Analysis of Ad5 hexon and 100K ts mutants using conformation-specific monoclonal antibodies

Activation of the NLRP3 inflammasome by human adenovirus type 7 L4 100-kilodalton protein

Human adenovirus type 7 (HAdV-7) is a significant viral pathogen that causes respiratory infections in children. Currently, there are no specific antiviral drugs or vaccines for children targeting HAdV-7, and the mechanisms of its pathogenesis remain unclear. The NLRP3 inflammasome-driven inflammatory cascade plays a crucial role in the host's antiviral immunity. Our previous study demonstrated that HAdV-7 infection activates the NLRP3 inflammasome. Building upon this finding, our current study has identified the L4 100 kDa protein encoded by HAdV-7 as the primary viral component responsible for NLRP3 inflammasome activation. By utilizing techniques such as co-immunoprecipitation, we have confirmed that the 100 kDa protein interacts with the NLRP3 protein and facilitates the assembly of the NLRP3 inflammasome by binding specifically to the NACHT and LRR domains of NLRP3. These insights offer a deeper understanding of HAdV-7 pathogenesis and contribute to the development of novel antiviral therapies.

Genetic modification regulates pathogenicity of a fowl adenovirus 4 strain after cell line adaptation (genetic mutation in FAdV-4 lowered pathogenicity)

Fowl adenovirus 4 (FAdV-4) is a major avian virus that induces fatal diseases in chicken such as, hydropericardium and hepatitis. The viral structure consists of hexon, penton, fiber-1, and fiber-2 which are associated with immunopathogenesis. In this study, we investigated the genetic modification of a FAdV-4 strain after continuous passages in a cell line and evaluated the pathogenicity associated with mutations. We used the FadV-4 KNU14061 strain, which was isolated from layers in 2014. The virus went through 80 passages in the Leghorn male hepatoma (LMH) cell line. The full genetic sequence was identified, and we found a frameshift in the fiber-2 amino acid sequence after the initial thirty passages. To examine whether the frameshift in the fiber-2 gene affects the pathogenicity in chicken, we inoculated LMH80 (80 times passaged) and LMH10 (10 times passaged) into 3-day-old chickens and examined the pathogenesis. LMH10 infection via intramuscular route induced fatal pathology, but LMH80 did not. Furthermore, LHM80 pre-treatment protected hosts from the LMH10 challenge. Thus, the genetic modification isolated by serial passage lowered pathogenicity and the resulting virus acted as an attenuated vaccine that can be a FAdV-4 vaccine strain candidate.

First identification of canine adenovirus 1 in mink and bioinformatics analysis of its 100 K protein

Introduction

Animal trade favors the spreading of emerging canine adenovirus 1 (CAdV-1) in mink. Because the 100K protein is not exposed to the viral surface at any stage, it can be used to differentiate the vaccine from wild virus infection. However, no related research has been conducted. This study aimed to find evidence of CAdV-1 in mink and predict the character of the 100K protein in the current circulating CAdV-1 strain of mink.

Method

In this experiment, the identification of CAdV-1, the phylogenetic tree, homology, and bioinformatics analysis of 100K were conducted.

Results

The results showed that the CAdV-1 was identified in the mink and that its Fiber was located in a separate branch. It was closely related to strains isolated from Norwegian Arctic fox and Red fox. 100K was located in a separate branch, which had the closest genetic relationship with skunks, porcupines, raccoons, and hedgehogs and a far genetic relationship with the strains in dogs. 100K protein is an unstable and hydrophobic protein. It had evidence of selective pressure and recombination, 1 glycosylation site, 48 phosphorylation sites, 60 dominant B cell epitopes, and 9 peptides of MHC-I and MHC-II. Its subcellular localization was mainly in the endoplasmic reticulum and mitochondria. The binding sites of 100K proteins were DBP proteins and 33K proteins.

Discussion

The stains in the mink were different from fox. The exploration of its genomic characteristics will provide us with a deeper understanding of the prevention of canine adenovirus.

Molecular Mechanism of Adenovirus Late Protein L4-100K Chaperones the Trimerization of Hexon

Assembly of the adenovirus capsid protein hexon depends on the assistance of the molecular chaperone L4-100K. However, the chaperone mechanisms remain unclear. In this study, we found that L4-100K was involved in the hexon translation process and could prevent hexon degradation by the proteasome in cotransfected human cells. Two nonadjacent domains, 84-133 and 656-697, at the N-terminal and C-terminal regions of human adenovirus type 5 L4-100K, respectively, were found to be crucial and cooperatively responsible for hexon trimer expression and assembly. These two chaperone-related domains were conserved in the sequence of L4-100K and in the function of hexon assembly across different adenovirus serotypes. Different degrees of cross-activity of hexon trimerization with different serotypes were detected in subgroups B, C, and D, which were proven to be controlled by the interaction between the C-terminal chaperone-related domain of L4-100K and hypervariable regions (HVR) of hexon. Additionally, HVR-chimeric hexon mutants were successfully assembled with the assistance of the 1-697 mutant. Structural analysis of 656-697 by nuclear magnetic resonance and structural prediction of L4-100K using Robetta showed that the two conserved domains are mainly composed of α-helices and are located on the surface of the highly folded core region. Our research provides a more complete understanding of hexon assembly and guidance for the development of hexon-chimeric adenovirus vectors that will be safer, smarter, and more efficient. IMPORTANCE Adenovirus vectors have been widely used in clinical trials of vaccines and gene therapy, although some deficiencies remain. Chimeric modification of the hexon was expected to improve the potency of preexisting immune evasion and targeting, but in many cases, viral packaging is prevented by the inability of the chimeric hexon to assemble correctly. So far, few studies have examined the mechanisms of hexon trimer assembly. Here, we show how the chaperone protein L4-100K contributes to the assembly of the adenovirus capsid protein hexon, and these data will provide a guide for novel adenovirus vector design and development, as we desired.

