CRISPR is an abbreviation of Clustered Regularly Interspaced Short Palindromic Repeats. It is a family of DNA sequences in bacteria and archaea [1]. The sequences contain fragments of DNA from viruses that have attacked the prokaryote. These fragments are used by the prokaryote to detect and destroy DNA from similar viruses during subsequent attacks. These sequences play a key role in a prokaryotic defense system, and form the basis of the CRISPR-Cas9 technology [2].

What Is CRISPR System?

The CRISPR-Cas system is a prokaryotic immune system that confers resistance to foreign genetic elements such as those present within plasmids and phages that provides a form of acquired immunity [3,4,5]. Upon the infection, new foreign DNA sequences are captured and integrated into the host CRISPR locus as new spacers. The CRISPR locus is transcribed and processed to generate mature CRISPR RNAs (crRNAs), each encoding a unique spacer sequence. Each crRNA associates with Cas effector proteins that use crRNAs as guides to silence foreign genetic elements that match the crRNA sequence. Some Cas (CRISPR-associated) proteins recognize and cut exogenous DNA. Other Cas proteins cut foreign RNA [6]. CRISPR systems are found in approximately 50% of sequenced bacterial genomes and nearly 90% of sequenced archaea [7].

The immune process of CRISPR system

Fig 1. The immune process of CRISPR system. From Doudna's Lab

CRISPR Related References

1. Barrangou R (2015). The roles of CRISPR-Cas systems in adaptive immunity and beyond. Current Opinion in Immunology. 32: 36–41.
2. Zhang F et al. (2014). CRISPR/Cas9 for genome editing: progress, implications and challenges. Human Molecular Genetics. 23 (R1): R40–6.
3. Redman M et al. (August 2016). What is CRISPR/Cas9?. Archives of Disease in Childhood. Education and Practice Edition. 101 (4): 213–5.
4. Barrangou R et al. (March 2007). CRISPR provides acquired resistance against viruses in prokaryotes. Science. 315 (5819): 1709–12.
5. Marraffini LA, Sontheimer EJ (2008). CRISPR interference limits horizontal gene transfer in staphylococci by targeting DNA. Science. 322(5909): 1843–5.
6. Mohanraju P et al. (2016). Diverse evolutionary roots and mechanistic variations of the CRISPR-Cas systems. Science. 353 (6299): aad5147.
7. Hille F et al. (March 2018). The Biology of CRISPR-Cas: Backward and Forward. Cell. 172 (6): 1239–1259.