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At least 325 records · Page 18Linked to original sources
PubMed1996

The determination of local structural units in amorphous SiBN(3)C by means of X-ray photoelectron and X-ray absorption spectroscopy.

X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy at the K-edge of Si, N, and B are presented as techniques suited to determine structural units in amorphous SiBN(3)C. The measurements reported give evidence for the presence of tetrahedral (SiN(4))- and planar (BN(3))-groups. It is concluded that these structural elements dominate the atomic surroundings of B and Si, respectively. From the spectroscopic results we conclude that C is mainly bonded to N and is not present as a pure carbide.

Journal Article↗
PubMed1997

Localization, structure and expression of the gene for translation initiation factor eIF-4E from Drosophila melanogaster.

Drosophila melanogaster contains a single copy of the gene encoding translation eukaryotic initiation factor eIF-4E, which maps in the 67A2B1 region of chromosome 3L. A genomic clone containing the entire eIF-4E gene was isolated and sequenced. Comparison of this sequence with a cDNA previously obtained in our laboratory and 5'-RACE analysis revealed the existence of three mRNAs that are generated by alternative splicing of a primary transcript. All of them have different 5' untranslated leader regions. Two of the mRNAs encode the same eIF-4E polypeptide, whose sequence has been deduced from the cDNA clone. The third mRNA species contains a new open reading frame, possibly encoding another isoform of eIF-4E, which is very similar in size to the other but has a different N-terminal sequence. Several sequences which may be involved in the regulation of transcription initiation of the eIF-4E gene, except for a consensus TATA box, were found upstream of the putative transcription initiation sites. Expression of the eIF-4E gene is spatially and temporally controlled during embryonic development. It is ubiquitously expressed during embryogenesis but transcripts preferentially accumulate in certain tissues, particularly in the pole cells, at different developmental stages.

Alternative Splicing↗
PubMed2001

Chromosomal localization, structure, single-nucleotide polymorphisms, and expression of the human H-protein gene of the glycine cleavage system (GCSH), a candidate gene for nonketotic hyperglycinemia.

Nonketotic hyperglycinemia (NKH) is an inborn error of metabolism caused by deficiency in the glycine cleavage system (GCS); this system consists of four individual constituents, P-, T-, H-, and L-proteins. Several mutations have been identified in P- and T-protein genes, but not in the H-protein gene (GCSH), despite the presence of case reports of H-protein deficiency. To facilitate the mutational and functional analyses of GCSH, we isolated and characterized a human p1-derived artificial chromosome (PAC) clone encoding GCSH. GCSH spanned 13.5kb and consisted of five exons. Using the PAC clone as a probe, we mapped GCSH to chromosome 16q24 by fluorescence in situ hybridization. The transcription initiation site was determined by the oligonucleotide-cap method, and potential binding sites for several transcriptional factors were found in the 5' upstream region. Direct sequencing analysis revealed five single-nucleotide polymorphisms. The expression profiles of P-, T-, and H-protein mRNAs were studied by dot-blot analysis, using total RNA from various human tissues. GCSH was expressed in all 29 tissues examined, while T-protein mRNA was detected in 27 of the 29 tissues. In contrast, the P-protein gene was expressed in a limited number of tissues, such as liver, kidney, brain, pituitary gland, and thyroid gland, suggesting distinct transcriptional regulation of each GCS constituent.

Alleles↗
PubMed1988

Use of Ar+ plasma etching to localize structural proteins in viruses: studies with adenovirus 2.

The experiments described here were undertaken to test the idea that low energy Ar+ plasma etching could be employed as the basis of a method to order viral structural polypeptides according to their physical proximity to the virus surface. Since low energy (500 eV) Ar+ ions do not penetrate deeply into virus surfaces, one expects that the outermost proteins will be damaged before internal ones when intact virions are irradiated. To test this expectation, we exposed adenovirus 2 to a 500-eV Ar+ plasma and then employed sodium dodecyl sulfate-polyacryl-amide gel electrophoresis to assess the extent of damage to the major structural polypeptides. Gel analyses showed that the proteins exposed on the virus surface (proteins II, III, and IV) were degraded rapidly during the first 10 s of irradiation while protein VII, the major core polypeptide, was almost completely protected. Proteins located between the capsid and the core, such as proteins IIIa and VI, were degraded at intermediate rates. Quantitative measurements demonstrated that the observed decay rate differences were not due simply to differences in protein target size; distance to the virion surface made an important contribution. The plasma etching technique, therefore, appears to have considerable potential for the structural analysis of viruses and other macromolecular assemblies where the proximity of individual proteins to the particle surface is unknown.

Adenoviridae↗
PubMed1985

Structural localization of the sequence alpha 235-242 of the nicotinic acetylcholine receptor.

Two monoclonal antibodies (mAb 254 and 255) were obtained against a synthetic peptide corresponding to the sequence 235-242 of the alpha-subunit of Torpedo acetylcholine receptor. These mAbs could bind to receptor in native membrane vesicles only when these vesicles were permeabilized, suggesting that the sequence alpha 235-242 is exposed on the cytoplasmic surface of the receptor. Further evidence for the cytoplasmic localization of this sequence was partial competition for binding between these mAbs and mAbs previously demonstrated to bind to the cytoplasmic part of the receptor. A model is proposed which accounts for all the experimental data obtained thus far on the transmembrane orientation of the subunit polypeptide chains.

