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J A Dodds

Publications and source records attributed to J A Dodds.

At least 19 recordsLinked to original sources
PubMed2006

Predictions of tensile strength of binary tablets using linear and power law mixing rules.

There has recently been an increased interest in predicting the tensile strength of binary tablets from the properties of the individual components. In this paper, measurements are reported for tensile strength of tablets compressed from single-component and binary powder mixtures of lactose with microcrystalline cellulose (MCC), and lactose with two types of silicified microcrystalline cellulose (SMCC and SMCC-HD), which are different in compressibility. Measurements show the tensile strength increases with the relative density for single powders, and both with the relative density and the mass fraction of cellulose in the mixtures. It was also observed, for binary mixtures compacted at 50 and 150 MPa, that there was a slight variation in porosity with the mass fraction of celluloses. The predictions of the tensile strength of binary tablets from the characteristics of the single-components was analysed with the extended Ryshkewitch-Duckworth model by assuming both linear and power law mixing rules for the determination of the parameters "tensile strength at zero porosity and bonding capacity constant". As consequence, four models were analysed and compared with measurements using criteria based on the standard deviation from the mean values. Results showed a good prediction using a linear mixing rule combined with the power law. However, as the predictions of these models depend on the powders and the porosity range for the characterization of single-components, none of them can be systematically considered as being the best to predict binary behaviour from data for individual powders.

Cellulose↗
PubMed2000

Electron microscopy of satellite tobacco mosaic virus crystals: metal-coated, negatively stained and stereo pairs.

Highly purified virions of satellite tobacco mosaic virus (STMV) were found to crystallize at relatively low concentrations (300-500 microg ml(-1)) in pure water. Small crystals of these preparations were examined in the transmission electron microscope after either being rotary shadowcast with metal or negatively stained with 4% uranyl acetate. Stereo views were also obtained of both types of preparations. Stereo pairs of metal-coated crystals provided good three-dimensional images. When stereo pairs of negatively stained crystals were printed from second negatives, they provided striking images although the three-dimensional aspect was not so pronounced. Images of both types of preparations were compared with a computer-generated model of the virus. This model was based on data obtained in earlier X-ray diffraction crystallographic studies. Measurements of crystal axes on the EM images were somewhat lower than those of the computer model. It is assumed the reason for this is the dehydration of crystals during preparation for electron microscopy. The EM images did verify the type of crystal lattice determined in the X-ray diffraction studies. Conversely, knowing the exact unit cell parameters and the distribution of virions in the crystal from X-ray diffraction data aids in the further interpretation of electron micrographs of virus crystals.

Crystallography↗
PubMed2000

Heterogeneity in the 3'-terminal untranslated region of tobacco mild green mosaic tobamoviruses from Nicotiana glauca resulting in variants with three or six pseudoknots.

Isolates of tobacco mild green mosaic tobamovirus (TMGMV) were obtained from 58 plants of Nicotiana glauca in southern California and placed in one of two groups (Small type and Large type) based on the size of the subgenomic RNA for the coat protein (CP). The CP sequence differed by no more than one amino acid for the two types, and the Small type was identical to that published for TMGMV. Thirty-six of the isolates had a double-stranded (ds)RNA profile that matched that of type TMGMV, and the nucleotide sequence of the 3' untranslated region (3'UTR) of six of these isolates was similar to the published sequence of TMGMV. Twenty-two isolates had a larger dsRNA for the CP subgenomic RNA. Six of these were sequenced and all had a repeat sequence of between 147 and 165 bases in the part of the 3'UTR that is involved in the formation of pseudoknots. These novel but common isolates are predicted to have six rather than three pseudoknots. Small types (three pseudoknots=type TMGMV) yielded twice as much virus after purification as Large types (six pseudoknots). The two groups of isolates could be distinguished in N. rustica (Large type, but not Small type gave a systemic infection), and N. clevelandii (Small type but not Large type induced systemic lethal necrosis). Almost all isolates of TMGMV used in this study were initially associated with satellite tobacco mosaic virus (STMV), and both types supported STMV experimentally.

3' Untranslated Regions↗
PubMed1999

Molecular characterization of an isolate of citrus tristeza virus that causes severe symptoms in sweet orange.

