Cas9 nuclease is a molecular tool derived from the bacterial defense mechanism known as the CRISPR-Cas system. In bacteria, Cas nucleases, such as Cas9, protect against viral infection by cutting, and thereby destroying, viral DNA. Due to its capacity to precisely cut double-stranded DNA, Cas9 nuclease is often referred to as molecular scissors. It is widely used in genome editing applications, allowing scientists to make precise modifications to the DNA of various organisms for research, therapeutic, and biotechnological purposes.
The DNA cutting process is initiated by the formation of a complex (a functional unit) of Cas9 with a short RNA sequence known as guide RNA (gRNA). The complex, known as ribonucleoprotein, then scans the DNA for a complementary match between gRNA and DNA sequences. At the precise match site, Cas9 cuts both strands of the double-stranded DNA, introducing double-stranded DNA breaks. These break sites can be used for silencing an unwanted gene function or for the introduction of new genes into the organism. The break sites in the DNA are corrected and bound together by the cell's DNA repair mechanism, which is activated upon detection of DNA breaks.
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