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PubMedDate not supplied

[Methodological approaches to decreasing the number of markers for the numerical classification of viruses].

Three methodical approaches were used for reduction of the number of markers necessary for division of viruses into groups corresponding to certain families. Division of the markers into groups characterizing various properties of virions and their components as well as certain stages of virus reproduction in sensitive systems allowed some groups of markers to be excluded without losing the informative value of the marker set. The use of correlationships between markers helped to replace 64 initial parameters with 26 factors. The employment of the method of major components demonstrated the possibility of further reduction of the size of space in which virus clustering is done.

Chemical Phenomena↗
PubMed1997

[What is a virus?].

Viruses are simple biological particles, consisting of a genome, a protein capsid and, in the case of enveloped viruses, an external lipidic envelope. Owing to the presence of envelope, most enveloped viruses are fragile although some exceptions may be observed. Viruses behave as complete intracellular parasites. Their multiplication results from the replication and self-assembly of viral components, this process being directed by the viral genome after it has been released within an infected cell. Virus classification is now essentially based on molecular properties, concerning both the structure and replication strategy of viruses. In virus taxonomy, serial hierarchical levels are family, subfamily, genus and species. Within species, lower hierarchical levels are type, subtype, variant and strain. Knowledge of virus structure and classification is essential for considering the physiopathology, diagnosis and therapy of viral infections.

Humans↗
PubMed1998

Dual resistance to zidovudine and lamivudine in patients treated with zidovudine-lamivudine combination therapy: association with therapy failure.

Human immunodeficiency virus type 1 (HIV-1) strains dually resistant to zidovudine and lamivudine (3TC) may arise during zidovudine-3TC combination therapy. The objective of this cross-sectional study (n = 43 patients) was to test the association between therapy response (clinical and immunologic) to zidovudine-3TC and the level of phenotypic zidovudine resistance and zidovudine resistance-associated genotype of 3TC-resistant isolates. Other variables included were baseline CD4+ cell count, baseline Centers for Disease Control and Prevention (CDC) classification, virus load, and time receiving zidovudine. Phenotypic resistance was assessed using a recombinant virus assay. Genotypic analysis was based on population sequencing of plasma HIV-1. In a univariate analysis using a logistic regression model, it was found that therapy response was significantly associated with phenotypic and genotypic zidovudine resistance, baseline CD4+ cell count, and virus load. After adjustment for all variables, phenotypic resistance to zidovudine remained the only significantly associated factor, independent of baseline CD4+ cell count, baseline CDC classification, and virus load.

Anti-HIV Agents↗
PubMed2006

Virus species and virus identification: past and current controversies.

The basic concepts used in virus classification are analyzed. A clear distinction is drawn between viruses that are real, concrete objects studied by virologists and virus species that are man-made taxonomic constructions that exist only in the mind. Classical views regarding the nature of biological species are reviewed and the concept of species used in virology is explained. The use of pair-wise sequence comparisons between the members of a virus family for delineating species and genera is reviewed. The difference between the process of virus identification using one or a few diagnostic properties and the process of creating virus taxa using a combination of many properties is emphasized. The names of virus species in current use are discussed as well as a binomial system that may be introduced in the future.

Classification↗
PubMed2003

Relationship of SARS-CoV to other pathogenic RNA viruses explored by tetranucleotide usage profiling.

BACKGROUND: The exact origin of the cause of the Severe Acute Respiratory Syndrome (SARS) is still an open question. The genomic sequence relationship of SARS-CoV with 30 different single-stranded RNA (ssRNA) viruses of various families was studied using two non-standard approaches. Both approaches began with the vectorial profiling of the tetra-nucleotide usage pattern V for each virus. In approach one, a distance measure of a vector V, based on correlation coefficient was devised to construct a relationship tree by the neighbor-joining algorithm. In approach two, a multivariate factor analysis was performed to derive the embedded tetra-nucleotide usage patterns. These patterns were subsequently used to classify the selected viruses. RESULTS: Both approaches yielded relationship outcomes that are consistent with the known virus classification. They also indicated that the genome of RNA viruses from the same family conform to a specific pattern of word usage. Based on the correlation of the overall tetra-nucleotide usage patterns, the Transmissible Gastroenteritis Virus (TGV) and the Feline CoronaVirus (FCoV) are closest to SARS-CoV. Surprisingly also, the RNA viruses that do not go through a DNA stage displayed a remarkable discrimination against the CpG and UpA di-nucleotide (z = -77.31, -52.48 respectively) and selection for UpG and CpA (z = 65.79,49.99 respectively). Potential factors influencing these biases are discussed. CONCLUSION: The study of genomic word usage is a powerful method to classify RNA viruses. The congruence of the relationship outcomes with the known classification indicates that there exist phylogenetic signals in the tetra-nucleotide usage patterns, that is most prominent in the replicase open reading frames.

