Evolution of an Extended Pathogenicity Motif in VP2 of Infectious Pancreatic Necrosis Virus Isolates from Farmed Rainbow Trout in Turkey.

Infectious pancreatic necrosis virus (IPNV) causes economic losses with a highly variable mortality rate worldwide, especially in rainbow trout. The virus has a double-stranded bi-partite RNA genome designated segment A and B. New complete genome sequences of nine rainbow trout isolates from Turkey were determined and subjected to phylogenetic analysis, identifying all as genotype 5 (serotype Sp). A time-dependent change in the extended pathogenicity motif of VP2 from P217T221A247 (PTA) to PTE P217T221E247 over a period of 10 years was identified. A wider analysis of 99 IPNV sequences from Turkey and Iran revealed the emergence of the motif PTE from 2007 to 2017, inducing significant morbidity in fry by 2013. In fact, displacement of the PTA motif, by the PTE motif in IPNV isolates appeared to be connected to a production peak of rainbow trout in 2013. An additional CAI analysis provided more evidence, indicating that rainbow trout culture in Turkey has an influence on the evolution of IPNV.

Systems approach to design multi-epitopic peptide vaccine candidate against fowl adenovirus structural proteins for Gallus gallus domesticus.

Introduction: Fowl adenovirus (FAdV) is a significant pathogen in poultry, causing various diseases such as hepatitis-hydropericardium, inclusion body hepatitis, and gizzard erosion. Different serotypes of FAdV are associated with specific conditions, highlighting the need for targeted prevention strategies. Given the rising prevalence of FAdV-related diseases globally, effective vaccination and biosecurity measures are crucial. In this study, we explore the potential of structural proteins to design a multi-epitope vaccine targeting FAdV. Methods: We employed an in silico approach to design the multi-epitope vaccine. Essential viral structural proteins, including hexon, penton, and fiber protein, were selected as vaccine targets. T-cell and B-cell epitopes binding to MHC-I and MHC-II molecules were predicted using computational methods. Molecular docking studies were conducted to validate the interaction of the multi-epitope vaccine candidate with chicken Toll-like receptors 2 and 5. Results: Our in silico methodology successfully identified potential T-cell and B-cell epitopes within the selected viral structural proteins. Molecular docking studies revealed strong interactions between the multi-epitope vaccine candidate and chicken Toll-like receptors 2 and 5, indicating the structural integrity and immunogenic potential of the designed vaccine. Discussion: The designed multi-epitope vaccine presents a promising approach for combating FAdV infections in chickens. By targeting essential viral structural proteins, the vaccine is expected to induce a robust immunological response. The in silico methodology utilized in this study provides a rapid and cost-effective means of vaccine design, offering insights into potential vaccine candidates before experimental validation. Future studies should focus on in vitro and in vivo evaluations to further assess the efficacy and safety of the proposed vaccine.

Codon Optimization-based Whole-gene Scanning Identifies Hidden Nucleotides Essential for Bombyx mori Nucleopolyhedrovirus polyhedrin Hyperexpression.

During the late stage of infection, alphabaculoviruses produce many occlusion bodies (OBs) in the nuclei of the insect host's cells through the hyperexpression of polyhedrin (POLH), a major OB component encoded by polh. The strong polh promoter has been used to develop a baculovirus expression vector system for recombinant protein expression in cultured insect cells and larvae. However, the relationship between POLH accumulation and the polh coding sequence remains largely unelucidated. This study aimed to assess the importance of polh codon usage and/or nucleotide sequences in POLH accumulation by generating a baculovirus Bombyx mori nucleopolyhedrovirus (BmNPV) expressing mutant polh (co-polh) optimized according to the codon preference of its host insect. Although the deduced amino acid sequence of CO-POLH was the same as that of wild-type POLH, POLH accumulation was significantly lower in cells infected with the co-polh mutant. This reduction was due to decreased polh mRNA levels rather than translational repression. Analysis of mutant viruses with chimeric polh revealed that a 30 base-pair (bp) 5' proximal polh coding region was necessary for maintaining high polh mRNA levels. Sequence comparison of wild-type polh and co-polh identified five nucleotide differences in this region, indicating that these nucleotides were critical for polh hyperexpression. Furthermore, luciferase reporter assays showed that the 30 bp 5' coding region was sufficient for maintaining the polh promoter-driven high level of polh mRNA. Thus, our whole-gene scanning by codon optimization identified important hidden nucleotides for polh hyperexpression in alphabaculoviruses.

