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PubMed1994

Nucleotide sequence of the genomic RNA of bamboo mosaic potexvirus.

The complete nucleotide sequence of the genomic RNA of bamboo mosaic virus (BaMV) was determined by sequencing a set of overlapping cDNA clones and by direct sequencing of the viral RNA. The RNA genome of BaMV is 6366 nucleotides long [excluding 3'poly(A) tail] and contains six open reading frames (ORFs 1 to 6) coding for polypeptides with M(r) values of 155K, 28K, 13K, 6K, 25K and 14K, respectively. The genome organization and sizes of the encoded proteins are very similar to those of other potexviruses which have been sequenced except that ORF 6 lies completely within ORF 1. The first five putative proteins of the BaMV genome show identities ranging between 44 to 59%, 26 to 49%, 30 to 53%, 15 to 35% and 20 to 30%, respectively, to the corresponding ORFs of other members of the potexvirus group. However the putative product ORF 6 shows no significant similarity to those of other potexvirus ORF products.

Amino Acid Sequence↗

PubMed2006

Movement of potexviruses requires species-specific interactions among the cognate triple gene block proteins, as revealed by a trans-complementation assay based on the bamboo mosaic virus satellite RNA-mediated expression system.

The intra- and intercellular transport of potexviruses require interactions among viral RNA, coat protein and elements of the triple gene block proteins (TGBps). In this study, the requirement of bamboo mosaic virus (BaMV) TGBps for movement functions and the compatibilities with those of two potexviruses, Potato virus X (PVX) and Foxtail mosaic virus (FoMV), were examined using a satellite RNA-mediated trans-complementation assay system. Single or multiple TGBps of BaMV, PVX and FoMV were expressed from BaMV satellite RNA (satBaMV RNA) vectors to complement the functions of green fluorescent protein-tagged, movement-defective BaMV with mutation(s) in the matching gene(s). It was found that individual BaMV TGBps expressed from the satellite vector could function normally in trans, whereas bi-gene BaMV TGBp constructs in which the expression of TGBp3 might be impaired and individual TGBp genes from PVX or FoMV could not complement the movement functions of the defective helper viruses. Furthermore, alterations of the ratio among TGBps by ectopic expression of individual components of TGBps from satBaMV RNA vectors did not affect the cell-to-cell movement capabilities of wild-type BaMV significantly. The results indicate that species-specific interactions among movement proteins are obligatory for the cell-to-cell movement of BaMV and possibly other potexviruses.

Genetic Techniques↗

PubMed1992

Mutagenesis of a hexanucleotide sequence conserved in potexvirus RNAs.

Biologically active in vitro transcripts were synthesized from a cloned cDNA of a defective RNA (D RNA) of clover yellow mosaic virus (CYMV) and were used to determine if a hexanucleotide motif (5'-ACUUAA) conserved in the 3' noncoding region of potexvirus RNAs is essential for accumulation of progeny D RNA in planta. Deletion of rearrangement of the entire hexanucleotide sequence in the D RNA resulted in no detectable accumulation of progeny D RNA when coinoculated with helper CYMV RNA. Single-base substitutions of the four central nucleotides of the hexanucleotide sequence revealed that viable D RNAs can tolerate single residue changes at positions 3 and 5 only. These results suggest that the hexamer motif is involved in the process of D RNA propagation. The hexanucleotide sequence was also identified in the negative strand of potexvirus RNAs in the regions proposed to represent subgenomic RNA (sgRNA) promoters. In addition, the hexamer motif is present in similar regions in carlavirus RNAs. The conservation of this hexanucleotide (in orientation and position) in potexvirus and carlavirus RNAs, which serve as templates for full-length negative-strand synthesis and sgRNA production, strongly suggests that it plays a functional role in the synthesis of viral RNAs. Taken together, our data support our previous proposal (Bancroft et al., 1991. J. Gen. Virol. 72, 2173-2181) that the hexanucleotide sequence acts as a cis element involved in synthesis of full-length negative-sense viral RNA and further implicate the sequence in a similar role in production of positive-sense sgRNA.

