NONSTRUCTURAL PROTEIN-2 AND THE REPLICATION OF CANINE PARVOVIRUS

The nonstructural protein-2 (NS2) of canine parvovirus (CPV) is produc ed from the left-hand open reading frame of the viral genome and conta ins 87 amino-terminal amino acids in common with nonstructural protein 1 (NS1) joined to 78 amino acids from an alternative open reading fra me. In the minute virus of mice parvovirus NS2 plays a role in control ling capsid protein assembly and translation in a host-specific manner . The predicted NS2 of CPV is divergent from the proteins of the roden t parvoviruses, and the protein and its functions have not been descri bed. We characterized the large and the small splices of CPV using rev erse transcriptase-PCR, NS2 was identified using anti-peptide antibodi es against the predicted C-terminal sequence and also by expressing th e protein from a plasmid vector. The protein could be detected at low levels in the nucleus and the cytoplasm of a proportion of CPV-infecte d cells, as well as in cells transfected with the expression plasmid. Virus genomes were prepared with mutations in the splice donor or acce ptor sites of the NS2-specific intron or with three different terminat ion codons in the NS2-unique exon. Both splice donor and acceptor muta tions resulted in the use of previously cryptic splice sites, and the virus containing the splice donor mutation replicated inefficiently. H owever, the other four mutant viruses were all viable and replicated e fficiently in cat and dog cells, and two mutant viruses that were test ed appeared to assemble their capsids in the same manner as did the wi ldtype. After inoculation of dogs an NS2 mutant virus with a terminati on codon in the NS2-unique exon replicated to titers similar to those seen for wildtype CPV in several tissues examined. (C) 1998 Academic P ress.