FTSJ3 is an RNA 2′- O -methyltransferase recruited by HIV to avoid innate immune sensing

In mammals, 2′- O -methylation of RNA is a molecular signature by which the cellular innate immune system distinguishes endogenous from exogenous messenger RNA 1 – 3 . However, the molecular functions of RNA 2′- O -methylation are not well understood. Here we have purified TAR RNA-binding protein (TRBP) and its interacting partners and identified a DICER-independent TRBP complex containing FTSJ3, a putative 2′- O -methyltransferase (2′ O -MTase). In vitro and ex vivo experiments show that FTSJ3 is a 2′ O -MTase that is recruited to HIV RNA through TRBP. Using RiboMethSeq analysis 4 , we identified predominantly FTSJ3-dependent 2′- O -methylations at specific residues on the viral genome. HIV-1 viruses produced in FTSJ3 knockdown cells show reduced 2′- O -methylation and trigger expression of type 1 interferons (IFNs) in human dendritic cells through the RNA sensor MDA5. This induction of IFN-α and IFN-β leads to a reduction in HIV expression. We have identified an unexpected mechanism used by HIV-1 to evade innate immune recognition: the recruitment of the TRBP–FTSJ3 complex to viral RNA and its 2′- O -methylation.