Site-specific replacement of large-scale DNA fragments in human cells

Despite advances in genome editing 1-4 , precisely replacing large-scale fragments in human cells remains a significant challenge. Here, we present a site-specific gene replacement tool, named Prime Assembly (PA), which adapts prime editors to produce one or two pairs of 3’-flaps on both the genome and donor plasmids. These 3’-flaps anneal to each other precisely, similar to “Gibson Assembly” in DNA oligonucleotides 5 , allowing megabase-scale genomic excision and/or kilobase-scale donor insertion at the gene of interest. The PA system achieves an efficiency of up to 57.8% in replacing endogenous sequences with a 2.9 kbp donor DNA fragment in HEK293T cells, and presents an accuracy of more than 99% for integrated PA fragments. Ultimately, the site-specific replacement of large-scale coding sequences (CDSs) in disease-related genes can restore gene function across numerous patients with different mutations, providing a gene implantation technique for genome editing and a universal therapeutic approach.