- Volume 86, Issue 10, 2005
Volume 86, Issue 10, 2005
- Animal
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- DNA viruses
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Open reading frame 73 is required for herpesvirus saimiri A11-S4 episomal persistence
More LessHerpesvirus saimiri (HVS) establishes a latent infection in which the viral genome persists as a non-integrated episome. Analysis has shown that only open reading frames (ORFs) 71–73 are transcribed in an in vitro model of HVS latency. ORF73 also colocalizes with HVS genomic DNA on host mitotic chromosomes and maintains the stability of HVS terminal-repeat-containing plasmids. However, it is not known whether ORF73 is the only HVS-encoded protein required for episomal maintenance. In this study, the elements required for episomal maintenance in the context of a full-length HVS genome were examined by mutational analysis. A recombinant virus, HVS-BACΔ71-73, lacking the latency-associated genes was unable to persist in a dividing cell population. However, retrofitting an ORF73 expression cassette into the recombinant virus rescued episomal maintenance. This indicates that ORF73 is the key trans-acting factor for episomal persistence and efficient establishment of a latent infection.
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Variants of human papillomaviruses 16 and 18 and their natural history in human immunodeficiency virus-positive women
Highly oncogenic human papillomavirus (HPV) 16 and 18 variants might be expected to be particularly aggressive in HIV-positive women. The association of HPV16 and 18 variant lineages with race, human immunodeficiency virus (HIV) coinfection, CD4+ T-cell count, HIV-RNA level, time-to-clearance of HPV infection and presence of squamous intraepithelial lesions (SIL) among women in the Women's Interagency HIV Study was studied. Subjects were followed semi-annually with Pap smear and cervicovaginal lavage (CVL). HPV DNA was detected in CVLs using MY09/11 L1 PCR assay. Specimens positive for HPV16/18 underwent E6 PCR and sequencing to determine the variant present. Specimens from 195 HPV16- and 162 HPV18-positive women were classified into variant lineages based on sequencing results. African variants of HPV16 and HPV18 were significantly more prevalent among African-Americans than among Caucasians [42 versus 14 % (P=0·001) and 60 versus 13 % (P<0·001), respectively]. However, it was not possible to detect associations between the HPV16 or 18 variant lineages and other factors studied. African variants of HPV16/18 were more common in women of African descent living outside Africa, which could reflect mixing behaviours and/or immunogenetic factors. However, in a large population of HIV-infected women, the variant of HPV16 or 18 was unrelated to persistence of infection or presence of SIL. If non-European variants are more oncogenic, the effect may involve a late stage in cervical tumorigenesis.
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Quantification of vertical transmission of Murine polyoma virus by real-time quantitative PCR
More LessPathogenesis studies of viral infections in vivo require sensitive assay methods. A sensitive and specific real-time quantitative PCR (RQ-PCR) assay was developed to detect Murine polyoma virus (MuPyV) DNA sequences. A quantitative assay to measure the single-copy murine wild-type p53 gene was developed to normalize viral gene copies to cell numbers. Both assays were sensitive over a seven-log dynamic range, with a reproducible detection limit of 10 copies per reaction. To determine viral loads and tissue distribution following vertical transmission of MuPyV, pregnant BALB/c mice were inoculated intraperitoneally with virus in late pregnancy. Progeny animals born to infected mothers were followed for 21 days. Viral loads in four tissues (salivary gland, kidney, liver and spleen) were highest at 7 days after birth and dropped to low levels by 14 and 21 days of age, with loads ranging from 5 to 2 million MuPyV copies per 103 cells. Significant animal-to-animal variation occurred. Fourteen of 21 (67 %) progeny were virus-positive in one or more tissue samples. Transplacental transmission was observed in 6/7 (86 %) litters. Infected fetuses per positive litter ranged from 1/7 (14 %) to 5/6 (83 %) with viral loads ranging from 5 to 25 417 MuPyV copies per 1000 fetal cells. Maternal tissues and blood were frequently highly positive 2 days after inoculation, but viral loads were low by day 14. This study demonstrated the vertical transmission, including transplacental transmission, of MuPyV following acute infection of pregnant mice. It should be considered that there is a possibility that other polyomaviruses, including those in humans, may be vertically transmitted.
