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Updated: Aug 19, 2025

CIRCLE-Seq for Interrogation of Off-Target Gene Editing
Published on: November 1, 2024
A quantitative model for the dynamics of target recognition and off-target rejection by the CRISPR-Cas Cascade
Marius Rutkauskas1, Inga Songailiene2, Patrick Irmisch1
1Peter Debye Institute for Soft Matter Physics, Universität Leipzig, 04103, Leipzig, Germany.
Abstract:
CRISPR-Cas effector complexes recognise nucleic acid targets by base pairing with their crRNA which enables easy re-programming of the target specificity in rapidly emerging genome engineering applications. However, undesired recognition of off-targets, that are only partially complementary to the crRNA, occurs frequently and represents a severe limitation of the technique. Off-targeting lacks comprehensive quantitative understanding and prediction. Here, we present a detailed analysis of the target recognition dynamics by the Cascade surveillance complex on a set of mismatched DNA targets using single-molecule supercoiling experiments. We demonstrate that the observed dynamics can be quantitatively modelled as a random walk over the length of the crRNA-DNA hybrid using a minimal set of parameters. The model accurately describes the recognition of targets with single and double mutations providing an important basis for quantitative off-target predictions. Importantly the model intrinsically accounts for observed bias regarding the position and the proximity between mutations and reveals that the seed length for the initiation of target recognition is controlled by DNA supercoiling rather than the Cascade structure.
Insights
CRISPR-Cas genome engineering relies on precise target recognition. This study models off-target DNA binding dynamics, revealing DNA supercoiling controls target recognition initiation, crucial for improving CRISPR-Cas specificity.
Area of Science:
- Molecular Biology
- Genetics
- Biophysics
Background:
- CRISPR-Cas systems are powerful genome engineering tools relying on crRNA-guided DNA targeting.
- Off-target recognition, due to partial complementarity, limits CRISPR-Cas precision and lacks predictive models.
- Understanding target recognition dynamics is key to mitigating off-target effects.
Purpose of the Study:
- To quantitatively analyze the target recognition dynamics of the CRISPR-Cas Cascade complex on mismatched DNA targets.
- To develop a predictive model for CRISPR-Cas off-target recognition.
- To elucidate the factors controlling the initiation of target recognition.
Main Methods:
- Utilized single-molecule supercoiling experiments to study Cascade complex interactions with various DNA targets.
- Developed a quantitative model based on a random walk mechanism to describe target recognition dynamics.
- Analyzed recognition of targets with single and double mutations, including positional effects.
Main Results:
- Demonstrated that target recognition dynamics can be modeled as a random walk along the crRNA-DNA hybrid.
- The model accurately predicts recognition of targets with single and double mutations, accounting for mutation position and proximity.
- Identified DNA supercoiling, not the Cascade structure, as the primary controller of the seed length for target recognition initiation.
Conclusions:
- The developed random walk model provides a quantitative basis for predicting CRISPR-Cas off-target effects.
- Understanding the role of DNA supercoiling in target recognition is critical for enhancing CRISPR-Cas specificity.
- This work advances the predictive power and precision of genome engineering technologies.
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