The complete sequence (19,249 nucleotides) of the genome of citrus tristeza virus (CTV) isolate SY568 was determined. The genome organization is identical to that of the previously determined CTV-T36 and CTV-VT isolates. Sequence comparisons revealed that CTV-SY568, a severe stem-pitting isolate from California, has more than 87% overall sequence identity with CTV-VT, a seedling yellows isolate from Israel. Although SY568 has an overall sequence identity of 81% with CTV-T36, a quick decline isolate from Florida, the sequence identity in the 3' half of the genome is over 90% while the sequence identity in the 5' half of the genome is as low as 56%. Based on the sequence alignments of these three isolates, sequences in the 3' half of the genome are generally well conserved, while the sequences in the 5' half are relatively divergent. Sequence data of independent overlapping clones from the CTV-SY568 genome revealed two regions with highly divergent sequences. In open reading frame 1b (RNA dependent RNA polymerase), there were 118 nucleotide differences that lead to 16 amino acid changes. In the open reading frame of the divergent coat protein gene, 5 amino acid changes result from 48 nucleotide differences. Most differences occurred in the third position of the codons, and resulted in silent amino acid substitutions. RNase protection assays demonstrated that most of the clones obtained are representative of the major RNA species of this isolate. Northern analysis indicated that CTV-SY568 accumulated more viral RNA including genomic and certain subgenomic RNAs than isolates VT or T36 in sweet orange.

Base Sequence↗
PubMed1998

Specific sequence changes in the 5'-terminal region of the genome of satellite tobacco mosaic virus are required for adaptation to tobacco mosaic virus.

The genome of satellite tobacco mosaic virus (STMV) adapted to tobacco mosaic virus (TMV), tomato mosaic virus or green tomato atypical mosaic virus consistently had two single base deletions at positions 1 and 61, corresponding to bases A and G, respectively, as compared to the type-strain genome which is naturally adapted to tobacco mild green mosaic virus (TMGMV). Transcript RNAs (STMV(TMV)) from clone pSTMV(TMV) which captured the deletions at positions 1 and 61 were infectious when co-inoculated to tobacco plants with either TMV or TMGMV at infection frequencies of > 90%. Two new STMV variants were created to investigate whether both deletions were essential for adaptation to TMV. These were STMV(TMGMV) deltaA1, which had the A at position 1 (A1) deleted, and STMV(TMGMV) deltaG61, which lacked G61. STMV(TMGMV) deltaA1 was infectious (75% frequency) in the presence of either TMV or TMGMV. Virion RNA of STMV(TMGMV) deltaA1 lost G61 after one infection cycle with TMV. This deletion did not occur in co-infections with TMGMV. STMV(TMGMV) deltaG61, like the clone STMV(TMGMV), was infectious (100% frequency) with TMGMV but TMV did not support this clone. When Nicotiana benthamiana protoplasts were transfected with STMV(TMGMV), STMV(TMGMV) deltaA1 or STMV(TMV), STMV replicated when TMGMV was the helper virus. STMV(TMV) and STMV(TMGMV) deltaA1 replicated in the presence of helper TMV, but STMV(TMGMV) did not, the same result as in whole plants. The deletion of A1 is thus essential for initial STMV adaptation to TMV and the eventual deletion of G61 is a predicted additional change.

Adaptation, Physiological↗
PubMed1998

Satellite tobacco mosaic virus.

Satellite tobacco mosaic virus (STMV) is a small, spherical ssRNA virus common in a natural wild plant, Nicotiana glauca or tree tobacco, in southern California and is one of the best-studied satellite viruses. It is the only satellite virus that has rod-shaped viruses (tobamoviruses) for its helper. In addition to describing the general properties of STMV, this review focuses on (a) the structural properties of the virus particle including the RNA within the particle that is partially double stranded; (b) the genetic diversity within the type strain before and after serial passage and between different field isolates; (c) the effect of experimental mutation on infectivity, replication, and symptomatology; and (d) the genetic changes that occur when the satellite virus adapts to different helper tobamoviruses.

Journal Article↗
PubMed1997

Replication of wild-type and mutant clones of satellite tobacco mosaic virus in Nicotiana benthamiana protoplasts.

