Engineered minimal type I CRISPR-Cas system for transcriptional activation and base editing in human cells

Type I CRISPR-Cas systems are widespread and have exhibited remarkable versatility and efficiency in genome editing and gene regulation in prokaryotes. However, due to the multi-subunit composition and large size, their application in eukaryotes has not been thoroughly investigated. Here, we demonstrate that the type I-F2 Cascade, the most compact among type I systems and significantly smaller than SpCas9, can be developed into programmable tools for use in human cells. For transcriptional activation, the efficiency of the tool based on the engineered I-F2 system can match or surpass that of dCas9. Besides, narrow editing windows limit the application of base editors. Although the R-loop formed by Cascade is much wider than that by Cas9 or Cas12, the potential of base editing with Cascade has not yet been explored. We successfully created a base editor with the I-F2 Cascade, which induces a considerably wide editing window ([~]30 nt) with a bimodal distribution. The wide editing window can expand the range of targetable sites and can be useful for disrupting functional sequences and genetic screening. The editing efficiency can achieve 50% in human cells. This research underscores the application potential of compact type I systems in eukaryotes and developed a new base editor with an extraordinary wide editing window.