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Drosha is a Class 2 ribonuclease III enzyme that in humans is encoded by the ''DROSHA'' (formerly ''RNASEN'') gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=29102 )〕 == Function == Members of the ribonuclease III superfamily of double-stranded (ds) RNA-specific endoribonucleases participate in diverse RNA maturation and decay pathways in eukaryotic and prokaryotic cells. The RNase III Drosha is the core nuclease that executes the initiation step of microRNA (miRNA) processing in the nucleus.〔 The microRNAs thus generated are short RNA molecules that regulate a wide variety of other genes by interacting with the RNA-induced silencing complex (RISC) to induce cleavage of complementary messenger RNA (mRNA) as part of the RNA interference pathway. A microRNA molecule is synthesized as a long RNA primary transcript known as a ''pri-miRNA'', which is cleaved by Drosha to produce a characteristic stem-loop structure of about 70 base pairs long, known as a ''pre-miRNA.'' Drosha exists as part of a protein complex called the ''Microprocessor complex'', which also contains the double-stranded RNA binding protein Pasha (also called DGCR8). Pasha is essential for Drosha activity and is capable of binding single-stranded fragments of the pri-miRNA that are required for proper processing. Human Drosha was cloned in 2000, when it was identified as a nuclear dsRNA ribonuclease involved in the processing of ribosomal RNA precursors. The other two human enzymes that participate in the processing and activity of miRNA are the Dicer and Argonaute proteins. Both Drosha and Pasha are localized to the cell nucleus, where processing of pri-miRNA to pre-miRNA occurs. This latter molecule is then further processed by the RNase Dicer into mature miRNAs in the cell cytoplasm.〔 Both Drosha and Dicer also participate in the DNA damage response. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「drosha」の詳細全文を読む スポンサード リンク
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