RNA transcribed from cloned satellite tobacco mosaic virus (STMV) cDNA replicated in Nicotiana benthamiana protoplasts when co-inoculated with tobacco mild green mosaic virus (TMGMV) genomic RNA, but degraded when inoculated alone. STMV genomic RNA extracted from wild-type virions replicated in protoplasts when co-inoculated with TMGMV, tobacco mosaic virus (TMV) or tomato mosaic virus (ToMV). Transcripts from clones of two STMV coat protein (CP) mutants accumulated to the same level as wild-type transcripts in protoplasts when co-inoculated with TMGMV, whereas a third mutant accumulated to detectable levels in some, but not all, experiments. These results confirm that STMV RNA requires helper virus for replication, and that the helper specificity exhibited by cloned STMV reflects a specific requirement for the TMGMV replicase. It also demonstrates that the low accumulation of STMV CP mutants observed previously in whole plants cannot be attributed to inefficient RNA replication.

Mutation↗
PubMed1996

Cell-to-cell transport of movement-defective cucumber mosaic and tobacco mosaic viruses in transgenic plants expressing heterologous movement protein genes.

To determine if the movement proteins (MPs) of cucumber mosaic cucumovirus (CMV) and tobacco mosaic tobamovirus (TMV) are complementary in function, transgenic plants expressing genes encoding TMV or CMV MP were inoculated with movement-defective mutants of TMV and CMV. Transgenic plants expressing the MP gene of CMV strain S (subgroup II) complemented the cell-to-cell and systemic spread of a movement-defective mutant of CMV strain Fny (subgroup I) but not the local or systemic spread of a movement-defective mutant of TMV. Plants that contained the MP gene from CMV-S were not resistant to wild-type TMV infection. When inoculated with a movement-defective mutant of TMV that produced beta-glucuronidase, transgenic plants with the CMV MP gene supported only subliminal infection. Conversely, immunodetection and in situ localization techniques revealed that transgenic plants accumulating the TMV MP supported cell-to-cell spread, but not systemic transport, of a movement-defective CMV. These studies suggest that the transgenic TMV MP shares some of the functions with the CMV MP required to transport CMV, whereas the transgenic CMV MP is deficient in functions that are needed to mobilize the spread of TMV infection.

Amino Acid Sequence↗
PubMed1995

Characterization of deletion and frameshift mutants of satellite tobacco mosaic virus.

A series of frameshift and deletion mutations was created in the genome of satellite tobacco mosaic virus (STMV) by modifying full-length cDNA clones of the type strain, from which biologically active transcripts could be synthesized in vitro. Deletions and frameshift mutations in the 5' open reading frame had no effect, compared to wild-type STMV, on RNA accumulation, systemic movement, or the symptoms induced by STMV in Nicotiana tabacum co-inoculated with tobacco mild green mosaic tobamovirus (TMGMV). This implies that the protein encoded by this reading frame is not necessary for biological activity. Deletions and frameshift mutations in the coat protein open reading frame resulted in decreased accumulation of STMV RNA in N. tabacum, although these mutants were still capable of systemic movement, presumably in a nonencapsidated or free RNA form. Furthermore, the mild symptoms induced in tobacco by co-inoculations of wild-type STMV/TMGMV or infection with TMGMV alone were altered to severe systemic necrosis when plants were co-inoculated with these STMV coat protein mutants and TMGMV. Mutants within the 3' untranslated region were much less able to accumulate in TMGMV-infected plants than was wild-type STMV, and under some growth conditions did not accumulate to detectable levels.

Capsid↗
PubMed1995

A defective movement protein of TMV in transgenic plants confers resistance to multiple viruses whereas the functional analog increases susceptibility.

Transgenic tobacco plants that express a gene encoding a defective mutant of the tobacco mosaic virus (TMV) movement protein which are known to be resistant to several tobamoviruses were inoculated with viruses from different taxonomic groups to determine the breadth of resistance. There were significant delays in the time of appearance of disease symptoms and/or there was reduced systemic accumulation of virus in upper leaves of plants inoculated with tobacco rattle tobravirus, tobacco ringspot nepovirus, alfalfa mosaic alfamovirus, peanut chlorotic streak caulimovirus, and cucumber mosaic cucumovirus. Conversely, tobacco plants that express a gene encoding the functional tobacco mosaic virus wild-type movement protein accelerated symptom development, enhanced the severity of symptom formation, and/or increased the accumulation of these viruses and, additionally, TMV. Our results indicate that there are similar functions among the movement proteins of a number of plant viruses despite the apparent lack of sequence similarity between them.

