RESUMEN

We report the measurement of the helicity asymmetry E for the pπ^{0} and nπ^{+} final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. The results agree very well with data that were taken with a circularly polarized photon beam, showing that it is possible to simultaneously measure polarization observables that require linearly (e.g., G) and circularly polarized photons (e.g., E) and a longitudinally polarized target. The new data cover a photon energy range 270-1400 MeV for the pπ^{0} final state (230-842 MeV for the nπ^{+} final state) and the full range of pion polar angles, θ, providing the most precise measurement of the observable E. A moment analysis gives a clear observation of the pη cusp in the pπ^{0} final state.

RESUMEN

The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive π0 and η photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the γp→π0p and γp→ηp reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the ηn system at W=1.68GeV. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the S11(1535) and S11(1650) resonances within the S11-partial wave.

RESUMEN

A precise measurement of the differential cross sections dσ/dΩ and the linearly polarized photon beam asymmetry Σ_{3} for Compton scattering on the proton below pion threshold has been performed with a tagged photon beam and almost 4π detector at the Mainz Microtron. The incident photons were produced by the recently upgraded Glasgow-Mainz photon tagging facility and impinged on a cryogenic liquid hydrogen target, with the scattered photons detected in the Crystal Ball/TAPS setup. Using the highest statistics Compton scattering data ever measured on the proton along with two effective field theories (both covariant baryon and heavy-baryon) and one fixed-t dispersion relation model, constraining the fits with the Baldin sum rule, we have obtained the proton electric and magnetic polarizabilities with unprecedented precision: α_{E1}=10.99±0.16±0.47±0.17±0.34, ß_{M1}=3.14±0.21±0.24±0.20±0.35; in units of 10^{-4} fm^{3} where the errors are statistical, systematic, spin polarizability dependent, and model dependent.

RESUMEN

The quasifree γ → d → π 0 n ( p ) photon beam asymmetry, Σ , has been measured at photon energies, E γ , from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 ∘ to 148 ∘ . In this kinematic region, polarization observables are sensitive to contributions from the Δ ( 1232 ) and N(1440) resonances. The extracted values of Σ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID and Bonn-Gatchina analyses; while a revised SAID fit, including the new Σ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict π 0 n photoproduction observables, based on fits to published data in the channels π 0 p , π + n and π - p .

RESUMEN

The double-polarization observable E and helicity-dependent cross sections σ_{1/2}, σ_{3/2} have been measured for the photoproduction of π^{0} pairs off quasifree protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost 4π covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the γN→Nπ^{0}π^{0} reaction. They are compared to predictions from reaction models in view of nucleon resonance contributions and also to a refit of one model that predicted results for the proton and for the neutron target. The comparison of the prediction and the refit demonstrates the large impact of the new data.

RESUMEN

We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300-700 MeV provides the first measurement of recoil neutron polarization at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarization in a narrow structure centered around E_{γ}∼570 MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behavior could be related to the excitation of the d^{*}(2380) hexaquark.

RESUMEN

Deinococcus radiodurans is extremely resistant to ionizing radiation. How this bacterium can grow under chronic gamma radiation [50 grays (Gy) per hour] or recover from acute doses greater than 10 kGy is unknown. We show that D. radiodurans accumulates very high intracellular manganese and low iron levels compared with radiation-sensitive bacteria and that resistance exhibits a concentration-dependent response to manganous chloride [Mn(II)]. Among the most radiation-resistant bacterial groups reported, Deinococcus, Enterococcus, Lactobacillus, and cyanobacteria accumulate Mn(II). In contrast, Shewanella oneidensis and Pseudomonas putida have high iron but low intracellular manganese concentrations and are very sensitive. We propose that Mn(II) accumulation facilitates recovery from radiation injury.

Asunto(s)

RESUMEN

A young lady initially found to have hydatid cysts in the lung only, subsequently within a very short period was found to develop cysts in the liver. Soon after, she developed cysts in the subcutaneous tissue over the anterolateral chest wall, which, on investigation, revealed hepatic cysts herniating through the chest wall defects caused by previous operations. The unique features of this case include the degree of dissemination, the multiplicity of sites and the peculiar nature of herniation of the hepatic cysts into the parietes.