Amino Acid Sequence↗
PubMed1975

The fine structural localization of glutamate decarboxylase in developing axonal processes and presynaptic terminals of rodent cerebellum.

The immunocytochemical localization of L-glutamate decarboxylase (GAD), the enzyme which which forms gamma-aminobutyric acid (GABA), has been studied in developing rodent cerebellum. During the first 3-4 postnatal days, GAD is distributed along non-terminal portions of axonal processes in close association with small vesicles. Some of the axonal processes emanate from profiles which resemble growth cone varicosities, and are presumed to be foliopodia which extend distally from axonal growth regions. At the end of the first postnatal week the GAD-containing axonal processes are seen to form protosynaptic contacts, and GAD is localized around synaptic vesicles and at presynaptic junctional membranes. During the second and third postnatal weeks GAD gradually becomes localized to mature synaptic terminals in association with synaptic vesicle, mitochondrial, and presynaptic junctional membranes. The results suggest that GAD is present in growing neurites in close association with small vesicles prior to the time the neurites make protosynaptic contacts, and that differentiation of these contacts results in a sequestering of GAD into synaptic terminals.

Age Factors↗
PubMed1979

Fine structural localization of glutamine synthetase in astrocytes of rat brain.

The distribution of glutamine synthetase was determined in rat brain by ultrastructural immunocytochemistry. Except for trace amounts in a rare indeterminate glial cell, all the reaction product was located in astrocytes. Specifically, none was observed in neurons, synaptic endings, oligodendrocytes, microglial cells, pericytes, endothelial cells and other mesenchymal vascular elements. The results of this study clearly indicate that the astrocyte forms the compartment in brain concerned with glutamine synthesis, thereby assigning a key role to the astrocyte in the metabolism of ammonia and the putative neurotransmitters, glutamic acid and gamma-aminobutyric acid. The localization of glutamine synthetase in astrocytes additionally provides a valuable marker for a number of neurobiological studies.

Animals↗
PubMed1987

Schistosoma mansoni: fine structural localization of tegumental adenosine triphosphatases.

The distribution of Ca2+-dependent adenosine triphosphatase (EC 3.6.1.3.) and nonspecific (Na-K-Mg) adenosine triphosphatase activity in the tegument and subtegumental tissues of Schistosoma mansoni from both mixed and single sex infections was investigated cytochemically. Differences in the distribution of tegumental Ca-adenosine triphosphatase activity in 60- to 70-day-old female worms were found which could be related to the degree of sexual development in the two types of females, with little or no tegumental activity being found in 70-day-old females from single sex infections. In contrast, 28-day-old females from single sex infections showed low levels of tegumental Ca-adenosine triphosphatase activity, suggesting that the lack of tegumental activity in 70-day-old single sex females may be due to a loss or suppression of activity as a consequence of the failure of females in single sex infections to pair and develop to full sexual maturity. No differences in the distribution of nonspecific (Na-K-Mg) adenosine triphosphatase activity between females from mixed and single sex infections were found. The sexual status or age of male worms appeared to have little or no effect on the distribution of tegumental adenosine triphosphatases.

Adenosine Triphosphatases↗
PubMed1977

Fine structural localization of phosphatases in cilia and basal bodies of Tetrahymena pyriformis.

Cytochemical localization of ATPase activities in cilia and basal bodies of Tetrahymena pyriformis revealed a number of possible sites of ATPases. In basal bodies, reaction product was localized on the periphery of basal body microtubules, in the core of the B-microtubules, on the dense basal body core, and on the basal plate; some reaction product was associated with the postciliary and basal microtubules. In the cilium, reaction product was associated with the ciliary membrane, the basal granule, the periphery of the outer doublet microtubules, in the core of the B-microtubules, and on the arms and either the central microtubules or the radial spoke heads. Reaction product deposition required ATP and either Ca2+ or Mg2+ or ADP and Mg2+. When incubated in the presence of ATP and Na+, reaction product was only found at the base of the cilium in the region of the ciliary necklace. Implications of the various sites of activity are discussed with respect to possible mechanisms of ciliary motility.

Adenosine Triphosphatases↗
PubMed1986

A dominant influence of flanking sequences on a local structural transition in DNA.

We have discovered a striking dependence of a structural transition in DNA on sequences that are distanced from those directly participating in the transformation. The dominant factor determining the selection of kinetic properties of cruciform extrusion is the sequence of the DNA that flanks the inverted repeat. The sequence of the inverted repeat itself appears to have little or no influence. The critical sequences that confer the unusual kinetics exhibited by the ColE1 cruciform are very A+T-rich. A single such sequence is sufficient, which may be as short as 100 bp, and it can control inverted repeats placed at either end. The effects operate in cis, are independent of polarity, and may be effective over relatively long distances. The influence of context has wide implications, possibly including the control of gene expression.

Bacteriocin Plasmids↗