2024 taxonomy update for the family Circoviridae.

Circovirids have a circular single-stranded DNA genome packed into a small icosahedral capsid. They are classified within two genera, Circovirus and Cyclovirus, in the family Circoviridae (phylum Cressdnaviricota, class Arfiviricetes, order Cirlivirales). Over the last five years, a number of new circovirids have been identified, and, as a result, 54 new species have been created for their classification based on the previously established species demarcation criterion, namely, that viruses classified into different species share less than 80% genome-wide pairwise sequence identity. Of note, one of the newly created species includes a circovirus that was identified in human hepatocytes and suspected of causing liver damage. Furthermore, to comply with binomial species nomenclature, all new and previously recognized species have been (re)named in binomial format with a freeform epithet. Here, we provide a summary of the properties of circovirid genomes and their classification as of June 2024 (65 species in the genus Circovirus and 90 species in the genus Cyclovirus). Finally, we provide reference datasets of the nucleotide and amino acid sequences representing each of the officially recognized circovirid species to facilitate further classification of newly discovered members of the Circoviridae.

Phylogenetic analysis of all available monkeypox virus strains shows the close relatedness of contemporary ones.

The present research aimed to evaluate the diversity of all monkeypox virus strains with a special focus on recently isolated ones by a comprehensive phylogenetic analysis of all available sequences, based on the concatenate of four viral genes. Almost all current strains from 2022 showed a high level of similarity to each other on the analyzed stretches: 218 strains shared identical sequence. Among all analyzed strains, the highest number of differences was counted compared to a RefSeq strain (Zaire-96-I-16) on the whole concatenate. Our analysis supported the distinction between Clade I (formerly Congo Basin clade), IIa and IIb (together formerly West African clade) strains and classified all 2022 strains in the last one. The high number of differences and long branch observable concerning strain Zaire-96-I-16 is most probably caused by a sequencing error. As this strain represents one of the two available reference sequences in GenBank, it is recommendable to confirm or exclude the concerning mutation. The developed method, based on four gene sequences, reflected the established whole-genome-based intraspecies classification. Although this method provides significantly less information about the strains compared to whole genome analyses, since its resolution is much lower, it still enables the rapid subspecies classification of the strains into the established clades. The genes in the analyzed concatenate are so conserved that further differentiation of contemporary strains is impossible; these strains are identical in the analyzed sections. On the other hand, since whole genome analyses are compute-intensive, the described method offers a simpler and more accessible alternative for monitoring and preliminary typing of newly sequenced monkeypox virus strains.

Characterization of monkey adenoviruses with three fiber genes.

Although the occurrence of three fiber genes in monkey adenoviruses had already been described, the relatedness of the "extra" fibers have not yet been discussed. Here we report the genome analysis of two simian adenovirus (SAdV) serotypes from Old World monkeys and the phylogenetic analysis of the multiple fiber genes found in these and related AdVs. One of the newly sequenced serotypes (SAdV-2), isolated from a rhesus macaque (Macaca mulatta), was classified into species Human mastadenovirus G (HAdV-G), while the other serotype (SAdV-17), originating from a grivet (Chlorocebus aethiops), classified to Simian mastadenovirus F (SAdV-F). We identified unique features in the gene content of these SAdVs compared to those typical for other members of the genus Mastadenovirus. Namely, in the E1B region of SAdV-2, the 19K gene was replaced by an ITR repetition and a copy of the E4 ORF1 gene. Among the 37 genes in both SAdVs, three genes of different lengths, predicted to code for the cellular attachment proteins (the fibers), were found. These proteins exhibit high diversity. Yet, phylogenetic calculations of their conserved parts could reveal the probable evolutionary steps leading to the multiple-fibered contemporary HAdV and SAdV species. Seemingly, there existed (a) common ancestor(s) with two fiber genes for the lineages of the AdVs in species SAdV-B, -E, -F and HAdV-F, alongside a double-fibered ancestor for today's SAdV-C and HAdV-G, which later diverged into descendants forming today's species. Additionally, some HAdV-G members picked up a third fiber gene either to the left-hand or to the in-between position from the existing two. A SAdV-F progenitor also obtained a third copy to the middle, as observed in SAdV-17. The existence of three fiber genes in these contemporary AdVs brings novel possibilities for the design of optimised AdV-based vectors with potential multiple target binding abilities.

