LEC18 - Regulatory RNAs Regulation of transcription...

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Regulatory RNAs Regulation of transcription termination, RNA stability and translation initiation Prokaryotes: sRNAs Riboswitches Attenuation CRISPR Eukaryotes miRNA: ~21-22 bases siRNA: ~21-24 bases piRNA: ~24-34 bases
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sRNA: trans-acting regulators RNAs (80-110 bases) encoded in genome to regulate other genes Post-transcriptional regulation Two possible outcomes: RNA degradation Translation inhibition or stimulation Mechanism: Bind to complementary sequences on mRNA dsRNA may then be substrate for degradation by RNAse E Alternatively, may affect availability of RBS altering frequency of translation initiation Mismatches may occur and binding is stabilized by an RNA chaperone Hfq Frequently single sRNA will regulate more than one mRNA
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sRNA Regulation
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When sRNAs stimulate degradation of the mRNA, what type of RNase degrades the RNA? A. 5’ exonuclease B. 3’ exonuclease C. double stranded endonuclease
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Example: Regulation of RpoS by two sRNAs: OxyS represses translation, DsrA activates translation
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Riboswitches: cis-acting regulators Riboswitches are structured elements typically found in the 5′ untranslated regions of mRNAs Regulate gene expression by binding to small metabolites Regulate expression at either transcription or translation level Function through changes in RNA secondary structure Pervasive in prokaryotes, some found in fungi and plants
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Two regions of importance Aptamer Binds small molecule ligand and undergoes conformational change Expression platform Changes conformation in response to aptamer
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Figure 20-3a Transcription riboswitches cause RNA synthesis to terminate in response to a metabolite
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Figure 20-3b Other types of riboswitches inhibit translation initiation
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  • Winter '12
  • Lin
  • DNA, RNA, CRISPR, RNA degradation, a. Cleavage

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