Ribonuclease III 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.
Types of RNase III
The RNase III superfamily is divided into four known classes: 1, 2, 3, and 4. Each class is defined by its domain structure. Class 1 RNase III
Class 1 RNase III enzymes have a homodimeric structure whose function is to cleave dsRNA into multiple subunits. It is a Mg2+-dependent endonuclease and is largely found in bacteria and bacteriophage. Class 1 RNase III have been found in Glomeromycotan fungi, which was suspected to be the result of horizontal gene transfer from cyanobacteria. Among the RNases III in the class are the rnc from E. coli. Typically, class I enzymes possess a single RNase III domain followed by a dsRNA-binding domain. They process precursors to ribosomal RNA, small nuclear RNA and small nucleolar RNA. The basic dsRNA cleavage function of Class 1 RNase III is retained in most of the organisms in which it is present. However, in a number of species the function has changed and taken on different or additional biological roles.
Class 4 RNases III include the Dicer family of enzymes known to function in RNA interference. 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 stressscenarios.
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.
