We attempted to allow accumulation of MP-12 NSs by using 293 cells. Cells were mock-infected or infected with rMP12-NSs-Flag, which encode Flag-tagged NSs in place of intact NSs, at an moi of 3, and subsequently mock-transfected (a control) or immediately transfected with in vitro synthesized RNA encoding CAT (a control), or NSs mutants, as described previously [17] . Cells were collected at 16 hpi, and the abundance of PKR and RVFV proteins were analyzed by Western blot. All cells infected with rMP12-NSs-Flag accumulated abundant levels of NSs (Fig. 5A) . PKR was degraded in infected cells mock-transfected or transfected with CAT RNA, while PKR was also degraded in infected cells transfected with RNA encoding NSD6-30, NSD31-55, NSD56-80, NSD81-105, NSD106-130, NSD131-155, NSD156-180, NSD181-205, NSD206-230 or NSD231-248. On the other hand, the expression of NSD249-265 lacking the Cterminus self-association domain slightly increased the abundance of PKR in cells infected with rMP12-NSs-Flag.