Biomedical subjects

K W Buck

Publications and source records attributed to K W Buck.

At least 37 records · Page 2Linked to original sources

PubMed1994

Plant proteins that bind to the 3'-terminal sequences of the negative-strand RNA of three diverse positive-strand RNA plant viruses.

The replication of positive-strand RNA plant viruses, which involves both virus-encoded and plant-encoded proteins, takes place in two stages: synthesis of a negative-strand RNA using the genomic positive-strand RNA as a template and synthesis of progeny positive-strand RNA using the negative-strand RNA as a template. Using gel mobility shift and photochemical crosslinking assays, we have identified three proteins of M(r) 32K, 50K and 100K in extracts of tobacco and spinach leaves that bind to the 3'-terminal sequences of the negative-strand RNA of three diverse positive-strand RNA plant viruses. The 32K protein was purified to near homogeneity by chromatography on columns of Macro-prep high Q, heparin-sepharose, single-stranded DNA cellulose and poly(U)-sepharose. No binding of any of the three proteins to the 3'-termini of the positive-strand RNA or the 5'-termini of the positive-strand RNA or negative-strand RNA of any of the three viruses, or the 3'-termini of the mRNAs of two chloroplast genes, psbA or petD, could be detected. We propose that 3'-terminal negative-strand RNA binding proteins, which may be widespread in the plant kingdom, could be utilised by at least three different positive-strand RNA plant viruses for the initiation of positive-strand RNA synthesis.

Base Sequence↗

PubMed1994

Localization of functional regions of the cucumber mosaic virus RNA replicase using monoclonal and polyclonal antibodies.

Monoclonal antibodies were produced using a purified cucumber mosaic virus (CMV) replicase complex, and Escherichia coli-expressed CMV 1a and 2a proteins, as immunogens. Five out of eight monoclonal antibodies, which bound to the 1a and 2a proteins in immunoblots, inhibited the RNA-dependent RNA polymerase (RdRp) activity of the purified replicase complex in vitro. Epitope mapping showed that two of the inhibitory antibodies interacted with regions of the 1a protein containing putative helicase and methyltransferase domains respectively. Two other inhibitory antibodies mapped to a region of the 2a protein containing the GDD motif which is highly conserved in RdRps. Prior interaction of the latter antibodies with a peptide containing the GDD motif prevented the antibody-mediated inhibition of the replicase. Polyclonal antibodies which inhibited the RdRp activity of the replicase complex were also produced using peptides corresponding to conserved helicase and polymerase motifs in the 1a and 2a proteins. The greatest inhibition was shown by antibodies to a peptide containing the GDD motif. These results demonstrate the functional importance of the identified sequence motifs in CMV RNA replication and indicate that the motifs are located in the replicase complex at positions accessible to antibodies, consistent with roles in interacting with the RNA template, RNA primer and enzyme substrates.

Amino Acid Sequence↗

PubMed1994

Simultaneous regulation of tomato golden mosaic virus coat protein and AL1 gene expression: expression of the AL4 gene may contribute to suppression of the AL1 gene.

The tomato golden mosaic virus (TGMV) coat protein and AL1 genes are located in opposite directions on either side of an intergenic region. To enable the effects of the AL1, AL2 and AL3 gene products on expression of the coat protein and AL1 genes to be studied simultaneously, a plasmid was constructed, containing the intergenic region linked on one side to a 5'-terminal portion of the AL1 gene fused to a beta-glucuronidase (GUS) reporter gene (to replace most of the AL1 gene) and on the other side to a neomycin phosphotransferase (NEO) reporter gene (to replace the coat protein gene). This GUS-NEO plasmid was mixed with plant expression plasmids containing the AL1, AL2 or AL3 coding regions, the DNA was transformed into Nicotiana benthamiana protoplasts and GUS activities and NEO protein levels were measured. Control transformations were carried out with the GUS-NEO plasmid mixed with the AL1, AL2 or AL3 plasmids in which mutations were introduced to prevent translation of the open reading frames (ORFs). The results showed that transactivation of the coat protein gene by the AL2 gene product and suppression of the AL1 gene by the expression of AL1 DNA (both reported previously) can occur simultaneously. It was also shown that expression of AL4, a small ORF contained within AL1 DNA but in a different reading frame, as well as expression of ORF AL1, can cause significant suppression of AL1 gene expression. Neither the AL1 nor the AL3 gene products affected the expression of the coat protein gene.

