Virus Genes

Poxviruses are complex in their nucleotide compositional features of the coding regions. The codon usages in Poxviruses are in accordance with their compositional bias. In the Poxviridae family, codon usage patterns and nucleotide compositional traits are widely divergent across species but some conservation was observed within a genus. Viruses from six Chordopox genera, i.e., Avipoxvirus, Capripoxvirus, Cervidpoxvirus, Orthopoxvirus, Suipoxvirus, Yatapoxvirus, and one Entomopox genus- Betaentomopoxvirus, and some unclassified Entomopoxvirus are significantly rich in AT composition. Four other Chordopox genera- Molluscipoxvirus, Orthopoxvirus, Parapoxvirus, and some unclassified Chordopoxvirus are dominated by the GC rich viruses. Poxviruses from these AT rich and GC rich genera preferred AT or GC ending codons owing to their respective nucleotide compositional bias. For example, viruses from AT rich Orthopoxvirus, or GC rich Parapoxvirus have evolved with mutually exclusive type codon preferences following their genus-specific nucleotide compositions. Additional factors like gene length and expression level also influenced their codon usage patterns to some extent in some Poxvirus genera. Evidences from correspondence analysis and cluster analysis on the extent of divergence in codon usage also support this genus specific evolution of Poxvirus codon usage. Analyzes suggest that most of the Poxviruses from different genera, have evolved in almost two different evolutionary trajectory in context of their nucleotide composition and codon usage.

Influenza A (IAV) is a major human respiratory pathogen that contributes to a significant threat to health security, worldwide. Despite vaccinations and previous immunisations through infections, humans can still be infected with influenza several times throughout their lives. This phenomenon is attributed to the antigenic changes of hemagglutinin (HA) and neuraminidase (NA) proteins in IAV via genetic mutation and reassortment, conferring antigenic drift and antigenic shift, respectively. Numerous findings indicate that slow antigenic drift and reassortment-derived antigenic shift exhibited by IAV are key processes that allow IAVs to overcome the previously acquired host immunity, which eventually leads to the annual re-emergence of seasonal influenza and even pandemic influenza, in rare occasions. As a result, current therapeutic options hit a brick wall quickly. As IAV remains a constant threat for new outbreaks worldwide, the underlying processes of genetic changes and alternative antiviral approaches for IAV should be further explored to improve disease management. In the light of the above, this review discusses the characteristics and mechanisms of mutations and reassortments that contribute to IAV’s evolution. We also discuss several alternative RNA-targeting antiviral approaches, namely the CRISPR/Cas13 systems, RNA interference (RNAi), and antisense oligonucleotides (ASO) as potential antiviral approaches against IAV.

The influenza A virus subtypes H1N1, H1N2 and H3N2 are prevalent in pig populations worldwide. In the present study, two relatively uncommon swine influenza virus (SIV) H1N2 subtypes, isolated in Sweden in 2009 and 2010, were compared regarding their molecular composition and biological characteristics. The differences regarding markers purportedly related to pathogenicity, host adaptation or replication efficiency. They included a truncated PB1-F2 protein in the earlier isolate but a full length version in the more recent one; differences in the number of haemagglutinin glycosylation sites, including a characteristic human one; and a nuclear export protein with altered export signal. Of particular interest, the NS1 amino acid sequence of swine H1N2-2009 and 2010 has a ‘unique or very unusual’ PDZ binding domain (RPKV) at the C-terminal of the protein, a motif that has been implicated as a virulence marker. Concerning biological properties, these viruses reached lower titre and showed reduced cytopathogenicity in MDCK cells compared with an avian-like H1N1 isolate A/swine/Lidkoping/1193/2002 belonging to the same lineage as the 2009 and 2010 isolates. The findings should contribute to better understanding of factors related to the survival/extinction of this uncommon reassortant variant.

Virus encoded deubiquitinating enzyme (DUB) plays important roles in viral replication and the regulation of host innate immunity. Bioinformatics-based analysis revealed the presence of an ovarian tumor (OTU) protease domain in the N terminus of rice stripe tenuivirus (RSV) Pc1. Many viral OTU domains have been reported to possess DUB activity, which suggests that RSV OTU probably also have DUB activity. To confirm this prediction, we first expressed and purified RSV OTU domain (the N-terminal 200 amino acids of Pc1) and its three mutants (D42A, C45A and H148A) from Escherichia coli and analyzed its DUB activity in vitro. The purified RSV OTU hydrolyzed both K48-linked and K63-linked polyubiquitin chains, indicating RSV OTU domain has DUB enzyme activity in vitro. The mutations of the predicted catalytic sites (Asp42, Cys45 and His148) resulted in the loss of DUB activity, demonstrating these three residues were required for enzyme activity. Then, RSV OTU and its mutants were expressed in insect cells and assayed their DUB activities in vivo by co-transfection with HA-tagged ubiquitin. RSV OTU dramatically reduced ubiquitin-conjugated cellular proteins compared to control and the mutants, showing that RSV OTU also displays DUB activity in vivo. Characterization of RSV OTU DUB enzyme activity and its key catalytic residues will facilitate the development of novel antiviral reagents against RSV.

