Properties of the Major Nucleocapsid Protein of Heliothis zea Singly Enveloped Nuclear Polyhedrosis Virus

Abstract

SUMMARYThe major nucleocapsid protein of Heliothis zea single nucleocapsid nuclear polyhedrosis virus is a low mol. wt., basic, DNA-binding protein present in the core of the capsid. It is rich in arginine and helix-destabilizing residues and possesses no lysine nor hydrophobic residues. Circular dichroism analysis showed that the protein undergoes a major conformational change in high salt solutions involving the tyrosine side chains. There is sufficient of this protein in the nucleocapsid for all the genome phosphate to be neutralized by arginine residues. A comparison of the protein with similar basic proteins from Spodoptera litura granulosis virus, Oryctes rhinoceros nonoccluded baculovirus, and Trichoplusia ni multiple nucleocapsid nuclear polyhedrosis virus showed that they are all arginine-rich, lysine-poor, DNA-binding proteins.

Specificity of Baculovirus P6.9 Basic DNA-Binding Proteins and Critical Role of the C Terminus in Virion Formation

“…Baculovirus P6.9 plays an important role in condensing the viral genome in the nucleocapsid (14,22,28). The binding of these small, positively charged proteins to DNA seems not to be sequence specific (22).…”

“…Playing a functionally similar role, baculovirus P6.9 is a small, heterogeneous arginine-and serine-rich protein, ranging from 49 to 109 aa ( Fig. 1C; see also the supplemental material), that, in its dephosphorylated form, is believed to bind to and condense viral DNA during nucleocapsid assembly and virion packaging (14,22,28,54) in an apparently sequence independent manner (22). In this study, we investigated whether P6.9 might contain domains that interact with other components specific to the species or genus during viral assembly.…”

“…Evidence indicates that P6.9 is prevented from binding to DNA as a result of posttranslational phosphorylation of arginine and serine residues (23,53,54). Upon viral assembly in the host nucleus, P6.9 is dephosphorylated, promoting DNA binding and enabling condensation of the viral genome and packaging into the viral nucleocapsid (14,22,28). In a newly infected cell, and following rephosphorylation by a capsid-associated kinase, P6.9 dissociates from the viral DNA, thereby releasing the viral genome into the nucleus (14,42,54).…”

“…The binding of P6.9 to DNA is apparently species independent, as evidenced by the facts that Heliothis zea single nucleopolyhedrovirus (HezeNPV) P6.9 can bind -DNA (22) and the P6.9 homolog VP15 of the unrelated white spot syndrome virus (WSSV) is able to bind Autographa californica multiple nucleopolyhedrovirus (AcMNPV) DNA (56). Although DNA binding by P6.9 exhibits a degree of species and sequence independence, we were interested in learning whether P6.9 possesses any species specificity for overall virion formation.…”

The Baculoviral Genome

“…A small basic protein, P6.9, directly interacts with DNA and is involved in the assembly of highly condensed DNA (Kelly et al, 1983). VP39 is the major nucleocapsid protein and, along with P6.9, is a core gene.…”