Asunto(s)

RESUMEN

Immense volumes of radioactive wastes, which were generated during nuclear weapons production, were disposed of directly in the ground during the Cold War, a period when national security priorities often surmounted concerns over the environment. The bacterium Deinococcus radiodurans is the most radiation-resistant organism known and is currently being engineered for remediation of the toxic metal and organic components of these environmental wastes. Understanding the biotic potential of D. radiodurans and its global physiological integrity in nutritionally restricted radioactive environments is important in development of this organism for in situ bioremediation. We have previously shown that D. radiodurans can grow on rich medium in the presence of continuous radiation (6,000 rads/h) without lethality. In this study we developed a chemically defined minimal medium that can be used to analyze growth of this organism in the presence and in the absence of continuous radiation; whereas cell growth was not affected in the absence of radiation, cells did not grow and were killed in the presence of continuous radiation. Under nutrient-limiting conditions, DNA repair was found to be limited by the metabolic capabilities of D. radiodurans and not by any nutritionally induced defect in genetic repair. The results of our growth studies and analysis of the complete D. radiodurans genomic sequence support the hypothesis that there are several defects in D. radiodurans global metabolic regulation that limit carbon, nitrogen, and DNA metabolism. We identified key nutritional constituents that restore growth of D. radiodurans in nutritionally limiting radioactive environments.

Asunto(s)

RESUMEN

Balanced diet fed (BDF) rats injected with Salmonella typhi 'H' antigen showed an initial suppression of an immunomodulatory bone marrow cytokine Frl (BM-Frl) followed by stimulation, whereas the cytokine secretory pattern showed only stimulation in immunized vitamin B complex malnourished rats. This nutritional-dependent differential response of a bone marrow cytokine to antigen is similar to that observed previously in brain adenosine triphosphatase (ATPase) function following immunization. An improvement in antibody response to S. typhi (p<0.01) and neutrophil function (p<0.05) was observed in cytokine-treated malnourished immunosuppressed rats further strengthening our previous observations that BM-Frl modulates both specific and non-specific immune systems. No significant change was observed in BDF animals indicating that malnourished rats gain more from cytokine therapy, whereas a negative feedback system might be present in BDF animals.

RESUMEN

In Alcaligenes eutrophus JMP134, pJP4 carries the genes coding for 2,4-dichlorophenoxyacetate (2,4-D) and 3-chlorobenzoate (3-Cba) degradation plus mercury resistance. The plasmid genes specifying 2,4-D and 3-Cba catabolism are organized in three operons: tfdA, tfdB, and tfdCDEF. Regulation of these operons by two unlinked genes, tfdR and tfdS, has been proposed. Physical and DNA sequence analyses revealed that the tfdR and tfdS genes were identical and were located within a longer inverted repeat of 1592 bp. Similar stem-loop structures were observed among other 2,4-D plasmids. The tfdR gene is 888 bp long and capable of encoding a polypeptide of 32 kDa. The deduced amino acid sequence of tfdR indicates that it is a member of the LysR-type activators. Investigation of the regulation of the catabolic gene clusters through the construction of a pJP4 defined deletion mutant, pYG1010, which lacks a 4.2 kilobase Xbal fragment containing the inverted repeat region carrying the tfdR and tfdS regulatory genes, showed that Pseudomonas cepacia strains containing pYG1010 became 2,4-D negative, but 3-Cba positive. In vivo recombinants of pYG1010 and a cloned tfdS gene rescued the 2,4-D phenotype, indicating that TfdS is a positive regulator of tfdA expression, but not for tfdCDEF expression.

Asunto(s)

RESUMEN

Intracellular distribution of selected reticuloplasmins, soluble proteins of the endoplasmic reticulum lumen, in rat mammary gland was investigated during pregnancy, lactation, and involution. During lactation the levels of the calcium binding protein calreticulin, and of protein disulfide isomerase, were elevated. Endoplasmic reticulum was as efficient as Golgi apparatus in sequestration and accumulation of Ca2+ from surrounding medium, as suggested from in vitro experiments with isolated cell fractions. Both protein disulfide isomerase and calreticulin were present in cytosol from homogenates of mammary gland prepared under mild conditions. Protein disulfide isomerase was abundant in intracellular lipid droplet precursors of milk lipid globules. Calreticulin and immunoglobulin binding protein (BiP, GRP 78) were associated with lipid droplets. Glucose-regulated protein (GRP 94) was not detected in association with intracellular lipid droplets. Milk lipid globule membrane lacked more than barely detectable quantities of protein disulfide isomerase, calreticulin, and immunoglobulin binding protein, suggesting that these proteins are lost from intracellular lipid droplets before or during their secretion as milk lipid globules. Immunocytochemical localization confirmed the presence of protein disulfide isomerase or calreticulin on intracellular lipid droplets and in non-endoplasmic reticulum regions of cells.