Complete Genome Sequence, Molecular Characterization and Phylogenetic Relationships of a Novel Tern Atadenovirus

Discovery and study of viruses carried by migratory birds are tasks of high importance due to the host's ability to spread infectious diseases over significant distances. With this paper, we present and characterize the first complete genome sequence of atadenovirus from a tern bird (common tern, Sterna hirundo) preliminarily named tern atadenovirus 1 (TeAdV-1). TeAdV-1 genome is a linear double-stranded DNA molecule, 31,334 base pairs which contain 30 methionine-initiated open reading frames with gene structure typical for Atadenovirus genus, and the shortest known inverted terminal repeats (ITRs) within the Atadenovirus genus consisted of 25 bases. The nucleotide composition of the genome is characterized by a low G + C content (33.86%), which is the most AT-rich genome of known avian adenoviruses within Atadenovirus genus. The nucleotide sequence of the TeAdV-1 genome shows high divergence compared to known representatives of the Atadenovirus genus with the highest similarity to the duck atadenovirus 1 (53.7%). Phylogenetic analysis of the protein sequences of core genes confirms the taxonomic affiliation of the new representative to the genus Atadenovirus with the degree of divergence from the known representatives exceeding the interspecies distance within the genus. Thereby we proposed a novel TeAdV-1 to be considered as a separate species.

Molecular characterization and pathogenicity of highly pathogenic fowl adenovirus serotype 4 isolated from laying flock with hydropericardium-hepatitis syndrome

Hydropericardium-hepatitis syndrome (HHS) is an important emerging disease responsible for huge economic losses to the poultry industry in China. HHS primarily affects 20 to 60-day-old broilers and rarely occurs in laying flock. In this study, the highly pathogenic fowl adenovirus (FAdV) strain, AH-F19, was isolated from the liver samples of 120-day-old laying flock with HHS and its phylogenetic information, genetic mutations, and pathogenicity was evaluated. The phylogenetic analysis revealed that AH-F19 belonged to the FAdV serotype 4 (FAdV-4) cluster, however, 100K differs from the other FAdV-4 strains and is divided into different branches. Amino acid variations in fiber-2 for pathogenic isolates and non-pathogenic isolates indicated that D219, T300, and T380 may not be responsible for virulence. Animal experiments revealed AH-F19 to be a highly pathogenic isolate that can cause 100% mortality in three-week-old specific pathogen-free (SPF) chickens, which exhibited typical hydropericardium and hepatitis. Microscopically, the presence of basophilic intranuclear inclusion bodies in hepatocytes, fractured heart muscle fibers, as well as kidney degeneration and necrosis was observed. Collectively, these findings enriched our understanding of FAdV-4 pathogenicity and provided a reference for further exploration into its pathogenicity.

Interaction between hexon and L4-100K determines virus rescue and growth of hexon-chimeric recombinant Ad5 vectors

The immunogenicity of recombinant adenovirus serotype 5 (rAd5) vectors has been shown to be suppressed by neutralizing antibodies (NAbs) directed primarily against hexon hypervariable regions (HVRs). Preexisting immunity can be circumvented by replacing HVRs of rAd5 hexon with those derived from alternate adenovirus serotypes. However, chimeric modification of rAd5 hexon HVRs tends to cause low packaging efficiency or low proliferation of rAd5 vectors, but the related mechanism remains unclear. In this study, several Ad5-based vectors with precise replacement of HVRs with those derived from Ad37 and Ad43 were generated. We first observed that a HVR-exchanged rAd5 vector displayed a higher efficacy of the recombinant virus rescue and growth improvement compared with the rAd5 vector, although most hexon-chimeric rAd5 vectors constructed by us and other groups have proven to be nonviable or growth defective. We therefore evaluated the structural stability of the chimeric hexons and their interactions with the L4-100K chaperone. We showed that the viability of hexon-chimeric Ad5 vectors was not attributed to the structural stability of the chimeric hexon, but rather to the hexon maturation which was assisted by L4-100K. Our results suggested that the intricate interaction between hexon and L4-100K would determine the virus rescue and proliferation efficiency of hexon-chimeric rAd5 vectors.

CRM1-dependent transport supports cytoplasmic accumulation of adenoviral early transcripts

The life cycle of adenoviruses is divided by convention into early and late phases, separated by the onset of viral genome replication. Early events include virus adsorption, transport of the genome into the nucleus, and the expression of early genes. After the onset of viral DNA replication, transcription of the major late transcription unit (MLTU) and thereby synthesis of late proteins is induced. These steps are controlled by an orchestra of regulatory processes and require import of the genome and numerous viral proteins into the nucleus, as well as active transport of viral transcripts and proteins from the nucleus to the cytoplasm. The latter is achieved by exploiting the shuttling functions of cellular transport receptors, which normally stimulate the nuclear export of cellular mRNA and protein cargos. A set of adenoviral early and late proteins contains a leucine-rich nuclear export signal of the HIV-1 Rev type, known to be recognized by the cellular export receptor CRM1. However, a role for CRM1-dependent export in supporting adenoviral replication has not been established. To address this issue in detail, we investigated the impact of two different CRM1 inhibitors on several steps of the adenoviral life cycle. Inhibition of CRM1 led to a reduction in viral early and late gene expression, viral genome replication, and progeny virus production. For the first time, our findings indicate that CRM1-dependent shuttling is required for the efficient export of adenoviral early mRNA.

Faithful chaperones

This review describes the properties of some rare eukaryotic chaperones that each assist in the folding of only one target protein. In particular, we describe (1) the tubulin cofactors, (2) p47, which assists in the folding of collagen, (3) α-hemoglobin stabilizing protein (AHSP), (4) the adenovirus L4-100 K protein, which is a chaperone of the major structural viral protein, hexon, and (5) HYPK, the huntingtin-interacting protein. These various-sized proteins (102–1,190 amino acids long) are all involved in the folding of oligomeric polypeptides but are otherwise functionally unique, as they each assist only one particular client. This raises a question regarding the biosynthetic cost of the high-level production of such chaperones. As the clients of faithful chaperones are all abundant proteins that are essential cellular or viral components, it is conceivable that this necessary metabolic expenditure withstood evolutionary pressure to minimize biosynthetic costs. Nevertheless, the complexity of the folding pathways in which these chaperones are involved results in error-prone processes. Several human disorders associated with these chaperones are discussed.

