Expression of cloned herpesvirus genes. I. Detection of nuclear antigens from herpes simplex virus type 2 inverted repeat regions in transfected mouse cells

Three different recombinant plasmids containing the entire 15-kilobase L and S inverted repeat sequence of herpes simplex virus type 2 DNA have been introduced into cultured LtK^- or BSC cells by both the calcium and DEAE-dextran transfection procedures. In each case, after 24 h approximately 1% of the cells gave strongly positive nuclear staining when assayed by immunofluorescence with hyperimmune antisera made against early and immediate-early infected-cell polypeptides. The nuclear fluorescence pattern and intensity mimicked that observed within 2 to 3 h after infection of Ltk^- cells with either herpes simplex virus type 1 or type 2 wild-type virus. Herpes simplex virus type 1 (KOStsB2)-infected Ltk^- cells under nonpermissive conditions did not express these antigens in the nucleus. Therefore, we conclude that either one or both of the 185,000- and 110,000-molecular-weight immediate early proteins, or some other as yet unknown gene product encoded entirely within the inverted repeats, can be transiently expressed in large amounts in transfected cells in the absence of other viral genes or accompanying virion components. Permament mouse cell lines derived from transfection with these plasmids by using the thymidine kinase coselection procedure did not express sufficient nuclear antigen to be detectable by immunofluorescence.