CRISPR (Clustered regularly interspaced short palindromic repeats) were discovered in prokaryotic DNA (E.coli) in 1987 (Ishino Y, Shinagawa H, Makino K, Amemura M, Nakata A, 1987). They contain short repetitions of base sequences (repeats). Further research revealed that the sequences of repeats in Bacteria chromosomes are interspaced with sequences derived from viruses.
Cas9 (CRISPR-associated protein 9) 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. CRISPR and Cas9 together form the basis of the CRISPR/Cas method for the production of genetically modified organisms (Zhang F, Wen Y, Guo X, 2014).
Zhang, Wen, Guo: "CRISPR/Cas9 for genome editing: progress, implications and challenges." in: Human molecular genetics, Vol. 23, Issue R1, pp. R40-6, (2015) (PubMed).
Ishino, Shinagawa, Makino, Amemura, Nakata: "Nucleotide sequence of the iap gene, responsible for alkaline phosphatase isozyme conversion in Escherichia coli, and identification of the gene product." in: Journal of bacteriology, Vol. 169, Issue 12, pp. 5429-33, (1988) (PubMed).