To know how quickly PKR downregulation occurred in MP-12infected cells, whole-cell extracts were prepared at 2, 4, 6 and 8 h.p.i. from MP-12-infected 293 cells and the amounts of NSs and PKR were determined ( Figure 7G ). In the absence of proteasome inhibitor, a substantial reduction of PKR abundance occurred as early as 4 h.p.i., where the abundance of NSs ( Figure 7G , lane 2) was not as great as that at 8 h.p.i. (Figure 7G , lane 4). In the presence of MG132, the abundance of PKR decreased only slightly, and NSs accumulation was also somewhat less efficient. A similar trend for less efficient NSs accumulation in the presence of proteasome inhibitors was also shown in the data for Figure 7F . Our observation of less efficient NSs accumulation in MG132-treated cells was consistent with the report that MG132 induces eIF2a phosphorylation through GCN2 activation and translational suppression [42] . The abundance of NSs in MG132treated cells at 8 h.p.i. and that in untreated cells at 4 h.p.i. was similar, and yet PKR abundance in the former cells was clearly higher than that in the latter cells. Taken together, these data strongly suggested that RVFV NSs promoted PKR degradation through the proteasome-dependent pathway.