Figure 3. RNA-guided gene repression using engineered CRISPR-Cas systems(a) Mutation of the essential residues of the RuvC and HNH nuclease domains converts Cas9 into a CRISPR RNA (crRNA)-guided DNA-binding protein (dCas9). Directing dCas9 to promoter sequences (either the top or bottom DNA strand) results in prevention of transcription initiation, most likely by preventing the binding of RNA polymerase (RNAP) to the promoter elements. (b) Directing dCas9 to the open reading frame regions of genes (with a crRNA that interacts with the coding but not the template strand) results in a transcription stop, presumably because the dCas9 complex blocks RNAP elongation. Arrows indicate the transcription start site. Abbreviations: cas, CRISPR-associated; CRISPR, clustered regularly interspaced short palindromic repeats; tracrRNA, trans-activating CRISPR RNA.
Image published in: Bikard D and Marraffini LA (2013)
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