Practice question
Question
In CRISPR-Cas9, what sequence is essential for Cas9 to recognize the target?
Explanation
Streptococcus pyogenes Cas9 requires a protospacer adjacent motif PAM downstream of target for binding and cleavage. The canonical PAM is 5'-NGG-3' on non-target strand. Guide RNA pairs with 20 nucleotides upstream of PAM, but Cas9 first scans DNA for PAM, triggering DNA unwinding and R-loop formation. Without PAM, even perfect guide complementarity fails to induce double strand break. PAM ensures self versus non-self discrimination since bacterial CRISPR array lacks PAM. Engineering higher fidelity Cas9 variants often alters PAM recognition profiles.
Related blogs
Guides and insights connected to this topic
SARS-CoV-2 Coronavirus: Structure, Genome, Proteins, Replication, Pathogenesis, and Host Interaction
Coronavirus Overview Coronaviruses (CoVs) are enveloped viruses (surrounded by a lipid membrane derived from host cells), belonging to the s...
Coronavirus Structure, Genome, Replication, Symptoms, Pathogenesis, and Prevention
Structure of Coronavirus Coronaviruses (enveloped RNA viruses) fall in the virus family Coronaviridae, order Nidovirales. They are enveloped...
Cucumber Mosaic Virus (CMV): Structure, Genome, Symptoms, Disease Cycle and Management
Cucumber Mosaic Virus (CMV): Introduction and Importance Cucumber Mosaic Virus (CMV) (plant-infecting RNA virus) is one of the most economic...