
  , and in the case of fungi, process precursors to small nuclear RNA
  Small nuclear RNA
  Small nuclear ribonucleic acid is a class of small RNA molecules that are found within the nucleus of eukaryotic cells. They are transcribed by RNA polymerase II or RNA polymerase III and are involved in a variety of important processes such as RNA splicing , regulation of transcription factors ...
  
   (snRNA) and small nucleolar RNA (snoRNA).

• Class 2 RNases III include the Drosha
  Drosha
  Drosha is a Class 2 RNase III enzyme responsible for initiating the processing of microRNA , or short RNA molecules naturally expressed by the cell that regulate a wide variety of other genes by interacting with the RNA-induced silencing complex to induce cleavage of complementary messenger RNA ...
  
   family of enzymes known to function in maturation of precursors to rRNA.

• Class 3 RNases III include the Dicer
  Dicer
  Dicer is an endoribonuclease in the RNase III family that cleaves double-stranded RNA and pre-microRNA into short double-stranded RNA fragments called small interfering RNA about 20-25 nucleotides long, usually with a two-base overhang on the 3' end...
  
   family of enzymes known to function in RNA interference
  RNA interference
  RNA interference is a process within living cells that moderates the activity of their genes. Historically, it was known by other names, including co-suppression, post transcriptional gene silencing , and quelling. Only after these apparently unrelated processes were fully understood did it become...
  
  (RNAi).