Bovine herpesvirus 1 UL49.5 homolog gene encodes a novel viral envelope protein that forms a disulfide-linked complex with a second virion structural protein

The Epstein-Barr virus (EBV) homolog of the conserved herpesvirus glycoprotein gN is predicted to be encoded by the BLRF1 open reading frame (ORF). Antipeptide antibody to a sequence corresponding to residues in the predicted BLRF1 ORF immunoprecipitated a doublet of approximately 8 kDa from cells expressing the BLRF1 ORF as a recombinant protein. In addition, four glycosylated proteins of 113, 84, 48, and 15 kDa could be immunoprecipitated from virus-producing cells by the same antibody. The 15-kDa species was the mature form of gN, which carried α2,6-sialic acid residues. The remaining glycoproteins which associated with gN were products of the BBRF3 ORF of EBV, which encodes the EBV gM homolog. The 8-kDa doublet seen in cells expressing recombinant gN comprised precursors of the mature 15-kDa gN. Coexpression of EBV gM with EBV gN was required for authentic processing of the 8-kDa forms to the 15-kDa form.

Section: Discussionsupporting

confidence: 66%

mentioning

confidence: 99%

The Epstein-Barr Virus (EBV) gN Homolog BLRF1 Encodes a 15-Kilodalton Glycoprotein That Cannot Be Authentically Processed unless It Is Coexpressed with the EBV gM Homolog BBRF3

Lake

Molesworth

Hutt-Fletcher

1998

“…For BHV-1, it was reported that the 8-kDa UL49.5 protein forms a disulfide-linked complex with another virion component of 39 kDa which may be located in the tegument, based on nonionic-detergent partition of purified virions (31). gM is predicted to be a multiply-membrane-spanning glycoprotein with eight predicted transmembrane domains (8).…”

Section: Discussionmentioning

confidence: 99%

“…However, the BHV-1 homolog is also a membrane protein and a constituent of mature BHV-1 virions. In addition, it was shown to form a complex with an unidentified 39-kDa virion protein (31).…”

mentioning

confidence: 99%

Glycoproteins M and N of Pseudorabies Virus Form a Disulfide-Linked Complex

Jöns

Dijkstra

Mettenleiter

1998

Genes homologous to the herpes simplex virus UL49.5 open reading frame are conserved throughout the Herpesviridae. In the alphaherpesvirus pseudorabies virus (PrV), the UL49.5 product is an O-glycosylated structural protein of the viral envelope, glycoprotein N (gN) (A. Jöns, H. Granzow, R. Kuchling, and T. C. Mettenleiter, J. Virol. 70:1237–1241, 1996). For functional characterization of gN, a gN-negative PrV mutant, PrV-gNβ, and the corresponding rescuant, PrV-gNβR, were constructed, gN-negative PrV was able to productively replicate on noncomplementing cells, and one-step growth in cell culture was only slightly reduced compared to that of wild-type PrV. However, penetration was significantly delayed. In indirect immunofluorescence assays with rabbit serum directed against baculovirus-expressed gN, specific staining of wild-type PrV-infected cells occurred only after permeabilization of cells, whereas live cells failed to react with the antiserum. This indicates the lack of surface accessibility of gN in the plasma membrane of a PrV-infected cell. Western blot analyses and radioimmunoprecipitation experiments under reducing and nonreducing conditions led to the discovery of a heteromeric complex composed of gM and gN. The complex was stable in the absence of 2-mercaptoethanol but dissociated after the addition of the reducing agent, indicating that the partners are linked by disulfide bonds. Finally, gN was absent from gM-negative PrV virions, whereas gM was readily detected in virions in the absence of gN. Thus, gM appears to be required for virion localization of gN.

“…The product of the second ORF is predicted to consist of 117 amino acids exhibiting characteristics of intrinsic membrane proteins, with two hydrophobic domains, one at the N terminus and one close to the C terminus, which could serve as signal and anchor sequences, respectively. The homologous UL49.5 proteins of PrV and BHV-1 were indeed shown to represent structural components of the viral envelope (21,28). The deduced 266-, 396-, and 557-amino-acid proteins of the three following ORFs are homologous to the virion tegument proteins encoded by the UL49, UL48, and UL46 genes of alphaherpesviruses (5,10,35,53).…”

mentioning

confidence: 90%

Gene Arrangement within the Unique Long Genome Region of Infectious Laryngotracheitis Virus Is Distinct from That of Other Alphaherpesviruses

Ziemann

Mettenleiter

Fuchs

1998

The genome of the avian alphaherpesvirus infectious laryngotracheitis virus (ILTV) comprises ca. 155 kbp of which ca. one-third have been sequenced so far. To gain additional sequence information we analyzed two stretches of 15.5 and 1.9 kbp of the ILTV unique long (UL) genome region. The larger fragment contains homologs of the herpes simplex virus (HSV) UL23 (thymidine kinase) and UL22 (glycoprotein H) genes followed by five open reading frames (ORF) encoding putative proteins of 334 to 410 amino acids which exhibit no homology to any known herpesvirus protein. RNA analyses showed that these unique ILTV genes are indeed expressed. An origin of replication separates this cluster of unique genes from a conserved gene cluster consisting of the UL45, UL46, UL48, UL49, UL49.5, and UL50 homologs. The absence of UL47 from this position coincides with the localization of a UL47-homologous ORF within the unique short (US) region of the ILTV genome (M. Wild, S. Cook, and M. Cochran, Virus Genes 12:107–116, 1996). Within the second analyzed region the ILTV UL21 homolog was found adjacent to the UL44 gene. We thus identified five novel herpesvirus genes in ILTV and present evidence for a large internal inversion in the ILTV ULregion, in contrast to the collinear genomes of other alphaherpesviruses. Interestingly, a similar inversion is also present in the porcine alphaherpesvirus pseudorabies virus.