Capsid↗

PubMed1989

A potexvirus isolated from Silene pratensis.

A potexvirus, silene virus X (SVX), was isolated from the weed Silene pratensis. Infectious preparations contained nucleoprotein rods predominantly 546 nm in length, consisting of a 6.9-kb polyadenylated single-stranded RNA and a 29-kd capsid protein. Double-stranded RNAs of 17.1, 7.0, 5.7, and 4.6 kbp were isolated from SVX-infected plants. In vitro translation products of SVX single-stranded or denatured double-stranded RNAs reacted with SVX antiserum. Hybridization studies with SVX cDNAs showed no nucleotide homology with seven other potexviruses. The virus is more closely related serologically to narcissus mosaic virus than to nine other potexviruses.

Capsid↗

PubMed1995

Subcellular immunolocalization of the coat protein of two potexviruses in infected Chenopodium quinoa.

The production of coat protein is necessary for cell-to-cell transport of potexviruses in plants. To investigate the role of coat protein in the movement process, the intracellular distribution of coat protein in tissues infected with either of two potexviruses was studied using immunocytochemical procedures. We report that coat protein antigens are associated with the plasmodesmata of infected cells.

Capsid↗

PubMed2004

The complete sequence of the genomic RNA of an isolate of Lily virus X (genus Potexvirus).

The complete sequence of the genomic RNA of an isolate of Lily virus X (LVX) has been determined for the first time. The isolate from the Netherlands was 5823 nucleotide (nt) long excluding the 3'-poly(A) tail, making it the shortest reported potexvirus sequence. The 5'-non-coding region begins with GGAAAA like that of Scallion virus X (ScaVX) and some isolates of Cymbidium mosaic virus (CymMV), whereas those of other sequenced potexviruses probably all begin with GAAAA. The genome organisation was similar to that of other members of the genus except that a TGBp3-like region lacked a normal AUG start codon. A phylogenetic analysis based on the entire coding sequence showed that LVX was most closely related to Strawberry mild yellow edge virus and belonged in a subgroup of the genus that also contains CymMV, Narcissus mosaic virus, ScaVX, Pepino mosaic virus, Potato aucuba mosaic virus and White clover mosaic virus.

Base Sequence↗

PubMed2006

Radial density distribution and symmetry of a Potexvirus, narcissus mosaic virus.

Narcissus mosaic virus is a Potexvirus, a member of the Flexiviridae family of filamentous plant viruses. Fiber diffraction patterns from oriented sols of narcissus mosaic virus have been used to determine the symmetry and structural parameters of the viral helix. The virions have a radius of 55+/-5 A. The viral helix has a pitch of 34.45+/-0.5 A, with 7.8 subunits per turn of the helix. We conclude that all members of the Potexvirus genus have close to 8 subunits per helical turn.

Narcissus↗

PubMed1998

Beet yellows closterovirus HSP70-like protein mediates the cell-to-cell movement of a potexvirus transport-deficient mutant and a hordeivirus-based chimeric virus.

It has been suggested that the beet yellows closterovirus (BYV)-encoded p65 protein, a homologue of HSP70 cell chaperones, plays a role as a virus movement protein (MP). To test this hypothesis, we used two types of complementation experiments with plant viruses containing the triple gene block (TGB) of MP genes. In one, the BYV p65 gene was cloned into a 35S promoter plasmid and introduced into Nicotiana benthamiana plants by microprojectile bombardment along with the 35S promoter-driven GUS gene-tagged cDNA of a transport-deficient potexvirus mutant. Transient expression of p65 complemented the mutant as visualized by the significant increase in the number of cells expressing the GUS reporter gene in the infection foci. In the other test, the p65 gene was inserted into the infectious cDNA of the hordeivirus RNA beta component to replace either the 58 kDa MP gene or the whole TGB. Inoculation of Chenopodium quinoa and Chenopodium amaranticolor plants with the T7 transcripts of the chimeric RNA beta, together with the hordeivirus RNA alpha and RNA gamma, caused symptomless infection in inoculated leaves detected by hybridization of the total leaf RNA with a specific cDNA probe. The ability of BYV p65 to substitute for the potexvirus or hordeivirus MPs provides direct evidence for its involvement in the cell-to-cell movement of closterovirus infection.