Base Sequence↗

PubMed1994

Synthesis of the tomato golden mosaic virus AL1, AL2, AL3 and AL4 proteins in vitro.

Transcripts derived from the leftward region of tomato golden mosaic virus DNA A were translated in wheat-germ and rabbit reticulocyte lysate systems. The largest protein (M(r) 40K) produced from transcripts encompassing open reading frame (ORF) AL1 was identified as the AL1 protein by immunoprecipitation with AL1-specific antibodies. However the main product was a protein of M(r) 10K, that was shown by in vitro mutagenesis to be the product of AL4, an ORF contained within AL1 DNA in a different reading frame. Translation of transcripts containing ORF AL2 or ORF AL3 gave the AL2 and AL3 proteins respectively; both proteins were also efficiently produced from transcripts containing both ORFs which overlap over about two-thirds of their length. Translation of a transcript containing the four ORFs gave all four proteins, consistent with a previous report that three of these (AL1, AL2 and AL3) can be translated from a single polycistronic RNA in transgenic tobacco plants. It is suggested that the leftward region of DNA A of the whitefly-transmitted geminiviruses may be expressed by two principal messenger RNAs, one encoding the AL1 and AL4 proteins and the other encoding the AL2 and AL3 proteins, and that the AL4 and AL3 proteins may be translated from the messenger RNAs by a leaky scanning mechanism.

Base Sequence↗

PubMed1993

TGMV replication protein AL1 preferentially binds to single-stranded DNA from the common region.

The AL1 protein of tomato golden mosaic virus (TGMV) is encoded by the viral DNA and has been shown to be essential for viral DNA replication. We have over-expressed the AL1 open reading frame in E. coli and purified the protein from bacterial extracts to near homogeneity. Using various different techniques we have studied the interaction of the AL1 protein with DNA. The AL1 protein is able to bind to DNA containing the common region of the viral genome, which can be demonstrated by photochemical cross-linking. Binding is 4-fold stronger to single-stranded than to double-stranded DNA. Antibodies against the AL1 protein can be used to precipitate the protein-DNA complex. The binding to single- and double-stranded DNA is specifically to the common region since a DNA fragment unrelated to TGMV is not shifted in a gel retardation assay.

Binding Sites↗

PubMed1993

De-novo generation of mitochondrial DNA plasmids following cytoplasmic transmission of a degenerative disease in Ophiostoma novo-ulmi.

A mitochondrial DNA plasmid was detected in an isolate of Ophiostoma novo-ulmi with a degenerative disease. The DNA plasmid was shown to be derived from the mitochondrial DNA and to map to a region corresponding to the large ribosomal RNA coding region. The DNA plasmid was not transmitted into sexual (ascospore) progeny, irrespective of whether the diseased isolate acted as the female or male parent. Transmission of the disease to healthy, plasmid-free, "recipient" isolates by hyphal anastomosis was not accompanied by transfer of mitochondrial DNA or DNA plasmid from the diseased "donor" isolate, but resulted in de-novo generation of different plasmids, derived from the recipient's mitochondrial DNA.

Blotting, Southern↗

PubMed1993

Localization of a single-stranded RNA-binding domain in the movement protein of red clover necrotic mosaic dianthovirus.

Mutant movement proteins of red clover necrotic mosaic dianthovirus (RCNMV), consisting of in-frame deletions or fusions with a maltose-binding protein, were produced in Escherichia coli using expression vectors. The ability of the mutant proteins to bind to ssRNA was tested by photochemical cross-linking and gel retardation. The results showed that the region between amino acids 181 and 225 of the RCNMV movement protein contains an ssRNA-binding domain.

Amino Acid Sequence↗

PubMed1992

Cooperative binding of the red clover necrotic mosaic virus movement protein to single-stranded nucleic acids.