Arginine methylation of human adenovirus type 5 L4 100-kilodalton protein is required for efficient virus production

The adenovirus type 5 (Ad5) late region 4 (L4) 100-kDa nonstructural protein (L4-100K) mediates inhibition of cellular protein synthesis and selective translation of tripartite leader (TL)-containing viral late mRNAs via ribosome shunting. In addition, L4-100K has been implicated in the trimerization and nuclear localization of hexon protein. We previously proved that L4-100K is a substrate of the protein arginine methylation machinery, an emergent posttranslational modification system involved in a growing list of cellular processes, including transcriptional regulation, cell signaling, RNA processing, and DNA repair. As understood at present, L4-100K arginine methylation involves protein arginine methyltransferase 1 (PRMT1), which asymmetrically dimethylates arginines embedded in arginine-glycine-glycine (RGG) or glycine-arginine-rich (GAR) domains. To identify the methylated arginine residues and assess the role of L4-100K arginine methylation, we generated amino acid substitution mutations in the RGG and GAR motifs to examine their effects in Ad-infected and plasmid-transfected cells. Arginine-to-glycine exchanges in the RGG boxes significantly diminished L4-100K methylation in the course of an infection and substantially reduced virus growth, demonstrating that L4-100K methylation in RGG motifs is an important host cell function required for efficient Ad replication. Our data further indicate that PRMT1-catalyzed arginine methylation in the RGG boxes regulates the binding of L4-100K to hexon and promotes the capsid assembly of the structural protein as well as modulating TL-mRNA interaction. Furthermore, substitutions in GAR, but not RGG, regions affected L4-100K nuclear import, implying that the nuclear localization signal of L4-100K is located within the GAR sequence.

Control of adenovirus packaging

The results of studies of Adenovirus have contributed to our basic understanding of the molecular biology of the cell. While a great body of knowledge has been developed concerning Ad gene expression, viral replication, and effects on the infected host, the molecular details of the assembly process of Adenovirus particles are largely unknown. In this article, we would like to propose a theoretical model for the packaging and assembly of Adenovirus and present an overview of the studies that have contributed to our present understanding. In particular, we will summarize the molecular details of the process for packaging of viral DNA into virus particles and highlight the events in packaging and assembly that require further study.

Critical role for arginine methylation in adenovirus-infected cells

During the late stages of adenovirus infection, the 100K protein (100K) inhibits the translation of cellular messages in the cytoplasm and regulates hexon trimerization and assembly in the nucleus. However, it is not known how it switches between these two functions. Here we show that 100K is methylated on arginine residues at its C terminus during infection and that this region is necessary for binding PRMT1 methylase. Methylated 100K is exclusively nuclear. Mutation of the third RGG motif (amino acids 741 to 743) prevents localization to the nucleus during infection, suggesting that methylation of that sequence is important for 100K shuttling. Treatment of infected cells with methylation inhibitors inhibits expression of late structural proteins. These data suggest that arginine methylation of 100K is necessary for its localization to the nucleus and is a critical cellular function necessary for productive adenovirus infection.

The 100K-chaperone protein from adenovirus serotype 2 (Subgroup C) assists in trimerization and nuclear localization of hexons from subgroups C and B adenoviruses

Recombinant hexons from subgroup C adenoviruses (Ad2 and Ad5) and from a member of subgroup B (Ad3) adenoviruses have been expressed in insect cells. When expressed alone, all three hexons were found to be insoluble and accumulated as inclusion bodies in the cytoplasm. However, co-expression of recombinant Ad2, Ad5 or Ad3 hexon with Ad2 L4-100K protein resulted in the formation of soluble trimeric hexons. EM analysis of hexons revealed that they were indistinguishable from native hexon capsomers isolated from Ad2-infected human cells, or released from partially disrupted adenovirions. This suggests that 100K acts as a chaperone for hexon folding and self-assembly into capsomer in insect cells. Since 100K protein assists in the trimerization of subgroup C hexon, and of subgroup B hexon protein, it implies that it functions in a manner that is both homo- and heterotypic. During the course of recombinant protein expression, the 100K protein was found in association with hexon monomers and trimers within the cytoplasm. In the nucleus, however, 100K was found in complexes with hexon trimers exclusively. EM observation of purified 100K protein samples showed a dumb-bell-shaped molecule compatible with a monomeric protein. EM analysis of hexon-100K protein complexes showed that interaction of hexon with the 100K protein occurred via one of the globular domains of the 100K protein molecule. Our data confirm the role of the 100K protein as a scaffold protein for hexon, and provide evidence suggesting its function in hexon nuclear import in insect cells.

Protein arginine methylation during lytic adenovirus infection

Arginine methylation of proteins affects major processes in the cell, including transcriptional regulation, mRNA metabolism, signal transduction and protein sorting. Arginine methylation of Ad (adenovirus) E1B 55-kDa-associated protein E1B-AP5 was recently described by us [Kzhyshkowska, Schutt, Liss, Kremmer, Stauber, Wolf and Dobner (2001) Biochem. J. 358, 305-314]. In this first example of protein arginine methylation analysis in Ad-infected cells, we investigated methylation of the E1B-AP5 and the viral L4-100 kDa protein. We demonstrate that E1B-AP5 methylation is enhanced during the course of infection in a cell-type-specific manner. We also show that L4-100 kDa is efficiently methylated in Ad-infected cells. L4-100 kDa formed complex with methyltransferase in vivo during productive infection, and can be methylated by HRMT1L2 (human protein arginine methyltransferase 1) in vitro. Comparative analysis of E1B-AP5 and L4-100 kDa protein methylation in Ad-infected HeLa, MCF-7 and H1299 cells revealed that the profile of protein arginine methylation correlates with the efficiency of Ad proteins production. Our results suggest that protein arginine methylation is an important host-cell function required for efficient Ad replication.

Role of Bovine Adenovirus-3 33K protein in viral replication

The L6 region of bovine adenovirus type (BAdV)-3 encodes a nonstructural protein named 33K. To identify and characterize the 33K protein, rabbit polyclonal antiserum was raised against a 33K-GST fusion protein expressed in bacteria. Anti-33K serum immunoprecipitated a protein of 42 kDa in in vitro translated and transcribed mRNA of 33K. However, three proteins of 42, 38, and 33 kDa were detected in BAdV-3 infected cells. To determine the role of this protein in virus replication, a recombinant BAV-33S1 containing insertional inactivation of 33K (a stop codon created at the seventh amino acid of 33K ORF) was constructed. Although BAV-33S1 could be isolated, the mutant showed a severe defect in the production of progeny virus. Inactivation of the 33K gene showed no effect on early and late viral gene expression in cells infected with BAV-33S1. However, formation of mature virions was significantly reduced in cells infected with BAV-33S1. Surprisingly, insertional inactivation of 33K at amino acid 97 (pFBAV-33.KS2) proved lethal for virus production. Although expression of early or late genes was not affected, no capsid formation could be observed in mutant DNA-transfected cells. These results suggest that 33K is required for capsid assembly and efficient DNA capsid interaction.

