Acetylation of late expression factor 4 is crucial for the transcription and proliferation of Bombyx mori nucleopolyhedrovirus

Abstract

Late expression factor 4 (LEF4), RNA polymerase subunit of Bombyx mori nucleopolyhedrovirus (BmNPV), plays an enzymatic role to enhance the capping of pre-mRNA of late and very late genes. Lysine acetylation is apost-translational modification process having many important functions associated with the regulation of agene expression. Our previous study on lysine acetylome in BmNPV infected BmN cells showed that LEF 4 was acetylated at lysine 76 (K76). However, it is still unclear whether the modification of K76 residue contributes to the modulation of viral gene transcription. To elucidate the role played by acetylation or deacetylation of LEF4 K76 in the transcription of viral genes, we constructed acetylation mimicking and deacetylation mimicking mutant virus, K76Q and K76R, respectively. We then transfected BmN cells with these mutants and analyzed the level of pre-mRNA at different times. The K76R showed asignificant decrease in the mRNA transcription level of vp39 and p10 genes at 48 and 72h post-transfection, while K76Q did not show any significant changes compared with lef4-Wt. We further detected the virus titer of lef4-Wt, K76Q [et] K76R, and it was found that K76R impaired the virus infectivity ability at 72 and 96h, while K76Q did not affect the virus infectivity. Moreover, the yeast two hybrid technique (Y2H) showed that both mutants (K76Q [et] K76R) affected the association of LEF 4 with the P47 protein. Taken together, these results indicated that acetylation modification of K76 is important for the proper transcription of late and very late genes, and the effectiveness of viral infection. Keywords: BmNPV lef4 gene; lysine acetylation, late genes transcription; BmNPV p47 gene; infectivity.