Chimera↗

PubMed1999

Identification of the RNA-binding sites of the triple gene block protein 1 of bamboo mosaic potexvirus.

The triple gene block protein 1 (TGBp1) encoded by open reading frame 2 of bamboo mosaic potexvirus (BaMV) was overexpressed in Escherichia coli and purified in order to test its RNA-binding activity. UV crosslinking assays revealed that the RNA-binding activity was present mainly in the soluble fraction of the refolded TGBp1. The binding activity was nonspecific and salt concentration-dependent: activity was present at 0-50 mM NaCl but was almost abolished at 200 mM. The RNA-binding domain was located by deletion mutagenesis to the N-terminal 3-24 amino acids of TGBp1. Sequence alignment analysis of the N-terminal 25 amino acids of the TGBp1 homologues of potexviruses identified three arginine residues. Arg-to-Ala substitution at any one of the three arginines eliminated most of the RNA-binding activity, indicating that they were all critical to the RNA-binding activity of the TGBp1 of BaMV.

Amino Acid Sequence↗

PubMed1999

Structural and functional analysis of the 3' untranslated region of bamboo mosaic potexvirus genomic RNA.

The secondary structure of a 170 nt transcript derived from a cDNA clone containing the 3' untranslated region of bamboo mosaic potexvirus (BaMV) with 32 adenine residues of the poly(A) tail, was investigated in solution by using enzymatic and chemical probes. Three consecutive stem-loops forming a cloverleaf-like structure (domain ABC) and a major stem-loop (domain D) containing a bulge and an internal loop were identified as connected to a previously identified pseudoknot domain (domain E) comprising at least 13 adenylate residues of the 3' poly(A) tail. The highly conserved hexamer nucleotides (ACc/uUAA) among potexviruses are located in loop D and the putative polyadenylation signal (AAUAAA) is located in the internal loop of domain D. Based on the data of the structural probing, a three-dimensional structure was modeled. Mutants with domain ABC deleted showed no detectable signal in protoplasts, while changes in domain D, except for the bulge deletion, showed interference of BaMV RNA accumulation in protoplasts. Mutants with disrupted stem D formation impaired BaMV accumulation. However, the mutant with compensatory mutations restored stem formation which could only improve the viral accumulation to 58 % that of the wild-type structure.

3' Untranslated Regions↗

PubMed1988

The complete nucleotide sequence of the potexvirus white clover mosaic virus.

The complete nucleotide sequence (5845 nucleotides) of the genomic RNA of the potexvirus white clover mosaic virus (WC1MV) has been determined from a set of overlapping cDNA clones. Forty of the most 5'-terminal nucleotides of WC1MV showed homology to the 5' sequences of other potexviruses. The genome contained five open reading frames which coded for proteins of Mr 147, 417, Mr 26,356, Mr 12,989, Mr 7,219 and Mr 20,684 (the coat protein). The Mr 147,417 protein had domains of amino acid sequence homology with putative polymerases of other RNA viruses. The Mr 26,356 and Mr 12,989 proteins had homology with proteins of the hordeivirus barley stripe mosaic virus RNA beta and the furovirus beet necrotic yellow vein virus (BNYVV) RNA-2. A portion of the Mr 26,356 protein was also conserved in the cylindrical inclusion proteins of two potyviruses. The Mr 7,219 protein had homology with the 25K putative fungal transmission factor of BNYVV RNA-3.

Amino Acid Sequence↗

PubMed1992

Nucleotide sequence of shallot virus X RNA reveals a 5'-proximal cistron closely related to those of potexviruses and a unique arrangement of the 3'-proximal cistrons.

