A type of DNA sequence found in prokaryotes such as bacteria and archaea, containing spacers cut from the DNA of viruses that have previously attacked the prokaryotic organism. The prokaryotic organism retains these spacers in its DNA and uses them to detect the DNA of those viruses in subsequent attacks, then destroys it with the help of the Cas9 protein.

Cas9, or CRISPR-associated protein 9, is a restriction enzyme that uses CRISPR sequences as a guide to recognize and then cut specific DNA sequences from other organisms (such as viruses that attack bacteria). CRISPR sequences, along with the Cas9 protein, thus form an important molecular defense mechanism in prokaryotes against invading viruses. Humans have recently taken advantage of this natural bacterial system, using it to modify the genomes of living organisms by easily cutting out parts of their DNA. This technology is now known as CRISPR-Cas9, which is used in a wide range of applications, including biological and medical research, the development of biotechnology products, and the treatment of diseases.

Components of CRISPR Technology

There are two main components of the CRISPR-Cas9 system:

The cas9 protein, or CRISPR-associated protein 9, is a non-specific endonuclease that cuts two strands of DNA like molecular scissors. It navigates to the target region based on the gRNA it carries and other factors, such as the presence of a specific recognition sequence in the DNA called the PAM sequence.

The guide RNA molecule, the gRNA, acts as a guide to direct the cas9 enzyme to a specific DNA sequence to make the cut. The variable portion of the gRNA, which consists of approximately 20 nucleotides, matches the genetic code to be cut, so the cas9 enzyme uses it to recognize the target region of the genome.

Conditions for cutting at a specific sequence:

The target sequence, consisting of approximately 20 nucleotides, must be unique and not repeated compared to the rest of the genome.

The region targeted for cutting must be located directly adjacent to a specific sequence of 2-6 nucleotides called the Protospacer Adjacent Motif (PAM). Cas9 will not cut without this sequence. This sequence plays an important role in bacteria because it is present in the DNA of the virus or the attacking plasmid and is not present in the bacterial CRISPR sequence, preventing the Cas9 enzyme from cutting the bacterial sequence.