The research presents programmable genome editing in human cells using RNA-directed bridging recombinases, specifically the ISCro4 recombinase from Citrobacter rodentium.[1][2][3] These IS110 family recombinases catalyze specific recombination between target and donor DNA via a bipartite RNA (bridge RNA) that contains a target binding loop (TBL) and a donor binding loop (DBL).[1][2][3] ISCro4 shows high activity in human cells when delivered via plasmids or RNA alone.[1][2][3] It enables programmable excision and inversion of multi-kilobase sequences, as well as insertion of donor DNA into the genome with an efficiency exceeding 6%.[1][2][3] The study provides structural insights into the enhanced activity of ISCro4 and evaluates its specificity and off-target activity.[1][2][3] The system allows manipulation of large genomic regions up to a million base pairs, including deletion of gene clusters or inversion of regulatory sequences.[4] Up to 20% insertion efficiency and up to 82% specificity were achieved after bridge RNA optimization and mutational analysis.[5] The results form the basis for the development of bridge recombinases as tools for advanced editing methods.[1][2][3]