The Gene 10 (UL49.5) Product of Equine Herpesvirus 1 Is Necessary and Sufficient for Functional Processing of Glycoprotein M

Abstract

The functional cooperation of equine herpesvirus 1 (EHV-1) glycoprotein M (gM) and the gene 10 (UL49.5) product was analyzed. Transient-transfection experiments using gM and UL49.5 expression plasmids as well as RK13 cell lines constitutively expressing UL49.5 (RK49.5) or gM (RKgM) demonstrated that the endo-␤-N-acetylglucosaminidase H (endo H)-resistant mature form of gM was detectable only after coexpression of the two proteins. Deletion of the EHV-1 UL49.5-homologous gene 10 in strain KyA resulted in a small-plaque phenotype and up to 190-fold-reduced virus titers. The growth defects of the mutant KyA⌬49.5 virus, which were very similar to those of a gM-negative KyA virus, could be completely compensated for by growth of the mutant virus on RK49.5 cells or by repairing the deletion of gene 10 in the revertant virus KyA⌬49.5R. Analysis of cells infected with the UL49.5-negative EHV-1 demonstrated that gM was not transported to the trans-Golgi network in the absence of the UL49.5 product. In contrast, gM was efficiently transported and processed to the endo H-resistant mature form in KyA⌬49.5-infected RK49.5 cells. Furthermore, radioimmunoprecipitation experiments demonstrated that gM maturation was observed only if a 10,000-M r protein was coprecipitated with gM in KyA-or KyA⌬49.5R-infected cells or virions. This protein was absent in cells infected with Ky⌬49.5 or KyA⌬gM, suggesting that it was the EHV-1 UL49.5 product. Taken together, our results demonstrate that the expression of the EHV-1 UL49.5 product is necessary and sufficient for gM processing and that it is required for efficient virus replication.

Herpes Simplex Virus 1 gN Partners with gM To Modulate the Viral Fusion Machinery

“…From alphaherpesviruses to gammaherpesviruses, gM interacts with gN, and the complex typically leads to changes in intracellular targeting of either or both proteins (15,21,30,36,37,40). The present study indicates that this extends to HSV-1 and further reveals that the amino terminal 132 amino acids of HSV-1 gM are important for an efficient interaction between the two proteins.…”

“…Interestingly, while gN is dominant and alters the localization and/or maturation of gM in BHV-1, equine herpesvirus 1 (EHV-1), and HHV-8 (21,30,40), the opposite seems true for HSV-1, EBV, and infectious ILTV, where gM is required for the transport and/or processing of gN (this study) (36,37). While the reasons for this distinction among herpesviruses are not clear, that the complex formation has targeting consequences for gM or gN in all herpesviruses studied so far appears well conserved.…”

Varicelloviruses avoid T cell recognition by UL49.5-mediated inactivation of the transporter associated with antigen processing

“…The UL49.5 ORF is relatively conserved among herpesviruses, and the interaction with gM is a common property of all UL49.5 homologs (36,42,48). So far, we have identified the UL49.5 homologs encoded by BHV1, PRV, and EHV1 as potent inhibitors of TAP.…”

High-Level Expression of Marek's Disease Virus Glycoprotein C Is Detrimental to Virus Growth In Vitro

“…It could be shown that MDV mutants lacking gB were nonviable; however, unlike other related viruses, MDV is unable to replicate in the absence of two major membrane protein complexes, the gE-gI and the gM-pU L 49.5 complex (61,62,67). While essentiality of gB has been shown for all herpesviruses analyzed thus far (53), most Alphaherpesvirinae are still able to grow in cultured cells in the absence of the other glycoproteins (2,3,22,32,37,51,56,77,78). Besides MDV, VZV is also an exception to the rule, because it requires expression of gE for growth in vitro and in vivo, while gI is required for VZV growth in Vero cells, but not in fibroblasts or melanoma cells (14,39,40,62).…”