Detection of Dengue 4 Virus Core Protein in the Nucleus. I. A Monoclonal Antibody to Dengue 4 Virus Reacts with the Antigen in the Nucleus and Cytoplasm

A mouse monoclonal antibody (MAb) to dengue 4 (DEN-4) virus reacted with the antigen in the nucleus as well as in the cytoplasm of DEN-4-infected mammalian and mosquito cells, as demonstrated by the peroxidase-antiperoxidase staining method. The intranuclear antigen appeared to accumulate at the nucleoli, forming spots, whereas the cytoplasmic antigen appeared to be localized mainly in large perinuclear foci in the infected cells. The MAb-reactive antigen was produced in the presence of actinomycin D, which caused the accumulation in the nucleus to be altered to a dispersed pattern. Radioimmunoprecipitation analysis of [35S]methionine-labelled purified virions and Western blot analysis of the antigens prepared from the infected mammalian and mosquito cells showed that the MAb was directed against the DEN-4 virus core protein (Mr 15.5K). These results indicated that the DEN-4 virus core protein was partially transported, soon after its synthesis in the cytoplasm, into the nucleus and accumulated at the nucleoli.