Initial characterization of the membrane-associated form of ICP4 of herpes simplex virus type 1

The immediate-early gene product, ICP4, of herpes simplex virus type 1 (HSV-1) is one of the major transcriptional regulatory proteins in the virus replicative process and is localized primarily within the nucleus soon after its synthesis. Earlier studies have shown that detectable amounts of ICP4 are also associated with the plasma membranes of infected cells (F. Yao and R. J. Courtney, J. Virol. 65:1516-1524, 1991). To extend our understanding of the properties of the membrane-associated ICP4, we have used various electrophoretic techniques, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two-dimensional gel electrophoresis, and isoelectric focusing, to compare the membrane- and nuclear-associated forms of ICP4. The data from all of these methods revealed that a single unique form of ICP4 associates with plasma membranes of HSV-1-infected cells. While multiple forms of ICP4 were detected in infected cell nuclei, the membrane-associated form of ICP4 appeared to have a lower apparent molecular weight and a more acidic pI than the various forms of ICP4 found in infected cell nuclei. These results suggest that a novel form of ICP4 may associate with plasma membranes of HSV-1-infected cells. A recombinant adenovirus, AdICP4 (encoding an ICP4 protein), was used to determine the role that other herpesvirus proteins may play in the membrane association of ICP4. The results suggest that the expression of other HSV-1 proteins is not required for the membrane association of ICP4.