The CRISPR-Cas3 system, the newest CRISPR-based gene editing tool, is able to erase longer strands of DNA in the human genome, whereas older systems such as the CRISPR-Cas9 are only able to snip a small portion from a targeted site. Wiping out longer sequences of DNA will enable scientists to determine which functions in an organism are affected due to the cut-out missing pieces. To seek its target, the CRISPR-Cas3 employs the Cascade, which is a ribonucleoprotein complex, and with the enzyme called Cas3, the tool shreds general material as it moves along a lengthy stretch of DNA.
CRISPR, which stands for Clustered Regularly Interspaced Short Palindromic Repeats, is a naturally-occurring bacterial defense system that fights against invading viruses in the body. It was first discovered and reported by microbiologist Francisco Mojica of the University of Alicante in Spain. Since then, CRISPR has went through several developments over the years, most notable of all is the CRISPR-Cas9. The process is similar to how CRISPR operates but with the addition of the enzyme Cas9, which is able to target a desired location in the human genome and allow existing genes to be removed or added, acting like a genetic scissors (as compared to the CRISPR-Cas3 which acts more like a shredder). Gene editing has been possible since the previous decades but the methods employed have raised concerns on its impracticality and its lack of precision. The earlier breakthroughs of CRISPR engineered by the Zhang lab and published at around 2013, such as the CRISPR-Cas9, has allowed a more efficient and highly selective method.
Feng Zhang, biochemist and the head of the Zhang lab, explains how the CRISPR gene editing tool works. According to him, CRISPR sequences are transcribed into RNA sequences, also known as CRISPR RNAs or crRNAS, which will then target the exact location of a matching DNA sequence and guide the system to the said location. Once the DNA is found, the enzyme Cas9 will bind to the DNA and cut it, shutting the targeted gene off. Other modified versions of Cas9 can activate a gene instead of cutting it off, which will allow scientists to study this particular gene’s function in the organism. The Cas9 enzyme can also modify the genes, correcting ‘errors’ in the three-billion-letter sequence of the human genome with the possibility of treating several genetic diseases.
The newest system, the CRISPR-Cas3, developed by a group of scientists led by the University of Cornell and the University of Michigan, has the potential of identifying the sequences that are responsible for ectopic viruses such as herpes simplex, Epstein-Barr, and hepatitis B and may be able to erase these from the human genome, according to the study. With the CRISPR-Cas3, scientists may also gain better knowledge of other various genetic diseases and develop advanced treatments for these. But the tool is currently still in its initial stages and it will take more time before it can used for therapeutic purposes.