Partial genetic characterisation of a novel alloherpesvirus detected by PCR in a farmed wels catfish (Silurus glanis).

By a broad-range PCR, we detected a novel herpesvirus (HV) in the specimen of a wels catfish (Silurus glanis) presenting disseminated, carp pox-like dermal lesions all over its body. The sequence analysis of the 463-bp PCR product from the viral DNA polymerase gene indicated the presence of a hitherto unknown virus, a putative member of the family Alloherpesviridae in the sample. Another PCR, targeting the terminase gene of fish HVs, provided an additional genomic fragment of over 1,000 bp. Surprisingly, the sequence of a co-amplified, off-target PCR product revealed its origin from a putative gene homologous to ORF87 and ORF45 of cyprinid HVs and anguillid herpesvirus 1 (AngHV-1), respectively. With specific primers, designed according to the genomic maps of the cyprinid and anguillid HVs, a genomic fragment of 15 kb was also amplified and sequenced by primer walking. In phylogeny inferences, based on several genes, the putative wels catfish HV clustered closest to various cyprinid HVs or to AngHV-1. The novel virus, named as silurid herpesvirus 2, represents a distinct species in the genus Cyprinivirus. However, its association with the skin disease remains unclear.

First DNA sequence proof for the occurrence of bovine adenovirus types 10 and 11 in continental Europe.

Bovine adenoviruses (BAdV) are known to cause respiratory and/or intestinal disease in calves. Infection can manifest as acute outbreaks, but more often only sporadic cases occur. Here we describe the PCR detection and partial sequence characterization of several BAdVs found in sick or dead calves on different farms in Western Hungary. Intermittent diarrhoeal illnesses occurred after weaning among calves on several farms located up to 40 km apart. A high-sensitivity, broad-spectrum nested PCR, developed for the general detection of adenoviruses, gave positive results in four independent cases. Direct sequencing of PCR products showed clear results from only two samples, whereas sequences from the other two amplicons were mixed. Molecular cloning of these heterogeneous PCR products was performed to separate each DNA fragment therein. By sequencing several plasmid clones from both mixed samples, we were able to detect the simultaneous presence of two different BAdV types, namely types 6 and 10 classified into two separate (Atadenovirus and Mastadenovirus) genera. The sequence of one homogenous sample was identified as being derived also from BAdV-10, whereas the other sample contained a novel type, proposed to be BAdV-11. We demonstrated, for the very first time, the occurrence of the two latter virus types in continental Europe. Their appearance in Hungary marks a significant shift in the types of BAdVs actually circulating in the country. Considering the similarity of the pathological findings to those, attributed to BAdV-10 infections reported to date, the causative role of the viruses in these cases seems to be plausible. Phylogeny reconstruction further confirmed that BAdVs represent multiple genetic lineages.

The genome and phylogenetic analyses of tit siadenoviruses reveal both a novel avian host and viral species.

In both a Eurasian blue tit (Cyanistes caeruleus) and a great tit (Parus major), found dead in North Rhine-Westphalia, Germany, intranuclear inclusion bodies were observed in the kidneys during the histologic examination. Siadenoviruses were detected in both samples, and the nucleotide sequence of the partial DNA polymerase, obtained from the blue tit, was almost identical with that of great tit adenovirus type 1, reported from Hungary previously. The sequence, derived from the German great tit sample was more similar to great tit adenovirus 2, yet divergent enough to forecast the possible establishment of a novel viral type and species. Therefore, the complete genome was subjected to next generation sequencing. The annotation revealed a typical siadenoviral genome layout, and phylogenetic analyses proved the distinctness of the novel virus type: great tit adenovirus 3. We propose the establishment of a new species (Siadenovirus carbocapituli) within the genus Siadenovirus to contain great tit adenovirus types 2 and 3. As both of the newly-detected viruses originated from histologically confirmed cases, and several siadenoviruses have been associated with avian nephritis earlier, we assume that the renal pathology might have been also of adenoviral origin. Additionally, we performed structural studies on two virus-coded proteins. The viral sialidase and the fiber knob were modeled using the AlphaFold2 program. According to the results of the sialic acid docking studies, the fiber trimer of the new great tit adenovirus 3 binds this acid with good affinity. As sialic acid is expressed in the kidney, it can be hypothesized that it is used during the receptor binding and entry of the virus. Strong binding of sialic acid was also predictable for the viral sialidase albeit its enzymatic activity remains disputable since, within its catalytic site, an asparagine residue was revealed instead of the conserved aspartic acid.

