Phosphorylation of the protamine-like protein from baculovirus affects its DNA binding and virus propagation

Viral DNA-binding proteins, a type of protamine-like protein, pack the viral genome and promote late viral gene expression. In baculovirus Autographa californica multiple nucleopolyhedrovirus, DNA-binding protein P6.9 plays a crucial role in the production of progeny viruses. Earlier studies suggested the importance of P6.9 phosphorylation states in its function, while the detailed mechanism remains elusive. Here, we demonstrated that permanent hypo- and hyper-phosphorylation on the N-terminus of viral P6.9 significantly inhibits the proliferation of progeny viruses. Our data revealed that phosphorylation changes the DNA binding affinity of P6.9, which determines the distinct localization of P6.9 in the host nucleus. Both viral and host gene expressions were largely up or downregulated by the phosphorylation states of P6.9, indicating the central role of P6.9 in governing the tempo of viral replication. Our work provides an intriguing model of how the phosphorylation/dephosphorylation dynamics of P6.9 regulate viral packaging and gene expression patterns, which sheds light on the general principle of viral-host interaction.