HSP70 positively regulates translation by interacting with the IRES and stabilizes the viral structural proteins VP1 and VP3 to facilitate duck hepatitis A virus type 1 replication.

The maintenance of viral protein homeostasis depends on the interaction between host cell proteins and viral proteins. As a molecular chaperone, heat shock protein 70 (HSP70) has been shown to play an important role in viral infection. Our results showed that HSP70 can affect translation, replication, assembly, and release during the life cycle of duck hepatitis A virus type 1 (DHAV-1). We demonstrated that HSP70 can regulate viral translation by interacting with the DHAV-1 internal ribosome entry site (IRES). In addition, HSP70 interacts with the viral capsid proteins VP1 and VP3 and promotes their stability by inhibiting proteasomal degradation, thereby facilitating the assembly of DHAV-1 virions. This study demonstrates the specific role of HSP70 in regulating DHAV-1 replication, which are helpful for understanding the pathogenesis of DHAV-1 infection and provide additional information about the role of HSP70 in infection by different kinds of picornaviruses, as well as the interaction between picornaviruses and host cells.

The HSV-1 pUL37 protein promotes cell invasion by regulating the kinesin-1 motor.

Neurotropic alphaherpesviruses, including herpes simplex virus type 1 (HSV-1), recruit microtubule motor proteins to invade cells. The incoming viral particle traffics to nuclei in a two-step process. First, the particle uses the dynein-dynactin motor to sustain transport to the centrosome. In neurons, this step is responsible for long-distance retrograde axonal transport and is an important component of the neuroinvasive property shared by these viruses. Second, a kinesin-dependent mechanism redirects the particle from the centrosome to the nucleus. We have reported that the kinesin motor used during the second step of invasion is assimilated into nascent virions during the previous round of infection. Here, we report that the HSV-1 pUL37 tegument protein suppresses the assimilated kinesin-1 motor during retrograde axonal transport. Region 2 (R2) of pUL37 was required for suppression and functioned independently of the autoinhibitory mechanism native to kinesin-1. Furthermore, the motor domain and proximal coiled coil of kinesin-1 were sufficient for HSV-1 assimilation, pUL37 suppression, and nuclear trafficking. pUL37 localized to the centrosome, the site of assimilated kinesin-1 activation during infection, when expressed in cells in the absence of other viral proteins; however, pUL37 did not suppress kinesin-1 in this context. These results indicate that the pUL37 tegument protein spatially and temporally regulates kinesin-1 via the amino-terminal motor region in the context of the incoming viral particle.

Cell Culture Adaptive Amino Acid Substitutions in FMDV Structural Proteins: A Key Mechanism for Altered Receptor Tropism.

The foot-and-mouth disease virus is a highly contagious and economically devastating virus of cloven-hooved animals, including cattle, buffalo, sheep, and goats, causing reduced animal productivity and posing international trade restrictions. For decades, chemically inactivated vaccines have been serving as the most effective strategy for the management of foot-and-mouth disease. Inactivated vaccines are commercially produced in cell culture systems, which require successful propagation and adaptation of field isolates, demanding a high cost and laborious time. Cell culture adaptation is chiefly indebted to amino acid substitutions in surface-exposed capsid proteins, altering the necessity of RGD-dependent receptors to heparan sulfate macromolecules for virus binding. Several amino acid substations in VP1, VP2, and VP3 capsid proteins of FMDV, both at structural and functional levels, have been characterized previously. This literature review combines frequently reported amino acid substitutions in virus capsid proteins, their critical roles in virus adaptation, and functional characterization of the substitutions. Furthermore, this data can facilitate molecular virologists to develop new vaccine strains against the foot-and-mouth disease virus, revolutionizing vaccinology via reverse genetic engineering and synthetic biology.

