Search PubMed⌕ Search

Biomedical subjects

J D Jones

Publications and source records attributed to J D Jones.

At least 55 records · Page 3Linked to original sources
PubMed1998

A novel signal recognition particle targets light-harvesting proteins to the thylakoid membranes.

The mechanisms involved in the posttranslational targeting of membrane proteins are not well understood. The light-harvesting chlorophyll proteins (LHCP) of the thylakoid membrane are a large family of hydrophobic proteins that are targeted in this manner. They are synthesized in the cytoplasm, translocated across the chloroplast envelope membranes into the stroma, bound by a stromal factor to form a soluble intermediate, "transit complex", and then integrated into the thylakoid membrane by a GTP dependent reaction. Signal recognition particle (SRP), a cytoplasmic ribonucleoprotein, is known to mediate the GTP dependent cotranslational targeting of proteins to the endoplasmic reticulum. We show that chloroplasts contain an SRP consisting of, cpSRP54, a homologue of SRP54 and a previously undescribed 43-kDa polypeptide (cpSRP43) instead of an RNA. We demonstrate that both subunits of cpSRP are required for the formation of the transit complex with LHCP. Furthermore, cpSRP54, cpSRP43, and LHCP are sufficient to form a complex that appears to be identical to authentic transit complex. We also show that the complex formed between LHCP and cpSRP, together with an additional soluble factor(s) are required for the proper integration of LHCP into the thylakoid membrane. It appears that the expanded role of cpSRP in posttranslational targeting of LHCP has arisen through the evolution of the 43-kDa protein.

Journal Article↗
PubMed1998

Analysis of 1.9 Mb of contiguous sequence from chromosome 4 of Arabidopsis thaliana.

The plant Arabidopsis thaliana (Arabidopsis) has become an important model species for the study of many aspects of plant biology. The relatively small size of the nuclear genome and the availability of extensive physical maps of the five chromosomes provide a feasible basis for initiating sequencing of the five chromosomes. The YAC (yeast artificial chromosome)-based physical map of chromosome 4 was used to construct a sequence-ready map of cosmid and BAC (bacterial artificial chromosome) clones covering a 1.9-megabase (Mb) contiguous region, and the sequence of this region is reported here. Analysis of the sequence revealed an average gene density of one gene every 4.8 kilobases (kb), and 54% of the predicted genes had significant similarity to known genes. Other interesting features were found, such as the sequence of a disease-resistance gene locus, the distribution of retroelements, the frequent occurrence of clustered gene families, and the sequence of several classes of genes not previously encountered in plants.

Arabidopsis↗
PubMed1998

Transmembrane domain of cystic fibrosis transmembrane conductance regulator: design, characterization, and secondary structure of synthetic peptides m1-m6.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) give rise to cystic fibrosis (CF), the most common genetic disease in the Caucasian population. CFTR is organized into five putative domains, including two that are predicted to be transmembrane and consist of six membrane-spanning segments each. CFTR mediates regulated anion transport across the apical membrane of epithelial cells. The pore through which CFTR transports its solutes is thought to be formed by some combination of the amino-terminal membrane-spanning segments. Although these sequences are predicted to be alpha-helical in secondary structure, to date, no direct structural evidence has been presented testing this hypothesis. Here, we present the biophysical characterization of six peptides (m1-m6) representing the predicted amino-terminal membrane-spanning domain of CFTR. The peptides can be incorporated into liposomes and are soluble in SDS micelles and trifluoroethanol (TFE). FTIR and CD spectroscopy indicate all six peptides adopt a stable, predominantly alpha-helical secondary structure in these environments. In contrast, peptide m6 undergoes a shift from alpha-helix to beta-sheet when dissolved in 20% methanol. Additionally, the peptides show an increase in beta-sheet in TFE, a known inducer of alpha-helices, relative to that seen in the nativelike environments. These results have implications for the folding of this complex membrane protein and suggest that the possible functional role of m6 is manifested through a shift in secondary structure.

