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A protein derived from the CRISPR-Cas bacterial immune system that has been co-opted for genome engineering. Uses an RNA molecule as a guide to find a complementary DNA sequence. Once the target DNA is identified, Cas12 cuts both strands. Has been compared to “molecular scissors” or a “genetic scalpel.” In CRISPR immunity, cutting viral DNA prevents it from destroying the host cell. In genome engineering, cutting genomic DNA initiates a repair process that ends up making a change or “edit” to its sequence.
Comparable to sticking a note that says “SKIP” onto a page of a book – a reader will ignore this page but the book itself has not been changed.
Scientists have also formed a version of the guide RNA that consists of a single molecule, the single-guide RNA (sgRNA).
An endonuclease cuts in the middle of RNA or DNA, while an exonuclease cuts from the end of the strand. Genome engineering tools like Cas9 are endonucleases.