Self-regulation of the CRISPR System in E. Coli

This illustration depicts the repression of the Cascade protein operon in E. Coli bacteria. The inset on the top left depicts the transcription of Cascade RNA when RNAP σ70 holoenzyme binds to the Cascade promoter sequence of the E. Coli genome. The inset on the bottom left shows the function of the Cascade protein, where Cascade uses CRISPR RNA to identify viral phage DNA that has invaded the cell and destroys it by forming a complex with the Cas3 protein. The primary image to the right of the insets depicts how the Cascade protein uses CRISPR-like RNA to bind to Cascade promoter of the E. Coli genome while blocking RNAP σ70 holoenzyme and Cas3, both preventing further transcription of Cascade and DNA cleavage. To ensure contrast and legibility, all text is above a 4.5:1 luminance ratio.