Although many viruses suppress PKR function using various strategies [32] , poliovirus is known to promote PKR degradation in infected cells [60, 61] ; poliovirus RNA and viral protein components are required for this activity [61] , and both eIF2a and PKR are highly activated in poliovirus-infected cells before PKR downregulation occurs [60] . In contrast to poliovirus, only RVFV NSs protein was probably required for PKR downregu-lation since the downregulation of PKR occurred as early as 4 h.p.i. in RVFV-infected cells ( Figure 7G ), whereas phosphorylated eIF2a accumulation occurred around 8 h.p.i. in rMP-12-rLuc-infected cells in the presence of ActD (Figure 4 ). Furthermore, NSs downregulated PKRK296R, a non-phosphorylatable mutant PKR ( Figure 7E ). These data suggest that the phosphorylation of PKR was not essential for the NSs-mediated PKR downregulation.