Abstract
The influenza virus protein PA-X modulates the host immune responses and viral pathogenicity through suppression of host protein expression. The endonuclease active site in the N-terminal region, the basic amino acid cluster in the C-terminal PA-X-specific region, and N-terminal acetylation of PA-X by NatB are important for the shutoff activity of PA-X. Here, we focused on the shutoff activity of PA-X derived from the A/California/04/2009 and A/WSN/33 viruses because these two PA-X proteins differ in their shutoff activity. Mutagenesis analysis revealed that proline and serine at positions 28 and 65, respectively, play a central role in this difference. Furthermore, we found that P28 and S65 also affect the shutoff activity of PA-X derived from other influenza virus subtypes. These data demonstrate that P28 and S65 contribute to enhanced shutoff activity of PA-X.
Highlights
Influenza A virus protein PA-X is encoded in the PA segment and expressed via a ribosomal frameshift (Jagger et al, 2012)
To pinpoint the PA-X region that contributes to the different shutoff activity between CA04 PA-X and WSN PA-X, we constructed a series of chimeric PA-X proteins between CA04 PAX and WSN PA-X (Figure 1A)
Since PA-X suppresses its own expression via its shutoff activity (Oishi et al, 2015), the expression of each wild-type or chimeric PA-X was assessed by western blotting
Summary
Influenza A virus protein PA-X is encoded in the PA segment and expressed via a ribosomal frameshift (Jagger et al, 2012). It comprises the N-terminal amino acids of PA and the C-terminal PA-X-specific amino acids that result from the frameshift (Jagger et al, 2012). During the course of infection, PA-X inhibits host antiviral responses, such as the induction of IFN-β production and anti-viral antibody production in vivo (Hayashi et al, 2015; Hu et al, 2018; Nogales et al, 2018). Several studies have attempted to elucidate the role of PA-X in viral pathogenicity by using different subtypes of PA-X-deficient mutant viruses, its role in this process remains controversial (Jagger et al, 2012; Gao et al, 2015; Hayashi et al, 2015; Lee et al, 2017; Hussain et al, 2019)
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