Nowak, C. M., et. al. (2016) Nucleic Acids Research http://nar.oxfordjournals.org/content/early/2016/10/12/nar.gkw908.full.pdf
The CRISPR/Cas9 system is composed of a nuclease, Cas9, and a guide RNA that directs Cas9. While various Cas9 modifications have been created, very few options of which Cas9 to use exist. In contrast, many guide RNA modifications have been proposed to help target Cas9 and decrease off-target effects. This review surveys the different guide RNA modifications and provides guidance on when to use each modification.