Activation of the early-late switch in adenovirus type 5 major late transcription unit expression by L4 gene products

The adenovirus major late transcription unit (MLTU) encodes multiple proteins from five regions, L1 to L5, through differential splicing and polyadenylation. MLTU expression is temporally regulated; only a single product from L1 (52/55K) is expressed prior to replication, but a subsequent switch, the mechanism of which has not been defined, leads to full expression that encompasses L1 IIIa and all L2 to L5 products. Transfection of a plasmid containing the complete MLTU gave a full array of proteins in proportions similar to those in a late infection, and in a time course, the temporal pattern of expression in a natural infection was reproduced. However, a plasmid truncated after the L3 poly(A) site exclusively expressed the L1 52/55K protein and was defective in the switch to full gene expression from L1 to L3. The L4 33K protein, supplied in trans, was sufficient to upregulate cytoplasmic mRNA for MLTU products characteristic of the late pattern of expression to levels comparable to those produced by the full-length MLTU. There was a corresponding increase in expression of the L1 IIIa, L2, and L3 proteins, except hexon. Hexon protein expression additionally required both the L4 100K protein in trans and sequences downstream of the L3 poly(A) site in cis. These results indicate that induction of L4 protein expression is a key event in the early-late switch in MLTU expression, which we propose is precipitated by small amounts of L4 expression in a feed-forward activation mechanism.

Structure of the herpesvirus major capsid protein

Herpes simplex virus-1 (HSV-1) virions are large, complex enveloped particles containing a proteinaceous tegument layer connected to an icosahedral capsid. The major capsid protein, VP5 (149 kDa), makes up both types of capsomere, pentons and hexons. Limited trypsin digestion of VP5 identified a single stable 65 kDa fragment which represents a proposed protein folding nucleus. We report the 2.9 A crystal structure of this fragment and its modeling into an 8.5 A resolution electron cryomicroscopy map of the HSV-1 capsid. The structure, the first for any capsid protein from Herpesviridae, revealed a novel fold, placing herpesviruses outside any of the structurally linked viral groupings. Alterations in the geometrical arrangements of the VP5 subunits in the capsomeres exposes different residues, resulting in the differential association of the tegument and VP26 with the pentons and hexons, respectively. The rearrangements of VP5 subunits required to form both pentavalent and hexavalent capsomeres result in structures that exhibit very different electrostatic properties. These differences may mediate the binding and release of other structural proteins during capsid maturation.

Truncation of the human adenovirus type 5 L4 33-kDa protein: evidence for an essential role of the carboxy-terminus in the viral infectious cycle

The subgroup C human adenovirus L4 33-kDa protein is a nuclear phosphoprotein that plays a direct, but dispensable, role in virion assembly. The r-strand open reading frame (ORF) for this protein lies opposite to the 5' end of the l-strand E2 early (E2E) transcription units. To facilitate studies of regulation of E2E transcription, we wished to construct a mutant virus in which the 33-kDa ORF was truncated to serve as a background into which specific E2E mutations could be introduced without also altering the 33-kDa protein. We constructed viral DNA (vDNA) containing within the 33-kDa ORF two tandem, premature stop codons that should prevent translation of the C-terminal 47 amino acids of the protein (Delta47). We report here the unanticipated lethality of such truncation of the L4 33-kDa protein. Viral DNA harboring the Delta47 mutations did not produce infectious virus when transfected into cultured cells. In contrast, infectious virus was recovered upon transfection of revertant vDNA, indicating that the Delta47 mutations were responsible for the observed phenotype. The Delta47 mutations did not affect E2E transcription or production of the E2 DNA-binding protein. Transfected Delta47 vDNA was replicated and directed the production of early and late viral proteins, including hexon protein in the trimer conformation. However, no virus particles of any kind were produced. We propose that truncation of the adenovirus 33-kDa protein results in a lethal, late block in the infectious cycle during the assembly of progeny virions and discuss the implications of this phenotype for the mechanism of virion assembly.

Adenovirus vectors with the 100K gene deleted and their potential for multiple gene therapy applications

The 100K protein has a number of critical roles vital for successful completion of the late phases of the adenovirus (Ad) life cycle. We hypothesized that the introduction of deletions within the 100K gene would allow for the production of a series of new classes of Ad vector, including one that is replication competent but blocked in the ability to carry out many late-phase Ad functions. Such a vector would have potential for several gene therapy applications, based upon its ability to increase the copy number of the transgene encoded by the vector (via genome replication) while decreasing the side effects associated with Ad late gene expression. To efficiently produce 100K-deleted Ad ([100K-]Ad) vectors, an E1- and 100K-complementing cell line (K-16) was successfully isolated. Transfection of an [E1-,100K-]Ad vector genome into the K-16 cells readily yielded high titers of the vector. After infection of noncomplementing cells, we demonstrated that [100K-]Ad vectors have a significantly decreased ability to express several Ad late genes. Additionally, if the E1 gene was present in the infected noncomplementing cells, [100K-]Ad vectors were capable of replicating their genomes to high copy number, but were significantly blocked in their ability to efficiently encapsidate the replicated genomes. Injection of an [E1-,100K-]Ad vector in vivo also correlated with significantly decreased hepatotoxicity, as well as prolonged vector persistence. In summary, the unique properties of [100K-]Ad vectors suggest that they may have utility in a variety of gene therapy applications.

Characterization of a recombinant fowlpox virus expressing the native hexon of hemorrhagic enteritis virus

The structure of the icosahedral adenovirus capsid is highly conserved among Adenoviridae. In its native form, the hexon is the major capsid protein. The nascent hexon requires the 100 kDa folding protein to fold into its native, trimeric form. The hexon and 100 kDa folding protein were co-expressed in a fowlpox virus (FPV) vector and in the recombinant FPVs (rFPVs) in which the hexon and 100 kDa folding protein genes are cloned head to tail, the native hexon could be detected with indirect immunofluorescence and immunoprecipitation using a native hexon monoclonal antibody. The FPV-@X100 construct, in which the 100kDa folding protein gene follows the hexon gene in a head to tail fashion, elicited the best humoral response in chickens. An attenuated HEV commercial vaccine elicited higher and longer lasting anti-HEV titers than FPV-@X100. Humoral immunity was also compared in turkeys inoculated with rFPVs expressing the hexon alone, the 100 kDa folding protein alone, or expressing both genes in different configurations. No anti-HEV humoral immune response was detected in turkeys inoculated with the rFPVs expressing the hexon alone or the 100 kDa folding protein alone.

