The equine herpesvirus 1 UL45 homolog encodes a glycosylated type II transmembrane protein and is involved in virus egress

The complete genome sequence of bearded dragon adenovirus 1 harbors three genes encoding proteins of the C-type lectin-like domain superfamily

Bearded dragon adenovirus 1 (BDAdV-1), also known as agamid adenovirus 1, has been described worldwide as a prevalent infectious agent of the inland bearded dragon (Pogona vitticeps), the most common squamate exotic pet reptile. Previous limited sequence data of the adenoviral DNA polymerase and hexon genes indicated that BDAdV-1 is a member of genus Atadenovirus family Adenoviridae. Atadenoviruses infect ruminants, marsupials, testudine reptiles and birds, yet the genus has been shown to be of squamate reptile origin. Here, we report a screening survey along with the complete genome sequence of BDAdV-1, derived directly from the sample of a deceased juvenile dragon showing central nervous system signs prior to passing. The BDAdV-1 genome is 35,276 bp and contains 32 putative genes. Its genome organization is characteristic of the members of genus Atadenovirus, however, a divergent LH3 gene indicates structural interactions of different nature compared to other genus members such as snake adenovirus 1. We identified five novel open reading frames (ORFs), three of which encode proteins of the C-type lectin-like domain (CTLD) superfamily. ORF3 has a CTLD group II-like domain architecture displaying structural similarity with natural killer cell surface receptors and with an alphaherpesviral virulence factor gene for neurotropism, UL45. ORF4 and 6 are extremely long compared to typical adenoviral right-end genes and possibly encode members of the CTLD superfamily with novel, previously undescribed domain architectures. BDAdV-1 is the hitherto most divergent member of genus Atadenovirus providing new insights on adenoviral diversity, evolution and pathogenesis.

Transcription phase, protein characteristics of DEV UL45 and prokaryotic expression, antibody preparation of the UL45 des-transmembrane domain

Background

Some UL45 gene function of Herpesvirus was reported. While there was no any report of the duck enteritis virus (DEV) UL45 protein as yet.

Results

The UL45 gene and des-transmembrane domain of UL45 (named UL45Δ gene, 295-675bp of UL45) of DEV were amplified by PCR and subcloned into the prokaryotic expression vector pET-32a(+). The constructed recombinant plasmids were transformed into the host strain BL21(DE3) PLysS and induced by IPTG. SDS-PAGE analysis showed the UL45 gene couldn't express while UL45Δ gene was highly expressed. His Purify Kit or salting-out could purify the protein effectively. Using the purified protein to immunize New-Zealand rabbits and produce polyclonal antibody. The agar diffusion reaction showed the titer of antibody was 1:32. Western blot analysis indicated the purified rabbit anti-UL45Δ IgG had a high level of specificity and the UL45 gene was a part of DEV genome. The transcription phase study of UL45 gene showed that expression of UL45 mRNA was at a low level from 0 to 18 h post-infection (pi), then accumulated quickly at 24 h pi and peaked at 42 h pi. It can be detected till 72 h pi. Besides, western blot analysis of purified virion and different viral ingredients showed that the UL45 protein resided in the purified virion and the viral envelope.

Conclusions

The rabbit anti-UL45Δ IgG was produced successfully and it can serve as a good tool for penetrating studies of the function of DEV UL45 protein. The transcription phase and protein characteristics analysis indicated that DEV UL45 gene was a late gene and UL45 protein may be a viral envelope protein.

The equine herpesvirus 1 UL20 product interacts with glycoprotein K and promotes egress of mature particles

The aim of the present study was to identify and functionally characterize the equine herpesvirus 1 (EHV-1) UL20 protein (UL20p). Using a specific antiserum, UL20p was shown to be associated with membranes of infected cells, as well as with envelopes of purified virions. By Western blot analysis, UL20p was detected in two main forms exhibiting M(r)s of 25,000 and 75,000. Both moieties did not enter the separating gel after heating of protein samples to 99 degrees C. The slower-migrating form of UL20p contains N-linked carbohydrates, and its presence is dependent of that of other viral proteins. Infection of cells that either constitutively express UL20p or a gK-green fluorescent protein (GFP) fusion protein with various EHV-1 deletion mutants revealed a relatively stable hetero-oligomer containing gK and UL20p with an apparent M(r) of 75,000. As demonstrated by confocal microscopy, UL20p distribution in Rk13 cells changed from a diffuse granular or netlike appearance to a pattern confined to the Golgi network when gK was coexpressed. Analysis of a UL20 deletion mutant of EHV-1 strain RacL11 indicated an involvement of UL20p in cell-to-cell spread, as well as in very late events in virus egress. Based on these and electron microscopic studies we suggest that the EHV-1 UL20 protein might be necessary to avoid fusion of mature virions with membranes of their transport vesicles.