Asunto(s)

RESUMEN

Secretion of milk lipid globules is achieved through encapsulation of triacylglycerol-rich lipid droplets in a specialized region of apical plasma membrane of mammary epithelial cells. A class of low molecular mass GTP-binding proteins were associated tightly with the lipid globule membrane, and these proteins appeared to change from peripheral to integral membrane proteins during intracellular growth and transit of lipid globule precursors. Inclusion of GTP or GTP gamma S in incubation medium stimulated secretion of lipids from primary cultures of permeabilized rat mammary epithelial cells. Six polypeptides with molecular masses between 28 and 21 kDa were detected by ability to bind GTP gamma S following separation of lipid-globule-associated proteins by SDS-PAGE and transblotting onto nitrocellulose. That all of these polypeptides were distinct immunologically from the archetype ras was evident from lack of immunoreactivity with p21 ras G-protein monoclonal antibody in Western blots. This monoclonal antibody bound to a 23 kDa polypeptide of lipid droplets that was not detected with the GTP gamma S binding assay. A 25 kDa component of milk lipid globules was a potent substrate for ADP-ribosylation by botulinum toxin C3, but cholera toxin was much less effective, suggesting that this component may belong to the rac class of G-proteins. The 21 kDa component was related immunologically to ADP ribosylation factor.

Asunto(s)

RESUMEN

1. Membrane-free cytosol contained over 4% of both the total lipids and phospholipids present in homogenates of lactating rat mammary gland, and much of this lipid was associated with a high molecular weight complex isolated from cytosol by gel exclusion chromatography or by density gradient centrifugation. 2. This complex principally consisted of polypeptides with apparent molecular weights of 220 and 116 kDa. Lipids associated with this complex were transferred to endoplasmic reticulum and to intracellular lipid droplet precursors of milk lipid globules upon incubation in a cell-free system. 3. This lipoprotein complex was abundant in cytosol from lactating mammary gland, but was diminished in amount in cytosol from involuted mammary glands. The 220 kDa constituent of this complex was identified as the monomer of fatty acid synthase. 4. These results suggest that fatty acid synthase complex in lactating mammary gland may function in transfer of lipids necessary for formation or growth of lipid droplet precursors of milk lipid globules.

Asunto(s)

RESUMEN

Lipid droplet precursors of milk lipid globules are believed to be derived from elements of endoplasmic reticulum in milk-secreting mammary epithelial cells. Endoplasmic reticulum isolated from mammary gland was able to generate small droplets morphologically resembling microlipid droplet precursors of milk lipid globules. Droplet generation was time and temperature dependent and required a cytosol fraction of Mr greater than 10,000. Droplet generation was enhanced by, but did not require, addition of nucleoside triphosphates, fatty acids, coenzyme A, glycerol-3-phosphate, and dithiothreitol. Microlipid droplets generated in this cell-free system were enriched in triacylglycerols and resembled microlipid droplets formed within mammary epithelial cells in polar lipid and polypeptide composition. Endoplasmic reticulum immobilized onto nitrocellulose retained activity in generation of putative microlipid droplets, and this immobilization method provided a facile means for separation of the donor from the generated products.

Asunto(s)

RESUMEN

Gene nahG of naphthalene/salicylate catabolic plasmid NAH7 encodes a protein of molecular weight 45,000, salicylate hydroxylase. This enzyme catalyzes the formation of catechol from salicylate, a key intermediate in naphthalene catabolism. DNA sequence analysis of the 3.1-kilobase HindIII fragment containing the nahG locus reveals an open reading frame (ORF) of 1305 base pairs that corresponds to a protein of 434 amino acid residues. The predicted amino acid sequence of salicylate hydroxylase is in agreement with the molecular weight, NH2-terminal amino acid sequence, and total amino acid composition of the purified salicylate hydroxylase [You, I.-S., Murray, R. I., Jollie, D., & Gunsalus, I. C. (1990) Biochem. Biophys. Res. Commun. 169, 1049-1054]. The amino acid sequence between positions 8 and 37 of salicylate hydroxylase shows homology with known ADP binding sites of other FAD-containing oxidoreductases, thus confirming its biochemical function. The sequence of the Pseudomonas putida salicylate hydroxylase was compared with those of other similar flavoproteins. A small DNA segment (831 base pairs) disrupts the continuity of the known gene order nahG and nahH, the latter encoding catechol 2,3-dioxygenase. The complete nucleotide sequence of the intergenic region spanning genes nahG and nahH has been determined and its biological role proposed.