Development of visual detection of African swine fever virus using CRISPR/LwCas13a lateral flow strip based on structural protein gene D117L.

African swine fever virus (ASFV) is a large double stranded DNA arbovirus that is highly contagious and seriously endangers domestic and wild pigs. In the past decade, African swine fever (ASF) has spread in many countries in the Caucasus, Russian Federation, Eastern Europe and Asia, causing significant losses to the pig industry. At present, there is a lack of effective vaccine and treatment for ASF. Therefore, the rapid and accurate detection is crucial for ASF prevention and control. In this study, we have developed a portable lateral flow strip (LFS) detection mediated by recombinase polymerase amplification (RPA) and CRISPR/LwCas13a, which is performed at 37 ℃ and visualized by eyes without the need for complex instruments. This RPA-LwCas13a-LFS is based on the ASFV structural protein p17 gene (D117L), with a detection sensitivity up to 2 gene copies. This method is highly specific and has no cross reactivity to 7 other pig viruses. In the detection of two batches of 100 clinical samples, the p17 (D117L) RPA-LwCas13a-LFS had 100% coincidence with conventional quantitative PCR (qPCR). These findings demonstrate the potential of this simple, rapid, sensitive, and specific ASFV detection method for on-site ASFV detection.

OASL suppresses infectious bursal disease virus replication by targeting VP2 for degrading through the autophagy pathway.

Infectious bursal disease (IBD) is an acute and fatal immunosuppressive disease caused by infectious bursal disease virus (IBDV). As an obligate intracellular parasite, IBDV infection is strictly regulated by host factors. Knowledge on the antiviral activity and possible mechanism of host factors might provide the theoretical basis for the prevention and control of IBD. In this study, RNA-sequencing results indicated that many host factors were induced by IBDV infection, among which the expression levels of OASL (2´,5´-oligadenylate synthetase-like protein) was significantly upregulated. OASL overexpression significantly inhibited IBDV replication, whereas OASL knockdown promoted IBDV replication. Interestingly, the antiviral ability of OASL was independent of its canonical enzymatic activity, i.e., OASL targeted viral protein VP2 for degradation, depending on the autophagy receptor p62/SQSTM1 in the autophagy pathway. Additionally, the 316 lysine (K) of VP2 was the key site for autophagy degradation, and its replacement with arginine disrupted VP2 degradation induced by OASL and enhanced IBDV replication. Importantly, our results for the first time indicate a unique and potent defense mechanism of OASL against double-stranded RNA virus by interaction with viral proteins, which leads to their degradation. IMPORTANCE: OASL (2´,5´-oligadenylate synthetase-like protein) exhibits broad-spectrum antiviral effects against single-stranded RNA viruses in mammals, potentially serving as a promising target for novel antiviral strategies. However, its role in inhibiting the replication of double-stranded RNA viruses (dsRNA viruses), such as infectious bursal disease virus (IBDV), in avian species remains unclear. Our findings indicated a unique and potent defense mechanism of OASL against dsRNA viruses. It has been previously shown in mammals that OASL inhibits virus replication through increasing interferon production. The groundbreaking aspect of our study is the finding that OASL has the ability to interact with IBDV viral protein VP2 and target it for degradation and thus exerts its antiviral effect. Our results reveal the interaction between avian natural antiviral immune response and IBDV infection. Our study not only enhances our understanding of bird defenses against viral infections but can also inform strategies for poultry disease management.

Loop PDE of viral capsid protein is involved in immune escape of the emerging novel variant infectious bursal disease virus.

