Dicer is an endoribonuclease in the RNase III family that cleaves double-stranded RNA (dsRNA) and pre-microRNA (miRNA) into short double-stranded RNA fragments about 20-25 base pairs long, with a two-base overhang on the 3' end. Dicer contains two RNase III domains and one PAZ domain; the distance between these two regions of the molecule is determined by the length and angle of the connector helix and influences the length of the siRNAs it produces. Dicers interact with several partner proteins (TRBP in humans, R2D2, Loqs in Drosophila). These partner proteins could play a role in dictating the substrate specificity of Dicer proteins.
Dicer facilitates the formation of the RNA-induced silencing complex (RISC), whose catalytic component argonaute is an endonuclease capable of degrading messenger RNA (mRNA). The human version of this gene is DICER1.
Dicer and other miRNA processing enzymes may be important in cancer prognosis. When researchers in British Columbia sequenced the genomes of rare ovarian, uterine, and testicular tumours, they found that the same fundamental mutation in the DICER gene showed up as the common process underlying all of the different cancers they had examined. The DICER gene regulates the development and behavior of normal cells in the body, and the mutation of this gene causes this regulating ability to be warped, producing cancerous cells. 
In the moss Physcomitrella patens DCL1b, one of four DICER proteins, is not involved in miRNA biogenesis but in dicing miRNA target transcripts. Thus, a novel mechanism for regulation of gene expression, the epigenetic silencing of genes by miRNAs, was discovered.
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- Discovery: microRNAs can directly turn off genes
- Dicer Enzyme at the US National Library of Medicine Medical Subject Headings (MeSH)
- Dicer1 GeneCard
- 3D electron microscopy structures of Dicer from the EM Data Bank(EMDB)