The invention relates to the field of genetic engineering tools, methods and techniques for gene or genome editing. Specifically, the invention concerns isolated polypeptides having nuclease activity, host cells and expression vectors comprising nucleic acids encoding said polypeptides as well as methods of cleaving and editing target nucleic acids in a sequence-specific manner. The polypeptides, nucleic acids, expression vectors, host cells and methods of the present invention have application in many fields of biotechnology, including, for example, synthetic biology and gene therapy.