Prkra dimer senses double-stranded RNAs to dictate global translation efficiency

Double-stranded RNAs (dsRNAs), known as conserved pathogen-associated molecular patterns, are recognized by interferon-induced protein kinase R (PKR) to trigger an integrated stress response, characterized by the inhibition of global translation. However, the interferon system is inactive in pluripotent cells, thus the mechanism underlying dsRNA sensing and translational control is unclear. In this study, we utilized early zebrafish embryos as a model of pluripotent cells and discovered a PKR-independent blockage of translation initiation induced by dsRNA stimulation. Prkra dimer was identified as the genuine dsRNA sensor. Upon binding to dsRNAs, the dimerized dsRNA binding domain 3 becomes activated to sequester the eIF2 complexes from the translation machinery, leading to a hindrance in global protein synthesis. This distinctive embryonic stress response restricts RNA virus SVCV replication in zebrafish embryos but is also conserved in early mouse embryos and embryonic stem cells. Therefore, the Prkra-mediated dsRNA sensing and translation blocking mechanism potentially represents a common strategy for reestablishing physiological homeostasis in response to environmental stresses.