LEF-6 phosphorylation regulates the binding and trafficking of baculovirus late gene transcripts

The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) LEF-6 has been shown to accelerate the infection cycle of AcMNPV, but its specific function is yet to be defined. In the present study, we identify LEF-6 as an RNA-binding protein that preferentially interacts with viral late transcripts. We demonstrate that the N-terminal half of LEF-6, which contains two typical ribonucleoprotein (RNP) motifs, is responsible for RNA binding, but its C-terminal half is required for the binding specificity to viral RNAs and for fulfilling its function in promoting virus infection. Further investigations reveal that LEF-6 has eight phosphorylated sites, and seven of them are located in the C-terminal half of LEF-6. The phosphorylation of LEF-6, especially the modification on the key site of S95, plays an important role in the binding and trafficking of viral late transcripts into the cytoplasm in baculovirus infection. These findings suggest that LEF-6 facilitates baculovirus infection through recognition and nuclear export of viral late mRNAs for protein translation.IMPORTANCEAcMNPV is the most well-studied baculovirus. As the viral vector in baculovirus expression vector system (BEVS), it has been widely used for the production of proteins in the basic research and pharmaceutical industry. In this study, we found that phosphorylated LEF-6 acted as a viral mRNA-binding and trafficking protein to accelerate the translation of viral late proteins and subsequently benefit baculovirus infection. The RNA-binding domain, nuclear localization signal motif, and phosphorylation sites of LEF-6 were determined. Our findings can help elucidate the roles of LEF-6 in baculovirus infectious cycle and improve the BEVS for protein production.