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Biomedical subjects

K W Buck

Publications and source records attributed to K W Buck.

At least 55 records · Page 3Linked to original sources
PubMed1988

From interferon induction to fungal viruses.

Viruses of fungi (mycoviruses) were first discovered in diseased mushrooms. However the finding that the antiviral and interferon-inducing activities of extracts of apparently healthy isolates of a number of Penicillium species were due to the presence of double-stranded (ds) RNA arising from mycovirus infections sparked off an explosion of interest in what has now become a distinct area of virology. Two families of dsRNA mycoviruses are now established: the Totiviridae and the Partitiviridae which comprise isometric viruses with genomes of one or two dsRNA segments respectively. Virus isolates in both families often contain additional satellite dsRNAs, which may in some fungi (e.g. Saccharomyces cerevisiae, Ustilago maydis) code for "killer" proteins which are toxic to other sensitive strains of the same or closely related species. In Endothia parasitica, which causes chestnut blight disease, dsRNA is associated with hypovirulence and is enclosed in lipid-rich vesicles. In Ophiostoma (Ceratocystis) ulmi, which causes Dutch elm disease, dsRNA is associated with the mitochondria and, in some diseased isolates of the fungus, specific dsRNA segments are associated with reduction of cytochrome oxidase and respiratory deficiency, resulting in slow growth and abnormal morphology.

Fungi↗
PubMed1988

Characterization of potato yellow mosaic virus as a geminivirus with a bipartite genome.

A whitefly-transmitted virus from Venezuela, potato yellow mosaic virus, has been propagated, isolated and characterized as a member of the Geminivirus group. The virus was transmitted to several species of Nicotiana and to Petunia hybrida by mechanical inoculation, and to potato and tomato plants by grafting. Purified virus possessed typical geminate particle morphology and encapsidated both genomic and subgenomic species consisting of single-stranded DNA. The genome of the virus was cloned into both bacteriophage and plasmid vectors following restriction of supercoiled double-stranded DNA species isolated from infected plant extracts. Two distinct classes of cloned DNA were generated, both about 2,500-2,600 base pairs in length and designated A and B, which when inoculated in combination to Nicotiana benthamiana were infectious after excision from the recombinant clones. The subgenomic DNA was shown to be related to DNA B.

Cloning, Molecular↗
PubMed1986

Molecular characterisation of subgenomic single-stranded and double-stranded DNA forms isolated from plants infected with tomato golden mosaic virus.

A subgenomic single-stranded DNA present in particles of the geminivirus, tomato golden mosaic virus, has been shown by electron microscope heteroduplex mapping and Southern hybridisation analysis to consist of circular molecules, ca. 1.2 kb in size, derived from the smaller of the two genomic DNA components, DNA B, by deletion of open reading frame (ORF) BR1 and the C-terminal portion of ORF BL1. A covalently closed circular, supercoiled, double-stranded form of the subgenomic DNA has been isolated from virus-infected plants and cloned into pEMBL9. Analysis of the sequence of 22 clones across the deletion boundaries revealed only four different deletion boundaries, derived from four different left hand borders and three different right hand borders. Each border was within a region of 11 nucleotides and gave rise to a narrow size range (1248-1261 nucleotides) for the population of 22 subgenomic DNAs. However apparently smaller subgenomic DNAs were sometimes formed when plants were inoculated with cloned subgenomic DNA, or a construct derived from a subgenomic DNA in which a neomycin phosphotransferase gene had been inserted, together with the genomic DNA components. Mechanisms to account for the size, specificity and formation of the subgenomic DNA are discussed.

Base Sequence↗
PubMed1985

DNA and RNA polymerase activities of nuclei and hypotonic extracts of nuclei isolated from tomato golden mosaic virus infected tobacco leaves.

Nuclei and hypotonically leached extracts of nuclei prepared from tomato golden mosaic virus (TGMV)-infected Nicotiana benthamiana leaves have been used in in vitro DNA and RNA polymerisation reactions. The synthesis of virus-specific DNA was resistant to aphidicolin, sensitive to N-ethylmaleimide and dideoxy TTP, and stimulated by KC1 and ATP. Variably virion (+) and complementary (-) strand DNA of both the A and B genomic components were synthesised. Virus-specific RNA was synthesised in reactions which were initiated prior to nuclei isolation and leaching. From inhibitor studies and salt requirements RNA synthesis appeared to be catalysed by a DNA-dependent RNA polymerase type II enzyme. Both components of the TGMV genome were transcribed in a bidirectional fashion with a prevalence in some experiments of transcripts derived from DNA component A.

