The CRISPR-Cas system is a sophisticated bacterial defense mechanism that protects against viral infections, specifically from bacteriophages, which are viruses that infect bacteria. The acronym CRISPR stands for "clusters of regularly interspaced short palindromic repeats," referring to specific sequences found in the bacterial chromosome. This system functions by storing segments of phage DNA, known as spacers, which serve as a historical record of past infections.
During the initial encounter with a phage, the bacterial cell can degrade the phage DNA into smaller fragments. Some of these fragments are integrated into the bacterial chromosome as spacers. When the bacterium faces a subsequent infection by the same phage, it can transcribe these spacer sequences into RNA. This RNA then forms a complex with a protein called Cas, resulting in a Cas-RNA complex.
The Cas-RNA complex plays a crucial role in targeting and cleaving the infecting phage DNA, effectively inactivating the virus. The RNA acts as a guide, with its sequence being complementary to the phage DNA, ensuring precise targeting. This mechanism not only protects the individual bacterium from repeated infections but also allows the CRISPR system to be inherited by future generations, equipping them with the same defense against specific phages.
In summary, the CRISPR-Cas system exemplifies a remarkable evolutionary adaptation that enables bacteria to remember and defend against viral threats, ensuring their survival and resilience in a constantly changing environment.
