Clustered regularly-interspaced short palindromic repeats (abbreviated as CRISPR, pronounced
crisper[2]) are segments of prokaryotic DNA containing short repetitions of base sequences.
Each repetition is followed by short segments of "spacer DNA" from previous exposures to
a bacterial virus or plasmid.[3]
The CRISPR/Cas system is a prokaryotic immune system that confers resistance to foreign
genetic elements such as plasmids and phages,[4][5] and provides a form of acquired immunity.
CRISPR spacers recognize and cut these exogenous genetic elements in a manner analogous to
RNA interference in eukaryotic organisms.[3] CRISPRs are found in approximately 40% of
sequenced bacteria genomes and 90% of sequenced archaea.[6][note 1]
The CRISPR interference technique has enormous potential application, including altering
the germline of humans, animals and other organisms, and modifying the genes of food
crops.
By delivering the Cas9 protein and appropriate guide RNAs into a cell, the organism's genome
can be cut at any desired location.[7][8][9] CRISPRs have been used in concert with specific
endonuclease enzymes for
genome
editing and gene regulation in species throughout the tree
of
life.[10] Ethical concerns have been expressed about this nascent biotechnology and the prospect
of
editing
the human germline.