page_title: CRISPR
section_title: Mechanism
hierarchical_section_title: CRISPR / Mechanism
caption_attribution_description: English: Cellular Repair Mechanisms of Double-Strand DNA Breaks can be exploited for Genetic Manipultions. When a double-strand break (DSB) is introduced in a cell’s DNA, there are two major repair pathways. In one pathway the blunt DNA ends are joined in a process called non-homologous end joining (NHEJ). This mechanism is error-prone and may produce insertions or deletions of bases. These alterations are collectively called Indel mutations. Indel mutations may result in a loss of function of the affected gene, e.g., by introducing a frameshift and/ or a premature stop codon. Another pathway is called homology directed repair (HDR). This pathway uses a DNA template to repair the site where the DSB occurred. When exogenous DNA is added, the sequence may serve as a template and is then integrated into the repair process. This may lead to the introduction of a new genetic sequence. Both repair pathways may result in a genetic alteration.
context_page_description: CRISPR is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea. These sequences are derived from DNA fragments of bacteriophages that had previously infected the prokaryote. They are used to detect and destroy DNA from similar bacteriophages during subsequent infections. Hence these sequences play a key role in the antiviral defense system of prokaryotes.
  Cas9 is an enzyme that uses CRISPR sequences as a guide to recognize and cleave specific strands of DNA that are complementary to the CRISPR sequence. Cas9 enzymes together with CRISPR sequences form the basis of a technology known as CRISPR-Cas9 that can be used to edit genes within organisms. This editing process has a wide variety of applications including basic biological research, development of biotechnology products, and treatment of diseases.
  The CRISPR-Cas system is a prokaryotic immune system that confers resistance to foreign genetic elements such as those present within plasmids and phages and provides a form of acquired immunity. RNA harboring the spacer sequence helps Cas proteins recognize and cut foreign pathogenic DNA. Other RNA-guided Cas proteins cut foreign RNA.
context_section_description: CRISPR-Cas immunity is a natural process of bacteria and archaea. CRISPR-Cas prevents bacteriophage infection, conjugation and natural transformation by degrading foreign nucleic acids that enter the cell.
caption: Double Strand DNA Breaks Introduced by CRISPR-Cas9 Allows Further Genetic Manipulation By Exploiting Endogenous DNA Repair Mechanisms.
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