Nucleocapsid protein VP15 is the basic DNA binding protein of white spot syndrome virus of shrimp.

White spot syndrome virus (WSSV) is type species of the genus Whispovirus of the new family Nimaviridae. Despite the elucidation of its genomic sequence, very little is known about the virus as only 6% of its ORFs show homology to known genes. One of the structural virion proteins, VP15, is part of the nucleocapsid of the virus and shows homology to some putative baculovirus DNA binding proteins. These DNA-binding or histone-like proteins are thought to be involved in the condensation and packaging of the genome in the nucleocapsid. Using bacterially expressed VP15 fusion proteins in ELISA and Far-Western experiments showed that VP15 interacts with itself, forming homomultimers, but not with the other major structural proteins of the WSSV virion. Antibodies against phosphorylated proteins revealed that VP15 originating from different sources was not phosphorylated. WSSV VP15 binds non-specifically to double-stranded DNA, but has a clear preference to supercoiled DNA suggesting that VP15 is involved in the packaging of the WSSV genome in the nucleocapsid. This research shed further light on the composition of WSSV virions and the function of one of its nucleocapsid proteins.