Spodoptera frugiperda mRNA export factor interacts with and mediates the nuclear import of autographa californica multiple nucleopolyhedrovirus ORF34 (Ac34).
Autographa californica multiple nucleopolyhedrovirus orf34 (ac34) is one of the unique genes of alphabaculoviruses. For successful alphabaculovirus replication, viral proteins must be transported to the nucleus. Our previous study showed that the nuclear localization of Ac34 was required for optimal production of budded virions. To investigate the mechanism of Ac34 nuclear import, mass spectrometric analysis was performed to identify potential proteins that may be involved in the nuclear import of Ac34. The result indicated that Spodoptera frugiperda mRNA export factor (SfMEF) may interact with Ac34 during baculovirus infection. Co-immunoprecipitation assays confirmed that Ac34 could interact with SfMEF in the absence of other baculovirus proteins. The deletion of ac34 did not affect the subcellular localization of SfMEF; however, knocking down Sfmef prevented the nuclear import of Ac34 in virus-infected cells. The mutations of C116 or C119 in a potential CCCH zinc finger motif (C116-X2-C119-X8-C128-X2-H131) of Ac34 led to an exclusive cytoplasmic distribution of Ac34, in consistent with our previous finding of mutations of C128 or H131 in this motif. Co-immunoprecipitation analysis showed that the above mutations in the potential zinc finger motif disrupted the interaction between Ac34 and SfMEF, and the loss of the interaction resulted in decreased BV production. Our findings demonstrated that SfMEF interacts with and mediates the nuclear import of Ac34, which is a new nucleocytoplasmic transport pathway used by alphabaculovirus to achieve successful viral replication within the nucleus of the infected cells.