On the analogy of baculovirus and whispovirus DNA binding proteins

The baculovirus DNA-binding proteins P6.9 are involved in the condensation and packing of the dsDNA genome. These proteins are rich in arginines and serines, but differ in length among virus species and their phosphorylation status is important for DNA (un)coating. The binding of P6.9 to DNA is sequence aspecific, but specificity may be brought in through the interaction between P6.9 and other viral proteins in the virus assembly. To investigate this aspect a p6.9null Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) bacmid was generated, which upon transfection into Sf21 cells did not lead to production of infectious virus particles. This defect was rescued by the insertion of the Spodoptera exigua (Se)MNPV p6.9 gene into the bacmid. However when the DNA binding protein gene vp15 of the unrelated White Spot Syndrome Virus (WSSV) was inserted, no infectious virus particles could be produced. Despite the presence of predicted phosporylation sites, phosporylated VP15 could be detected neither in WSSV-infected shrimp tissue nor in baculovirus-infected insect cells. Thus, either DNA condensation and packing relies on different mechanisms in the different virus families or, in contrast to SeMNPV P6.9, WSSV VP15 is unable to have a specific interaction with some AcMNPV proteins involved in viral assembly.