Evolution and molecular mechanism of CRISPR/Cas9 systems.

CRISPR/Cas module is an RNA-guided adaptive immune system, provides sequence-specific immunity against phages and (conjugative)plasmids. CRISPR/Cas system is basically categorized into three types: (type I, II and III), on the basis of effector complexes. CRISPR/Cas9 system is repercussion of evolutionary everlasting arm race between bacteria and phages. Molecular mechanism underlying the CRISPR system entails three distinct mechanistic stages: spacer acquisition, crRNA biogenesis and interference. CRISPR/Cas9 system composed of a combination of Cas9 (an endonuclease)and a customizable single guide RNA (sgRNA), the later directs the Cas9 for recognition and degradation of invading DNA. Furthermore, Cas9 and their ilk proteins with unique properties have opened a plethora of options including DNA/RNA genome targeting, transcription/translation regulation and empower researchers to edit genes with highly precision and speed.