Being frequently exposed to foreign nucleic acids, bacteria and archaea have developed an
ingenious adaptive defense system, called CRISPR-Cas. The system is composed of the
Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) array, together with
CRISPR (cas)-associated genes. This system consists of a complex machinery that
integrates fragments of foreign nucleic acids from viruses and mobile genetic elements
(MGEs), into CRISPR arrays. The inserted segments (spacers) are transcribed and then …