Fig. 1.

Schematic representation of the Crispr-Cas-adaptive immune response pathway in Prokaryotes. A Crispr locus showing crispr array, leader sequence, and Cas genes. B Three stages of Crispr-Cas pathway: as the viral genetic material is injected into the cell, cas1-cas2 complex identifies the PAM (protospacer adjacent motif) site and cleaves the protospacer sequence on the genetic material and integrates it into the host genome as spacer in Crispr loci (spacer acquisition). Pre-crRNA is transcribed from the Crispr array (expression) and processed to form mature crRNA, which binds to the Cas proteins forming an effector complex. When the same virus invades the cell, the crRNA-Cas protein recognizes and binds to the complementary sequence on the viral genome thereby cleaving it