Analysis of synthesis, stability, phosphorylation, and interacting polypeptides of the 34-kilodalton product of open reading frame 6 of the early region 4 protein of human adenovirus type 5

The 34-kDa early-region 4 open reading frame 6 (E4orf6) product of human adenovirus type 5 forms complexes with both the cellular tumor suppressor p53 and the viral E1B 55-kDa protein (E1B-55kDa). E4orf6 can inhibit p53 transactivation activity, as can E1B-55kDa, and in combination these viral proteins cause the rapid turnover of p53. In addition, E4orf6-55kDa complexes play a critical role at later times in the regulation of viral mRNA transport and shutoff of host cell protein synthesis. In the present study, we have further characterized some of the biological properties of E4orf6. Analysis of extracts from infected cells by Western blotting indicated that E4orf6, like E1A and E1B products, is present at high levels until very late times, suggesting that it is available to act throughout the infectious cycle. This pattern is similar to that of E4orf4 but differs markedly from that of another E4 product, E4orf6/7, which is present only transiently. Synthesis of E4orf6 is maximal at early stages but ceases completely with the onset of shutoff of host protein synthesis; however, it was found that unlike E4orf6/7, E4orf6 is very stable, thus allowing high levels to be maintained even at late times. E4orf6 was shown to be phosphorylated at low levels. Coimmunoprecipitation studies in cells lacking p53 indicated that E4orf6 interacts with a number of other proteins. Five of these were shown to be viral or virally induced proteins ranging in size from 102 to 27 kDa, including E1B-55kDa. One such species, of 72 kDa, was shown not to represent the E2 DNA-binding protein and thus remains to be identified. Another appeared to be the L4 100-kDa nonstructural adenovirus late product, but it appeared to be present nonspecifically and not as part of an E4orf6 complex. Apart from p53, three additional cellular proteins, of 84, 19, and 14 kDa were detected by using an adenovirus vector that expresses only E4orf6. The 19-kDa species and a 16-kDa cellular protein were also shown to interact with E4orf6/7. It is possible that complex formation with these viral and cellular proteins plays a role in one or more of the biological activities associated with E4orf6 and E4orf6/7.

Nucleotide sequence and transcription map of porcine adenovirus type 3

The complete nucleotide sequence of porcine adenovirus type 3 was determined and a transcriptional map for the genome was constructed. The size of the genome is 34094 bp in length with an unusually high G + C content (63.7%), the highest thus far reported for any adenovirus. Overall organization of the genome is similar to that for previously sequenced adenoviral DNAs, but there also were distinct differences. The late regions genes are organized into six families, instead of five as they are in human adenovirus type 2. In contrast to bovine adenovirus type 3 and ovine adenovirus, which lack virion-associated RNA genes, the nucleotide sequence analysis of the viral genome indicates that it encodes one short VA RNA species. With the exception of the fiber and a 33-kDa nonstructural protein, the predicted amino acid sequences of the open reading frames in the late regions and the E2 region and IVa2 exhibited a high level of homology, whereas the deduced amino acid sequences of ORFs in E1, E3, and E4 regions, and the pIX showed a lesser homology with the corresponding proteins of other adenoviruses. The proteins V, VII, and IX are unusually long, and the protein VII lacks the consensus protease cleavage site. Genomic and cDNA sequence analysis has identified promoters, cap sites, intron-exon boundaries, polyadenylation signals, and polyadenylation sites in the viral genome.

Cytomegalovirus assembly protein precursor and proteinase precursor contain two nuclear localization signals that mediate their own nuclear translocation and that of the major capsid protein

The cytomegalovirus (CMV) assembly protein precursor (pAP) interacts with the major capsid protein (MCP), and this interaction is required for nuclear translocation of the MCP, which otherwise remains in the cytoplasm of transfected cells (L. J. Wood et al., J. Virol. 71:179-190, 1997). We have interpreted this finding to indicate that the CMV MCP lacks its own nuclear localization signal (NLS) and utilizes the pAP as an NLS-bearing escort into the nucleus. The CMV pAP amino acid sequence has two clusters of basic residues (e.g., KRRRER [NLS1] and KARKRLK [NLS2], for simian CMV) that resemble the simian virus 40 large-T-antigen NLS (D. Kalderon et al., Cell 39:499-509, 1984) and one of these (NLS1) has a counterpart in the pAP homologs of other herpesviruses. The work described here establishes that NLS1 and NLS2 are mutually independent NLS that can act (i) in cis to translocate pAP and the related proteinase precursor (pNP1) into the nucleus and (ii) in trans to transport MCP into the nucleus. By using combinations of NLS mutants and carboxy-terminal deletion constructs, we demonstrated a self-interaction of pAP and cytoplasmic interactions of pAP with pNP1 and of pNP1 with itself. The relevance of these findings to early steps in capsid assembly, the mechanism of MCP nuclear transport, and the possible cytoplasmic formation of protocapsomeric substructures is discussed.

Nucleotide and amino acid sequence analysis of the 100K protein of a serotype 3 porcine adenovirus

The genomic region between map units 69 and 78 of a type 3 porcine adenovirus (PAV3) was sequenced and analysed. An open reading frame (ORF) of 2514 nucleotides encoding a polypeptide of 838 amino acids and approximately 94.1 kDa was found. The size and location of the ORF suggested it was the PAV3 homologue of the 100K gene and this was confirmed by nucleotide sequence comparison with the 100K of human adenovirus type 2. Amino acid sequence alignment of the predicted polypeptide with the sequences of the 100K proteins of four human adenoviruses and type 10 fowl adenovirus revealed sequence identities of between 31% and 52%. Although amino acid conservation was present throughout the entire sequences compared, lower identity was noted in both the amino- and carboxy-termini.

