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CRISPR interference (CRISPRi) is a genetic perturbation technique that allows for sequence-specific repression of gene expression in prokaryotic and eukaryotic cells. [1] It was first developed by Stanley Qi and colleagues in the laboratories of Wendell Lim , Adam Arkin, Jonathan Weissman , and Jennifer Doudna . [ 2 ]
CRISPR gene editing (CRISPR, pronounced / ˈ k r ɪ s p ə r / (crisper), refers to a clustered regularly interspaced short palindromic repeats") is a genetic engineering technique in molecular biology by which the genomes of living organisms may be modified.
CRISPR-associated transposons have been harnessed for in vitro and in vivo gene editing at different targets, in different hosts, and with different payloads. All CAST components of the Tn6677 system from Vibrio cholerae have been combined into a single plasmid and confirmed to deliver up to 10kb transposons at near 100% efficiency. [ 16 ]
Cas9 (or "CRISPR-associated protein 9") is an enzyme that uses CRISPR sequences as a guide to recognize and open up specific strands of DNA that are complementary to the CRISPR sequence. Cas9 enzymes together with CRISPR sequences form the basis of a technology known as CRISPR-Cas9 that can be used to edit genes within living organisms.
Targeted gene knockout using CRISPR/Cas9 requires the use of a delivery system to introduce the sgRNA and Cas9 into the cell. Although a number of different delivery systems are potentially available for CRISPR, [37] [38] genome-wide loss-of-function screens are predominantly carried out using third generation lentiviral vectors.
See: Guide RNA, CRISPR. Complementary base pairing between the sgRNA and genomic DNA allows targeting of Cas9 or dCas9. A small guide RNA (sgRNA), or gRNA is an RNA with around 20 nucleotides used to direct Cas9 or dCas9 to their targets. gRNAs contain two major regions of importance for CRISPR systems: the scaffold and spacer regions.
CRISPR interference (CRISPRi) on the other hand utilizes a catalytically inactive nuclease to physically block RNA polymerase, effectively preventing or halting transcription. [8] Perturb-seq has been utilized with both the knockout and CRISPRi approaches in the Dixit et al. paper [ 2 ] and the Adamson et al. paper, [ 1 ] respectively.
Diagram showing type I-F CRISPR-Cas system, as well as inhibition mechanisms of three type I-F anti-CRISPRs. Type I-F CRISPR complex is made of 60 crRNA nucleotides and nine Cas proteins (the protein type is specified by the numbers 5,8,7,6). AcrF1 goes to Cas7f, preventing target DNA access to the crRNA guide.