IDENTIFICATION OF THE SEQUENCES RESPONSIBLE FOR NUCLEAR TARGETING OF THE V-PROTEIN OF HUMAN PARAINFLUENZA VIRUS TYPE-2

In human parainfluenza virus type 2 (hPIV-2)-infected cells, anti-phos phoprotein (P)-specific monoclonal antibody (MAb) densely stained the perinuclear regions of infected cells throughout infection, indicating that the P protein was localized exclusively in the cell cytoplasm. B y contrast, antigens recognized by MAbs directed against the P-V-commo n domain of hPIV-2 were located predominantly in the cytoplasm, but in some hPIV-2-infected cells they were also found in the nuclei, sugges ting that a fraction of hPIV-2 V protein is localized there. hPIV-2 V protein expressed from a cDNA clone was localized in the nuclei of tra nsfected cells. By using indirect immunofluorescence analyses, we exam ined the intracellular localization of various sequentially deleted V proteins, to determine the nuclear localization signals (NLS) of the V protein. Two noncontiguous regions in the V protein were required for nuclear localization and retention, since deletion of these regions [ region I (aa 1-46) and region II (aa 175-196)] resulted in cytoplasmic localization. Both regions resulted in nuclear localization independe ntly. A nucleoplasmin-like NLS was identified in region II but no cons ensus targeting sequence could be found in region I. When NP protein w as co-expressed with V protein or the N-terminal fragment (aa 1-46) of V protein, a fraction of the NP protein was translocated into cell nu clei.