Asunto(s)

RESUMEN

The C1 locus of Zea mays (maize) controls the expression of genes involved in anthocyanin biosynthesis in aleurone and scutellar tissue and encodes a protein with the features of a transcriptional activator. C1-I is a dominant negative mutant which inhibits pigment formation. The structure of the C1-I allele was determined by cloning and sequencing of this allele and of two distinct C1-I derived cDNAs. C1-I has two major and several minor sequence differences with respect to the wild-type C1 allele. Transcription initiation occurs at the same position as in wild-type but transcription yields two different products, one major RNA of 1.3 kb and one minor RNA of 1.45 kb in length, encoding two proteins of 252 and 108 amino acids respectively. The longer 252 amino acid C1-I protein differs from the 273 amino acid wild-type C1 protein at several positions but most prominently at its carboxy terminus, resulting in reduced acidity of the C1-I protein. A similar change in acidity of the Gal4 protein of yeast converted this transcriptional activator into a repressor protein. We discuss the dominant phenotype of C1-I with respect to its possible repressor function in contrast to the activator function of the C1 gene product.

Asunto(s)

RESUMEN

Alcaligenes eutrophus harboring plasmid pJP4 (strain JMP134) is capable of growing on both 2,4-dichlorophenoxyacetate (2,4-D) and 3-chlorobenzoate (3-Cba), while Pseudomonas putida carrying plasmid pAC27 (strain AC867) can utilize only 3-Cba as the sole carbon source. The tfdCDEF operon of the pJP4 plasmid and the clcABD operon of plasmid pAC27 each encode enzymes for the degradation of chlorocatechols (Clc), key intermediates in the catabolism of 2,4-D and 3-Cba. Similarities in the nucleotide (nt) sequences of genes tfdC and clcA, encoding pyrocatechases, were reported earlier [Ghosal and You, Mol. Gen. Genet. 211 (1988a) 113-120]. Genes tfdD and clcB, encoding Clc-specific cycloisomerases, have been completely sequenced. The tfdD gene (1107 bp) is slightly smaller than gene clcB (1113 bp). Comparison of the two cycloisomerase-encoding genes reveals that the nt sequences are 63% homologous with 62% homology in the deduced amino acid (aa) sequences of the polypeptides they encode. Genes tfdD and tfdE are contiguous in the tfdCDEF operon, whereas the corresponding genes, clcB and clcD, of the clcABD operon, are known to be separated by a long open reading frame of unknown function. The predicted N-terminal aa sequences of the two hydrolase-encoding genes, tfdE and clcD, also show homology. The structural and nt homologies between the two Clc operons, tfdCDEF and clcABD, suggest their relatedness.

Asunto(s)

RESUMEN

The nah and sal operons of the 80-kilobase-pair (kb) NAH7 plasmid specify catabolism of naphthalene and salicylate under positive regulation by gene nahR. A 1.75-kb fragment (PstI-HindIII) cloned into the pCP13 derivative of vector RK2 complemented in trans five nahR mutations. The fragment sequence contained a 1,122-base-pair open reading frame with a predicted sequence of 374 residues that was rich in basic amino acids with regions similar to known DNA-binding proteins. Clones from the nahR gene region were expressed in mexicells. Plasmid pY1923, carrying the 1.75-kb PstI-HindIII fragment, expressed a protein of Mr ca. 35,000 which bound to the upstream region of gene nahR in a gel electrophoresis DNA-binding assay. Other clones expressed proteins of currently unknown function; pY1311, with the 1.1-kb HindIII fragment, produced a polypeptide with an Mr of 23,000, and pY1812, with the 1.2-kb PstI-SphI fragment, produced a polypeptide (Mr 41,000) which appeared to be a fused nahR-lacZ product.

Asunto(s)

RESUMEN

A sequence homologous to the conventional nifH gene has been cloned from a different region of the Azotobacter vinelandii genome. Tn5 insertions were obtained in this clone and the mutagenized plasmid was used for marker exchange with A. vinelandii strain CA12 (delta nifHDK) to obtain Tn5 mutants. These mutants exhibited a Nif- phenotype in the presence of vanadium, unlike CA12 which was Nif+ on vanadium-containing medium. The gene in the cloned nifH-like region is therefore apparently involved in the vanadium dependent alternative pathway of nitrogen fixation. This gene, nifH2, has been sequenced and encodes a protein of 289 amino acids that is similar to nifH in nucleotide sequence, deduced amino acid sequence, predicted secondary structure and hydrophobicity profile. A second open reading frame downstream of nifH2 codes for a protein of 64 amino acids, similar to the ferredoxin (Fd)-like protein encoded downstream of nifH* in A. chroococum. Sequence analysis suggests that the nifH2 and Fd-like genes are in a single operon.

Asunto(s)