The movement protein of red clover necrotic mosaic dianthovirus was produced in Escherichia coli using an expression vector. Gel retardation analysis and u.v. cross-linking studies showed that the movement protein bound cooperatively to ssRNA and ssDNA, but not to dsDNA. Binding competition experiments established that the movement protein bound to ssRNA and ssDNA with similar affinities and that the binding was not sequence-specific in the experimental conditions employed. A truncated movement protein lacking the C-terminal 88 amino acids was also shown to bind to ssRNA.

Binding, Competitive↗

PubMed1992

Complete replication of a satellite RNA in vitro by a purified RNA-dependent RNA polymerase.

The 334 nucleotide R satellite RNA was used as a template for purified RNA-dependent RNA polymerase (RdRp) from cucumber mosaic virus-infected tobacco plants. The products of the reaction were dsRNA and positive-strand RNA of the same size as the R satellite RNA. Similar products were obtained when T7 RNA polymerase positive-strand transcripts of a cDNA clone of the satellite RNA, designed to have the same 5' and 3' ends as the satellite RNA, were used as templates. The formation of the positive strands demonstrates complete replication of the satellite RNA. A positive-strand transcript with 65 and 255 additional nucleotides at the 5' and 3' ends of the satellite RNA respectively was also utilized as a template by the RdRp, but only dsRNA was formed. However, no products could be detected when the RdRp was programmed with transcripts corresponding to the negative-strand satellite RNA, either with no additional terminal nucleotides or with 24 and 310 additional nucleotides at the 5' and 3' ends respectively.

Base Sequence↗

PubMed1991

Expression of an antisense viral gene in transgenic tobacco confers resistance to the DNA virus tomato golden mosaic virus.

Transgenic tobacco plants carrying a genetic cassette including an antisense DNA sequence of the virally encoded AL1 gene of the geminivirus tomato golden mosaic virus (TGMV) were constructed; AL1 encodes a protein absolutely required for TGMV DNA replication. These genetic cassettes also contained, on the same transcription unit, a gene encoding hygromycin resistance, which allowed selection for concomitant expression of the antisense gene. In transgenic lines, RNA transcripts of the predicted size and strand specificity were detected in antisense plants and sense controls. After infection of plants with TGMV, by agroinoculation, the frequency of symptom development was very significantly reduced in a number of antisense lines and correlated, broadly, with the abundance of antisense RNA transcript and with a reduction in viral DNA harvested from infected leaf tissue. We used an in vitro assay to study viral DNA replication in the absence of cell-to-cell spread; no replication was seen in five of the six antisense lines studied, in contrast to controls.

DNA Viruses↗

PubMed1991

The detection of beet western yellows virus and beet mild yellowing virus in crop plants using the polymerase chain reaction.

Oligonucleotide primers were synthesised corresponding to conserved sequences between three isolates of beet western yellows virus (BWYV), flanking a 913 base fragment of BWYV genomic RNA. Using the polymerase chain reaction (PCR), these primers successfully amplified the target fragment in total RNA extracts from two oilseed rape plants infected with different isolates of BWYV. The PCR products were readily detected by staining with ethidium bromide following agarose gel electrophoresis, but the limit of detection could be increased further by Southern blotting. However, three isolates of beet mild yellowing virus (BMYV) in sugar beet did not give a signal which could be detected by ethidium bromide staining, although the target fragment could be detected by Southern blotting. The primers used have the potential to detect BWYV in crops with far greater sensitivity than enzyme-linked immunosorbent assay or nucleic acid hybridisation (dot-blotting) and may be capable of distinguishing between BWYV and BMYV. The application of PCR to detection and distinction of luteoviruses in general is discussed.

Base Sequence↗

PubMed1991

Nucleotide sequence of RNA 2 of a Czechoslovakian isolate of red clover necrotic mosaic virus.

