CRISPR (/ ˈ k r ɪ s p ər /) is a family of DNA sequences in bacteria. The sequences contain snippets of DNA from viruses that have attacked the bacterium.
A major addition to the understanding of CRISPR came with Jansen's observation that the prokaryote repeat cluster was accompanied by a set of homologous genes that make up CRISPR-associated systems or cas genes. Four cas genes ( cas 1 to 4) were initially recognized. The Cas proteins showed helicase and nuclease motifs, suggesting a role in the dynamic structure of the CRISPR loci.  In this publication the acronym CRISPR was coined as the universal name of this pattern. However, the CRISPR function remained enigmatic.