Cell Fractionation↗
PubMed1985

S1-sensitive sites in the supercoiled double-stranded form of tomato golden mosaic virus DNA component B: identification of regions of potential alternative secondary structure and regulatory function.

The sensitivity of the supercoiled double-stranded form of the DNA of tomato golden mosaic virus (TGMV), a geminivirus, to the single-strand specific enzyme S1 nuclease has been demonstrated. Specific S1 cleavage sites were identified in TGMV DNA component B by cloning into the single-strand bacteriophage vector M13 mp8 and sequencing of the inserted DNA. Analysis of the DNA sequence at the sites of S1 sensitivity in TGMV DNA component B revealed several possible regions of alternative secondary structure which were clustered in an intergenic region upstream of the starts of the two major open reading frames which are in opposite orientations. This region contains putative transcriptional promoter and modulatory sequences and a possible replication origin. The extreme S1 sensitivity of the supercoiled form of TGMV DNA component A precluded its cloning under the conditions employed for selective cleavage of DNA component B.

Base Sequence↗
PubMed1985

The nucleotide sequence of cloned wheat dwarf virus DNA.

Restriction analysis and cloning of virus-specific double-stranded DNA isolated from plants infected with wheat dwarf virus (WDV) indicated that the virus genome, like that of maize streak virus (MSV), consists of a single DNA circle. The complete nucleotide sequence of cloned WDV DNA (2749 nucleotides) has been determined. Comparison of the potential coding regions in WDV DNA with those in the DNA of two strains of MSV suggests that these viruses encode at least two functional proteins, the coat protein read in the virion (+) DNA sense and a composite protein, formed from two open reading regions, in the complementary (-) DNA sense. Although WDV and MSV are serologically unrelated their coat proteins showed 35% direct amino acid sequence and their DNAs showed 46% nucleotide sequence homology. There was too little homology between the DNAs of WDV and those of two geminiviruses with bipartite genomes, cassava latent virus (CLV) and tomato golden mosaic virus (TGMV), to align the sequences. However comparison of the amino acid sequences of predicted proteins of WDV, MSV, TGMV and CLV revealed clear relationships between these viruses and suggested that the monopartite and the bipartite geminiviruses have a common ancestral origin. Four inverted repeat sequences which have the potential to form hairpin structures of deltaG >/= -14 kcal/mol were detected in WDV DNA. The sequence TAATATTAC present in the loop of one of these hairpins is conserved in similar putative structures in MSV DNA and in both DNA components of CLV and TGMV and may function as a recognition sequence for a protein involved in virus DNA replication.

Amino Acid Sequence↗
PubMed1984

Negatively supercoiled DNA from plants infected with a single-stranded DNA virus.

A method for isolating covalently closed circular double-stranded DNA from plants infected with the geminivirus, tomato golden mosaic virus, is described. Ethidium bromide titration showed this DNA to be negatively supercoiled with a superhelical density of -0.062. The presence of S1 nuclease-sensitive secondary structure in the supercoiled DNA was demonstrated by its conversion to the open circular and linear DNA forms on treatment with this enzyme.

DNA, Circular↗
PubMed1984

Complete nucleotide sequence of the infectious cloned DNA components of tomato golden mosaic virus: potential coding regions and regulatory sequences.

The nucleotide sequences of the infectious cloned DNA components of tomato golden mosaic virus (TGMV) have been determined. DNA A (2588 nucleotides) and DNA B (2508 nucleotides) have little sequence homology except for a region of 200 bases which is almost identical in the two molecules. Analysis of open reading frames revealed six potential coding regions for proteins of mol. wt. >10 000, four in DNA A and two in DNA B. Possible regulatory signals are identified and a model for bidirectional transcription of the two genome components is presented. Comparison of the nucleotide sequences of the DNAs of TGMV and cassava latent virus (CLV) revealed a fairly close relationship between TGMV DNA A and CLV DNA 1 and a comparatively distant relationship between TGMV DNA B and CLV DNA 2. All the potential coding regions in the TGMV DNAs had counterparts in the CLV DNAs suggesting an overall similarity in genome organisation, but six potential coding regions in the CLV DNAs had no counterparts in the TGMV DNAs. The 200-base region common to the two DNAs of each virus had little sequence homology, except for a highly conserved 33-base sequence potentially capable of forming a stable hairpin structure.

