Another novel finding is that all of truncation mutants; i.e., NSD6-30, NSD31-55, NSD56-80, NSD81-105, NSD106-130, NSD131-155, NSD156-180, NSD181-205, NSD206-230, NSD231-248 and NSD249-265, had lacked both PKR degradation and IFN-b suppression functions. This suggests that conformation structure might be important for those NSs functions rather than the presence of linear domain. Our results suggest that those truncated NSs decrease accumulation level, and change the localization pattern in cells. The stability and cellular localization of NSs, which are probably controlled by conformational domain, might be important for biological functions of NSs. Although the C-terminus 17 amino acids were determined as a self-association domain important for filament formation [65] , our result suggests that filament formation does not occur by NSs encoding an in-frame truncation with 25 amino acids. It is possible that the C-terminus 17 amino acids are the prerequisite of NSs self-association, and other structural domains play a role in the filament formation through the C-terminus domain.