What is CRISPR and how does it work?

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) are repetitive regions of DNA, originally discovered in bacteria that serve as a primitive form of an immune system. When CRISPR and the downstream regions of DNA (termed “spacer” regions and originally taken from viral genomes) are transcribed, the CRISPR element allows for the binding to Cas (CRISPR associated) enzymes. When the CRISPR-Cas complex binds to the region targeted by the spacer, the Cas enzyme gets activated and cleaves the targeted nucleic acid.