Algorithms↗
PubMed1985

Species classification problems in virus taxonomy.

Although the species is the fundamental unit of taxonomy, virologists only recently have begun to classify virus species in a systematic way under the leadership of the International Committee on Taxonomy of Viruses. Progress has been slow and uneven for several reasons: (i) Attempts to sort species are hampered even when the distinction between classification and nomenclature is blurred. Classifying is based on observation and involves deductive reasoning, whereas naming can be as arbitrary as desired, even to the point of dispensing with the traditional Latin binomial form. (ii) Some virologists deny the possibility of applying the species concept to asexual organisms, such as viruses. Those persons are influenced by an obsolete definition of biological species which rests on observed or inferred barriers to sexual reproduction. (iii) New taxonomic tools, such as mathematical (numerical) taxonomy, might be applied profitably to virus classification, but are unfamiliar to many virologists.

Adenoviridae↗
PubMed1993

Evolution and taxonomy of positive-strand RNA viruses: implications of comparative analysis of amino acid sequences.

Despite the rapid mutational change that is typical of positive-strand RNA viruses, enzymes mediating the replication and expression of virus genomes contain arrays of conserved sequence motifs. Proteins with such motifs include RNA-dependent RNA polymerase, putative RNA helicase, chymotrypsin-like and papain-like proteases, and methyltransferases. The genes for these proteins form partially conserved modules in large subsets of viruses. A concept of the virus genome as a relatively evolutionarily stable "core" of housekeeping genes accompanied by a much more flexible "shell" consisting mostly of genes coding for virion components and various accessory proteins is discussed. Shuffling of the "shell" genes including genome reorganization and recombination between remote groups of viruses is considered to be one of the major factors of virus evolution. Multiple alignments for the conserved viral proteins were constructed and used to generate the respective phylogenetic trees. Based primarily on the tentative phylogeny for the RNA-dependent RNA polymerase, which is the only universally conserved protein of positive-strand RNA viruses, three large classes of viruses, each consisting of distinct smaller divisions, were delineated. A strong correlation was observed between this grouping and the tentative phylogenies for the other conserved proteins as well as the arrangement of genes encoding these proteins in the virus genome. A comparable correlation with the polymerase phylogeny was not found for genes encoding virion components or for genome expression strategies. It is surmised that several types of arrangement of the "shell" genes as well as basic mechanisms of expression could have evolved independently in different evolutionary lineages. The grouping revealed by phylogenetic analysis may provide the basis for revision of virus classification, and phylogenetic taxonomy of positive-strand RNA viruses is outlined. Some of the phylogenetically derived divisions of positive-strand RNA viruses also include double-stranded RNA viruses, indicating that in certain cases the type of genome nucleic acid may not be a reliable taxonomic criterion for viruses. Hypothetical evolutionary scenarios for positive-strand RNA viruses are proposed. It is hypothesized that all positive-strand RNA viruses and some related double-stranded RNA viruses could have evolved from a common ancestor virus that contained genes for RNA-dependent RNA polymerase, a chymotrypsin-related protease that also functioned as the capsid protein, and possibly an RNA helicase.

Amino Acid Sequence↗
PubMed1975

The structure of togaviruses and bunyaviruses.

This article reviews the properties of arthropod-borne and nonarbo togaviruses and members of the Bunyaviridae family. Averaged information is given on the morphology and substructure of the virion, its physical properties, its chemical composition and the function of its constituents. Special attention is given to distinctive traits which might be useful for virus classification.

Arboviruses↗
PubMed1994

Genomic organization and expression of astroviruses and caliciviruses.

Astroviruses and caliciviruses are two families defined initially by their characteristic morphology. Many of these viruses have been difficult to grow in culture. Molecular biology has now provided a valuable insight into the nature of these viruses, and in many respects knowledge of genome structure now outstrips that of more classical virological features. However these advances have allowed a more detailed approach to virus classification and have led to the establishment of the Astroviridae as a distinct virus family.

Amino Acid Sequence↗
PubMed2007

Full-length sequencing and genomic characterization of Bagaza, Kedougou, and Zika viruses.

Many members of the genus Flavivirus are the agents of important diseases of humans, livestock, and wildlife. Currently, no complete genome sequence is available for the three African viruses, Bagaza, Zika, and Kedougou viruses, each representing a distinct virus subgroup according to the latest virus classification. In this study, we obtained a complete genome sequence of each of those three viruses and characterized the open reading frames (ORFs) with respect to gene sizes, cleavage sites, potential glycosylation sites, distribution of cysteine residues, and unique motifs. The sequences of the three viruses were then scanned across the entire length of the ORF against available sequences of other African flaviviruses and selected reference viruses for genetic relatedness. The data collectively indicated that Kedougou virus was close to dengue viruses but nonetheless distinct, while Bagaza virus shared genetic relatedness with West Nile virus in several genomic regions. In the non-coding regions, it was found that a particular organizational pattern of conserved sequences in the 3' terminal region generally correlated with the current virus grouping.

