Interaction of herpes simplex virus 1 alpha regulatory protein ICP0 with elongation factor 1delta: ICP0 affects translational machinery.

The herpes simplex virus 1 (HSV-1)-infected cell protein 0 (ICP0) is a promiscuous transactivator, and by necessity, its functions must be mediated through cellular gene products. In an attempt to identify cellular factors interacting with ICP0, we used the carboxyl-terminal domain of ICP0 as "bait" in the yeast (Saccharomyces cerevisiae) two-hybrid system. Our results were as follows: (i) All 43 cDNAs in positive yeast colonies were found to encode the same translation factor, elongation factor delta-1 (EF-1delta). (ii) Purified chimeric protein consisting of glutathione S-transferase (GST) fused to EF-1delta specifically formed complexes with ICP0 contained in HSV-1-infected cell lysate. (iii) Fractionation of infected HEp-2 cells and immunofluorescence studies revealed that ICP0 was localized both in the nucleus and in the cytoplasm. In primary human foreskin fibroblasts, ICP0 was localized predominantly in the cytoplasm throughout HSV-1 infection even early in infection. (iv) Addition of the chimeric protein GST-carboxyl-terminal domain of ICP0 to the rabbit reticulocyte lysate in vitro translation system resulted in a dose-dependent decrease in protein synthesis. In contrast, GST alone or GST fused to the amino-terminal domain of ICP0 had no effect on the in vitro translation system. (v) The predominant forms of EF-1delta on electrophoresis in denaturing gels have apparent Mrs of 38,000 and 40,000. The higher-Mr form is a minor species in mock-infected cells, whereas in human fibroblasts and Vero cells infected with HSV-1, this isoform becomes dominant. These results indicate that ICP0 is present and may have a significant role in the cytoplasm of infected cells, possibly by altering the efficiency of translation of viral mRNAs.