Human adenovirus type 5 variants with sequence alterations flanking the E2A gene: effects on E2 expression and DNA replication

The human adenovirus type 5 (Ad5) E2 transcription unit is divided into a promoter-proximal region, E2A, and a distal region, E2B, each with its own polyadenylation site. Together these regions encode the three virus-derived proteins necessary for genome replication. Ad5 variants were produced that carried linker insertion mutations immediately 5' and/or 3' to the coding sequence for the E2A gene DNA binding protein (DBP). Two variants carrying solely a 5' lesion showed decreased usage of the adjacent 3' splice site, via which the DBP mRNA is produced, and an increased usage of the alternative downstream splice sites in the E2B region, wherein viral DNA polymerase and terminal protein precursor are encoded; these viruses showed somewhat reduced growth. A variant carrying a 3' lesion showed a marginal increase in DBP expression and slightly accelerated growth. When lesions 5' and 3' to the DBP coding sequence were combined in cis, the resulting virus was severely defective for growth and expressed E2B products to the virtual exclusion of E2A DBP. These data indicate that interactions must occur between the E2A 3' splice site and polyadenylation site before this region can be treated as an exon by the RNA processing machinery, and that a sequence alteration at the polyadenylation site that alone has only minor effects on the pattern of RNA processing can drastically affect terminal exon usage when placed in cis with a mutation that reduces splicing efficiency at the upstream 3' splice site. The data further indicate that, in vivo, Ad5 DNA replication is limited by prevailing DBP levels rather than by levels of polymerase or terminal protein precursor.

RNA-binding properties of a translational activator, the adenovirus L4 100-kilodalton protein

The adenovirus L4 100-kDa nonstructural protein (100K protein) is required for efficient initiation of translation of viral late mRNA species during the late mRNA species during the late phase of infection (B. W. Hayes, G. C. Telling, M. M. Myat, J. F. Williams, and S. J. Flint, J. Virol. 64:2732-2742, 1990). The RNA-binding properties of this protein were analyzed in an immunoprecipitation assay with the 100K-specific monoclonal antibody 2100K-1 (C. L. Cepko and P. A. Sharp, Virology 129:137-154, 1983). Coprecipitation of the 100K protein and 3H-infected cell RNA was demonstrated. The RNA-binding activity of the 100K protein was inhibited by single-stranded DNA but not by double-stranded DNA, double-stranded RNA, or tRNA. Competition assays were used to investigate the specificity with which the 100K protein binds to RNA in vitro. Although the protein exhibited a strong preference for the ribohomopolymer poly(U) or poly(G), no specific binding to viral mRNA species could be detected; uninfected or adenovirus type 5-infected HeLa cell poly(A)-containing and poly(A)-lacking RNAs were all effective inhibitors of binding of the protein to viral late mRNA. Similar results were obtained when the binding of the 100K protein to a single, in vitro-synthesized L2 mRNA was assessed. The poly(U)-binding activity of the 100K protein was used to compare the RNA-binding properties of the 100K protein prepared from cells infected by adenovirus type 5 and the H5ts1 mutant (B. W. Hayes, G. C. Telling, M. M. Myat, J. F. Williams, and S. J. Flint, J. Virol. 64:2732-2742, 1990). A temperature-dependent decrease in H5ts1 100K protein binding was observed, correlating with the impaired translational function of this protein in vivo. By contrast, wild-type 100K protein RNA binding was unaffected by temperature. These data suggest that the 100K protein acts to increase the translational efficiency of viral late mRNA species by a mechanism that involves binding to RNA.

Protection of turkeys against haemorrhagic enteritis by monoclonal antibody and hexon immunization

Virus-neutralizing monoclonal antibodies specific for the hexon of haemorrhagic enteritis virus (HEV), a turkey adenovirus, were examined for their ability to confer passive protection against haemorrhagic enteritis (HE) in turkeys. A high dose of antibody prevented clinical disease and reduced virus replication in experimentally infected birds. This suggests that virus neutralization might be an important mechanism for protection against HE. Subsequently, the use of the hexon protein as a subunit vaccine was investigated by immunizing birds with affinity-purified HEV hexon. The birds were tested for the appearance of hexon-specific antibodies in their sera, for protection from clinical disease, and prevention of virus replication after challenge with virulent HEV (HEV-V). Regardless of whether birds were immunized with native or denatured hexon, high ELISA antibody titres were produced to each immunogen. A virus-neutralizing antibody response was induced by immunization with the native hexon but not by immunization with the denatured protein. All turkeys twice immunized with a dose of at least 1 microgram, and four out of five birds immunized with two doses of 0.3 micrograms of purified native hexon, were protected against virus-induced disease and virus replication. In contrast, birds inoculated with denatured hexon were not protected. These results demonstrate the importance of the native (trimeric) structure of the hexon protein for eliciting a protective immune response. The impact of these results on the development of a vaccine for HE in turkeys produced by recombinant DNA technology is discussed.

Conserved sequences of the adenovirus genome for detection of all human adenovirus types by hybridization

The application of DNA hybridization directly to clinical specimens has the potential of improving the diagnosis of fastidious types of adenovirus. In this study, the genome of one adenovirus type from each human subgenus (A to F) was systematically evaluated by hybridization for homologous sequences to find the optimal common probe for detection of all human adenovirus types. The area of cross-hybridization, most closely defined with adenovirus type 2 (Ad2), mapped from map units 11.4 to 16.1 and 26.9 to 29.7 and, principally, to a central area of the genome between map units 47.5 and 65.2. The last area, enclosing the hexon gene, was highly conserved. Cloned probes generated from this area demonstrated the greatest homology to heterologous types by hybridization analysis. A HindIII-BglII clone containing the hexon gene of Ad2 within narrow confines reacted most evenly with all adenoviral types and detected the DNA of all other subgenera with a sensitivity 2 logs greater than that of a complete genomic Ad2 probe. The most homologous adenoviral gene sequences were observed in genes involved with DNA replication or intimately connected to the hexon in the early capsid formation. These results show that the hexon gene constitutes the best single region of the adenovirus genome for use as a genus-specific probe for the diagnosis of all human adenoviral subgenera by DNA hybridization.