The complete nucleotide sequence (1448 nucleotides) of RNA 2 of a Czechoslovakian isolate TpM-34 of red clover necrotic mosaic virus (RCNMV-TpM-34) has been determined. The sequence contained one major open reading frame (ORF) with the potential to encode a protein of 326 amino acids (Mr 35755), designated P2. The nucleotide sequence of RNA 2 of RCNMV-TpM-34 and the previously published sequence of RNA 2 of an Australian isolate of the virus (RCNMV-Aus) were 83% identical and there was 80% amino acid sequence identity between the P2 proteins of these isolates. However the N-terminal two-thirds of the P2 proteins shared a higher degree of similarity than the C-terminal regions which were predicted to have a more flexible structure. An ORF in the 3' portion of RNA 2 of RCNMV-Aus, which could encode a protein of Mr 5000, was not present in RNA 2 of RCNMV-TpM-34. RNAs 1 and 2 of RCNMV-TpM-34 and RCNMV-Aus are bilaterally compatible.

Amino Acid Sequence↗

PubMed1991

Detection of the movement protein of red clover necrotic mosaic virus in a cell wall fraction from infected Nicotiana clevelandii plants.

The movement protein of red clover necrotic mosaic virus (RCNMV) was expressed in Escherichia coli as a fusion with a maltose-binding protein using the vector pMAL-cRI and used to produce an antiserum. The RCNMV movement protein was detected in a cell wall fraction obtained from infected Nicotiana clevelandii leaf tissue by immunoblotting using the movement protein antiserum. The movement protein could be detected 6 h after inoculation and reached a maximum after 24 h. In contrast, the virus capsid protein, detected in a soluble fraction by immunoblotting using a capsid antiserum, continued to increase for 72 h after inoculation.

ATP-Binding Cassette Transporters↗

PubMed1991

A spontaneous red clover necrotic mosaic virus mutant with a truncated movement protein.

A spontaneous red clover necrotic mosaic virus mutant, TpM-341, was isolated by multiple passage of Czechoslovakian isolate TpM-34 in beans, followed by three cycles of single lesion isolation in cowpea and in Chenopodium quinoa. The symptoms induced in cowpea by TpM-34 and TpM-341 differed. TpM-34 gave rise to chlorotic lesions which expanded with time, often becoming confluent with adjacent lesions, and developed necrotic margins; the plants became systemically infected. TpM-341 induced necrotic lesions which, once developed, did not expand further; plants did not become systemically infected. Analysis of pseudorecombinants formed between the RNAs of TpM-34 and TpM-341 showed that RNA 2 determined the difference in symptoms. Comparison of the nucleotide sequence of the open reading frames (ORFs) encoding the P2 movement proteins of the two isolates revealed only one difference, a deletion of an A residue in a sequence of four A residues (nucleotides 790 to 793). Construction of full-length TpM-34 and TpM-341 RNA 2 cDNA clones, from which infectious RNA 2 could be transcribed in vitro, and in vitro mutagenesis of a cDNA clone of TpM-341, confirmed that the difference in the symptoms induced by TpM-341 was caused by the loss of this A residue. This single base deletion was predicted to cause a translational frame-shift in the P2 ORF causing the loss of 88 amino acids at the C terminus which were replaced by a sequence of 34 different amino acids, producing a truncated P2 protein. In vitro translation of RNA 2 transcribed from cDNA clones showed that RNA with four or three A residues starting at nucleotide 790 produced proteins of Mr 36K and 30K respectively, in agreement with the predictions based on the nucleotide sequence.

Base Sequence↗

PubMed1990

Complete replication of a eukaryotic virus RNA in vitro by a purified RNA-dependent RNA polymerase.

A soluble RNA-dependent RNA polymerase was isolated from Nicotiana tabacum plants infected with cucumber mosaic virus (CMV), which has a genome of three positive-strand RNA components, 1, 2, and 3. The purified polymerase contained two virus-encoded polypeptides and one host polypeptide. Polymerase activity was completely dependent on addition of CMV RNA as template, and the products of reaction were single-stranded (ss) RNA and double-stranded (ds) RNA, corresponding to RNAs 1, 2, and 3, and a subgenomic RNA (RNA 4) derived from RNA 3. The ratio of ssRNA to dsRNA was about 5:1, and the ssRNA was shown to be predominantly the positive strand. This demonstrates the complete replication of a eukaryotic virus RNA in vitro by a template-dependent RNA polymerase.

