Comparison of the intranuclear distributions of herpes simplex virus proteins involved in various viral functions

Herpesviral transcription, DNA synthesis, and capsid assembly occur within the infected cell nucleus. To further define the spatial relationship among these processes, we have examined the intranuclear distributions of viral DNA replication, gene regulatory, and capsid proteins using dual label immunofluorescence and confocal microscopy. We observed that several of the viral DNA replication proteins localize preferentially to punctate structures within replication compartments while the major transcriptional activator, ICP4, and the ICP27 regulatory protein show a more diffuse distribution within replication compartments. The viral proteins that show a punctate distribution in replication compartments redistribute from these compartments to prereplicative sites when viral DNA replication is inhibited, whereas viral proteins that show a diffuse distribution remain within replication compartments when viral DNA replication is inhibited. Thus the sites of viral DNA replication and late transcription appear to be distinct but codistribute within the boundaries of replication compartments. The major capsid protein, ICP5, also localizes initially to a diffuse distribution within replication compartments, but during the time of maximal progeny virus assembly, ICP5 becomes localized to punctate structures within replication compartments that are often near the punctate structures occupied by viral DNA replication proteins. Hence the processes of viral DNA replication, late transcription, and capsid assembly show a general overlapping distribution within replication compartments but appear to be located at distinct sites within these regions of the infected cell nucleus.