Mosaic Viruses↗
PubMed1995

Differences in the subcellular localization of tobacco mosaic virus and cucumber mosaic virus movement proteins in infected and transgenic plants.

Our study reveals differences in the way that tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV) movement proteins (MPs) partition with cellular components separated into four fractions from different aged leaves of infected and transgenic plants. Immunoblot analyses showed that TMV and CMV MPs associated predominantly with components in the cell wall fractions from leaves of transgenic plants. In infected tissue, highest levels of TMV MP were found in the organelle fractions from young and middle-aged leaves whereas most of the CMV MP was found in the detergent wash of the cell wall fraction. These results remained consistent even when plants were doubly infected with TMV and CMV. These results imply that MPs of plant viruses from different taxonomic groups differentially associate with subcellular components and that MP produced by a viral infection is targeted to additional subcellular destinations than MP produced in transgenic plants.

Cell Fractionation↗
PubMed1995

Mutation analyses of molecularly cloned satellite tobacco mosaic virus during serial passage in plants: evidence for hotspots of genetic change.

The high level of genetic diversity and rapid evolution of viral RNA genomes are well documented, but few studies have characterized the rate and nature of ongoing genetic change over time under controlled experimental conditions, especially in plant hosts. The RNA genome of satellite tobacco mosaic virus (STMV) was used as an effective model for such studies because of advantageous features of its genome structure and because the extant genetic heterogeneity of STMV has been characterized previously. In the present study, the process of genetic change over time was studied by monitoring multiple serial passage lines of STMV populations for changes in their consensus sequences. A total of 42 passage lines were initiated by inoculation of tobacco plants with a helper tobamovirus and one of four STMV RNA inocula that were transcribed from full-length infectious STMV clones or extracted from purified STMV type strain virions. Ten serial passages were carried out for each line and the consensus genotypes of progeny STMV populations were assessed for genetic change by RNase protection analyses of the entire 1,059-nt STMV genome. Three different types of genetic change were observed, including the fixation of novel mutations in 9 of 42 lines, mutation at the major heterogeneity site near nt 751 in 5 of the 19 lines inoculated with a single genotype, and selection of a single major genotype in 6 of the 23 lines inoculated with mixed genotypes. Sequence analyses showed that the majority of mutations were single base substitutions. The distribution of mutation sites included three clusters in which mutations occurred at or very near the same site, suggesting hot spots of genetic change in the STMV genome. The diversity of genetic changes in sibling lines is clear evidence for the important role of chance and random sampling events in the process of genetic diversification of STMV virus populations.

Biological Evolution↗
PubMed1994

Satellite tobacco mosaic virus sequence variants with only five nucleotide differences can interfere with each other in a cross protection-like phenomenon in plants.

The type strain of satellite tobacco mosaic virus (STMV) contains two major variants, designated type 5 (T5) and type 6 (T6), which can be easily distinguished by RNase protection analyses. Clones containing cDNA of representative T5 and T6 STMV genomes have only five single-base differences in the entire 1059-nucleotide genome, and RNA transcribed from each clone is highly infectious when inoculated onto tobacco plants. The different RNase protection assay patterns can be used as genetic markers to identify individual STMV variants and to follow the interactions of variants and their progeny during coinfections in plants. The study described here investigated the effects of coinoculation and various delayed inoculations of T5 and T6 variants on the composition of the progeny STMV populations in systemically infected tobacco tissues. When T5 and T6 STMV RNAs were coinoculated or inoculated with 1-hr delays, the progeny from individual plants most often contained a mixture of T5 and T6 genomes. However, when there was a 24-hr delay between inoculations, the balance of T5 and T6 components in the progeny populations shifted toward predominance of the first variant inoculated. With delays of 3 or 7 days only the first variant was evident in the progeny populations, indicating that established replication of one STMV variant interferes with replication of another in a manner similar to the cross protection phenomenon.