ICTV Virus Taxonomy Profile: Adenoviridae 2022.

The family Adenoviridae includes non-enveloped viruses with linear dsDNA genomes of 25-48 kb and medium-sized icosahedral capsids. Adenoviruses have been discovered in vertebrates from fish to humans. The family is divided into six genera, each of which is more common in certain animal groups. The outcome of infection may vary from subclinical to lethal disease. This is a summary of the ICTV Report on the family Adenoviridae, which is available at ictv.global/report/adenoviridae.

Novel adenovirus associated with common tern (Sterna hirundo) chicks.

Adenoviruses have been identified in a wide variety of avian species, and in some species, they have been shown to cause disease and increase mortality. As part of an endeavor to investigate viruses associated with common terns (Sterna hirundo), a novel adenovirus was identified in fecal samples from two common terns on Gull Island, Lake Ontario, Canada. The coding-complete genome sequence of the new adenovirus is 31,094 bp, containing 28 putative genes, and this is the first adenovirus to be associated with terns. The virus was identified in two out of 13 fecal samples from tern chicks, and it was found to be most closely related to duck adenovirus 1, with the DNA polymerase sharing 58% amino acid sequence identity. Phylogenetic analysis based on DNA polymerase protein sequences showed that the new virus forms a distinct sub-branch within the atadenovirus clade and likely represents a new species in this genus.

ICTV Virus Taxonomy Profile: Herpesviridae 2021.

Members of the family Herpesviridae have enveloped, spherical virions with characteristic complex structures consisting of symmetrical and non-symmetrical components. The linear, double-stranded DNA genomes of 125-241 kbp contain 70-170 genes, of which 43 have been inherited from an ancestral herpesvirus. In general, herpesviruses have coevolved with and are highly adapted to their hosts, which comprise many mammalian, avian and reptilian species. Following primary infection, they are able to establish lifelong latent infection, during which there is limited viral gene expression. Severe disease is usually observed only in the foetus, the very young, the immunocompromised or following infection of an alternative host. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Herpesviridae, which is available at ictv.global/report/herpesviridae.

Full genome sequence analysis of a novel adenovirus from a captive polar bear (Ursus maritimus).

The presence of a novel adenovirus (AdV) was detected by PCR and sequencing, in the internal organs of a captive polar bear that had died in the Budapest zoo. The virus content of the samples proved to be high enough to allow for conventional Sanger sequencing on PCR-amplified genomic fragments. With this approach, the sequence of the entire genome of the putative polar bear adenovirus 1 (PBAdV-1) was obtained. Although the genome was found to be short, consisting of 27,952 base pairs merely, with a relatively balanced G + C content of 46.3 %, its organisation corresponded largely to that of a typical mastadenovirus. Every genus-common gene could be identified except that of protein IX. The short E3 region of the PBAdV-1 consisted of two novel, supposedly type-specific ORFs only, whereas no homologue of any of the E3 genes, usually conserved in mastadenoviruses, such as for example that of the 12.5 K protein, were present. In the E4 region, only the highly conserved gene of the 34 K protein was found besides two novel ORFs showing no homology to any known E4 ORFs. In silico sequence analysis revealed putative splicing donor and acceptor sites in the genes of the E1A, IVa2, DNA-dependent DNA polymerase, pTP, 33 K proteins, and also of U exon protein, all being characteristic for mastadenoviruses. Phylogenetic calculations, based on various proteins, further supported that the newly-detected PBAdV is the representative of a new species within the genus Mastadenovirus, and may represent the evolutionary lineage of adenoviruses that coevolved with carnivorans.

Adenoviruses across the animal kingdom: a walk in the zoo.

