AcMNPV PKIP is required for hyperexpression of very late genes and involved in the hyperphosphorylation of the viral basic protein P6.9

Abstract A previous study showed that a mutation in Autographa californica multiple nucleopolyhedrovirus pkip (ac24) led to severe defects in progeny budded virion (BV) production and very late gene transcription at non-permissive temperature. To dissect the underlying mechanism, our early study showed that PKIP is associated with nucleocapsid of BV and involved in nucleocapsid assembly. However, how pkip affects very late gene transcription has not been determined. In the present study, double-stranded RNA was used to silence pkip expression during virus infection, resulting in the significant reduction of occlusion body production and polyhedrin expression. To find out whether PKIP regulates polyhedrin expression by affecting the transcription of other viral genes for very late gene expression, a comparative transcriptome analysis of viral genes was performed by RNA sequencing and the result showed that silencing pkip specifically down-regulated transcription of very late genes, while the transcription patterns of the viral genes associated with very late gene transcription were not affected. Since PKIP was reported to interact with and stimulate the activity of virus-encoded protein kinase PK1 and PK1 was involved in the hyperphosphorylation of viral basic protein P6.9, which was required for the maximal hyperexpression of very late genes, we sought to determine the association between PKIP and P6.9. Further experiments showed that PKIP interacted with P6.9 during virus infection, and the deletion of pkip resulted in decreased hyperphosphorylation of P6.9. Taken together, our results indicated that PKIP is involved in hyperphosphorylation of P6.9, which in return maybe required for hyperexpression of very late genes.