In vitro transposon mutagenesis of an equine herpesvirus 1 genome cloned as a bacterial artificial chromosome

The 150-kbp genome of the alphaherpesvirus equine herpesvirus 1 (EHV-1) strain HVS25A was cloned as a bacterial artificial chromosome (EHV-1 BAC), with mini F plasmid sequences inserted between genes 62 and 63. Transfection of EHV-1 BAC DNA purified from E. coli gave rise to progeny virus that had a similar growth rate and yield in mammalian cell culture to those of parental wild-type EHV-1. Using in vitro mutagenesis with a Mu transposon, a large library of EHV-1 BAC mutants was generated, and sequence analysis indicated that insertions were dispersed randomly across the EHV-1 genome. Following transfections of a pilot sample of mutant EHV-1 BAC DNAs into mammalian cells, no CPE was observable by light microscopy for mutants carrying insertions in genes for the major capsid protein, large tegument protein, glycoprotein K, catalytic subunit of DNA polymerase, or single-stranded DNA-binding protein. Mutants that were able to produce CPE similar to wild-type EHV-1 included those with interruptions in ORFs of several tegument proteins. Analysis of several glycoprotein gene mutants indicated that those carrying insertions near the start of genes encoding glycoproteins E and I were viable, but showed markedly diminished plaque areas. These results were supported by confocal microscopy of transfected or infected cultures. Electron microscopy of cells infected with a gE mutant revealed accumulations of particles within cytoplasmic vesicles, consistent with a partial obstruction of maturation. The transposon library is a resource for comprehensive functional analysis of the HVS25A genome, with multiple mutants available in any of the predicted genes of EHV-1.

Equine herpesvirus type 1 (EHV-1) glycoprotein K is required for efficient cell-to-cell spread and virus egress

The function of the equine herpesvirus type 1 (EHV-1) glycoprotein K (gK) homologue was investigated. Deletion of 88% of the UL53-homologous open reading frame in EHV-1 strain RacH resulted in a severe growth defect of the gK-negative virus (HDeltagK) as reflected by a significant decrease in the production of infectious virus progeny on RK13 cells. The HDeltagK virus induced only minute plaques, was unable to form syncytia, and its penetration efficiency into RK13 cells was reduced by approximately 40%. To further analyze gK function and intracellular trafficking, gK of strain RacH was replaced by a C-terminally truncated gK-green fluorescent protein fusion protein (gK-GFP). The generated recombinant virus was shown to replicate well on non-complementing cells, and virus penetration and syncytium formation were comparable to parental RacH. A reduction in plaque size and slightly decreased intra- and extracellular virus titers, however, were observed. The gK-GFP fusion protein was expressed with early-late kinetics, and multiple forms of the protein exhibiting M(r)s between 50,000 and 85,000 were detected by Western blot analysis. The various gK-GFP forms were shown to be N-glycosylated, associated with membranes of the Golgi apparatus, and were incorporated into extracellular virions. Complete processing of gK-GFP was only observed within the context of viral infection. From the results, we concluded that EHV-1 gK is required for efficient virus growth in vitro and that the carboxy-terminal amino acids are not required for its function, because the gK-GFP fusion protein was able to complement for EHV-1 growth in the absence of authentic gK.

The equine herpesvirus 1 UL11 gene product localizes to the trans-golgi network and is involved in cell-to-cell spread

Experiments were conducted to identify and characterize the equine herpesvirus type 1 (EHV-1) UL11 homologous protein. At early-late times after EHV-1 infection of Rk13 cells several proteins at an M(r) of 8000 to 12,000 were detected using a UL11 protein-specific antiserum. Particularly, an M(r) of 11,000 protein was found abundantly in purified virions and could be assigned to the tegument fraction. As demonstrated by confocal laser scanning microscopy, UL11 reactivity localized predominantly to the trans-Golgi network of infected cells, but was also noted at the plasma membrane, specifically of transfected cells. Deletion of UL11 sequences in EHV-1 vaccine strain RacH (Hdelta11) and in the virulent isolate RacL22 (Ldelta11) resulted in viruses that were able to replicate on noncomplementing cells. It was shown in one-step growth kinetics on Rk13 cells that the reduction of intracellular and of extracellular virus titers caused by the absence of UL11 expression in either virus was somewhat variable, but approximately 10- to 20-fold. In contrast, a marked influence on the plaque phenotype was noted, as mean maximal diameters of plaques were reduced to 23.2% (RacL22) or 34.7% (RacH) of parental virus plaques and as an effect on the ability of RacH to cause syncytia upon infection was noted. It was therefore concluded that the EHV-1 UL11 product is not essential for virus replication in Rk13 cells but is involved in cell-to-cell spread.

The equine herpesvirus 1 UL34 gene product is involved in an early step in virus egress and can be efficiently replaced by a UL34-GFP fusion protein

The structure and function of the equine herpesvirus type 1 (EHV-1) UL34 homologous protein were characterized. A UL34 protein-specific antiserum reacted with an M(r)28,000 protein that could not be detected in purified extracellular virions. Confocal laser scanning microscopy demonstrated that UL34 reactivity mainly concentrated at the nuclear rim, which changed into a punctuate and filamentous pattern at late times after infection. These changes in UL34 distribution were especially prominent when analyzing the distribution of a GFP-UL34 fusion protein. A UL34-negative EHV-1 was generated by mutagenesis of a recently established BAC clone of EHV-1 strain RacH (pRacH). Release of extracellular infectious virus was severely impaired after infection of Rk13 cells with HDelta34. Electron microscopy revealed a virtual absence of virus particles in the cytoplasm of infected cells, whereas nucleocapsid formation and maturation within the nucleus appeared unaffected. A UL34-GFP fusion protein with GFP linked to the C-terminus of UL34 was able to complement for the UL34 deletion in trans, while a GFP-UL34-fusion protein with GFP linked to the N-terminus of UL34 was able to only partially restore virus growth. It was concluded that the EHV-1 UL34 product is essential for an early step in virus egress, i.e., release of capsids from infected-cell nuclei.