In this invention, the HNH domain of a Cas9 is replaced by a domain that could have diverse enzymatic activities. This invention enables engineering of Cas9 chimeras that possess novel, conformation-sensitive enzymatic activity to perform specific genome editing in vitro, in vivo, and ex vivo.
Prior to this invention, all of the strategies to engineer Cas9 fusion proteins and provide Cas9 with non-natural enzymatic activity for genome manipulations were engineered by fusing specific domains to the N- or C-terminus of Cas9 via long and flexible linkers, or through domain insertion approach. The disadvantages of these synthetic Cas9 chimeras are that the attached domain is on the long flexible linker, and it is very dynamic. Thus, these fusions have a broad activity window and they are large, which makes it difficult to deliver them to the cells.
This approach has several advantages such as the smaller size of engineered fusion, less off-targets, and narrower activity window because of conformational activation of the new domain upon a Cas9 interaction with the DNA target.