The 8890 nucleotide RNA sequence of shallot virus X (ShVX), a new virus isolated from shallot, has been determined. The sequence contains six open reading frames (ORFs) which encode putative proteins (in the 5' to 3' direction) of M(r) 194528 (ORF1), 26333 (ORF2), 11245 (ORF3), 42209 (ORF4), 28486 (ORF5) and 14741 (ORF6). The ORF1 protein was found to be highly homologous to the putative potexvirus RNA replicases; ORF2, -3, -5 and -6 proteins also have analogues among the potex- and/or carlavirus-encoded proteins. ORF3 is followed by an AUG-lacking frame coding for an amino acid sequence homologous to that of the 7K to 8K proteins of the triple gene block of the above-mentioned viruses. The putative ORF4 protein has no reliable homology with proteins in the database. The results obtained testify that, except for the unique 42K protein gene, the ShVX genome combines a number of elements typical of both carla- and potexviruses.

Amino Acid Sequence↗

PubMed1992

The nucleotide sequence and genome organization of strawberry mild yellow edge-associated potexvirus.

The nucleotide sequence (5966 nucleotides) of cDNA clones of strawberry mild yellow edge-associated potexvirus was determined. The genome contains six open reading frames (ORFs) encoding putative proteins with Mrs of 149,423, 25,344, 11,576, 8079, 25,714 and 11,216. In the first three putative proteins and the coat protein considerable similarity was found to comparable polypeptides of the potexviruses potato virus X, clover yellow mosaic virus, narcissus mosaic virus, papaya mosaic virus, white clover mosaic virus and lily virus X.

Amino Acid Sequence↗

PubMed1999

Influence of white clover mosaic potexvirus infection on the endogenous cytokinin content of bean

The cytokinin content in the primary leaves of bean (Phaseolus vulgaris) was monitored for 10 d after inoculation with white clover mosaic potexvirus. The cytokinins were isolated, purified, separated by high-performance liquid chromatography, and quantified by radioimmunoassay. The cytokinins detected at the time of inoculation (d 0) were: (a) the free bases, zeatin (Z), dihydrozeatin (DZ), and isopentenyladenine; (b) the riboside, DZ riboside (DZR); (c) the O-glucosides of DZ, DZR, and Z riboside; (d) the nucleotides, Z riboside-5'-monophosphate and isopentenyladenosine-5'-monophosphate; and (e) trace amounts of Z-9-glucoside and DZ-9-glucoside. During the 10 d after inoculation with white clover mosaic potexvirus, marked quantitative changes in this cytokinin profile were observed. The concentration of the free bases and DZR decreased, accompanied by an increase in the 9-glucosides and the nucleotides. Virus titer increased rapidly 3 d after inoculation, attaining a maximum level at d 5. This increase coincided with the increases in the 9-glucosides and the nucleotides. We propose that the decline in the cytokinin free bases and riboside may allow the increase of virus titer in bean and lead to the senescence of infected leaves.

Journal Article↗

PubMed1987

Lack of homology among potexvirus RNAs.

Representative cDNAs prepared against each of five different potexvirus RNAs were annealed to these and other viral RNAs to assess the extent to which these viruses might be related. In all cases, the cDNA hybridized to completion with its homologous RNA but failed to cross-hybridize significantly to any other viral RNA. Partial hybridization was detected when the cDNA of one virus was annealed to the RNA of a distinct strain of the same virus. We conclude that despite their morphological similarities, members of the potexvirus group have diverged substantially in nucleotide sequence.

Base Sequence↗

PubMed1994

Purification, properties, and subcellular localization of foxtail mosaic potexvirus 26-kDa protein.