Infectious bursa disease (IBD) is an acute, highly contactable, lethal, immunosuppressive infectious disease caused by the Infectious bursa disease virus (IBDV). Currently, the emerged novel variant IBDV (nVarIBDV) and the sustainedly prevalent very virulent IBDV (vvIBDV) are the two most prevalent strains of IBDV in China. The antigenic properties of the two prevalent strains differed significantly, which led to the escape of nVarIBDV from the immune protection provided by the existing vvIBDV vaccine. However, the molecular basis of the nVarIBDV immune escape remains unclear. In this study, we demonstrated, for the first time, that residues 252, 254, and 256 in the PDE of VP2 are involved in the immune escape of the emerging nVarIBDV. Firstly, the IFA-mediated antigen-antibody affinity assay showed that PBC and PDE of VP2 could affect the affinity of vvIBDV antiserum to VP2, of which PDE was more significant. The key amino acids of PDE influencing the antigen-antibody affinity were also identified, with G254N being the most significant, followed by V252I and I256V. Then the mutated virus with point or combined mutations was rescued by reverse genetics. it was further demonstrated that mutations of V252I, G254N, and I256V in PDE could individually or collaboratively reduce antigen-antibody affinity and interfere with antiserum neutralization, with G254N being the most significant. This study revealed the reasons for the widespread prevalence of nVarIBDV in immunized chicken flocks and provided innovative ideas for designing novel vaccines that match the antigen of the epidemic strain.

The mRNA Vaccine Expressing Single and Fused Structural Proteins of Porcine Reproductive and Respiratory Syndrome Induces Strong Cellular and Humoral Immune Responses in BalB/C Mice.

PRRS is a viral disease that profoundly impacts the global swine industry, causing significant economic losses. The development of a novel and effective vaccine is crucial to halt the rapid transmission of this virus. There have been several vaccination attempts against PRRSV using both traditional and alternative vaccine design development approaches. Unfortunately, there is no currently available vaccine that can completely control this disease. Thus, our study aimed to develop an mRNA vaccine using the antigens expressed by single or fused PRRSV structural proteins. In this study, the nucleotide sequence of the immunogenic mRNA was determined by considering the antigenicity of structural proteins and the stability of spatial structure. Purified GP5 protein served as the detection antigen in the immunological evaluation. Furthermore, cellular mRNA expression was detected by immunofluorescence and western blotting. In a mice experiment, the Ab titer in serum and the activation of spleen lymphocytes triggered by the antigen were detected by ELISA and ICS, respectively. Our findings demonstrated that both mRNA vaccines can significantly stimulate cellular and humoral immune responses. More specifically, the GP5-mRNA exhibited an immunological response that was similar to that of the commercially available vaccine when administered in high doses. To conclude, our vaccine may show promising results against the wild-type virus in a natural host.

Research Note: Characterization and phylodynamic analysis of new infectious bursal disease virus variants circulating in Argentina.

Infectious Bursal Disease is a highly contagious disease that affects young chickens and leads to significant economic losses. Its causal agent is a double-stranded RNA virus that, due to its high error rate during the replication process, gives rise to a constant generation of new virus variants. Until 2014, strains of Infectious Bursal Diseases Virus (IBDV) belonging to genogroup 4 predominated in Argentina, but there have been no reports since then regarding the circulating genogroups in poultry. In this study, 11 recent sequences of Argentine from the hypervariable region of VP2 protein (hvVP2) were analyzed to determine their genogroup, origin, evolution, and amino acid sequence. Samples from chickens showing signs of IBDV infection were collected, and the hvVP2 region was amplified using RT-PCR, followed by sequencing. The results indicated that the analyzed strains belong to genogroup 2, with an estimated evolutionary rate of 1.74 × 10-3 substitutions/site/year. It is speculated that the predominant group of sequences began to spread in Argentina around 2014 and had its origins in China. Another sample is related to strains from South Korea and is not closely linked to the main group. Furthermore, the predicted amino acid sequences show similarity to strains that can evade vaccine-induced immunity. These findings underscore the importance of active surveillance in poultry to mitigate losses caused by IBDV.

African swine fever virus A137R assembles into a dodecahedron cage.

