A Study of CRISPR Ribonucleoprotein Displacement in Cell-Free Systems.

Area of Science:

• Synthetic Biology
• Molecular Biology
• Biochemistry

Background:

• CRISPR/Cas systems are programmable tools for gene expression control in cellular and cell-free environments.
• RNA engineering offers potential for dynamic control of CRISPR/Cas transcription factor activity.
• CRISPR interference (CRISPRi) using catalytically inactive dCas9 is a method to repress gene expression.

Purpose of the Study:

• To investigate the use of RNA strand displacement systems for removing CRISPR/Cas ribonucleoprotein complexes from target DNA in cell-free systems.
• To engineer an antisense RNA to trigger rapid removal of bound CRISPR/Cas ribonucleoproteins via strand displacement.
• To assess the efficacy of RNA strand displacement for dynamic control of dCas9 binding.

Main Methods:

• Utilized an *E. coli*-based cell-free expression system.
• Engineered a guide RNA with an extended toehold.
• Expressed an antisense RNA complementary to the guide RNA's toehold to induce strand displacement.
• Monitored dCas9 binding via CRISPR interference repression of a reporter protein.

Main Results:

• CRISPR/Cas ribonucleoprotein complexes, specifically dCas9, demonstrated significant resistance to removal by the designed RNA strand displacement system.
• The antisense RNA did not effectively displace bound dCas9 from the target DNA in the cell-free system.
• The study highlights unexpected stability of dCas9 binding under these conditions.

Conclusions:

• RNA strand displacement, as implemented, is not an effective strategy for the dynamic removal of bound dCas9 in cell-free systems.
• The observed resistance of dCas9 suggests limitations of this approach for rapid, on-demand deactivation of CRISPR/Cas transcription factors.
• Alternative strategies may be required for achieving dynamic control and efficient removal of CRISPR/Cas proteins in engineered genetic networks.