On July 15-19, 2024, the largest congress Viruses of Microbes 2024 in the field of microbiology of viral infections was held in Cairns (Australia). On behalf of Skoltech, the head of the laboratory at the Center for Molecular and Cellular Biology Artem Isaev gave a presentation titled “Viral proteins activate PARIS-mediated tRNA degradation and viral tRNAs rescue infection,” which introduced the results of establishing the mechanism of action of the PARIS abortive immunity system and clarifying the role of viral tRNAs as anti-immune genes.

Viruses compete with each other for limited cellular resources, and some viruses deliver defense mechanisms that protect the host from competing genetic parasites. PARIS is a defense system, often encoded in viral genomes, that is composed of a 53 kDa ABC ATPase (AriA) and a 35 kDa TOPRIM nuclease (AriB). The researchers showed that AriA and AriB assemble into a 425 kDa supramolecular immune complex and used cryo-EM to determine the structure of this complex which explains how six molecules of AriA assemble into a propeller-shaped scaffold that coordinates three subunits of AriB. ATP-dependent detection of foreign proteins triggers the release of AriB, which assembles into a homodimeric nuclease that blocks infection by cleaving the host tRNA Lys. Phage T5 subverts PARIS immunity through expression of a tRNA Lys variant that prevents PARIS-mediated cleavage, and thereby restores viral infection.