CRISPR is an adaptive immune system in prokaryotes, where RNA-guided nucleases silence foreign bacteriophage or viral nucleic acids. It has since evolved into the widely-used CRISPR/Cas gene editing technology, applicable to both prokaryotes and eukaryotes. CRISPR-Cas systems are categorized into two classes based on the Cas proteins in the crRNA-effector complex. Class I CRISPR-Cas systems function with multi-protein effector complexes and are subdivided into three types and 12 subtypes. Class II systems require a single Cas effector protein to recognize and cleave foreign nucleic acids and are divided into three types and nine subtypes.

The simplicity of Class II systems has attracted significant attention, with CRISPR-Cas9 being a type II system (type II-A), CRISPR-Cas12a (Cpf1) classified as type II-V, and CRISPR-Cas13a as type II-VI. Cas9 and Cas12 are extensively used in DNA editing, while Cas13 plays an important role in RNA regulation. Cas13 has been applied to transcriptome engineering, virus interference, nucleic acid detection, and RNA imaging.