African swine fever (ASF) is a highly contagious viral disease that affects domestic and wild pigs. The causative agent of ASF is African swine fever virus (ASFV), a large double-stranded DNA virus with a complex virion structure. Among the various proteins encoded by ASFV, A137R is a crucial structural protein associated with its virulence. However, the structure and molecular mechanisms underlying the functions of A137R remain largely unknown. In this study, we present the structure of A137R determined by cryogenic electron microscopy single-particle reconstruction, which reveals that A137R self-oligomerizes to form a dodecahedron-shaped cage composed of 60 polymers. The dodecahedron is literally equivalent to a T = 1 icosahedron where the icosahedral vertexes are located in the center of each dodecahedral facet. Within each facet, five A137R protomers are arranged in a head-to-tail orientation with a long N-terminal helix forming the edge through which adjacent facets stitch together to form the dodecahedral cage. Combining structural analysis and biochemical evidence, we demonstrate that the N-terminal domain of A137R is crucial and sufficient for mediating the assembly of the dodecahedron. These findings imply the role of A137R cage as a core component in the icosahedral ASFV virion and suggest a promising molecular scaffold for nanotechnology applications. IMPORTANCE: African swine fever (ASF) is a lethal viral disease of pigs caused by African swine fever virus (ASFV). No commercial vaccines and antiviral treatments are available for the prevention and control of the disease. A137R is a structural protein of ASFV that is associated with its virulence. The discovery of the dodecahedron-shaped cage structure of A137R in this study is of great importance in understanding ASFV pathogenicity. This finding sheds light on the molecular mechanisms underlying the functions of A137R. Furthermore, the dodecahedral cage formed by A137R shows promise as a molecular scaffold for nanoparticle vectors. Overall, this study provides valuable insights into the structure and function of A137R, contributing to our understanding of ASFV and potentially opening up new avenues for the development of vaccines or treatments for ASF.

Nucleocytoplasmic shuttling of BEFV M protein-modulated by lamin A/C and chromosome maintenance region 1 through a transcription-, carrier- and energy-dependent pathway.

This study demonstrates for the first time that the matrix (M) protein of BEFV is a nuclear targeting protein that shuttles between the nucleus and the cytoplasm in a transcription-, carrier-, and energy-dependent manner. Experiments performed in both intact cells and digitonin-permeabilized cells revealed that M protein targets the nucleolus and requires carrier, cytosolic factors or energy input. By employing sequence and mutagenesis analyses, we have determined both nuclear localization signal (NLS) 6KKGKSK11 and nuclear export signal (NES) 98LIITSYL TI106 of M protein that are important for the nucleocytoplasmic shuttling of M protein. Furthermore, we found that both lamin A/C and chromosome maintenance region 1 (CRM-1) proteins could be coimmunoprecipitated and colocalized with the BEFV M protein. Knockdown of lamin A/C by shRNA and inhibition of CRM-1 by leptomycin B significantly reduced virus yield. Collectively, this study provides novel insights into nucleocytoplasmic shuttling of the BEFV M protein modulated by lamin A/C and CRM-1 and by a transcription- and carrier- and energy-dependent pathway.

Continuous clinicopathological and molecular recognition of very virulent infectious bursal disease virus in commercial broiler chickens.

