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

Z(alpha) 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(alpha) domains. To investigate the mechanism, we determined the interactions and localization pattern for the N-terminal region of human DAI (Z(alpha beta)(DAI)), which harbours two Z(alpha) domains, and for a Z(alpha beta)(DAI) mutant deficient in nucleic acid binding. Electrophoretic mobility shift assays demonstrated the ability of Z(alpha beta)(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(alpha beta)(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(alpha) domain-containing proteins to SGs is mainly mediated by the nucleic acid-binding ability of their Z(alpha) domains. This article has an associated First Person interview with Bharath Srinivasan, joint first author of the paper.