The products of herpes simplex virus type 1 gene UL26 which are involved in DNA packaging are strongly associated with empty but not with full capsids.

We report on the properties of a family of related herpes simplex virus type 1 polypeptides (designated p40) of Mr around 40,000. The intracellular localization of these polypeptides has been examined using monoclonal antibodies and their association with viral capsids within the nuclei of infected cells has been demonstrated directly by immunoelectron microscopy. Specific DNA staining and the use of mutants defective for DNA packaging has revealed, in contrast to earlier findings, that p40 is present in empty capsids. Protein p40 is not present as a major component of full capsids or of mature virions indicating that it is transiently associated with capsids and that its removal from capsids is linked with the process of DNA packaging.