The classic development of vaccines is lengthy, tedious, and may not necessarily be successful as demonstrated by the case of HIV. This is especially a problem for emerging pathogens that are newly introduced into the human population and carry the inherent risk of pandemic spread in a naïve population. For such situations, a considerable number of different platform technologies are under development. These are also under development for pathogens, where directly derived vaccines are regarded as too complicated or even dangerous due to the induction of inefficient or unwanted immune responses causing considerable side-effects as for dengue virus. Among platform technologies are plasmid-based DNA vaccines, RNA replicons, single-round infectious vector particles, or replicating vaccine-based vectors encoding (a) critical antigen(s) of the target pathogens. Among the latter, recombinant measles viruses derived from vaccine strains have been tested. Measles vaccines are among the most effective and safest life-attenuated vaccines known. Therefore, the development of Schwarz-, Moraten-, or AIK-C-strain derived recombinant vaccines against a wide range of mostly viral, but also bacterial pathogens was quite straightforward. These vaccines generally induce powerful humoral and cellular immune responses in appropriate animal models, i.e., transgenic mice or non-human primates. Also in the recent first clinical phase I trial, the results have been quite encouraging. The trial indicated the expected safety and efficacy also in human patients, interestingly independent from the level of prevalent anti-measles immunity before the trial. Thereby, recombinant measles vaccines expressing additional antigens are a promising platform for future vaccines.

Two new strains of Abutilon mosaic virus (AbMV; Geminiviridae) from Germany (Stuttgart) and France (Paris) have been characterized by circomics, direct pyrosequencing of rolling circle amplification (RCA) products, as well as conventional cloning and Sanger sequencing. RCA combined with an analysis of restriction fragment length polymorphisms confirmed the completeness of the sequence determination and a close relationship of both isolates for DNA A with 99 % nucleotide sequence identity. Phylogenetic tree reconstruction supported their clustering with other AbMV strains in a clade with Middle American begomoviruses, whereas South American begomoviruses that infect Abutilon or Sida micrantha are less closely related. Comparing the coat protein (CP) genes of the AbMV cluster, with those of related Middle and South American begomoviruses revealed a remarkable overrepresentation for non-synonymous nucleotide exchanges for certain amino acid positions in the AbMV cluster. Projection of these positions to a structural model of the African cassava mosaic virus CP yielded a non-random distribution at the periphery and, most importantly, highlighted those amino acids that had been identified in whitefly-transmission experiments before. These results establish the basis for an analysis of the evolutionary liberty of certain amino acid positions of the CP, and their impact on the deciphering of insect transmission determinants is discussed.

The complete nucleotide sequence of a potyvirus causing severe maize dwarf mosaic disease in Shaanxi province, northwestern China was determined (GenBank accession No. AY569692). The full genome is 9596 nucleotides in length excluding the 3 ′-terminal poly (A) sequence. It contains a large open reading frame (ORF) flanked by a 149 nt 5′-untranslated region (UTR) and a 255 nt 3′-UTR. The putative polyprotein encoded by this large ORF comprises of 3063 amino acid residues. Sequence comparisons and phylogenetic analyses showed that this potyvirus is an isolate of Sugarcane mosaic virus (SCMV). The entire sequences shared identities of 89.6–97.6 % and 79.3–93.3% with 9 sequenced SCMV isolates at the nucleotide and deduced amino acid levels, respectively. But it showed much lower identities with Maize dwarf mosaic virus (MDMV), Sorghum mosaic virus (SrMV) and Johnsongrass mosaic virus (JGMV) isolates. The putative coat protein sequence is identical to that of a Chinese maize isolate SCMV-HZ. However, partition comparisons and phylogenetic profile analyses of the viral nucleotide sequences indicated that it is a recombinant isolate of SCMV. The recombination sites are located within the 6K1 and CI coding regions.