Preferential virosomal location of underphosphorylated H5R protein synthesized in vaccinia virus-infected cells.

The phosphorylation state of vaccinia virus (VV) protein H5R synthesized in infected cells was investigated by two-dimensional gel electrophoresis. Most of the H5R protein was underphosphorylated (pI 5.9 to 6.8) and, on centrifugation of cell lysates, was associated with virosomes sedimenting with nuclei. However, about a quarter of the H5R protein synthesized was highly phosphorylated (pI 5.5), and this was the major form of the H5R protein present in cytoplasmic extracts. Immunofluorescence of VV-infected cells in the absence of DNA replication showed that underphosphorylated H5R protein, specifically recognized by antibody, was abundantly distributed throughout the cytoplasm but also present in punctate particles, whereas most of the B1R protein detected was in the punctate particles. Late gene expression was not required for the H5R protein to accumulate in virosomes--viral DNA synthesis was sufficient. The different phosphorylation states and cytological locations of the H5R protein suggest it has multiple roles in VV development.