Helper Viruses↗
PubMed1994

A single temperature amplification technique applied to the detection of citrus tristeza viral RNA in plant nucleic acid extracts.

A procedure for the successful detection of citrus tristeza virus (CTV) RNA in total crude nucleic acid extracts of infected citrus whole leaves and bark is described. The method requires the isolation and precipitation of total nucleic acids from either infected whole leaf or bark tissue. The CTV viral RNA is then specifically amplified using a single temperature RNA Self-Sustained Sequence Replication technique (3SR) performed at 42 degrees C for 60 minutes. The amplified negative-sense viral RNA product can subsequently be detected by fixing a portion of the reaction mixture onto a nylon membrane and hybridizing with positive sense tristeza specific DNA oligonucleotide probes. Central California isolates of CTV were readily detected by this method. Denatured viral specific dsRNA was also a suitable template for the specific detection of CTV.

Base Sequence↗
PubMed1994

Anatomy of the anterior cruciate ligament: a blueprint for repair and reconstruction.

The anterior cruciate ligament of the knee joint is a complex structure whose orientation, construct, and biology are directly related to its function as a constraint of knee joint motion. While the complexity of its design allows the ligament to function through the normal range of motion as a static stabilizer of the knee, it also makes the exact duplication of this structure very difficult. A fundamental knowledge of the functional anatomy of the anterior cruciate ligament provides the orthopaedic surgeon with an essential blueprint on which to base techniques of repair and reconstruction.

Anterior Cruciate Ligament↗
PubMed1993

Three-dimensional structure of satellite tobacco mosaic virus at 2.9 A resolution.

The crystal structure of satellite tobacco mosaic virus (STMV) has been solved by a combination of multiple isomorphous replacement and molecular replacement methods and refined at 2.9 A resolution to a conventional R-factor of 0.215. STMV, a T = 1 icosahedral virus, is the smallest whose structure has been determined. The coat protein is an eight-stranded "Swiss roll" beta-barrel with an amino-terminal strand that extends away from the beta-barrel by more than 60 A. This strand is primarily responsible for quaternary interactions within the capsid. The most arresting feature of the virus structure is the intimate association of each capsid protein dimer with a Watson-Crick base-paired segment of RNA double helix on the interior of the virion. The icosahedral 2-fold axis of each dimer pair is coincident with that of the central base-pair of each helical RNA segment whose helical axis is along the edge of the icosahedron. The helical RNA segments are seven base-pairs in length with a stacked base at each 3' end so that a total of 16 nucleotides is clearly visible. The character of the RNA helix is somewhat different than any of the canonical forms. Assuming full occupancy, then approximately 45% of the total RNA genome is present in the electron density map. The close association of capsid with highly structured nucleic acid suggests that assembly of STMV is likely to be a highly co-operative process involving both protein and RNA. The nucleic acid is distributed within the virion with a high degree of order. The capsid protein is a true double helical RNA binding protein and a number of prominent interactions between protein and RNA can be clearly seen.

Capsid↗
PubMed1993

Double-helical RNA in satellite tobacco mosaic virus.

Satellite tobacco mosaic virus (STMV) is the spherical satellite to an obligatory rod-shaped helper tobacco mosaic virus (TMV), which is required for replication. STMV has 60 protein subunits of M(r) 17,500 on a T = 1 icosahedral capsid containing a single-stranded RNA genome of 1,059 bases. STMV appears similar to another virus, STNV, but is approximately 20 per cent smaller. It shows no amino-acid homology or immunological cross-reactivity with either STNV or its host TMV. Here we report the X-ray crystal structure of STMV, which shows that the coat protein of STMV contains a 'Swiss roll' beta-barrel. An amino-terminal strand extends more than 60A and is primarily responsible for quaternary interactions. Each capsid dimer is associated with a segment of genomic RNA double helix comprising seven base pairs. The dyad of each protein dimer is coincident with that of the central base pair of the associated RNA segment whose helix axis is directed along an icosahedral edge. Protein-nucleic acid interactions are extensive. The RNA helices, which have additional stacked bases at their 3' termini, differ significantly from canonical nucleic acid helical forms.

Capsid↗