Gumboro virus is one of the most dangerous immunosuppressant viruses that infect chickens and causes massive financial losses worldwide. The current study aims to conduct a molecular characterization of chicken farms for the infectious bursal disease virus (IBDV). Based on postmortem (PM) lesions, 125 bursal samples from 25 farms were collected from clinically diseased commercial chicken farms with increased mortality and suspected Gumboro virus infection. Pooled bursal samples from suspected IBD-vaccinated flocks were tested for IBDV by reverse transcriptase polymerase chain reaction (RT-PCR). Fifteen out of 25 pooled specimens were found positive for IBDV, with a 60% detection rate, and confirmed positive for very virulent IBDV (vvIBDV) by sequence analysis. Nucleotide phylogenetic analysis of VP1 and VP2 genes was employed to compare the 5 chosen isolates with strains representing different governorates in Egypt during 2022. All strains were clustered with vvIBDV with no evidence of reassortment in the VP1 gene. The VP1 and VP2 genes are divided into groups (I, II). The strains in our study were related to group II, and it acquired a new mutation in the VP2 gene that clustered it into new subgroup B. By mutation analysis, the VP2 gene of all strains had a characteristic mutation to vvIBDV. It acquired new mutations in HVRs compared with HK46 in Y220F, A222T/V in all strains in our study, and Q221K that was found in IBD-EGY-AH5 and AH2 in the loop PBC in addition to G254S in all strains in our study and Q249k that found in IBD-EGY-AH1 and AH3 in the loop PDE. These mutations are important in the virulency and antigenicity of the virus. The VP1 had 242E, 390M, and 393D which were characteristic of vvIBDV and KpnI restriction enzyme (777GGTAC/C782) in addition to a new mutation (F243Y and N383H) in IBD-EGY-AH1 and AH4 strains. According to the current study, the strains were distinct from the vaccinal strain; they could be responsible for the most recent IBDV outbreaks observed in flocks instead of received vaccinations. The current study highlighted the importance of molecular monitoring to keep up to date on the circulating IBDV for regular evaluation of commercial vaccination programs against circulating field viruses.

Molecular epidemiology of infectious bursal disease virus in the Near East and Persian Gulf regions.

RESEARCH HIGHLIGHTS: Different field IBDVs were found to circulate in the Near and Middle East.Multiple atypical genotypes (A3B1, A4B1, A6B1) were found to circulate extensively.Traditional very virulent IBDVs (A3B2) were a minority of the detected strains.Viral exchanges can be hypothesized between the region and different continents.

Protein kinase Cdc7 supports viral replication by phosphorylating Avibirnavirus VP3 protein.

IMPORTANCE: The Avibirnavirus infectious bursal disease virus is still an important agent which largely threatens global poultry farming industry economics. VP3 is a multifunctional scaffold structural protein that is involved in virus morphogenesis and the regulation of diverse cellular signaling pathways. However, little is known about the roles of VP3 phosphorylation during the IBDV life cycle. In this study, we determined that IBDV infection induced the upregulation of Cdc7 expression and phosphorylated the VP3 Ser13 site to promote viral replication. Moreover, we confirmed that the negative charge addition of phosphoserine on VP3 at the S13 site was essential for IBDV proliferation. This study provides novel insight into the molecular mechanisms of VP3 phosphorylation-mediated regulation of IBDV replication.

Whole Genome Sequencing of Infectious Bursal Disease Viruses Isolated from a Californian Outbreak Unravels the Underlying Virulence Markers and Highlights Positive Selection Incidence.

Outbreaks of the immunosuppressive infectious bursal disease (IBD) are frequently reported worldwide, despite the vaccination regimes. A 2009 Californian IBD outbreak caused by rA and rB isolates was described as very virulent (vv) IBD virus (IBDV); however, molecular factors beyond this virulence were not fully uncovered. Therefore, segments of both isolates were amplified, successfully cloned, whole genome sequenced by Next Generation Sequencing, genotyped, and the leading virulence factors were entirely investigated in terms of phylogenetic and amino acid analysis and protein modeling for positive selection orientation and interaction analysis. rA and rB isolates displayed the highest amino acid identity (97.84-100%) with Genotype 3 strains. Interestingly, rA and rB contained all virulence hallmarks of hypervariable (HVR), including 222A, 242I, 249Q, 256I, 284A, 286T, 294I, 299S, and 318G, as well as the serine-rich heptapeptide sequence. Moreover, we pinpointed the A3B2 genotype of rA and rB, predominant in non-reassortants, and we highlighted the absence of recombination events. Furthermore, gene-wise phylogenetic analysis showed the entire genes of rA and rB clustered with the vvIBDVs and emphasized their share in IBDV virulence. VP5 showed a virulence marker, MLSL (amino acid sequence). VP2 encountered three significant novel mutations apart from the HVR, including G163E in rA and Y173C and V178A in rB, all residing within interacting motifs. VP4 contained 168Y, 173N, 203S, and 239D characteristic for the vv phenotype. A235V mutation was detected at the dsRNA binding domain of VP3. In VP1, the TDN triplet and the mutation (V4I) were detected, characteristic of hypervirulence occurring at the N-terminus responsible for protein priming. Although selection analysis revealed seven sites, codon 222 was the only statistically significant selection site. The VP2 modeling of rA and rB highlighted great structure fitness, with 96.14% Ramachandran favored positioning including the 222A, i.e., not influencing the structure stability. The 222A was found to be non-interface surface residue, associated with no interaction with the attachment-mediated ligand motif. Our findings provide pivotal insights into the evolution and underlying virulence factors and will assist in the development of control strategies via sequence-based continuous monitoring for the early detection of novel vv strains.