Amino Acid Sequence↗
PubMed1998

A new gingival retraction impression system for a one-stage root-form implant.

Displacement of soft tissue adjacent to an implant abutment is arduous. Currently, gingival retraction cord is used before making an impression for cement-retained implant restoration. This article presents a new impression system for a cementable abutment/implant. The advantages of a cement-retained implant crown are described. This system provides efficient and accurate impressions.

Cementation↗
PubMed1998

Six Arabidopsis thaliana homologues of the human respiratory burst oxidase (gp91phox).

An NADPH oxidase analogous to that in mammalian phagocytes has been hypothesized to produce reactive oxygen species (ROS) in the plant defence response. A. thaliana contains at least six gp91phox homologues, designated AtrbohA-F (A. thaliana Respiratory Burst Oxidase Homologues), which map to different positions. Transcripts of three of these genes can be detected in healthy plants by RNA gel blot analyses. The Atrboh gene products are closely related to gp91phox and the intron locations suggest a common evolutionary origin. A putative EF-hand Ca(2+)-binding motif in the extended N-terminal region of the Atrboh proteins suggests a direct regulatory effect of Ca2+ on the activity of the NADPH oxidase in plants.

Amino Acid Sequence↗
PubMed1998

Epigenetic instability and trans-silencing interactions associated with an SPT::Ac T-DNA locus in tobacco.

Progeny of tobacco line 2853.6, which carries a streptomycin phosphotransferase (SPT) gene interrupted by the maize element Activator (Ac), were selected for streptomycin resistance (Spr) because of germinal Ac excision. Some events gave rise to Spr alleles that were unstable and exhibited a mottled phenotype on streptomycin-containing medium due to somatic loss of SPT function. This instability was most pronounced in one particular line, Spr12F. Other Spr alleles rarely exhibited silencing of SPT. Streptomycin-sensitive, homozygous Spr12F plants were recovered, and crosses were performed with other, more stable Spr lines. A high proportion of the resulting heterozygous progeny were silenced for SPT expression. The silenced state was heritable even after the Spr12F allele segregated away. No correlation could be made between silencing and methylation of the SPTgene. Structural analysis of allele Spr12F showed that the SPT gene from which Ac had excised was flanked by direct repeats of Ac. A search was carried out among 110 additional Spr alleles for new independent unstable alleles, and four were identified. All of these alleles also carried an SPT gene flanked by direct repeats of Ac. Thus, there is a strong correlation between this structure and instability of SPT expression.

Alleles↗
PubMed1998

Three genes of the Arabidopsis RPP1 complex resistance locus recognize distinct Peronospora parasitica avirulence determinants.

Plant resistance (R) genes have evolved specific recognition capabilities in defense against pathogens. The evolution of R gene function and maintenance of R gene diversity within a plant species are therefore of great interest. In the Arabidopsis accession Wassilewskija, the RPP1 region on chromosome 3 contains four genetically linked recognition specificities, conditioning resistance to different isolates of the biotrophic oomycete Peronospora parasitica (downy mildew). We show that three of four tightly linked genes in this region, designated RPP1-WsA, RPP1-WsB, and RPP1-WsC, encode functional products of the NBS-LRR (nucleotide binding site-leucine-rich repeat) R protein class. They possess a TIR (Toll, interleukin-1, resistance) domain that is characteristic of certain other NBS-LRR-type R proteins, but in addition, they have unique hydrophilic or hydrophobic N termini. Together, the three RPP1 genes account for the spectrum of resistance previously assigned to the RPP1 region and thus comprise a complex R locus. The distinct but partially overlapping resistance capabilities conferred by these genes are best explained by the hypothesis that each recognizes a different pathogen avirulence determinant. We present evidence suggesting that the RPP genes at this locus are subject to the same selective forces that have been demonstrated for structurally different LRR-type R genes.

Alleles↗
PubMed1998

The tomato Cf-5 disease resistance gene and six homologs show pronounced allelic variation in leucine-rich repeat copy number.

