Identification of the non-structural influenza A viral protein NS1A as a bona fide target of the Small Ubiquitin-like MOdifier by the use of dicistronic expression constructs

The cellular SUMOylation system affects the function of numerous viral proteins. Hence, the identification of novel viral targets for the Small Ubiquitin-like MOdifier (SUMO) is key to our understanding of virus–host interactions. The data obtained in this study demonstrate that the non-structural influenza A viral protein NS1A is an authentic SUMO target through the use of a dicistronic expression plasmid containing SUMO (the modifier) and Ubc9 (the SUMO-conjugating enzyme) separated by an Internal Ribosomal Entry Site (IRES). This dual expression plasmid produces a robust increase in cellular SUMOylation, therefore facilitating the characterization of cellular and viral SUMO targets. The identification of NS1A as a bona fide SUMO target suggests, for the first time, a role for SUMOylation during influenza virus infection.