The product of the US10 gene of herpes simplex virus type 1 is a capsid/tegument-associated phosphoprotein which copurifies with the nuclear matrix

We have identified the herpes simplex virus type 1 (HSV-1) US10 gene product using rabbit polyclonal antisera raised against a recombinant 6xHis-US10 fusion protein expressed in Escherichia coli. The antiserum reacted specifically with 34 and 36 kDa proteins in HSV-1 KOS-infected cells as shown by Western blotting and immunoprecipitation experiments. The 36 kDa protein was immunoprecipitated with the US10 antiserum from ³²P-labelled lysates of Vero cells infected with HSV-1 KOS, demonstrating that the US10 protein was phosphorylated. Indirect immunofluorescence studies localized the US10 protein mainly to nuclei as large discrete particles at later times post-infection (p.i.), and nuclear fractionation studies revealed that the protein was tightly associated with the nuclear matrix. Moreover, analysis of isolated intracellular capsids showed that both phosphorylated and unphosphorylated forms of the US10 product were also associated with the capsid/tegument. These results indicate that the US10 gene of HSV-1 encodes a capsid/tegument-associated phosphoprotein which copurifies with the nuclear matrix.