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Virulence and competitiveness of Cydia pomonella granulovirus mutants: parameters that do not match
More LessThe LD50, median survival time (ST50) and virus production are virulence parameters that are commonly used to describe the biological characteristics of viruses. In this study, these parameters were determined for Cydia pomonella granulovirus (CpGV-M) and two naturally occurring mutants (CpGV-MCp4 and -MCp5) that carry Tc1-like insect transposable elements. The three virus genotypes were similar in their LD50, ST50 and virus production. However, the mutant genotypes MCp4 and MCp5 were very effectively out-competed by CpGV-M in direct competition experiments, where Cydia pomonella larvae were co-infected with known ratios of occlusion bodies or budded virus of CpGV-M and one of the two mutants. It was demonstrated that MCp5 and MCp4 could not be sustained in the virus population when the progeny viruses of different co-infections were used as inocula to infect next passage larvae. These results show that the virulence parameters LD50, ST50 and virus production alone do not adequately reflect the competitiveness of the virus and are thus not suitable to describe virus population dynamics.
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- Plant Viruses
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Isolation and characterization of a new type of chlorovirus that infects an endosymbiotic Chlorella strain of the heliozoon Acanthocystis turfacea
More LessA novel virus, named Acanthocystis turfacea Chlorella virus (ATCV), that infects endosymbiotic Chlorella algae of the heliozoon Acanthocystis turfacea was isolated from freshwater samples. Electron microscopic analysis of ATCV revealed that the viral capsid has a distinct icosahedral shape with a diameter of 140–190 nm. Filamentous structures extending from some of the virus vertices, which may aid attachment of the virus to host cells, were also observed. The capsid is made up of one major coat protein of about 50 kDa and contains a large dsDNA genome. ATCV is a member of the genus Chlorovirus, which belongs to the family Phycodnaviridae, a group of large, icosahedral, dsDNA-containing viruses that infect algae and are ubiquitous in natural environments. However, ATCV is clearly distinct from the prototype Chlorovirus, Paramecium bursaria Chlorella virus (PBCV-1), in some aspects of its genome structure and gene content and therefore must be regarded as a member of a new group of Chlorella viruses.
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Expression, localization and effects on virulence of the cysteine-rich 8 kDa protein of Potato mop-top virus
Potato mop-top virus (PMTV) RNA3 contains a triple gene block (TGB) encoding viral movement proteins and an open reading frame for a putative 8 kDa cysteine-rich protein (CRP). In this study, PMTV CRP was shown to be expressed in the course of virus infection, and a PMTV CRP-specific subgenomic RNA was mapped. CRP has previously been shown to be dispensable for infection of PMTV in Nicotiana benthamiana. In this study, PMTV CRP was found to increase the severity of disease symptoms when expressed from Potato virus X or Tobacco mosaic virus in N. benthamiana and Nicotiana tabacum, suggesting that the protein affects virulence of the virus or might suppress a host defence mechanism. However, PMTV CRP did not show RNA silencing suppression activity in three assays. Host responses to the PMTV CRP expression from different viral genomes ranged from an absence of response to extreme resistance at a single cell level and were dependent on the viral genome. These findings emphasized involvement of viral proteins and/or virus-induced cell components in the plant reaction to CRP. PMTV CRP was predicted to possess a transmembrane segment. CRP fused to the green fluorescent protein was associated with endoplasmic reticulum-derived membranes and induced dramatic rearrangements of the endoplasmic reticulum structure, which might account for protein functions as a virulence factor of the virus.
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Nucleolar localization of potato leafroll virus capsid proteins
Potato leafroll virus (PLRV) encodes two capsid proteins, major protein (CP) and minor protein (P5), an extended version of the CP produced by occasional translational ‘readthrough’ of the CP gene. Immunogold electron microscopy showed that PLRV CP is located in the cytoplasm and also localized in the nucleus, preferentially targeting the nucleolus. The nucleolar localization of PLRV CP was also confirmed when it was expressed as a fusion with green fluorescent protein (GFP) via an Agrobacterium vector. Mutational analysis identified a particular sequence within PLRV CP involved in nucleolar targeting [the nucleolar localization signal (NoLS)]. Minor protein P5 also contains the same NoLS, and was targeted to the nucleolus when it was expressed as a fusion with GFP from Agrobacterium. However, P5–GFP lost its nucleolar localization in the presence of replicating PLRV.
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Phylogenetic analysis of isolates of Beet necrotic yellow vein virus collected worldwide
A study of molecular diversity was carried out on 136 sugar beets infected with Beet necrotic yellow vein virus (BNYVV, Benyvirus) collected worldwide. The nucleotide sequences of the RNA-2-encoded CP, RNA-3-encoded p25 and RNA-5-encoded p26 proteins were analysed. The resulting phylogenetic trees allowed BNYVV to be classified into groups that show correlations between the virus clusters and geographic origins. The selective constraints on these three sequences were measured by estimating the ratio between synonymous and non-synonymous substitution rates (ω) with maximum-likelihood models. The results suggest that selective constraints are exerted differently on the proteins. CP was the most conserved, with mean ω values ranging from 0·12 to 0·15, while p26 was less constrained, with mean ω values ranging from 0·20 to 0·33. Selection was detected in three amino acid positions of p26, with ω values of about 5·0. The p25 sequences presented the highest mean ω values (0·36–1·10), with strong positive selection (ω=4·7–54·7) acting on 14 amino acids, and particularly on amino acid 68, where the ω value was the highest so far encountered in plant viruses.