The tomato Cf-2 and Cf-5 genes confer resistance to Cladosporium fulvum and map to a complex locus on chromosome 6. The Cf-5 gene has been isolated and is predicted to encode a largely extracytoplasmic protein containing 32 leucine-rich repeats (LRRs), resembling the previously isolated Cf-2 gene, which has 38 LRRs. Three haplotypes of this locus from Lycopersicon esculentum, L. pimpinellifolium, and L. esculentum var cerasiforme were compared, and five additional homologs of Cf-5 were sequenced. All share extensive sequence identity, particularly within the C-terminal portions of the predicted proteins. In striking contrast to the Cf-9 gene family, six of seven homologs in the Cf-2/Cf-5 gene family vary in LRR copy number, ranging from 25 to 38 LRRs. Cf-5 and one adjacent homolog differ by only two LRRs. Recombination events that vary the LRR copy number in this region could provide a mechanism for the generation of new specificities for recognition of different ligands. A recombination breakpoint between the Cf-2 and Cf-5 loci was fully characterized and shown to be intragenic.

Alleles↗
PubMed1998

Transposon tagging of the Defective embryo and meristems gene of tomato.

The shoot and root apical meristems (SAMs and RAMs, respectively) of higher plants are mechanistically and structurally similar. This has led previously to the suggestion that the SAM and RAM represent modifications of a fundamentally homologous plan of organization. Despite recent interest in plant development, especially in the areas of meristem regulation, genes specifically required for the function of both the SAM and RAM have not yet been identified. Here, we report on a novel gene, Defective embryo and meristems (Dem), of tomato. This gene is required for the correct organization of shoot apical tissues of developing embryos, SAM development, and correct cell division patterns and meristem maintenance in roots. Dem was cloned using transposon tagging and shown to encode a novel protein of 72 kD with significant homology to YNV2, a protein of unknown function of Saccharomyces cerevisiae. Dem is expressed in root and shoot meristems and organ primordia but not in callus. The expression pattern of Dem mRNA in combination with the dem mutant phenotype suggests that Dem plays an important role within apical meristems.

Amino Acid Sequence↗
PubMed1998

Palatogram assessment of maxillary complete dentures.

Phonetics, esthetics, function, and comfort form the foundation of a successful dental prosthesis. A review of the mechanics of speech as well as common speech problems encountered with a removable maxillary prosthesis are presented. The use of a palatogram to aid the clinician in the assessment and resolution of speech problems associated with a maxillary denture is demonstrated.

Denture, Complete, Upper↗
PubMed1998

Molecular, genetic and physiological analysis of Cladosporium resistance gene function in tomato.

Characterization of the DNA sequence of 4 tomato leaf mould disease resistance genes (Cf-2, Cf-4, Cf-5 and Cf-9) leads to the prediction that they encode C-terminally membrane anchored glycopeptides with many extracytoplasmic leucine rich repeats (LRRs). The N terminal LRRs are variable between the Cf-genes, suggesting a role in specificity, and the C terminal LRRs are more conserved, suggesting a role in signal transduction. Genetic analysis has revealed several Rcr genes that are required for Cf-gene function; their isolation will help us understand how Cf-genes work. Cf-9 confers responsiveness to pathogen-encoded Avr9 peptide on introduction to tobacco. Tobacco suspension cultures carrying the Cf-9 gene produce reactive oxygen species in response to Avr9 peptide, whereas untransformed cultures do not. The significance of these observations is discussed.

Cladosporium↗
PubMed1997

Novel disease resistance specificities result from sequence exchange between tandemly repeated genes at the Cf-4/9 locus of tomato.

Tomato Cf genes confer resistance to C. fulvum, reside in complex loci carrying multiple genes, and encode predicted membrane-bound proteins with extracytoplasmic leucine-rich repeats. At least two Cf-9 homologs confer novel C. fulvum resistance specificities. Comparison of 11 genes revealed 7 hypervariable amino acid positions in a motif of the leucine-rich repeats predicted to form a beta-strand/beta-turn in which the hypervariable residues are solvent exposed and potentially contribute to recognition specificity. Higher nonsynonymous than synonymous substitution rates in this region imply selection for sequence diversification. We propose that the level of polymorphism between intergenic regions determines the frequency of sequence exchange between the tandemly repeated genes. This permits sufficient exchange to generate sequence diversity but prevents sequence homogenization.

