Structural feature of type I CRISPR-Cas system and its application in gene editing

The CRISPR-Cas (clustered regularly interspaced short palindromic repeats and CRISPR-associated) system is an "adaptive immune system" found in the genomes of bacteria and archaea which is mediated by RNA and resists foreign nucleic acid invasion.Take advantage of specific recognition of target nucleic acid, CRISPR-Cas system can efficiently edit their target site or accurately regulate gene expression, and now have been developed into a powerful tool for gene editing.According to the different compositions of the effector complex, the system has been divided into two categories: class 1 (type I, type IV, and type III) and class 2 (type II, type V, and type VI).Class 2 system, like the CRISPR-Cas9, is widely used in basic research due to the earliest discovery and best research.However, class 1 has not been maturely developed and utilized though it makes up 90% of the entire CRISPR-Cas system.In this essay, the classification of subtype, the assembly of Cascade complex, the cleavage and degradation mechanism of Cas3, and the application in gene editing of class 1 type I CRISPR-Cas system will be discussed and summarized to provide new ideas and methods for further mechanism studying and application of this category.