The amino terminus of the adenovirus fiber protein encodes the nuclear localization signal

Using a recombinant vaccinia virus vector, the fiber protein from adenovirus serotype 2 has been expressed in human cells; the protein expressed was correctly assembled into trimers, glycosylated, and transported to the nucleus. Deletion of amino acids 2-5 (KRAR) resulted in accumulation of fiber in the cytoplasm; fusion of the sequence TKRVRL, found at the beginning of Ad7 fiber, to the N-terminus of this mutant restored correct targeting. Changing the charge of amino acids 91 and 92 within another potential targeting sequence (LKKTK to LEETK) had little effect on nuclear targeting. When fused to the N-terminus of beta-galactosidase and expressed in recombinant vaccinia virus, neither MKRARP nor MTKRVRL (from Ad2 and Ad7 fibers, respectively), were sufficient for efficient transport of the hybrid protein to the nucleus; on the other hand, fusions of either MKRARPSEDTF (from Ad2 fiber) or of MKRPRP (a known targeting sequence from the C-terminus of Ad2 E1A proteins) to beta-galactosidase were localized to the nucleus. These results suggest that sequences at the N-terminus of Ad2 and Ad7 fiber are required for correct nuclear targeting.

Association of HSP70 with the adenovirus type 5 fiber protein in infected HEp-2 cells

Although maximal synthesis of HSP70 is induced early (6-12 hr) after adenovirus type 5 (Ad5) infection of HEp-2 or HeLa cells, the total amount of HSP70 appears to be increased at late times of infection (18-24 hr). Since virion structural proteins also accumulate at these times, we investigated the possible interaction between Ad5 structural proteins and HSP70 by immunoprecipitation of infected cell extracts with antibodies to either ATP-affinity-purified HSP70 or to CsCl-gradient-purified Ad5 virions. We found that HSP70 and a 62-kDa Ad-specific protein coimmunoprecipitated from infected cell extracts. Antibody which recognizes one of these two proteins does not cross-react with the other. Thus, the association between HSP70 and the 62-kDa protein appears specific. Using different antisera to specific adenovirus structural proteins, we have identified the 62-kDa protein as the Ad5 fiber protein.

The adenovirus L4 100-kilodalton protein is necessary for efficient translation of viral late mRNA species

When screening a number of adenovirus type 5 (Ad5) temperature-sensitive mutants for defects in viral gene expression, we observed that H5ts1-infected 293 cells accumulated reduced levels of newly synthesized viral late proteins. Pulse-labeling and pulse-chase experiments were used to establish that the late proteins synthesized in H5ts1-infected cells under nonpermissive conditions were as stable as those made in Ad5-infected cells. H5ts1-infected cells contained normal levels of viral late mRNAs. Because these observations implied that translation of viral mRNA species was defective in mutant virus-infected cells, the association of viral late mRNAs with polyribosomes was examined during the late phase of infection at a nonpermissive temperature. In Ad5-infected cells, the majority of the viral L2, L3, L4, pIX, and IVa2 late mRNA species were polyribosome bound. By contrast, these same mRNA species were recovered from H5ts1-infected cells in fractions nearer the top of polyribosome gradients, suggesting that initiation of translation was impaired. During the late phase of infection, neither the polyribosome association nor the translation of most viral early mRNA species was affected by the H5ts1 mutation. This lesion, mapped by marker rescue to the L4 100-kilodalton (kDa) nonstructural protein, has been identified as a single base pair substitution that replaces Ser-466 of the Ad5 100-kDa protein with Pro. A set of temperature-independent revertants of H5ts1 was isolated and characterized. Either true reversion of the H5ts1 mutation or second-site mutation of Pro-466 of the H5ts1 100-kDa protein to Thre, Leu, or His restored both temperature-independent growth and the efficient synthesis of viral late proteins. We therefore conclude that the Ad5 L4 100-kDa protein is necessary for efficient initiation of translation of viral late mRNA species during the late phase of infection.

Functional dissection of adenovirus VAI RNA

During the course of adenovirus infection, the VAI RNA protects the translation apparatus of host cells by preventing the activation of host double-stranded RNA-activated protein kinase, which phosphorylates and thereby inactivates the protein synthesis initiation factor eIF-2. In the absence of VAI RNA, protein synthesis is drastically inhibited at late times in infected cells. The experimentally derived secondary structure of VAI RNA consists of two extended base-paired regions, stems I and III, which are joined by a short base-paired region, stem II, at the center. Stems I and II are joined by a small loop, A, and stem III contains a hairpin loop, B. At the center of the molecule and at the 3' side, stems II and III are connected by a short stem-loop (stem IV and hairpin loop C). A fourth, minor loop, D, exists between stems II and IV. To determine sequences and domains critical for function within this VAI RNA structure, we have constructed adenovirus mutants with linker-scan substitution mutations in defined regions of the molecule. Cells infected with these mutants were analyzed for polypeptide synthesis, virus yield, and eIF-2 alpha kinase activity. Our results showed that disruption of base-paired regions in the distal parts of the longest stems, I and III, did not affect function, whereas mutations causing structural perturbations in the central part of the molecule containing stem II, the proximal part of stem III, and the central short stem-loop led to loss of function. Surprisingly, one substitution mutant, sub742, although dramatically perturbing the integrity of the structure of this central portion, showed a wild-type phenotype, suggesting that an RNA with an alternate secondary structure is functional. On the basis of sensitivity to single-strand-specific RNases, we can derive a novel secondary structure for the mutant RNA in which a portion of the sequences may fold to form a structure that resembles the central part of the wild-type molecule, which suggests that only the short stem-loop located in the center of the molecule and the adjoining base-paired regions may define the functional domain. These results also imply that only a portion of the VAI RNA structure may be recognized by the host factor(s).

Efficient expression of small RNA polymerase III genes from a novel simian virus 40 vector and their effect on viral gene expression

In the past, simian virus 40 (SV40) has been used as a cloning vehicle to clone foreign genes by substituting portions of the viral genome vital for viral replication. Propagation of these defective viruses required a helper virus and the recombinant viruses obtained could be grown only as a mixture. In this study, we describe a novel nondefective SV40 vector to clone small RNA polymerase III genes. Two small RNA polymerase III genes, an amber suppressor human serine tRNA gene and the adenovirus (Ad) VAI RNA gene, were cloned in the intron region of the large-T antigen gene of SV40 after deleting DNA sequences coding for the small-t polypeptide. The recombinant viruses grew to wild type levels and showed no growth defects. When CV-1p cells were infected with these viruses, the cloned RNA polymerase III genes were expressed at high levels at late times. Interestingly, large amounts VAI RNA in CV-1p cells infected with SV40-VA recombinant virus, did not enhance translation of viral mRNAs significantly but did lead to a 3 to 4 fold increase in the steady state levels of large-T mRNA suggesting a novel function for VAI RNA in SV40 infected monkey cells. Furthermore, VAI mutants which fail to function in Ad infected human cells also failed to enhance the levels of large-T mRNAs in monkey cells infected with SV40. The simple SV40 vector described here may be useful to study the structure and function of small RNA polymerase III genes in the context of a eucaryotic chromosome. In addition, the nondefective recombinant SV40 which expresses the suppressor tRNA gene at high levels may provide a useful helper system to propagate animal viruses with amber mutations in essential genes.

