The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
Masahiro Terada - One of the best experts on this subject based on the ideXlab platform.
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relay catalysis by a metal complex bronsted acid binary system in a tandem isomerization carbon carbon bond Forming Sequence
Journal of the American Chemical Society, 2008Co-Authors: Kenji Sorimachi, Masahiro TeradaAbstract:A one-pot tandem isomerization/carbon−carbon bond Forming Sequence catalyzed by a ruthenium complex/Bronsted acid binary system is demonstrated. The method enables the use of readily available allylamides to deliver reactive imines under relay catalysis using a binary catalytic system. Subsequent Bronsted acid catalyzed carbon−carbon bond Forming reactions of the generated imines with nucleophilic components afforded Friedel−Crafts and Mannich products in good yields.
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Relay catalysis by a metal-complex/Brønsted acid binary system in a tandem isomerization/carbon-carbon bond Forming Sequence.
Journal of the American Chemical Society, 2008Co-Authors: Keiichi Sorimachi, Masahiro TeradaAbstract:A one-pot tandem isomerization/carbon−carbon bond Forming Sequence catalyzed by a ruthenium complex/Bronsted acid binary system is demonstrated. The method enables the use of readily available allylamides to deliver reactive imines under relay catalysis using a binary catalytic system. Subsequent Bronsted acid catalyzed carbon−carbon bond Forming reactions of the generated imines with nucleophilic components afforded Friedel−Crafts and Mannich products in good yields.
L. O. Winstrom - One of the best experts on this subject based on the ideXlab platform.
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Evidence for Ubiquitous Collimated Galactic-Scale Outflows along the Star-Forming Sequence at z~0.5
The Astrophysical Journal, 2014Co-Authors: Kate H. R. Rubin, J. Xavier Prochaska, David C. Koo, Andrew C. Phillips, Crystal L. Martin, L. O. WinstromAbstract:We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption line profiles in individual spectra of 105 galaxies at 0.3 9.5 at 0.3 50 degrees (edge-on). Combined with the comparatively weak dependence of the wind detection rate on intrinsic galaxy properties, this suggests that biconical outflows are ubiquitous in normal, star-Forming galaxies at z~0.5. We find that the wind velocity is correlated with host galaxy M_* at 3.4-sigma significance, while the equivalent width of the flow is correlated with host galaxy SFR at 3.5-sigma significance, suggesting that hosts with higher SFR may launch more material into outflows and/or generate a larger velocity spread for the absorbing clouds. Assuming that the gas is launched into dark matter halos with simple, isothermal density profiles, the wind velocities measured for the bulk of the cool material (~200-400 km/s) are sufficient to enable escape from the halo potentials only for the lowest-M_* systems in the sample. However, the outflows typically carry sufficient energy to reach distances of >50 kpc, and may therefore be a viable source of cool material for the massive circumgalactic medium observed around bright galaxies at z~0. [abridged]
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evidence for ubiquitous collimated galactic scale outflows along the star Forming Sequence at z 0 5
The Astrophysical Journal, 2014Co-Authors: Kate H. R. Rubin, David C. Koo, Andrew C. Phillips, Crystal L. Martin, Xavier J Prochaska, L. O. WinstromAbstract:We analyze Mg II λλ2796, 2803 and Fe II λλ2586, 2600 absorption profiles in individual spectra of 105 galaxies at 0.3 50° (edge-on). Combined with the comparatively weak dependence of wind detection rate on intrinsic galaxy properties, this implies that biconical outflows are ubiquitous in normal, star-Forming galaxies at z ~ 0.5. We find that wind velocity is correlated with galaxy M * at 3.4σ significance, while outflow equivalent width is correlated with SFR at 3.5σ significance, suggesting hosts with higher SFR launch more material and/or generate a larger velocity spread for the absorbing clouds. Assuming the gas is driven into halos with isothermal density profiles, the wind velocities (~200-400 km s–1) permit escape from the halo potentials only for the lowest-M * systems in the sample. However, the gas carries sufficient energy to reach distances 50 kpc, and may therefore be a viable source of material for the massive, cool circumgalactic medium around bright galaxies at z ~ 0.