3' Untranslated Regions↗
PubMed2002

The current naming of plant viruses: a critical appraisal.

The revised International Code of Virus Classification and Nomenclature [7] followed by the Seventh Report of the International Committee on Taxonomy of Viruses (ICTV) [9] have generated a lot of criticism [2,4-6]. The main causes of criticism are (i) use of monomials instead of non-latinized binomials, as has been practice for some time in the past, e.g., tobacco mosaic tobamovirus, tobacco ringspot nepovirus etc. (ii) in toto italicization of official virus names. Following the expression of different views among virologists on this issue, it is being debated and an opportunity has been provided for reconsideration of the revised ICTV code [1,8,10]. This note attempts to analyse the existing criticisms being raised and justifies the continuation of the present ICTV code.

Plant Viruses↗
PubMed2006

Towards a classification of icosahedral viruses in terms of indexed polyhedra.

The standard Caspar & Klug classification of icosahedral viruses by means of triangulation numbers and the more recent novel characterization of Twarock leading to a Penrose-like tessellation of the capsid of viruses not obeying the Caspar-Klug rules can be obtained as a special case in a new approach to the morphology of icosahedral viruses. Considered are polyhedra with icosahedral symmetry and rational indices. The law of rational indices, fundamental for crystals, implies vertices at points of a lattice (here icosahedral). In the present approach, in addition to the rotations of the icosahedral group 235, crystallographic scalings play an important rôle. Crystallographic means that the scalings leave the icosahedral lattice invariant or transform it to a sublattice (or to a superlattice). The combination of the rotations with these scalings (linear, planar and radial) permits edge, face and vertex decoration of the polyhedra. In the last case, satellite polyhedra are attached to the vertices of a central polyhedron, the whole being generated by the icosahedral group from a finite set of points with integer indices. Three viruses with a polyhedral enclosing form given by an icosahedron, a dodecahedron and a triacontahedron, respectively, are presented as illustration. Their cores share the same polyhedron as the capsid, both being in a crystallographic scaling relation.

Biophysical Phenomena↗
PubMedDate not supplied

[A system of the means of genetic information transfer and the possible routes of viral evolution].

A system of means of genetic information transmission (MGIT) modeling the main features of modes of virus reproduction as well as an algorithmic approach to its construction and means of its schematic representation are proposed. The system may be used as the basis for virus classification including taxonomic categories above the family level and for the study of possible evolution relationships between virus groups. One of the variants of virus macroevolution model is described.

Biological Evolution↗
PubMed2002

The origin of modern plant virology.

Plant virology, born with Mayer's work, saw a first (embryonic) phase of development during two decades (1900-1920) with outstanding contributions from Dimitri Ivanovski, Martinus Beijerinck, Erwin Baur and Harry Allard. Between 1920 and 1930 a second phase saw the elaboration of surprising hypotheses concerning the enigmatic nature of viruses and experimental evidence of great stress was obtained. Revolutionary renewal began from the mid-1930s on the basis of a body of knowledge which was organically assembled into the first textbook of plant virology published by Kenneth Smith in 1933. In 1922, the geneticist Hermann Muller put forward the hypothesis that considered viruses as possible genes. The theory was resumed in an apparently independent way by Benjamin Duggar and Joanne Karrer Armstrong in 1923, who considered TMV a biocolloidal self-reproducing protein, like genes appeared to be. This hypothesis, even if neglected by virologists, anticipated by some decades the functional nature of viruses and represented the first conceptual response to virus enigma. Considerable experimental results were obtained by James Johnson, who showed that plants could be infected by different viruses and who introduced a first rational system of plant virus classification. Harold McKinney showed that TMV could mutate. Harold Storey, Kenneth Smith and Harry Severin demonstrated that several viruses could be transmitted by insects and supplied the first interpretation of the relationship between virus and insect. Mayme Dvorak and Helen Purdy obtained the first experimental evidence of the antigenic power of plant viruses. Virus purification, first tentatively accomplished with physical methods, was brilliantly performed by chemical means. Finally, Francis Holmes elaborated the first suitable test to estimate virus infectivity. The evolution of plant virology from an empirical discipline to a biological science took place thanks to the work of one group of American and English scientists who must be regarded as the fathers of modern plant virology.

History, 20th Century↗