The roles of CRISPR-Cas systems in adaptive immunity and beyond

Clustered regularly interspaced short palindromic repeats (CRISPR) and accompanying Cas proteins constitute the adaptive CRISPR-Cas immune system in bacteria and archaea. This DNA-encoded, RNA-mediated defense system provides sequence-specific recognition, targeting and degradation of exogenous nucleic acid. Though the primary established role of CRISPR-Cas systems is in bona fide adaptive antiviral defense in bacteria, a growing body of evidence indicates that it also plays critical functional roles beyond immunity, such as endogenous transcriptional control. Furthermore, benefits inherent to maintaining genome homeostasis also come at the cost of reduced uptake of beneficial DNA, and preventing strategic adaptation to the environment. This opens new avenues for the investigation of CRISPR-Cas systems and their functional characterization beyond adaptive immunity.