lecture12_bartel

lecture12_bartel - David Bartel RNA Silencing 7.90 6.874...

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David Bartel RNA Silencing 3/29/2005 7.90 / 6.874 Lecture siRNA Exogenously introduced dsRNA, processed by dicer into siRNAs (small interfering 22-mer RNAs) siRNAs complex with RISC (RNA induced silencing complex), bind to mRNA -> break the mRNA Happening in the cytoplasm RIST (nuclear version of RISC) siRNAs that silence DNA H3K9 is methylated in this reaction (found in S. pombe) Exists (siRNA) ncRNA that is responsible for silencing DNA lin-4 (1993) hairpin loop (miRNAs) Targets lin-14 or lin-28 3' UTR mRNA miRNA genomics in animals 22-mer Hairpin precusor Dicer / Drosha processed (Drosha recognizes hairpin) ncRNA genes (e.g. mir-1) -- mostly Pol II transcription Some miRNAs transcribed as a cluster (e.g. miR-35 - miR41) Expression profile of miRNAs in 24 human tissues (within 50 KB - they are co-expressed, probably from the same transcript) Some are expressed from introns (correlated with expression of host gene) 10^3 -> .5 x 10^5 miRNA copies / cell One miRNA can target 20 mRNAs / hour in vitro
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