RNA-guided transposases: the successors to CRISPR

Abstract

CRISPR undoubtedly transformed genome editing, but it left two crucial problems unsolved. Cas nucleases cut the chromosome and leave the cell to repair the break, an error-prone process that is inefficient for installing new DNA, and Cas9 is large relative to the cargo that viral vectors can carry for gene therapy. A new generation of genome editors derived from mobile genetic elements is emerging to address both issues, particularly from the bacterial transposons and insertion sequences colloquially known as ‘jumping genes’. Like CRISPR, these systems use short, programmable RNAs to locate their target sequence, but each new system offers distinct advantages. CRISPR-associated transposases (CASTs) insert whole genes at defined sites without double-stranded breaks, the compact TnpB and IscB nucleases are around a third of the size of Cas9 and fit well inside viral vectors for gene therapy delivery, IS110 bridge recombinases can insert, excise and invert DNA without scarring, and the newly discovered TIGR-Tas systems read their target with paired guide sequences for added precision. This review traces the origins of these tools in bacterial mobile genetic elements and how they edit DNA, what sets them apart from CRISPR, and their emerging uses across medicine, agriculture and microbial engineering.