The open reading frame 2 (ORF2) of the potexviral genome encodes a 24- to 26-kDa protein which is part of the "triple gene block," a group of overlapping ORFs also present in the genomes of the carla-, hordei-, and furoviruses. The product of these ORFs is believed to play a role in the cell-to-cell movement of the viruses in host plants. The amino acid sequences of the homologous ORF2 products encoded by these related viruses suggest that they specify NTP binding and possibly helicase activities. We have used an Escherichia coli expression system to produce significant amounts of the 26-kDa protein (p26) encoded by foxtail mosaic potexvirus ORF2. p28 was purified to near homogeneity by conventional purification methods and some of its biochemical properties were determined. We present evidence that p26 is an ATP, CTP, and RNA binding protein with apparent ATPase activity. Western blot analysis of infected plant extracts using a polyclonal antiserum produced against p26 indicates that it is a relatively stable protein maintained at high levels for at least 6 days following its peak level of expression. Moreover, it is found predominantly in the soluble fraction of infected tissues. An immunocytochemical analysis of infected Chenopodium quinoa leaves reveals that p26 is exclusively associated with cytoplasmic inclusions in proximity to but distinct from aggregates of viral particles.

Adenosine Triphosphatases↗

PubMed1996

Tobamovirus cross protection using a potexvirus vector.

Cross protection is the ability of one virus to prevent or delay infection by a related challenge virus. To examine this phenomena, a potato X potexvirus (PVX) vector (Chapman et al., 1992, Plant J. 2, 549) was used to systemically express the tobacco mosaic tobamovirus (TMV) coat protein (CP) open reading frame in Nicotiana benthamiana. PVX constructs induce mild mosaic symptoms in N. benthamiana, whereas TMV infection results in rapid systemic necrosis and plant death. Healthy plants or plants preinfected with the unmodified PVX vector succumbed to necrosis within 1 week of TMV challenge inoculation. However, plants preinfected with PVX vectors expressing the TMV CP or RNA coding sequence displayed a 1- to 2-week delay in the appearance of TMV-induced necrosis along with reduced accumulations of TMV. Symptom delay and reductions in the accumulation of TMV were more pronounced in plants protected with the vector expressing the TMV CP than with the vector expressing a nontranslatable CP sequence. Protection was overcome more quickly using a 10-fold higher concentration of challenge inoculum and was ineffective against TMV RNA or a TMV construct expressing a distantly related tobamovirus CP. These findings demonstrate that both RNA and protein are involved in this cross protection phenomenon, but that CP is the main contributor to protection. Taken together, these studies indicate that virus vectors can be used to simulate both cross protection and transgene-derived coat protein-mediated protection, thus providing a new method to further investigate the mechanisms behind each.

Capsid↗

PubMed2000

Functional analyses and identification of two arginine residues essential to the ATP-utilizing activity of the triple gene block protein 1 of bamboo mosaic potexvirus.

The TGBp1 of bamboo mosaic potexvirus (BaMV) is encoded by the first overlapping gene of the triple-gene-block (TGB), whose products are thought to play roles in virus movement between plant cells. This protein forms cytoplasmic inclusions associated with virus particles in the BaMV-infected tissues. It has been proposed that the inclusion is one of the active forms of TGBp1. To prove this idea, we purified the TGBp1 inclusions from both the BaMV-infected Chenopodium quinoa and Escherichia coli cells overexpressing this protein to test some of their biochemical activities. We found that the TGBp1 inclusions isolated from the infected plant leaves, but not from E. coli, possess the NTP-binding and NTPase activities. However, they lack the RNA-binding activity possessed by the soluble TGBp1. These results indicate that the TGBp1 proteins in the BaMV-infected tissues assume two different functional forms. Mutational analyses and competition experiments show that the two arginine residues, Arg-16 and Arg-21, essential to RNA binding, are also required for the ATP-utilizing activity of the soluble TGBp1. This indicates that a same-structure motif is required for the two functions of the soluble TGBp1. The location of the two arginine residues outside the seven conserved motifs of the NTP-utilizing superfamily I RNA helicases, to which TGBp1 belongs, suggests that an extra-structure motif, besides the seven conserved ones, is required for the NTP-utilizing activity of the TGBp1 protein of BaMV.

Acid Anhydride Hydrolases↗