Adenovirus proteins associated with mRNA and hnRNA in infected HeLa cells

The proteins that interact with cytoplasmic and nuclear polyadenylated RNA in adenovirus type 5 (Ad5) infection of HeLa cells were examined by UV-induced RNA-protein cross-linking in intact cells. The Ad5 100-kilodalton late nonvirion protein (100K protein) was cross-linked to both host and viral polyadenylated cytoplasmic RNA (mRNA). The cross-linking of the 100K protein to mRNA appears to correlate with productive infection, because the protein is not cross-linked to mRNA in abortive infection of wild-type Ad5 in monkey cells (CV-1) even though normal amounts of it are produced. However, when CV-1 cells are infected with Ad5 hr404, and Ad5 mutant which overcomes the host restriction to wild-type Ad5 infection in these cells, the 100K protein is cross-linked to mRNA. To identify and obtain antibodies to RNA-contacting proteins, a mouse was immunized with oligo(dT)-selected cross-linked RNA-protein complexes from Ad5-infected cells and the serum was used for immunoblotting experiments. It was found that in addition to the 100K protein, the Ad5 72K DNA-binding protein is also associated with RNA in the infected cells. The 72K DNA-binding protein is cross-linked to polyadenylated nuclear RNA sequences. These findings indicate that adenovirus proteins interact with RNAs in the infected cell and suggest possible mechanisms for the effects of the virus on mRNA metabolism.

Suppression of the translation defect phenotype specific for a virus-associated RNA-deficient adenovirus mutant in monkey cells by simian virus 40

Human cells infected with adenovirus type 2 (Ad2) or Ad5 require VAI RNA for efficient translation of viral mRNAs at late times after infection. The Ad5 mutant dl-sub720 synthesized neither virus-associated I (VAI) nor VAII RNAs, and infection of human cells with this mutant resulted in reduced virion polypeptide synthesis. Infection of monkey cells with this mutant also resulted in drastic reduction of polypeptide synthesis compared with wild-type (WT) adenovirus infections. Steady-state levels of hexon-specific mRNA were found to be comparable in WT- and mutant-infected monkey cells. The in vitro translation experiments showed that double-mutant- and WT-infected cells contained comparable levels of translatable hexon mRNA (and other adenovirus late mRNAs), suggesting that the severe inhibition of hexon protein synthesis in the VA mutant involves a translation block. Preinfection of monkey cells with simian virus 40 fully restored the efficient translation of this mRNA in the VA mutant infections to the level observed in WT-infected cultures. These results raise the possibility that simian virus 40 may encode or induce factors that suppress the translation block that occurs during adenovirus infections in the absence of the VA RNAs.

Hexon trimerization occurring in an assembly-defective, 100K temperature-sensitive mutant of adenovirus 2

Analysis of 100K-defective temperature-sensitive adenovirus mutants confirmed the multifunctional character of the nonstructural, virus-coded 100K protein. In addition to its function in hexon trimerization (altered in H5ts1), and its possible direct or indirect role in hexon transport to nucleus (mutated in H2ts118), genetic and biochemical evidence was presented that 100K play some critical role in the scaffolding process of adenovirus capsid. This function appeared to be defective in H2ts107 and to map between coordinates 69.0 and 69.9, leftward from the H5ts1 lesion (70-73 map units; Arrand, 1978). This corresponded to the central domain of the 100K protein, between amino acid 300 and 400 from the N end. DNA sequencing of cloned fragments of H2ts107 DNA overlapping the mutation revealed two point mutations on the same codon at nucleotide 25,082 and 25,083 (GAC----GCA), corresponding to a nonconservative amino acid change (aspartic acid----alanine) at position 324 in the 100K sequence. 100K of adenovirus 2 wild type (WT) was found to bind in significant amounts to novobiocin-affinity column, and to be coeluted with hexon, penton, IIIa, and cellular topoisomerase II activity, by novobiocin- or ATP-Mg2+-containing buffers. H2ts107 100K also bound to novobiocin column, but the elution pattern differed from that of WT, suggesting some alteration in the affinity of the mutated 100K for novobiocin. The same behavior on affinity column as H2ts107 100K was observed for 90K, a cleavage product of the 100K, found in great abundance in H2ts107 at 39.5 degrees and corresponding to the C-terminal moiety of the 100K molecule. This implied that the "novobiocin-binding" domain of the 100K was not confined at its N terminus, and was altered in the H2ts107 mutant.

Construction and analysis of additional adenovirus substitution mutants confirm the complementation of VAI RNA function by two small RNAs encoded by Epstein-Barr virus

Adenovirus VAI RNA is essential for the efficient initiation of translation of viral mRNAs at late times after infection. Recently, by constructing an adenovirus type 5 substitution mutant, we showed that the Epstein-Barr virus encoded two small RNAs complemented for the VAI RNA function in the adenovirus type 5 lytic growth (Bhat and Thimmappaya, Proc. Natl. Acad. Sci. USA 80:4789-4793, 1983). This observation was based on our inability to propagate an adenovirus type 5 mutant lacking functional VAI and VAII genes. Subsequently, it was found that this mutant was viable and able to grow to a low titer. Therefore, we examined the complementation of the VAI RNA function by the Epstein-Barr virus-encoded RNAs by constructing additional adenovirus type 5 substitution mutants containing multiple copies of the Epstein-Barr virus-encoded RNA genes in nonessential early transcriptional region III. The new substitution mutants synthesized viral polypeptides at late times at levels comparable to those observed in wild type-infected cells. Our results convincingly demonstrated that the two Epstein-Barr virus-encoded RNAs can efficiently complement for the VAI RNA-mediated translational defect in adenovirus-infected cells.