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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.

=Types of RNase III=

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 with the Class 1 RNase III domain :


 * RNT1 (UniProtKB Q02555) - S. cerevisiae - this RNase III is involved in the transcription and processing of rDNA, the 3' end formation of U2 snRNA via cleavage of the terminal loop, cell wall stress response and degradation, and regulation of morphogenesis checkpoint genes.


 * Pac1 (UniProtKB P22192) - S. pombe - this RNase III is located on chromosome II of the yeast nuclease and when over expressed, is directly involved in the sterility, lack of mating efficiency, abnormal mitotic cell cycle, and mutation suppression of the organism..


 * Rnc (UniProtKB P0A7Y0) - E.Coli - this RNase III is involved in the processing of viral transcripts and some mRNAs through the cleavage of multiple areas on the dsRNA. This cleavage can be influenced by ribosomal protein presence.

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 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