Comprehensive Analysis of the Tegument Proteins Involved in Capsid Transport and Virion Morphogenesis of Alpha, Beta and Gamma Herpesviruses.

Herpesviruses are enveloped and have an amorphous protein layer surrounding the capsid, which is termed the tegument. Tegument proteins perform critical functions throughout the viral life cycle. This review provides a comprehensive and comparative analysis of the roles of specific tegument proteins in capsid transport and virion morphogenesis of selected, well-studied prototypes of each of the three subfamilies of Herpesviridae i.e., human herpesvirus-1/herpes simplex virus-1 (Alphaherpesvirinae), human herpesvirus-5/cytomegalovirus (Betaherpesvirinae) and human herpesvirus -8/Kaposi's sarcomavirus (Gammaherpesvirinae). Most of the current knowledge is based on alpha herpesviruses, in particular HSV-1. While some tegument proteins are released into the cytoplasm after virus entry, several tegument proteins remain associated with the capsid and are responsible for transport to and docking at the nucleus. After replication and capsid formation, the capsid is enveloped at the nuclear membrane, which is referred to as primary envelopment, followed by de-envelopment and release into the cytoplasm. This requires involvement of at least three tegument proteins. Subsequently, multiple interactions between tegument proteins and capsid proteins, other tegument proteins and glycoproteins are required for assembly of the virus particles and envelopment at the Golgi, with certain tegument proteins acting as the central hub for these interactions. Some redundancy in these interactions ensures appropriate morphogenesis.

Transcriptome screening identifies TIPARP as an antiviral host factor against the Getah virus.

IMPORTANCE: Alphaviruses threaten public health continuously, and Getah virus (GETV) is a re-emerging alphavirus that can potentially infect humans. Approved antiviral drugs and vaccines against alphaviruses are few available, but several host antiviral factors have been reported. Here, we used GETV as a model of alphaviruses to screen for additional host factors. Tetrachlorodibenzo-p-dioxin-inducible poly(ADP ribose) polymerase was identified to inhibit GETV replication by inducing ubiquitination of the glycoprotein E2, causing its degradation by recruiting the E3 ubiquitin ligase membrane-associated RING-CH8 (MARCH8). Using GETV as a model virus, focusing on the relationship between viral structural proteins and host factors to screen antiviral host factors provides new insights for antiviral studies on alphaviruses.

A seamless connection from the burst sequence to the start codon is essential for polyhedrin hyperexpression in alphabaculoviruses.

Alphabaculoviruses produce a large number of occlusion bodies (OBs) in host cells during the late stage of infection. OBs are mainly composed of polyhedrin (POLH), and high-level transcription of the polh gene has been exploited to express foreign proteins in insect cells. While making Bombyx mori nucleopolyhedrovirus (BmNPV) polh mutants using a conventional transfer vector-based method, we noticed that a virus with a short sequence insertion just before the polh start codon produces fewer very small OBs. Detailed analysis of several BmNPV mutants revealed that insertions between the burst sequence and start codon markedly decrease POLH accumulation and polh transcription. We further confirmed this decrease using recombinant viruses expressing a reporter gene driven by the polh promoter. These findings underscore the critical importance of a seamless connection from the burst sequence to the start codon for baculovirus polh hyperexpression.