IFI207, a young and fast-evolving antiviral factor, stabilizes STING.

Mammalian ALR proteins bind nucleic acids and initiate production of type I interferons or inflammasome assembly, thereby contributing to host innate immunity. s are encoded at a single genetic locus. In mice, the locus is highly polymorphic at the sequence and copy number level. We suggest that one rapidly evolving member of the family, , was introduced to the genome by a recent recombination event. has a large, distinctive repeat region that differs in sequence and length in different strains. We show that IFI207 plays a key role in the STING-mediated response to cGAMP, DNA, and MLV, and that IFI207 controls MLV infection in vivo. Uniquely, IFI207 acts by stabilizing STING protein via its repeat region. Our studies suggest that under the pressure of host-pathogen coevolution, in a dynamic locus such as the , recombination between gene family members creates new genes with novel and essential functions that play diverse roles in biological processes.