95 research outputs found
High Energy Gamma-Ray Emission From Blazars: EGRET Observations
We will present a summary of the observations of blazars by the Energetic
Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory
(CGRO). EGRET has detected high energy gamma-ray emission at energies greater
than 100 MeV from more that 50 blazars. These sources show inferred isotropic
luminosities as large as ergs s. One of the most
remarkable characteristics of the EGRET observations is that the gamma-ray
luminosity often dominates the bolometric power of the blazar. A few of the
blazars are seen to exhibit variability on very short time-scales of one day or
less. The combination of high luminosities and time variations seen in the
gamma-ray data indicate that gamma-rays are an important component of the
relativistic jet thought to characterize blazars. Currently most models for
blazars involve a beaming scenario. In leptonic models, where electrons are the
primary accelerated particles, gamma-ray emission is believed to be due to
inverse Compton scattering of low energy photons, although opinions differ as
to the source of the soft photons. Hardronic models involve secondary
production or photomeson production followed by pair cascades, and predict
associated neutrino production.Comment: 16 pages, 7 figures, style files included. Invited review paper in
"Observational Evidence for Black Holes in the Universe," 1999, ed. S. K.
Chakrabarti (Dordrecht: Kluwer), 215-23
Catalytic Roles of Flexible Regions at the Active Site of Ribulose-Bisphosphate Carboxylase/Oxygenase (Rubisco)
Chemical and mutagenesis studies of Rubisco have identified Lys329 and Glu48 as active-site residues that are located in distinct, interacting domains from adjacent subunits. Crystallographic analyses have shown that Lys329 is the apical residue in a 12-residue flexible loop (loop 6) of the {Beta},{alpha}-barrel domain of the active site and that Glu48 resides at the end of helix B of the N-terminal domain of the active site. When phosphorylated ligands are bound by the enzyme, loop 6 adopts a closed conformation and, in concert with repositioning of helix B, thereby occludes the active site from the external environment. In this closed conformation, the {gamma}-carboxylate of Glu48 and the {epsilon}-amino group of Lys329 engage in intersubunit electrostatic interaction. By use of appropriate site-directed mutants of Rhodospirillum rubrum Rubisco, we are addressing several issues: the catalytic roles of Lys329 and Glu48, the functional significance of the intersubunit salt bridge comprised of these two residues, and the roles of loop 6 and helix B in stabilizing labile reaction intermediates. Characterization of novel products derived from misprocessing of D-ribulose-1,5-bisphosphate (RuBP) by the mutant proteins have illuminated the structure of the key intermediate in the normal oxygenase pathway
GLAST: Understanding the High Energy Gamma-Ray Sky
We discuss the ability of the GLAST Large Area Telescope (LAT) to identify,
resolve, and study the high energy gamma-ray sky. Compared to previous
instruments the telescope will have greatly improved sensitivity and ability to
localize gamma-ray point sources. The ability to resolve the location and
identity of EGRET unidentified sources is described. We summarize the current
knowledge of the high energy gamma-ray sky and discuss the astrophysics of
known and some prospective classes of gamma-ray emitters. In addition, we also
describe the potential of GLAST to resolve old puzzles and to discover new
classes of sources.Comment: To appear in Cosmic Gamma Ray Sources, Kluwer ASSL Series, Edited by
K.S. Cheng and G.E. Romer
Using Genomic Sequencing for Classical Genetics in E. coli K12
We here develop computational methods to facilitate use of 454 whole genome shotgun sequencing to identify mutations in Escherichia coli K12. We had Roche sequence eight related strains derived as spontaneous mutants in a background without a whole genome sequence. They provided difference tables based on assembling each genome to reference strain E. coli MG1655 (NC_000913). Due to the evolutionary distance to MG1655, these contained a large number of both false negatives and positives. By manual analysis of the dataset, we detected all the known mutations (24 at nine locations) and identified and genetically confirmed new mutations necessary and sufficient for the phenotypes we had selected in four strains. We then had Roche assemble contigs de novo, which we further assembled to full-length pseudomolecules based on synteny with MG1655. This hybrid method facilitated detection of insertion mutations and allowed annotation from MG1655. After removing one genome with less than the optimal 20- to 30-fold sequence coverage, we identified 544 putative polymorphisms that included all of the known and selected mutations apart from insertions. Finally, we detected seven new mutations in a total of only 41 candidates by comparing single genomes to composite data for the remaining six and using a ranking system to penalize homopolymer sequencing and misassembly errors. An additional benefit of the analysis is a table of differences between MG1655 and a physiologically robust E. coli wild-type strain NCM3722. Both projects were greatly facilitated by use of comparative genomics tools in the CoGe software package (http://genomevolution.org/)
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Erratum: Genetic loci associated with heart rate variability and their effects on cardiac disease risk
Correction to article number 15805 published in June 2017 in Nature Communications, vol 8
Erratum: Genetic loci associated with heart rate variability and their effects on cardiac disease risk
Correction to article number 15805 published in June 2017 in Nature Communications, vol 8
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