Adenoviruses (AdVs) infect representatives of numerous species from almost every major vertebrate class, albeit their incidence shows great variability. AdVs infecting birds, reptiles, and bats are the most common and diverse, whereas only one AdV has been so far isolated both from fish and amphibians. The family Adenoviridae is divided into five genera, each corresponding to an independent evolutionary lineage that supposedly coevolved with its respective vertebrate hosts. Members of genera Mastadenovirus and Aviadenovirus seem to infect exclusively mammals and birds, respectively. The genus Ichtadenovirus includes the single known AdV from fish. The majority of AdVs in the genus Atadenovirus originated from squamate reptiles (lizards and snakes), but also certain mammalian and avian AdVs are classified within this genus. The genus Siadenovirus contains the only AdV isolated from frog, along with numerous avian AdVs. In turtles, members of a sixth AdV lineage have been discovered, pending official recognition as an independent genus. The most likely scenario for AdV evolution includes long-term cospeciation with the hosts, as well as occasional switches between closely or, rarely, more distantly related hosts.

Unconventional gene arrangement and content revealed by full genome analysis of the white sturgeon adenovirus, the single member of the genus Ichtadenovirus.

Adenoviruses are commonly found in members of almost every vertebrate lineage except fish and amphibians, from each of which only a single isolate is available as yet. In this work, the complete genomic sequence of a fish adenovirus, originating from the white sturgeon (Acipenser transmontanus), was determined and analyzed. Several exceptional features were observed including the longest hitherto known genome size (of 48,395 bp) and a strange location of the putative fiber genes resulting in an unconventional organization pattern. The left genome end contained four fiber-like genes, three of them in a tandem position on the r (rightward transcribed) strand, followed by a fourth one on the l strand. Rightward from these, the conserved adenoviral gene cassette, encompassing 16 family-common genes, was identified. In the right-hand part, amounting for >42% of the entire genome, the presence of 28 ORFs, with a coding capacity of larger than 50 amino acids, was revealed. Interestingly, most of these showed no similarity to any adenoviral genes except two ORFs, resembling slightly the parvoviral NS gene, homologues of which occur in certain avian adenoviruses. These specific traits, together with the results of phylogeny reconstructions, fully justified the separation of the white sturgeon adenovirus into the recently established new genus Ichtadenovirus. Targeted attempts to find additional adenoviruses in any other fish species were to no avail as yet. Thus the founding member, WSAdV-1 still remains the only representative of ichtadenoviruses.

An emerging new fowl adenovirus genotype.

In this work, we examined the diversity of fowl adenovirus (FAdV) types occurring in Hungary. From diseased chicken flocks in Eastern Hungary, 29 FAdV strains were isolated between 2011 and 2015. We performed molecular typing of the isolates based on their partial hexon sequences. The results showed that representatives from every FAdV species from A to E are present in Hungary, but compared to the findings from our previous survey, a lower number of different FAdV types were detected. Inclusion body hepatitis was always associated with FAdV-2 or -8b, gizzard erosion was caused in almost every case by FAdV-1. Numerous strains belonging to species FAdV-B were found. The complete genome sequence of a candidate new genotype strain, showing the highest divergence from the reference FAdV-5, was determined using next generation sequencing. In order to provide results compatible with the serology-based type classification, multiple genomic regions, including the major antigenic determinants, of the new isolate (strain 40440-M/2015) were compared to their counterparts in the prototype FAdV-5 (strain 340) from species FAdV-B, at both nucleotide and amino acid sequence levels. In different comparative analyses, the two strains were always found to have larger divergence between each other than any two of the most closely related FAdV serotypes. This new emerging FAdV genotype is already present in Hungary and Austria, though its exact pathological role requires further investigations. The introduction of a novel FAdV (geno)type for the classification of these strains is further supported.

Structure and N-acetylglucosamine binding of the distal domain of mouse adenovirus 2 fibre.

Murine adenovirus 2 (MAdV-2) infects cells of the mouse gastrointestinal tract. Like human adenoviruses, it is a member of the genus Mastadenovirus, family Adenoviridae. The MAdV-2 genome has a single fibre gene that expresses a 787 residue-long protein. Through analogy to other adenovirus fibre proteins, it is expected that the carboxy-terminal virus-distal head domain of the fibre is responsible for binding to the host cell, although the natural receptor is unknown. The putative head domain has little sequence identity to adenovirus fibres of known structure. In this report, we present high-resolution crystal structures of the carboxy-terminal part of the MAdV-2 fibre. The structures reveal a domain with the typical adenovirus fibre head topology and a domain containing two triple ß-spiral repeats of the shaft domain. Through glycan microarray profiling, saturation transfer difference nuclear magnetic resonance spectroscopy, isothermal titration calorimetry and site-directed mutagenesis, we show that the fibre specifically binds to the monosaccharide N-acetylglucosamine (GlcNAc). The crystal structure of the complex reveals that GlcNAc binds between the AB and CD loops at the top of each of the three monomers of the MAdV-2 fibre head. However, infection competition assays show that soluble GlcNAc monosaccharide and natural GlcNAc-containing polymers do not inhibit infection by MAdV-2. Furthermore, site-directed mutation of the GlcNAc-binding residues does not prevent the inhibition of infection by soluble fibre protein. On the other hand, we show that the MAdV-2 fibre protein binds GlcNAc-containing mucin glycans, which suggests that the MAdV-2 fibre protein may play a role in viral mucin penetration in the mouse gut.