Amino Acid Sequence↗
PubMed1997

Hereditary disorders of purine and pyrimidine metabolism: identification of their biochemical phenotypes in the clinical laboratory.

OBJECTIVE: To describe a laboratory approach to the diagnosis of hereditary diseases of purine and pyrimidine metabolism and emphasize clinical situations in which these disorders should be considered in the differential diagnosis. DESIGN: Disease-specific patterns were identified in random specimens of ultrafiltered urine by using gradient high-performance liquid chromatography with diode-array detection, and reference ranges were established for uric acid, hypoxanthine, xanthine, and uracil expressed per creatinine in random specimens of urine. MATERIAL AND METHODS: Diagnostically significant purines and pyrimidines were separated with use of a Supelco LC-18-S nucleoside column eluted with 25 mmol/L ammonium acetate buffer and acetonitrile-methanol-water. Biologic fluids were prepared by ultrafiltration after addition of 3-methyluridine as internal standard. We used specimens negative for screening of metabolic disorders to establish reference ranges. RESULTS: Disease-specific patterns were identified in specimens with purine and pyrimidine disorders and several urea cycle disorders characterized by increased production of pyrimidine. CONCLUSION: The approach described identified disease-specific patterns of purine and pyrimidine disorders and several urea cycle disorders. We suggest that testing for purine and pyrimidine disorders be done in specimens evaluated in metabolic laboratories for "screening for inborn errors of metabolism."

Chromatography, High Pressure Liquid↗
PubMed1997

Black bear (Ursus americanus) bile composition: seasonal changes.

Gallbladder contents from 8 active and 14 dormant black bears were analyzed for individual bile acids by high-performance liquid chromatography and for cholesterol, phospholipids, sodium, potassium, calcium, magnesium, zinc, iron, and copper. Only three bile acids occurring as taurine conjugates were detected: tauroursodeoxycholate, taurochenodeoxycholate, and taurocholate. The proportion of tauroursodeoxycholate to the sum of the three bile acids decreased. Calcium, cholesterol, phospholipids, magnesium, zinc, and copper concentrations were increased in dormancy. Standardized collection and handling procedures yielded more consistent data than previously available. The decrease in tauroursodeoxycholate and absence of deoxycholate and lithocholate are consistent with our working hypothesis that a marked reduction in metabolic activity of the gut flora is an integral part of the adaptation to metabolic stability of the dormant bear.

Animals↗
PubMed1997

First U.S. case of adenylosuccinate lyase deficiency with severe hypotonia.

Adenylosuccinate lyase (ASL) deficiency is a defect in purine de novo synthesis pathway. The disease has variable clinical presentation involving psychomotor retardation, seizures, hypotonia, and autism. The presence of succinyladenosine and succinylaminoimidazole carboxamide riboside (SAICA riboside) in body fluids characterizes the biochemical phenotype. All cases of ASL deficiency described to date have been diagnosed in Europe. Using a high-resolution thin-layer chromatography (TLC) technique combining screening for ASL deficiency and disorders of saccharide metabolism, we found the first case of this disease in the US. The patient presented with delayed motor development and profound hypotonia. The family history and routine laboratory tests were negative. Screening for metabolic disorders detected the presence of succinyladenosine and SAICA riboside in urine. The activity of ASL in the patient's skin fibroblasts was 43% of controls (patient, mean = 1.20 nmol/min/mg of protein, s = 0.21, n = 3; controls, mean = 2.78 nmol/min/mig of protein, s = 0.61, n = 7). In a 15-month-old girl with profound hypotonia, we established the diagnosis of ASL deficiency by demonstrating succinyladenosine and SAICA riboside in urine and decreased residual activity of ASL in skin fibroblasts.

Adenylosuccinate Lyase↗