CRISPR stands for clustered regularly interspaced short palindromic repeats. It refers to segments of repetitive DNA found in bacteria and archaea that, together with associated Cas proteins, form an adaptive immune system. These sequences store fragments of viral DNA from previous infections and guide enzymes to recognize and cut matching sequences in invading bacteriophages.
Explanation
CRISPR loci contain short repeat sequences separated by spacer segments derived from foreign genetic material. When a virus infects a bacterium, small pieces of the viral genome are integrated into the CRISPR array as new spacers. The array is transcribed into RNA molecules that include these spacer sequences, and the resulting guide RNAs direct Cas enzymes to complementary sequences in the viral DNA. Upon binding, the Cas proteins make a double‑stranded break, neutralising the invader. This mechanism provides a form of acquired immunity in prokaryotes and allows the organism to respond more quickly to subsequent attacks by the same virus. Researchers have adapted the CRISPR–Cas9 system as a genome‑editing tool by designing guide RNAs that target specific DNA sequences in other organisms. When introduced into cells, the guide RNA directs the Cas9 enzyme to the chosen genomic site, where it cuts the DNA. The cell’s own repair processes can then introduce mutations or insert new DNA. This technology has become an important method for studying gene function, engineering microbes, creating disease models and exploring treatments for genetic disorders. Its programmability and relative ease of use have led to widespread adoption of the CRISPR–Cas system in laboratories around the world.
Notable Uses
Beyond its natural role as a microbial immune system, CRISPR–Cas technology has transformed genetic research. Microbiologists use it to create targeted knockouts in bacteria and archaea to investigate gene function. In agriculture, CRISPR has been applied to develop crop varieties with enhanced resistance to pests or improved nutritional content. In medical research, it enables the generation of animal models carrying human disease mutations and the correction of faulty genes in cultured cells. Diagnostic methods such as SHERLOCK and DETECTR exploit CRISPR enzymes to detect viral RNA with high specificity. The importance of this system was highlighted when the 2020 Nobel Prize in Chemistry was awarded to Emmanuelle Charpentier and Jennifer Doudna for their pioneering work on CRISPR–Cas9.
CRISPR began as a curious pattern in bacterial DNA and is now a central tool in molecular biology. Understanding its natural function provides insight into microbial defences, and its adaptation for genome editing continues to shape research and potential therapies.
Related Terms: Cas9, genome editing, guide RNA, spacer, bacteriophage