In Western blot as shown in Fig. 2A , all NSs mutants, except for NSD249-265, could be detectable by using anti-RVFV mouse polyclonal antibody. It was possible the anti-RVFV polyclonal antibody does not sufficiently contain antibodies reactive to linear epitopes except for the C-terminus. Thus, we next tested the accumulation of NSD249-265 by using indirect immunofluorescent assay to know if the same anti-RVFV polyclonal antibody can recognize conformational epitopes on NSD249-265. 293 cells were transfected with in vitro synthesized RNA encoding NSs of MP-12, NSD249-265 or chloramphenicol acetyltransferase (CAT) (control), and the cells were fixed with methanol at 16 hours post transfection. Nuclear filamentous inclusion was observed in cells expressing NSs of MP-12 or NSD249-265, while the specific signals of NSs accumulation were weaker in cells expressing NSD249-265 than those expressing MP-12 NSs (Fig. 3) . NSD249-265 was also accumulated in cytoplasm.