A fish herpesvirus highlights functional diversities among Z alpha domains related to phase separation induction and A-to-Z conversion

Abstract

Zalpha (Z alpha) domains bind to left-handed Z-DNA and Z-RNA. The Z alpha domain protein family includes cellular (ADAR1, ZBP1 and PKZ) and viral (vaccinia virus E3 and cyprinid herpesvirus 3 (CyHV-3) ORF112) proteins. We studied CyHV-3 ORF112, which contains an intrinsically disordered region and a Z alpha domain. Genome editing of CyHV-3 indicated that the expression of only the Z alpha domain of ORF112 was sufficient for normal viral replication in cell culture and virulence in carp. In contrast, its deletion was lethal for the virus. These observations revealed the potential of the CyHV-3 model as a unique platform to compare the exchangeability of Z alpha domains expressed alone in living cells. Attempts to rescue the ORF112 deletion by a broad spectrum of cellular, viral, and artificial Z alpha domains showed that only those expressing Z-binding activity, the capacity to induce liquid-liquid phase separation (LLPS), and A-to-Z conversion, could rescue viral replication. For the first time, this study reports the ability of some Z alpha domains to induce LLPS and supports the biological relevance of dsRNA A-to-Z conversion mediated by Z alpha domains. This study expands the functional diversity of Z alpha domains and stimulates new hypotheses concerning the mechanisms of action of proteins containing Z alpha domains.