Adenoviruses of the most ancient primate lineages support the theory on virus-host co-evolution.

The scarcity or complete lack of information on the adenoviruses (AdVs) occurring in the most ancient non-human primates resulted in the initiation of a study for exploring their abundance and diversity in prosimians and New World monkeys (NWMs). In order to assess the variability of these AdVs and the possible signs of the hypothesised virus-host co-evolution, samples from almost every family of NWMs and prosimians were screened for the presence of AdVs. A PCRscreening of 171 faecal or organ samples from live or dead, captive or wild-living prosimians and NWMs was performed. The PCR products from the gene of the IVa2 protein were sequenced and used in phylogeny calculations. The presence of 10 and 15 new AdVs in seven and ten different species of prosimians and NWMs was revealed, respectively. Phylogenetic analysis indicated that the tentative novel AdVs cluster into two separate groups, which form the most basal branches among the primate AdVs, and therefore support the theory on the co-evolution of primate AdVs with their hosts. This is the first report that provides a comprehensive overview of the AdVs occurring in prosimians and NWMs, and the first insight into the evolutionary relationships among AdVs from all major primate groups.

Polysialic acid is a cellular receptor for human adenovirus 52.

Human adenovirus 52 (HAdV-52) is one of only three known HAdVs equipped with both a long and a short fiber protein. While the long fiber binds to the coxsackie and adenovirus receptor, the function of the short fiber in the virus life cycle is poorly understood. Here, we show, by glycan microarray analysis and cellular studies, that the short fiber knob (SFK) of HAdV-52 recognizes long chains of α-2,8-linked polysialic acid (polySia), a large posttranslational modification of selected carrier proteins, and that HAdV-52 can use polySia as a receptor on target cells. X-ray crystallography, NMR, molecular dynamics simulation, and structure-guided mutagenesis of the SFK reveal that the nonreducing, terminal sialic acid of polySia engages the protein with direct contacts, and that specificity for polySia is achieved through subtle, transient electrostatic interactions with additional sialic acid residues. In this study, we present a previously unrecognized role for polySia as a cellular receptor for a human viral pathogen. Our detailed analysis of the determinants of specificity for this interaction has general implications for protein-carbohydrate interactions, particularly concerning highly charged glycan structures, and provides interesting dimensions on the biology and evolution of members of Human mastadenovirus G.

Consensus statement: Virus taxonomy in the age of metagenomics.

The number and diversity of viral sequences that are identified in metagenomic data far exceeds that of experimentally characterized virus isolates. In a recent workshop, a panel of experts discussed the proposal that, with appropriate quality control, viruses that are known only from metagenomic data can, and should be, incorporated into the official classification scheme of the International Committee on Taxonomy of Viruses (ICTV). Although a taxonomy that is based on metagenomic sequence data alone represents a substantial departure from the traditional reliance on phenotypic properties, the development of a robust framework for sequence-based virus taxonomy is indispensable for the comprehensive characterization of the global virome. In this Consensus Statement article, we consider the rationale for why metagenomic sequence data should, and how it can, be incorporated into the ICTV taxonomy, and present proposals that have been endorsed by the Executive Committee of the ICTV.

Possibility and Challenges of Conversion of Current Virus Species Names to Linnaean Binomials.

