Identification of a virus-specified protein in the nucleus of vaccinia virus-infected cells

A new protein has been detected in the nuclei of vaccinia virus-infected cells. This protein has an apparent mol. wt. of 28000 (VP28) on SDS--polyacrylamide gels and has been detected in Triton X-100-treated nuclei of infected BSC-40, L-929 and CVC cells. Within the infected cells, VP 28 was synthesized maximally at 1 to 2 h p.i. in the cytoplasm and accumulated in the nuclei at 4 to 5 h p.i. The appearance of VP28 was not affected by cytosine arabinoside (25 microgram/ml), an inhibitor of virus DNA synthesis, or rifampicin (100 microgram/ml), an inhibitor of vaccinia assembly, but was inhibited by irradiation of the infecting virions; thus classifying it as an early vaccinia virus gene product. Nuclear--cytoplasmic mixing experiments suggested that the nuclear location of VP28 was not an artefact of the cell fractionation techniques employed. VP28 did not appear to be phosphorylated.