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Processing of primary microRNAs by the Microprocessor complex


Mature microRNAs (miRNAs) are generated via a two-step processing pathway to yield 22-nucleotide small RNAs that regulate gene expression at the post-transcriptional level1. Initial cleavage is catalysed by Drosha, a nuclease of the RNase III family, which acts on primary miRNA transcripts (pri-miRNAs) in the nucleus2. Here we show that Drosha exists in a multiprotein complex, the Microprocessor, and begin the process of deconstructing that complex into its constituent components. Along with Drosha, the Microprocessor also contains Pasha (partner of Drosha), a double-stranded RNA binding protein. Suppression of Pasha expression in Drosophila cells or Caenorhabditis elegans interferes with pri-miRNA processing, leading to an accumulation of pri-miRNAs and a reduction in mature miRNAs. Finally, depletion or mutation of pash-1 in C. elegans causes de-repression of a let-7 reporter and the appearance of phenotypic defects overlapping those observed upon examination of worms with lesions in Dicer (dcr-1) or Drosha (drsh-1). Considered together, these results indicate a role for Pasha in miRNA maturation and miRNA-mediated gene regulation.

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Figure 1: Pri-miRNA processing is conserved in Drosophila.
Figure 2: Pasha, a nuclear dsRNA binding domain (dsRBD) protein, associates with Drosha.
Figure 3: Drosha and Pasha co-exist in a Microprocessor complex.
Figure 4: Depletion of Pasha reduces pri-miRNA processing.


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We thank F. Rivas for critical reading of the manuscript. Strain BC3825 was obtained from the C. elegans Genetics Center, and drsh-1(tm0654) was obtained from the NBP in Japan (Mitani laboratory). We thank E. Cuppen and his group for help in target-selected mutagenesis. A.M.D. is a David Koch Fellow of the Watson School of Biological Sciences. G.J.H. is supported by an Innovator Award from the US Army Breast Cancer Research Program. This work was also supported by a grant from the NIH (G.J.H.) and by a VENI fellowship from the Netherlands Organisation for Scientific Research (R.F.K.).

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Correspondence to Gregory J. Hannon.

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Denli, A., Tops, B., Plasterk, R. et al. Processing of primary microRNAs by the Microprocessor complex. Nature 432, 231–235 (2004).

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