CRISPR powers everything from gene editing to rapid diagnostics, but how did one of its most versatile branches arise? A new Cell study, “Functional RNA splitting drove the evolutionary emergence of type V CRISPR-Cas systems from transposons,” shows that an RNA-splitting event transformed transposons into Type V Cas12 immune systems.
Long before CRISPR became a clinical staple, it was a routine tool for microbiologists—workhorse enough to slip into undergraduate yeast labs and powerful enough to rewire entire genomes. In the decade since those early demonstrations, CRISPR technologies have revolutionized basic research and medicine. Scientists now use them to correct disease-causing mutations, create model organisms with unprecedented speed, and engineer crops that resist pests or survive drought. Diagnostic platforms such as SHERLOCK and DETECTR harness CRISPR enzymes to detect viral infections in minutes. Even gene drives aimed at controlling malaria-carrying mosquitoes rely on CRISPR’s precision.
Among CRISPR’s many variants, the compact Type V Cas12 enzymes—key players in genome editing, diagnostics, and even emerging base-editing approaches—stand out. Their small size also makes them attractive for therapeutic delivery, where every nucleotide counts, leaving researchers eager to trace their evolutionary roots.
Despite these advances, scientists had only hints of where Type V systems came from. Biochemists had long suspected a link to TnpB nucleases, proteins encoded by mobile genetic elements called IS200/605 transposons. These “jumping genes” move around bacterial genomes and were thought to be distant ancestors of Cas12. However, the molecular mechanisms bridging transposon activity and CRISPR immunity remained unclear, wrote the authors.
Research led by Caixia Gao, PhD, from the Institute of Genetics and Developmental Biology (IGDB) at the Chinese Academy of Sciences (CAS), with colleagues at Tsinghua University and the Institute of Zoology of CAS, has now filled in the missing pieces. By mining prokaryotic and metagenomic databases, the team uncovered 146 previously hidden relatives of TnpB. Phylogenetic analyses, AlphaFold structural predictions, and functional assays revealed six intermediate clades they dubbed “TranCs”—short for transposon-CRISPR intermediates.
These TranCs proved to be evolutionary hybrids. Like modern Cas12 proteins, they could use CRISPR RNAs (crRNAs) to find DNA targets. Yet they also retained the ancestral ability to work with transposon-derived right-end (re)RNAs, or ωRNAs. Cryo-EM snapshots of one system, LaTranC-sgRNA-DNA, showed why: its guide RNA had split into two parts—a tracrRNA and a crRNA—mirroring modern CRISPR architecture.
That seemingly subtle RNA split was transformative. Engineering experiments confirmed that artificially cleaving TnpB’s reRNA was enough to make it behave like a CRISPR system capable of drawing guides from a CRISPR array. In other words, RNA-level innovation—not a major protein redesign—sparked the emergence of the entire Type V branch.
Beyond satisfying evolutionary curiosity, the discovery points to practical opportunities. TranC enzymes are small and naturally flexible in the guides they accept, offering fresh templates for next-generation CRISPR tools that are easier to deliver and control.
As CRISPR continues to drive breakthroughs in medicine, agriculture, and synthetic biology, understanding its origins does more than tell an ancient story. It provides a blueprint for engineering the next wave of genome-editing technologies—reminding us that sometimes, a simple molecular split can change the course of biology.
