Identification of Spodoptera frugiperda importin alphas that facilitate the nuclear import of Autographa californica multiple nucleopolyhedrovirus DNA polymerase.

Proteins containing nuclear localization signals (NLSs) are actively transported into the nucleus via the classic importin-α/β-mediated pathway, and NLSs are recognized by members of the importin-α family. Most studies of insect importin-αs have focused on Drosophila to date, little is known about the importin-α proteins in Lepidoptera insects. In this study, we identified four putative importin-α homologues, Spodoptera frugiperda importin-α1 (SfIMA1), SfIMA2, SfIMA4 and SfIMA7, from Sf9 cells. Immunofluorescence analysis showed that SfIMA2, SfIMA4 and SfIMA7 localized to the nucleus, while SfIMA1 distributed in cytoplasm. Additionally, SfIMA4 and SfIMA7 were also detected in the nuclear membrane of Sf9 cells. SfIMA1, SfIMA4 and SfIMA7, but not SfIMA2, were found to associate with the C terminus of AcMNPV DNA polymerase (DNApol) that harbours a typical monopartite NLS and a classic bipartite NLS. Further analysis of protein-protein interactions revealed that SfIMA1 specifically recognizes the bipartite NLS, while SfIMA4 and SfIMA7 bind to both monopartite and bipartite NLSs. Together, our results suggested that SfIMA1, SfIMA4 and SfIMA7 play important roles in the nuclear import of AcMNPV DNApol C terminus in Sf9 cells.