Identification of a novel nuclear localization signal of baculovirus late expression factor 11

•BmNPV LEF-11 could migrate to the nucleus in the absence of viral proteins.•We characterized a novel nuclear location signal at LEF-11 C-terminus.•Importin α-3 is required for the nuclear import of LEF-11.•LEF-11 co-localized with IE-1 at viral DNA replication sites in the nucleus.•Interaction of LEF-11 with LEF-3 and LEF-11 itself.

The baculovirus late expression factor 11 (LEF-11) has been reported to be involved in viral DNA replication and late/very late gene activation. In this study, serial N- and C-terminal truncations of Bombyx mori nucleopolyhedrovirus (BmNPV) LEF-11 protein were fused with DsRed to investigate the nuclear localization signal by which LEF-11 enters the nucleus. Results show that 72-101 residues at the C-terminus are essential for BmNPV LEF-11 nuclear localization. Sequence alignment of this NLS from multiple LEF-11 homologs revealed high conservation in general. Site-directed mutation analysis showed that five basic residue clusters, namely, K75/R76, H81, K83/R84, R87 and K100, were critical for the nuclear localization of BmNPV LEF-11. Co-IP analysis shows that LEF-11 binds directly to host importin α-3. Immunofluorescence analysis demonstrated that LEF-11 co-localizes with the immediate-early protein IE-1 at viral DNA replication sites in the nucleus. Further BiFC assays demonstrated the interaction of LEF-11 with LEF-3 and LEF-11 itself in the nucleus. Together, these results reveal a previous unknown mechanism for nuclear translocation of baculovirus LEF-11.