Journal Article↗
PubMed1984

Mitochondrial DNA in Fusarium oxysporum is a 46.5 kilobase pair circular molecule.

Purified mitochondria were obtained from the phytopathogenic fungus Fusarium oxysporum f. sp. lycopersici by mechanical disruption of protoplasts, followed by differential and density gradient centrifugation. DNA, extracted from the mitochondria, was shown by electron microscopy and restriction endonuclease analysis to be a 46.5 kilobase pair circular molecule.

Base Composition↗
PubMed1984

Six groups of double-stranded RNA mycoviruses.

Six groups of double-stranded (ds) RNA mycoviruses have been proposed. The main characteristics which define a group are described, and the properties of members and probable members of each group are tabulated. Possibilities for organization of the groups into families, genera and species are discussed. The classification scheme could ultimately accommodate the majority of the well-characterized dsRNA mycoviruses.

Fungi↗
PubMed1983

Demonstration of the bipartite nature of the genome of a single-stranded DNA plant virus by infection with the cloned DNA components.

Linear double-stranded (ds)DNA, obtained by excision of the cloned A and B components of tomato golden mosaic virus (TGMV) from recombinant plasmids, was found to infect plants and to elicit symptoms identical to those obtained with TGMV or TGMV DNA. Progeny virus isolated from plants infected with cloned DNA was infective and indistinguishable from TGMV on the basis of (a) its circular single-stranded (ss)DNA genome, (b) its capsid polypeptide, (c) its particle morphology and (d) serological identity. Southern blot analysis of DNA extracted from cells infected with cloned DNA, or TGMV DNA, revealed the same intracellular ss and dsDNA species, represented in both A and B components, except for a subgenomic, possibly defective, DNA, which was not detected in infections with cloned DNA. Infection with cloned DNA was achieved when cloned A and B components were both present, but not with either cloned A or B components separately. TGMV is the first DNA virus for which unequivocal proof of a bipartite genome has been obtained.

Cloning, Molecular↗
PubMed1983

Sequence complexities of the nuclear and mitochondrial genomes of the take-all fungus, Gaeumannomyces graminis var. tritici.

The nuclear (n) and mitochondrial (mt) genomes of the take-all fungus, Gaeumannomyces graminis var. tritici, were examined by reassociation kinetics with Escherichia coli DNA as internal standard. Only one kinetic component was detected in each DNA, with second-order rate constants of 0.022 M-1 S-1 for nDNA and 10.9 M-1 S-1 for mtDNA, corresponding to sequence complexities of 29 X 10(6) base pairs and 60 X 10(3) base pairs respectively.

Ascomycota↗
PubMed1982

Identification of novel DNA forms in tomato golden mosaic virus infected tissue. Evidence for a two component viral genome.

Extracts obtained from cells infected with the geminivirus tomato golden mosaic (TGMV) are shown to contain, in addition to viral single-stranded DNA, several novel species of virus-specific single- and double- stranded DNA (ss and ds DNA). The results of nuclease studies and electron microscopy suggest that three of the intracellular DNAs are unit-genome length duplexes of closed circular, relaxed circular, and linear form. The remaining ds DNA species are of high molecular weight and appear to be concatamers consisting of two or more unit-length circular ds TGMV DNA resulted in fragments whose combined size is twice the unit-genome length. Thus ds TGMV is composed of two components of nearly identical size but different nucleotide sequence.

Base Sequence↗
PubMed1982

Molecular cloning and characterisation of the two DNA components of tomato golden mosaic virus.

We report the molecular cloning of the tomato golden mosaic virus (TGMV) genome in the E. coli plasmid pAT 153. The results of this work conclusively show that TGMV DNA consists of two components (designated A and B) of almost, but not exactly, the same size. Four different recombinant plasmids are described, two containing component A in opposite orientation and two containing component B in opposite orientation. Southern blot analysis revealed little sequence homology between A and B and showed both components to be equally represented in viral and intracellular DNA forms. Detailed restriction maps of the cloned DNAs are presented, and a comparison of these with digests of intracellular viral dsDNA indicates that the former are full-length faithful copies of TGMV DNA. This is the first report of the cloning of a geminivirus genome.

Base Sequence↗