The CRISPR-Cas system acts as the immune system for bacteria. This system includes CRISPR loci and cas genes. There are repeats in the CRISPR locus, which are separated by short stretches of non-repetitive DNA called spacers. The spacers come from invading plasmids or phage DNA. First adaptation or immunization happens with acquiring the spacers from degraded phage or plasmid DNA. Second is biogenesis, when the CRISPR locus is transcribed into a long mRNA. This mRNA consists of the array of transcribed different spacers acquired by the cell separated by repeat sequences. Following transcription, the mRNA is cleaved at the 3′ end of the repeat sequence and RNAs consisting of one spacer and one repeat sequence are released. These RNAs bind to Cas proteins, forming a complex. The complexes circulate within the cell and bind to any foreign DNA that carries a sequence identical to that of a spacer and cleave the DNA at the site the complex is bound to the DNA (interference). If the spacer sequence of the RNA/Cas complex was identical to that within the DNA of a phage, the phage DNA will cut and the bacterium has survived entry of a deadly foe. This system can be utilized for genetic engineering by combining synthetic spacers with a sequence identical to a region of a targeted gene with a repeat sequence combined with Cas protein.
Scientists have used this tool to make modifications to an organism’s genome by either “turning off” a gene or deleting it. Once the genome is cut, you can either insert or delete genes. As explained above, the CRISPR system naturally occurring in bacteria took in the foreign DNA from the virus to remember it, and then later use it to infect the virus’ DNA if the bacteria was re-exposed to the virus. Scientists now have the choice to delete the DNA altogether, introduce new DNA, or just inactivate the targeted genes.
CRISPR/CAS9 can be used in various scientific fields, which makes this gene editing tool such a revolutionary technological advancement. It has applications in food products, human health, and can be used in bacteria and animals (including people). This technology helps us understand the genomes of organisms better and more easily than practices used previously. It’s also important to note that this gene editing tool is exactly that, it doesn’t necessarily introduce foreign DNA into an organism, in which case the final product can not be labelled as a GMO.