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- Other Agents
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Prion clearance in bigenic mice
The clearance of prions from the brain was investigated in bigenic mice designated Tg(tTA : PrP+/0)3, in which expression of the cellular prion protein (PrPC) was regulated by oral doxycycline administration. With suppression of PrPC expression, the incubation time for RML prions was prolonged almost threefold from ∼150 to ∼430 days. To determine the clearance rate of disease-causing PrPSc, bigenic mice were given oral doxycycline beginning 98 days after inoculation with RML prions and sacrificed at various time points over the subsequent 56 days. The half-life (t 1/2) for PrPSc was ∼1·5 days in mouse brain, in reasonable agreement with the apparent t 1/2 of 30 h that was determined in a separate study for scrapie-infected mouse neuroblastoma (ScN2a) cells in culture. Both protease-sensitive and -resistant conformers of PrPSc were cleared at the same rate. The t 1/2 value for PrPC clearance from brain was ∼18 h, which was considerably longer than the t 1/2 of 5 h found in ScN2a cells. The capability of the brain to clear prions raises the possibility that PrPSc is normally made at low levels and continually cleared, and that PrPSc may have a function in cellular metabolism. Moreover, these bigenic mice make it possible to determine both components of PrPSc accumulation, i.e. the rates of formation and clearance, for various strains of prions exhibiting different incubation times.
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- Jgv Direct
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A tale of two clades: monkeypox viruses
Human monkeypox was first recognized outside Africa in 2003 during an outbreak in the USA that was traced to imported monkeypox virus (MPXV)-infected West African rodents. Unlike the smallpox-like disease described in the Democratic Republic of the Congo (DRC; a Congo Basin country), disease in the USA appeared milder. Here, analyses compared clinical, laboratory and epidemiological features of confirmed human monkeypox case-patients, using data from outbreaks in the USA and the Congo Basin, and the results suggested that human disease pathogenicity was associated with the viral strain. Genomic sequencing of USA, Western and Central African MPXV isolates confirmed the existence of two MPXV clades. A comparison of open reading frames between MPXV clades permitted prediction of viral proteins that could cause the observed differences in human pathogenicity between these two clades. Understanding the molecular pathogenesis and clinical and epidemiological properties of MPXV can improve monkeypox prevention and control.
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Volumes and issues
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Volume 105 (2024)
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Volume 104 (2023)
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Volume 103 (2022)
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Volume 102 (2021)
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Volume 101 (2020)
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Volume 100 (2019)
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Volume 99 (2018)
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Volume 98 (2017)
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Volume 97 (2016)
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Volume 96 (2015)
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Volume 86 (2005)
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Volume 73 (1992)
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Volume 72 (1991)
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Volume 71 (1990)
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Volume 53 (1981)
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Volume 52 (1981)
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Volume 50 (1980)
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Volume 49 (1980)
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Volume 48 (1980)
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Volume 47 (1980)
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Volume 46 (1980)
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Volume 45 (1979)
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Volume 44 (1979)
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Volume 43 (1979)
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Volume 42 (1979)
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Volume 41 (1978)
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Volume 40 (1978)
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Volume 39 (1978)
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Volume 38 (1978)
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Volume 37 (1977)
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Volume 36 (1977)
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Volume 35 (1977)
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Volume 34 (1977)
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Volume 33 (1976)
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Volume 32 (1976)
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Volume 31 (1976)
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Volume 30 (1976)
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Volume 29 (1975)
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Volume 28 (1975)
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Volume 27 (1975)
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Volume 26 (1975)
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Volume 25 (1974)
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Volume 24 (1974)
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Volume 23 (1974)
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Volume 22 (1974)
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Volume 21 (1973)
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Volume 20 (1973)
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Volume 19 (1973)
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Volume 18 (1973)
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Volume 17 (1972)
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Volume 16 (1972)
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Volume 15 (1972)
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Volume 14 (1972)
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Volume 13 (1971)
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Volume 12 (1971)
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Volume 11 (1971)
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Volume 10 (1971)
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Volume 9 (1970)
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Volume 8 (1970)
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Volume 7 (1970)
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Volume 6 (1970)
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Volume 5 (1969)
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Volume 4 (1969)
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Volume 3 (1968)
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Volume 2 (1968)
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Volume 1 (1967)