The CRISPR history of discovery is vital when studying what is CRISPR Cas9. CRISPR means Clustered Regularly Interspaced Short Palindromic Repeats. They are pieces of genetic code whose foundational discoveries began in 1993 when repetitive palindromic segments of DNA interspaced with other fragments of genetic material were identified by researchers in prokaryotes.
After years of looking into the genetic motifs of CRISPR, it was concluded in 2007 that immunity is related to its function. With the combined efforts, research groups were able to shed light on the underlying molecular mechanism behind the CRISPR system in the next 5 years.
Based on their studies, bacteria and archaea use the CRISPR-Cas9 system to ward off invading viruses called bacteriophages. If a prokaryotic cell encounters a viral infection, it creates a double-strand break (DSB) in its target loci to snip-off a piece of viral DNA by employing a special CRISPR-associated nuclease (Cas9).
CRISPR History of Discovery | DNA right on target
How are the targeted DNA recognized by the Cas9 protein? A short RNA fragment called guide RNA (gRNA) directs it to the target sequence. Complementary to a segment of the viral genome, the guide RNA allows Cas9 to cleave DNA with a high degree of specificity. This destroys the virus and even allows the fragment of foreign DNA called “spacer” to be stored between the palindromic sequences of the CRISPR array which can retain a genetic memory of past infections. This means that if the virus would re-invade, it could easily be targeted and destroyed by the CRISPR-Cas9 system. This library of viral fragments can similarly act like our immune system which stores antigens in preparation for future infections.
With an understanding of the mechanism of CRISPR in prokaryotes, it did not take scientists a long time to realize its potential in engineering the genomes of microbes, plants, and animals. At present, CRISPR is used in a variety of applications and is continuously being adopted in laboratories worldwide.