Enrichment of Zα domains at cytoplasmic stress granules is due to their innate ability to bind to nucleic acids

Z_α domains recognize the left-handed helical Z conformation of double-stranded nucleic acids. They are found in proteins involved in the nucleic acid sensory pathway of the vertebrate innate immune system and host evasion by viral pathogens. Previously, it has been demonstrated that ADAR1 (encoded by ADAR in humans) and DAI (also known as ZBP1) localize to cytoplasmic stress granules (SGs), and this localization is mediated by their Z_α domains. To investigate the mechanism, we determined the interactions and localization pattern for the N-terminal region of human DAI (Z_αβ^DAI), which harbours two Z_α domains, and for a Z_αβ^DAI mutant deficient in nucleic acid binding. Electrophoretic mobility shift assays demonstrated the ability of Z_αβ^DAI to bind to hyperedited nucleic acids, which are enriched in SGs. Furthermore, using immunofluorescence and immunoprecipitation coupled with mass spectrometry, we identified several interacting partners of the Z_αβ^DAI–RNA complex in vivo under conditions of arsenite-induced stress. These interactions are lost upon loss of nucleic acid-binding ability or upon RNase treatment. Thus, we posit that the mechanism for the translocation of Z_α domain-containing proteins to SGs is mainly mediated by the nucleic acid-binding ability of their Z_α domains.