Base Sequence↗

PubMed1990

Infectious cucumber mosaic virus RNA transcribed in vitro from clones obtained from cDNA amplified using the polymerase chain reaction.

Full-length cDNA to RNA 1, RNA 2 and RNA 3 of cucumber mosaic virus strain Q (CMV-Q) was amplified using the polymerase chain reaction (PCR). The first-strand primer contained a BamHI site and sequences complementary to the 3' terminus of the RNA. The second-strand primers contained a BamHI site, a T7 promoter and sequences corresponding to the 5' terminus of each RNA. After cleavage with BamHI, the PCR products were cloned into the BamHI site of the vector pEMBL9(+). Five clones of each RNA were selected and RNA transcripts were synthesized in vitro from each clone using T7 RNA polymerase. The constructs were designed to allow transcription to initiate precisely at the 5' terminus of each RNA. All the transcripts were found to be infectious when inoculated onto Nicotiana tabacum cv. Samsun plants in sets of three, corresponding to RNA 1, RNA 2 and RNA 3. Of the transcript sets, four induced symptoms indistinguishable from symptoms induced by CMV-Q RNAs. However a fifth transcript set induced much more severe symptoms. Plasmids were also constructed to allow synthesis of transcripts with one or two additional G residues at the 5' terminus of each RNA. Although the yields of such transcripts synthesized in vitro with T7 RNA polymerase were higher, their infectivity was lower than that of those with no additional residues at their 5' termini.

Base Sequence↗

PubMed1989

Replication of tomato golden mosaic virus DNA B in transgenic plants expressing open reading frames (ORFs) of DNA A: requirement of ORF AL2 for production of single-stranded DNA.

Tomato golden mosaic geminivirus has a genome of two single-stranded (ss) DNA components, A and B. An almost identical 'common' region in DNA A and DNA B is thought to contain sequence elements controlling replication and transcription. Hence investigation of sequences important for DNA replication by in vitro mutagenesis is complicated by possible effects on the transcription of genes for replication proteins. To overcome this problem, transgenic plants expressing open reading frames (ORFs) of DNA A from an enhanced cauliflower mosaic virus 35S RNA promoter were constructed and tested for their ability to support the replication of DNA B and DNA B mutants. The results show that plants transgenic for ORF AL1 are able to support the replication of the double-stranded (ds) forms of DNA B, but that ORF AL2 is required in addition to produce ssDNA B. ORFs AL3, BL1 or BR1 were not required for replication of ds or ssDNA B. To the best of our knowledge this is the first time that essential replication proteins of a geminivirus have been expressed constitutively from a plant genome without giving rise to replicating DNA A molecules, thereby allowing DNA B to replicate alone. Such transgenic plants should enable not only the mutational analysis of sequence elements within the replication origin region, but also the construction of a new generation of vectors for gene amplification in plants, based on a minimal virus replicon.

DNA Probes↗

PubMed1989

Stability and expression of bacterial genes in replicating geminivirus vectors in plants.

Bacterial beta-glucuronidase (gus) and neomycin phosphotransferase (neo) genes were introduced into coat protein replacement vectors based on DNA A of tomato golden mosaic virus (TGMV). Recombinant gus and neo vectors up to 1.1 kbp larger than DNA A were shown to replicate stably in transgenic plants containing partial dimers (master copies) of the vectors integrated into their chromosomal DNA in the absence of DNA B. Beta-glucuronidase and neomycin phosphotransferase activities in independently transformed plants were proportional to the copy number of the double-stranded forms of the vector. Deletion analysis has shown that an essential part of the TGMV coat protein promoter, including a TATA box, lies within 76 nt upstream of the initiation codon of the gene. An increase in expression of a neo gene was obtained by replacing this 76 nt sequence by an 800 nt sequence containing a cauliflower mosaic virus 35S RNA promoter with no effect on the ability of the vector to replicate or on its stability in transgenic plants. Systemic infection of plants by agroinoculation with TGMV vectors larger than DNA A in the presence of DNA B resulted in deletions in the vector DNA in some, but not all, plants. Possible reasons for vector instability in systemically infected plants, and vector stability in transgenic plants containing master copies of the vector, are discussed.

Chromosome Deletion↗