Restoration of replication-defective dengue type 1 virus bearing mutations in the N-terminal cytoplasmic portion of NS4A by additional mutations in NS4B
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Flavivirus NS4A has an N-terminal hydrophilic cytoplasmic portion; however, the role of this portion remains poorly understood. In this study, we show that a recombinant dengue type 1 virus (DENV-1) in which a subportion (amino acids 27–34) of the N-terminal portion of NS4A is replaced by the corresponding region from Japanese encephalitis virus (JEV) is defective in replication. Using the defective mutant clone NS4A(27–34JEV), we recovered suppressor mutant viruses that carry various non-synonymous mutations. Site-directed mutational analysis indicated that a single non-synonymous mutation in NS4B that is found in the suppressor viruses is sufficient to restore NS4A(27–34JEV). Recombinant DENV-1 with single mutations in NS4B had increased growth properties as compared to the wild-type virus and NS4A(27–34JEV) virus bearing the same NS4B mutation. Collectively, our results suggest that the NS4B mutation enhanced the growth of DENV-1, irrespective of the sequence of the 27–34 subportion NS4A.
KeywordsWest Nile Virus Vero Cell Japanese Encephalitis Virus Dengue Haemorrhagic Fever Replication Complex
This work was partially supported by grants for the Research on Emerging and Re-emerging Infectious Diseases from the Ministry of Health, Labour, and Welfare (H20-Shinkou-ippan-003, H20-Shinkou-ippan 015, and H20-Iyaku-ippan-077) and a Grant-in-Aid for Scientific Research (C) (22590423) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.
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