Search results for "viruses"
showing 10 items of 1182 documents
Fixation of mutations at the VP1 gene of foot-and-mouth disease virus. Can quasispecies define a transient molecular clock?
1991
The number of nucleotide (nt) substitutions found in the VP1 gene (encoding viral capsid protein) between any two of 16 closely related isolates of foot-and-mouth disease virus (FMDV) has been quantified as a function of the time interval between isolations [Villaverde et al.,J. Mol. Biol. 204(1988)771-776]. One of them (isolate C-S12) includes some replacements found in isolates that preceded it and other replacements found in later isolates. The study has revealed alternating periods of rapid evolution and of relative genetic stability of VP1. During a defined period of acute disease, the rate of fixation of replacements at the VP1 coding segment was 6 × 10-3 substitutions per nt per year…
Development of cytoplasmically incompatible and integrated (translocated incompatible) strains ofCulex pipiens fatigans for use in genetic control
1976
Crosses were made between strains of the Culex pipiens complex to select and develop strains with suitable cytoplasmic incompatibility properties for use in field experiments in genetic control of Culex pipiens fatigans near Delhi, India.
Is group selection a factor modulating the virulence of RNA viruses?
1997
RNA viruses consist of populations of extremely high genetic heterogeneity called quasispecies. Based on theoretical considerations, it has been suggested that the unit of selection in such complex genetic populations is not the single viral particle but a set of genetically related particles which form the quasispecies. In the present study we carried out a set of experiments with the vesicular stomatitis virus (VSV) dealing with the evolution of life-history characters under selection acting at two factors either in the same or in opposite directions. The two factors at which selective pressure is applied are the individual and the group. We show evidence that group selection modulates th…
The evolution of RNA viruses: A population genetics view.
2000
RNA viruses are excellent experimental models for studying evolution under the theoretical framework of population genetics. For a proper justification of this thesis we have introduced some properties of RNA viruses that are relevant for studying evolution. On the other hand, population genetics is a reductionistic theory of evolution. It does not consider or make simplistic assumptions on the transformation laws within and between genotypic and phenotypic spaces. However, such laws are minimized in the case of RNA viruses because the phenotypic space maps onto the genotypic space in a much more linear way than on higher DNA-based organisms. Under experimental conditions, we have tested th…
Prisoner's dilemma in an RNA virus
1999
The evolution of competitive interactions among viruses1 was studied in the RNA phage φ6 at high and low multiplicities of infection (that is, at high and low ratios of infecting phage to host cells). At high multiplicities, many phage infect and reproduce in the same host cell, whereas at low multiplicities the viruses reproduce mainly as clones. An unexpected result of this study1 was that phage grown at high rates of co-infection increased in fitness initially, but then evolved lowered fitness. Here we show that the fitness of the high-multiplicity phage relative to their ancestors generates a pay-off matrix conforming to the prisoner's dilemma strategy of game theory2,3. In this strateg…
EXPERIMENTAL EVOLUTION OF RNA VERSUS DNA VIRUSES
2011
Based on their extremely high mutation rates, RNA viruses have been traditionally considered as the fastest evolving entities in nature. However, recent work has revealed that, despite their greater replication fidelity, single-stranded (ss) DNA viruses can evolve fast in a similar way. To further investigate this issue, we have compared the rates of adaptation and molecular evolution of ssRNA and ssDNA viruses under highly controlled laboratory conditions using the bacteriophages ΦX174, G4, f1, Qβ, SP, and MS2 as model systems. Our results indicate that ssRNA phages evolve faster than ssDNA phages under strong selective pressure, and that their extremely high mutation rates appear to be op…
Molecular basis of adaptive convergence in experimental populations of RNA viruses
2002
Abstract Characterizing the molecular basis of adaptation is one of the most important goals in modern evolutionary genetics. Here, we report a full-genome sequence analysis of 21 independent populations of vesicular stomatitis ribovirus evolved on the same cell type but under different demographic regimes. Each demographic regime differed in the effective viral population size. Evolutionary convergences are widespread both at synonymous and nonsynonymous replacements as well as in an intergenic region. We also found evidence for epistasis among sites of the same and different loci. We explain convergences as the consequence of four factors: (1) environmental homogeneity that supposes an id…
A genome-wide association study identifies Arabidopsis thaliana genes that contribute to differences in the outcome of infection with two Turnip mosa…
2021
Viruses lie in a continuum between generalism and specialism depending on their ability to infect more or less hosts. While generalists are able to successfully infect a wide variety of hosts, specialists are limited to one or a few. Even though generalists seem to gain an advantage due to their wide host range, they usually pay a pleiotropic fitness cost within each host. On the contrary, a specialist has maximal fitness within its own host. A relevant yet poorly explored question is whether viruses differ in the way they interact with their hosts’ gene expression depending on their degree of specialization. Using a genome-wide association study approach, we have identified host genes whos…
Analysis of tombusvirus revertants to identify essential amino acid residues within RNA-dependent RNA polymerase motifs
2005
The RNA-dependent RNA polymerase (RdRp) of Tomato bushy stunt virus (TBSV) contains an arginine- and proline-rich (RPR) motif. This motif functions as an RNA-binding domain and is essential for tombusvirus replication. A mutant carrying three arginine substitutions in this motif rendered the virus unable to replicate in Nicotiana benthamiana plants and protoplasts. When the replicase function was provided in trans, by expressing the TBSV RdRp in N. benthamiana plants, an infectious variant could be isolated. Sequence analysis showed that only the substituted glycine residue (position 216) had reverted to arginine; all other substitutions remained unchanged. This finding suggested that stron…
Mutational fitness effects in RNA and single-stranded DNA viruses: common patterns revealed by site-directed mutagenesis studies
2010
The fitness effects of mutations are central to evolution, yet have begun to be characterized in detail only recently. Site-directed mutagenesis is a powerful tool for achieving this goal, which is particularly suited for viruses because of their small genomes. Here, I discuss the evolutionary relevance of mutational fitness effects and critically review previous site-directed mutagenesis studies. The effects of single-nucleotide substitutions are standardized and compared for five RNA or single-stranded DNA viruses infecting bacteria, plants or animals. All viruses examined show very low tolerance to mutation when compared with cellular organisms. Moreover, for non-lethal mutations, the me…