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Drosha is a Class 2 RNase III enzyme responsible for initiating the processing of microRNA (miRNA), or short RNA molecules naturally expressed by the cell 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 RNAi 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.[1] 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),[2] which is essential for Drosha activity and is capable of binding single-stranded fragments of the pri-miRNA that are required for proper processing.[3] Human Drosha was cloned in 2000, when it was identified as a nuclear dsRNA ribonuclease involved in the processing of ribosomal RNA precursors.[4] 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.[1]

Drosha and other miRNA processing enzymes may be important in cancer prognosis.[5]


  1. ^ a b Lee Y, Ahn C, Han J, Choi H, Kim J, Yim J, Lee J, Provost P, Rådmark O, Kim S, Kim VN (September 2003). "The nuclear RNase III Drosha initiates microRNA processing". Nature 425 (6956): 415–9. doi:10.1038/nature01957. PMID 14508493. 
  2. ^ Denli AM, Tops BB, Plasterk RH, Ketting RF, Hannon GJ (November 2004). "Processing of primary microRNAs by the Microprocessor complex". Nature 432 (7014): 231–5. doi:10.1038/nature03049. PMID 15531879. 
  3. ^ Han J, Lee Y, Yeom KH, Nam JW, Heo I, Rhee JK, Sohn SY, Cho Y, Zhang BT, Kim VN (June 2006). "Molecular basis for the recognition of primary microRNAs by the Drosha-DGCR8 complex". Cell 125 (5): 887–901. doi:10.1016/j.cell.2006.03.043. PMID 16751099. 
  4. ^ Wu H, Xu H, Miraglia LJ, Crooke ST (November 2000). "Human RNase III is a 160-kDa protein involved in preribosomal RNA processing". J. Biol. Chem. 275 (47): 36957–65. doi:10.1074/jbc.M005494200. PMID 10948199. 
  5. ^ Slack FJ, Weidhaas JB (December 2008). "MicroRNA in cancer prognosis". N. Engl. J. Med. 359 (25): 2720–2. doi:10.1056/NEJMe0808667. PMID 19092157. 
Note: Drosha is an anagram for the word "hoards", and equally irrelevant to this article about molecular biology, Drosha, or Droshah, is the Hebrew and Yiddish word for sermon in Judaism.