Botanical, mycological, zoological, and prokaryotic species names follow the Linnaean format, consisting of an italicized Latinized binomen with a capitalized genus name and a lower case species epithet (e.g., Homo sapiens). Virus species names, however, do not follow a uniform format, and, even when binomial, are not Linnaean in style. In this thought exercise, we attempted to convert all currently official names of species included in the virus family Arenaviridae and the virus order Mononegavirales to Linnaean binomials, and to identify and address associated challenges and concerns. Surprisingly, this endeavor was not as complicated or time-consuming as even the authors of this article expected when conceiving the experiment. [Arenaviridae; binomials; ICTV; International Committee on Taxonomy of Viruses; Mononegavirales; virus nomenclature; virus taxonomy.].

Random Sampling of Squamate Reptiles in Spanish Natural Reserves Reveals the Presence of Novel Adenoviruses in Lacertids (Family Lacertidae) and Worm Lizards (Amphisbaenia).

Here, we report the results of a large-scale PCR survey on the prevalence and diversity of adenoviruses (AdVs) in samples collected randomly from free-living reptiles. On the territories of the Guadarrama Mountains National Park in Central Spain and of the Chafarinas Islands in North Africa, cloacal swabs were taken from 318 specimens of eight native species representing five squamate reptilian families. The healthy-looking animals had been captured temporarily for physiological and ethological examinations, after which they were released. We found 22 AdV-positive samples in representatives of three species, all from Central Spain. Sequence analysis of the PCR products revealed the existence of three hitherto unknown AdVs in 11 Carpetane rock lizards (Iberolacerta cyreni), nine Iberian worm lizards (Blanus cinereus), and two Iberian green lizards (Lacerta schreiberi), respectively. Phylogeny inference showed every novel putative virus to be a member of the genus Atadenovirus. This is the very first description of the occurrence of AdVs in amphisbaenian and lacertid hosts. Unlike all squamate atadenoviruses examined previously, two of the novel putative AdVs had A+T rich DNA, a feature generally deemed to mirror previous host switch events. Our results shed new light on the diversity and evolution of atadenoviruses.

Using the E4orf6-Based E3 Ubiquitin Ligase as a Tool To Analyze the Evolution of Adenoviruses.

UNLABELLED: E4orf6 proteins from all human adenoviruses form Cullin-based ubiquitin ligase complexes that, in association with E1B55K, target cellular proteins for degradation. While most are assembled with Cul5, a few utilize Cul2. BC-box motifs enable all these E4orf6 proteins to assemble ligase complexes with Elongins B and C. We also identified a Cul2-box motif used for Cul2 selection in all Cul2-based complexes. With this information, we set out to determine if other adenoviruses also possess the ability to form the ligase complex and, if so, to predict their Cullin usage. Here we report that all adenoviruses known to encode an E4orf6-like protein (mastadenoviruses and atadenoviruses) maintain the potential to form the ligase complex. We could accurately predict Cullin usage for E4orf6 products of mastadenoviruses and all but one atadenovirus. Interestingly, in nonhuman primate adenoviruses, we found a clear segregation of Cullin binding, with Cul5 utilized by viruses infecting great apes and Cul2 by Old/New World monkey viruses, suggesting that a switch from Cul2 to Cul5 binding occurred during the period when great apes diverged from monkeys. Based on the analysis of Cullin selection, we also suggest that the majority of human adenoviruses, which exhibit a broader tropism for the eye and the respiratory tract, exhibit Cul5 specificity and resemble viruses infecting great apes, whereas those that infect the gastrointestinal tract may have originated from monkey viruses that share Cul2 specificity. Finally, aviadenoviruses also appear to contain E4orf6 genes that encode proteins with a conserved XCXC motif followed by, in most cases, a BC-box motif. IMPORTANCE: Two early adenoviral proteins, E4orf6 and E1B55K, form a ubiquitin ligase complex with cellular proteins to ubiquitinate specific substrates, leading to their degradation by the proteasome. In studies with representatives of each human adenovirus species, we (and others) previously discovered that some viruses use Cul2 to form the complex, while others use Cul5. In the present study, we expanded our analyses to all sequenced adenoviruses and found that E4orf6 genes from all mast- and atadenoviruses encode proteins containing the motifs necessary to form the ligase complex. We found a clear separation in Cullin specificity between adenoviruses of great apes and Old/New World monkeys, lending support for a monkey origin for human viruses of the Human mastadenovirus A, F, and G species. We also identified previously unrecognized E4orf6 genes in the aviadenoviruses that encode proteins containing motifs permitting formation of the ubiquitin ligase.