Characterization of the nuclear localization signals of duck circovirus replication proteins

Duck circovirus (DuCV) possess a circular, single-stranded DNA genome that requires the replication protein (Rep) for its replication. Based on the viral genotype, there are two categories of Rep proteins: Repl and Rep2. To characterize the nuclear localization signals (NLSs) conferring the nuclear localization of the Rep proteins, defined coding regions of the rep gene of two genotypes of DuCV were cloned and co-expressed with the red fluorescent protein DsRed2. The results showed that deleting the putative N-terminal NLS located at amino acid residues 10-37 of Repl and Rep2 abrogated nuclear translocation, while deleting the putative C-terminal NLS located at residues 244-274 of Repl did not significantly alter its subcellular localization, confirming that only the NLS located at residues 10-37 in the N-termini of the Rep proteins had nuclear targeting activity.