NUCLEAR TARGETING ACTIVITY ASSOCIATED WITH THE AMINO-TERMINAL REGION OF THE BORNA-DISEASE VIRUS NUCLEOPROTEIN

The Borna disease virus (BDV) replicates in the nucleus. The viral p40 protein (N), which is found abundantly in the nucleus in BDV-infected cells, may play an important role in virus replication. To analyze th e amino acid residues involved in the nuclear targeting of BDV N, a se ries of eukaryotic expression plasmids encoding deletion mutants of N was constructed and transfected into COS-7 cells. In indirect immunofl uorescence assays with a rabbit anti-BDV N antiserum, wild-type N was located in the nucleus of transfected cells in the absence of other vi ral constituents. In contrast, mutants tacking the 13 NH2-terminal ami no acid residues (1)MPPKRRLVDDADA(13) in common gave a cytoplasmic loc alization pattern. Similarly, a mutant with substitution of 4KRR6 by ( 4)NSG(6) was retained in the cytoplasm. Furthermore, a nonapeptide, (3 )PKRRLVDDA(11), derived from the NH2-terminal region of N conferred nu clear targeting activity to beta-galactosidase, which normally resides in the cytoplasm. Thus, we have identified the nuclear targeting sign al of the BDV N and narrowed it to the NH2-terminal region where 4KRR6 basic amino acid residues are located. (C) 1998 Academic Press.