Complementation of the human adenovirus type 5 VA RNAI defect by the Vaccinia virus E3L protein and serotype-specific VA RNAIs

•The VACV E3L protein partially substitutes for HAdV-5 VA RNAI functions.•The E3L protein rescues HAdV-5 VA RNAI mutant virus capsid protein synthesis.•The E3L C-terminal region is needed to enhance HAdV-5 VA RNAI mutant virus growth.•HAdV-4 and HAdV-37 VA RNAI efficiently substitute for HAdV-5 VA RNAI functions.

Human adenoviruses (HAdVs) encode for multifunctional non-coding virus-associated (VA) RNAs, which function as powerful suppressors of the cellular interferon (IFN) and RNA interference (RNAi) systems. In this study we tested the ability of various plant and animal virus encoded RNAi and IFN suppressor proteins to functionally substitute for the HAdV-5 VA RNAI. Our results revealed that only the Vaccinia virus (VACV) E3L protein was able to substitute for the HAdV-5 VA RNAI functions in virus-infected cells. Interestingly, the E3L protein rescues the translational defect but does not stimulate viral capsid mRNA accumulation observed with VA RNA. We further show that the E3L C-terminal region containing the dsRNA-binding domain is needed to enhance VA RNAI mutant virus replication. Additionally, we show that the HAdV-4 and HAdV-37 VA RNAI are more effective than the HAdV-5 VA RNAI in rescuing virus replication.