The product of the herpes simplex virus type 1 UL25 gene is required for encapsidation but not for cleavage of replicated viral DNA.

The herpes simplex virus type 1 (HSV-1) UL25 gene contains a 580-amino-acid open reading frame that codes for an essential protein. Previous studies have shown that the UL25 gene product is a virion component (M. A. Ali et al., Virology 216:278-283, 1996) involved in virus penetration and capsid assembly (C. Addison et al., Virology 138:246-259, 1984). In this study, we describe the isolation of a UL25 mutant (KUL25NS) that was constructed by insertion of an in-frame stop codon in the UL25 open reading frame and propagated on a complementing cell line. Although the mutant was capable of synthesis of viral DNA, it did not form plaques or produce infectious virus in noncomplementing cells. Antibodies specific for the UL25 protein were used to demonstrate that KUL25NS-infected Vero cells did not express the UL25 protein. Western immunoblotting showed that the UL25 protein was associated with purified, wild-type HSV A, B, and C capsids. Transmission electron microscopy indicated that the nucleus of Vero cells infected with KUL25NS contained large numbers of both A and B capsids but no C capsids. Analysis of infected cells by sucrose gradient sedimentation analysis confirmed that the ratio of A to B capsids was elevated in KUL25NS-infected Vero cells. Following restriction enzyme digestion, specific terminal fragments were observed in DNA isolated from KUL25NS-infected Vero cells, indicating that the UL25 gene was not required for cleavage of replicated viral DNA. The latter result was confirmed by pulsed-field gel electrophoresis (PFGE), which showed the presence of genome-size viral DNA in KUL25NS-infected Vero cells. DNase I treatment prior to PFGE demonstrated that monomeric HSV DNA was not packaged in the absence of the UL25 protein. Our results indicate that the product of the UL25 gene is required for packaging but not cleavage of replicated viral DNA.

Assembly of herpes simplex virus (HSV) intermediate capsids in insect cells infected with recombinant baculoviruses expressing HSV capsid proteins.

The capsid of herpes simplex virus type 1 (HSV-1) is composed of seven proteins, VP5, VP19C, VP21, VP22a, VP23, VP24, and VP26, which are the products of six HSV-1 genes. Recombinant baculoviruses were used to express the six capsid genes (UL18, UL19, UL26, UL26.5, UL35, and UL38) in insect cells. All constructs expressed the appropriate-size HSV proteins, and insect cells infected with a mixture of the six recombinant baculoviruses contained large numbers of HSV-like capsids. Capsids were purified by sucrose gradient centrifugation, and electron microscopy showed that the capsids made in Sf9 cells had the same size and appearance as authentic HSV B capsids. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis demonstrated that the protein composition of these capsids was nearly identical to that of B capsids isolated from HSV-infected Vero cells. Electron microscopy of thin sections clearly demonstrated that the capsids made in insect cells contained the inner electron-translucent core associated with HSV B capsids. In infections in which single capsid genes were left out, it was found that the UL18 (VP23), UL19 (VP5), UL38 (VP19C), and either the UL26 (VP21 and VP24) or the UL26.5 (VP22a) genes were required for assembly of 100-nm capsids. VP22a was shown to form the inner core of the B capsid, since in infections in which the UL26.5 gene was omitted the 100-nm capsids that formed lacked the inner core. The UL35 (VP26) gene was not required for assembly of 100-nm capsids, although assembly of B capsids was more efficient when it was present. These and other observations indicate that (i) the products of the UL18, UL19, UL35, and UL38 genes self-assemble into structures that form the outer surface (icosahedral shell) of the capsid, (ii) the products of the UL26 and/or UL26.5 genes are required (as scaffolds) for assembly of 100-nm capsids, and (iii) the interaction of the outer surface of the capsid with the scaffolding proteins requires the product of the UL18 gene (VP23).

Comparison of soluble and secreted forms of human parainfluenza virus type 3 glycoproteins expressed from mammalian and insect cells as subunit vaccines.

Human parainfluenza virus type 3 (PIV-3) is one of the leading causes of paediatric viral respiratory disease. The PIV-3 genome encodes two envelope glycoproteins, F and HN, which are the major targets for the host antibody response. We have expressed secreted forms of the F and HN proteins and a novel chimeric FHN glycoprotein in insect cells using recombinant baculovirus vectors and secreted forms of the F and FHN glycoproteins in stably transformed Chinese hamster ovary (CHO) cells. Comparison of the mammalian cell- and insect cell-expressed F and FHN proteins by SDS-PAGE showed that the CHO cell-expressed proteins are several kilodaltons larger in size than the baculovirus-produced proteins. A partial characterization of the oligosaccharide structures of the F and FHN proteins revealed that the size difference is due to the different oligosaccharide structures added to these proteins by the two cell lines. The F, HN and FHN proteins were immunoaffinity-purified from the culture medium of baculovirus-infected Sf9 cells and the F and FHN proteins were immunoaffinity-purified from the culture medium of CHO cells. A comparison of the immunogenicity and efficacy of the mammalian cell- and insect cell-produced FHN proteins was tested in cotton rats. The CHO cell- and baculovirus-produced FHN proteins were found to induce similar levels of PIV-3-specific ELISA-positive and neutralizing antibodies and both proteins provided near complete protection when animals were vaccinated with low doses of the FHN protein.

Cloning of the orotidine 5'-phosphate decarboxylase (ODC) gene of Schwanniomyces occidentalis by complementation of the ura3 mutation in S. cerevisiae.

A DNA fragment containing the gene encoding orotidine 5'-phosphate decarboxylase (ODC) from the yeast, Schwanniomyces occidentalis (formerly castellii) has been isolated from a genomic library constructed in the S. cerevisiae expression vector, pYcDE8. A recombinant plasmid, p2-1A, containing a 2.47 kb insert was shown to complement the ura3-52 mutation of several strains of S. cerevisiae. This DNA insert was shown to be from Schwanniomyces occidentalis by Southern hybridization analysis. A restriction enzyme cleavage map of the insert has been derived and the ODC gene localized to a 1.1 kb region by deletion analysis. In addition, we have demonstrated that expression of ODC is not dependent on the ADH1 promoter carried on pYcDE8. This is the first report of the cloning of a gene from a member of the genus Schwanniomyces.