Cross-species analysis of the nuclease Artemis highlights its evolving function in domesticating RAG-like transposons and residues that are crucial for activity.

The discovery of the ProtoRAG transposon in lancelets revealed that V(D)J recombination originates from the Recombination activating gene-like (RAGL) transposon. Analogous to the vertebrate RAG complex, the RAGL transposase nicks host flanking DNA and leads to the formation of hairpin ends. Here, we showed that the Artemis nuclease, which is capable of resolving DNA hairpin ends generated during V(D)J recombination, is also responsible for unraveling ProtoRAG-mediated DNA hairpin ends. Notably, like the RAGL transposon, Artemis originated from the eukaryotic common ancestor. By tracing the evolving function of Artemis from cephalochordates to vertebrates, we revealed the lineage specific allele polymorphism of lancelet Artemis and uncovered an increased activity on hairpin DNA opening in vertebrate Artemis. Additionally, the evolutionarily conserved LYCS motif in Artemis β6, which may be associated with disease, is demonstrated to be crucial for its function. Overall, this study highlights the evolving function of Artemis, identifies novel critical residues, and provides new insights into the evolution of RAG-mediated recombination and the clinical therapy of Artemis deficient disease.