Since the virus itself reduces Ub and ISG15 coupling to cell proteins, we wanted to confirm that the OTU domain is responsible for these decreased levels of conjugates in NSDV/ GV as it is for CCHFV. For these studies we used 293 cells, as those were the cells used in the studies on CCHFV proteins. We determined the level of ubiquitination in the presence of the GV L1-169 protein in 293FT cells and compared it to the level found in cells transfected with empty plasmid or with the CCHFV L1-354 protein (containing the OTU domain of CCHFV) (fig. 7c) . The CCHFV OTU-containing protein contains an HA tag and so appears in the same blots as the HA-Ub and HA-Ub conjugates. The CCHFV OTU completely abolished ubiquitination as previously shown [24] . The GV OTU was also effective in decreasing the levels of cellular Ub-conjugates, but was less effective compared to the CCHFV OTU domain. In the same way we investigated whether the OTU domain of NSDV/GV was responsible for the reduction in ISG15ylation. For this purpose we transfected 293FT cells with the core components of the ISG15 . 7d) . Expression of the GV OTU domain efficiently blocked conjugation of ISG15 to cellular proteins. The CCHFV OTU also blocked ISG15ylation in 293FT cells as already published [24] . Again the CCHFV OTU was more efficient than the GV OTU in reducing the amounts of ISG15conjugated proteins in the cell. Both virus isolates of NSDV are therefore able to decrease total cellular ubiquitination and ISG15ylation levels during infection. The GV OTU domain, when expressed alone, could reproduce these effects exerted by the virus during infection.