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Dicer
Dicer, also known as endoribonuclease Dicer or helicase with RNase motif, is an enzyme that in humans is encoded by the ''DICER1'' gene. Being part of the RNase III family, Dicer cleaves double-stranded RNA (dsRNA) and pre-microRNA (pre-miRNA) into short double-stranded RNA fragments called small interfering RNA and microRNA, respectively. These fragments are approximately 20-25 base pairs long with a two-base overhang on the 3' end. Dicer facilitates the activation of the RNA-induced silencing complex (RISC), which is essential for RNA interference. RISC has a catalytic component argonaute, which is an endonuclease capable of degrading messenger RNA (mRNA).
== Discovery ==
Dicer was given its name in 2001 by Emily Bernstein, a graduate student in Greg Hannon's lab at Cold Spring Harbor Laboratory, who sought to discover the enzyme responsible for generating small RNA fragments from double-stranded RNA. Dicer's ability to generate ~22 nucleotide RNA fragments was discovered by separating it from the RISC enzyme complex after initiating the RNAi pathway with dsRNA transfection. This experiment showed that RISC was not responsible for generating the observable small nucleotide fragments. Subsequent experiments testing RNase III family enzymes abilities to create RNA fragments narrowed the search to ''Drosophila'' CG4792, now named Dicer.
Dicer orthologs are present in many other organisms. 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.
In terms of crystal structure, the first Dicer to be explored was that from the protozoan ''Giardia intestinalis''. A PAZ domain and two RNase III domains were discovered by X-ray crystallography. The protein size is 82 kDa, while it is larger in other organisms; for example, it is 219 kDa in humans. The difference in size from humans to ''G. intestinalis'' Dicer is due to at least five different domains being present within human Dicer. These domains are important in Dicer activity regulation, dsRNA processing, and RNA interference protein factor functioning.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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