CHARACTERIZATION OF A NUCLEAR-LOCALIZATION SIGNAL OF CANINE PARVOVIRUS CAPSID PROTEINS

We investigated the abilities of synthetic peptides mimicking the pote ntial nuclear localization signal of canine parvovirus (CPV) capsid pr oteins to translocate a carrier protein to the nucleus following micro injection into the cytoplasm of A72 cells. Possible nuclear localizati on sequences were chosen for synthesis from CPV capsid protein sequenc es (VP1, VP2) on the basis of the presence of clustered basic residues , which is a common theme in most of the previously identified targeti ng peptides. Nuclear targeting activity was found within the N-termina l residues 4-13 (PAKRARRGYK) of the VPI capsid protein. While replacem ent of Arg10 with glycine did not affect the activity, replacement of Lys6, Arg7, or Arg9 with glycine abolished it. The targeting activity was found to residue in a cluster of basic residues, Lys5, Arg7, and A rg9. Nuclear import was saturated by excess of unlabelled peptide conj ugates (showing that it was a receptor-mediated process). Transport in to the nucleus was an energy-dependent and temperature-dependent proce ss actively mediated by the nuclear pores and inhibited by wheat germ agglutinin.