Ribonuclease III (RNase III or RNase C)(BRENDA 3.1.26.3) is a type of ribonuclease that recognizes dsRNA and cleaves it at specific targeted locations to transform them into mature RNAs. These enzymes are a group of endoribonucleases that are characterized by their ribonuclease domain, which is labelled the RNase III domain. They are ubiquitous compounds in the cell and play a major role in pathways such as RNA precursor synthesis, RNA Silencing, and the pnp autoregulatory mechanism.
Within the RNase III superfamily, there are four known classes: 1, 2, 3, and 4. Each class is defined by both its functional and structural differences.
Class 1 RNase III
Class 1 RNase III have a dimer structure whose function is to cleave dsRNA into multiple subunits. It is a Mg2+ dependent endonuclease and is largely found in bacteria, bacteriophage, 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. They process precursors to ribosomal RNA, and in the case of fungi, process precursors to small nuclear RNA (snRNA) and small nucleolar RNA (snoRNA). The basic dsRNA cleavage function of Class 1 RNase III is similar in most of the organisms in which it is present. However, as the enzyme was conserved in various species over time, the restraints of its function has changed and expanded to meet the biological needs of each organism.
Yeast nucleases with the Class 1 RNase III domain:
Class 2 RNase III
Class 2 RNases III include the Drosha family of enzymes known to function in maturation of precursors to miRNA.
Class 3 RNase III
Class 3 RNases III include the Dicer family of enzymes known to function in RNA interference (RNAi). Class III RNases are S-RNase components. It is a component of the self-incompatibility system in Rosaceae, Solanaceae, and Plantaginaceae. They are recruited to cope with various environmental stress scenarios.
Dicer enzymes process dsRNA subtrates into small RNA fragments of individual size ranging from 21-27 nucleotides in length. Dicer has an N-terminal helicase/ATPase domain which is followed by another domain of an unknown function. It is centrally positioned PAZ domain and a C-terminal configuration which includes one dsRBD and two RNase III catalytic domains. Interactions of Dicer occurs with other proteins, which includes TRBP, PACT, and Ago2. RNAs that are produced by Dicer act as guides for a sequence of particular silencing of cognate genes through RNAi and related pathways.
Class 4 RNase III
Class 4 RNases III, called Mini-III, are homodimeric enzymes and consist solely of the RNase III domains.
Human proteins containing RNase III domain
DICER1
DROSHA