Kate H. R. Rubin - One of the best experts on this subject based on the ideXlab platform.
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Evidence for Ubiquitous Collimated Galactic-Scale Outflows along the Star-Forming Sequence at z~0.5
The Astrophysical Journal, 2014Co-Authors: Kate H. R. Rubin, J. Xavier Prochaska, David C. Koo, Andrew C. Phillips, Crystal L. Martin, L. O. WinstromAbstract:We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption line profiles in individual spectra of 105 galaxies at 0.3 9.5 at 0.3 50 degrees (edge-on). Combined with the comparatively weak dependence of the wind detection rate on intrinsic galaxy properties, this suggests that biconical outflows are ubiquitous in normal, star-Forming galaxies at z~0.5. We find that the wind velocity is correlated with host galaxy M_* at 3.4-sigma significance, while the equivalent width of the flow is correlated with host galaxy SFR at 3.5-sigma significance, suggesting that hosts with higher SFR may launch more material into outflows and/or generate a larger velocity spread for the absorbing clouds. Assuming that the gas is launched into dark matter halos with simple, isothermal density profiles, the wind velocities measured for the bulk of the cool material (~200-400 km/s) are sufficient to enable escape from the halo potentials only for the lowest-M_* systems in the sample. However, the outflows typically carry sufficient energy to reach distances of >50 kpc, and may therefore be a viable source of cool material for the massive circumgalactic medium observed around bright galaxies at z~0. [abridged]
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evidence for ubiquitous collimated galactic scale outflows along the star Forming Sequence at z 0 5
The Astrophysical Journal, 2014Co-Authors: Kate H. R. Rubin, David C. Koo, Andrew C. Phillips, Crystal L. Martin, Xavier J Prochaska, L. O. WinstromAbstract:We analyze Mg II λλ2796, 2803 and Fe II λλ2586, 2600 absorption profiles in individual spectra of 105 galaxies at 0.3 50° (edge-on). Combined with the comparatively weak dependence of wind detection rate on intrinsic galaxy properties, this implies that biconical outflows are ubiquitous in normal, star-Forming galaxies at z ~ 0.5. We find that wind velocity is correlated with galaxy M * at 3.4σ significance, while outflow equivalent width is correlated with SFR at 3.5σ significance, suggesting hosts with higher SFR launch more material and/or generate a larger velocity spread for the absorbing clouds. Assuming the gas is driven into halos with isothermal density profiles, the wind velocities (~200-400 km s–1) permit escape from the halo potentials only for the lowest-M * systems in the sample. However, the gas carries sufficient energy to reach distances 50 kpc, and may therefore be a viable source of material for the massive, cool circumgalactic medium around bright galaxies at z ~ 0.
Crystal L. Martin - One of the best experts on this subject based on the ideXlab platform.
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Evidence for Ubiquitous Collimated Galactic-Scale Outflows along the Star-Forming Sequence at z~0.5
The Astrophysical Journal, 2014Co-Authors: Kate H. R. Rubin, J. Xavier Prochaska, David C. Koo, Andrew C. Phillips, Crystal L. Martin, L. O. WinstromAbstract:We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption line profiles in individual spectra of 105 galaxies at 0.3 9.5 at 0.3 50 degrees (edge-on). Combined with the comparatively weak dependence of the wind detection rate on intrinsic galaxy properties, this suggests that biconical outflows are ubiquitous in normal, star-Forming galaxies at z~0.5. We find that the wind velocity is correlated with host galaxy M_* at 3.4-sigma significance, while the equivalent width of the flow is correlated with host galaxy SFR at 3.5-sigma significance, suggesting that hosts with higher SFR may launch more material into outflows and/or generate a larger velocity spread for the absorbing clouds. Assuming that the gas is launched into dark matter halos with simple, isothermal density profiles, the wind velocities measured for the bulk of the cool material (~200-400 km/s) are sufficient to enable escape from the halo potentials only for the lowest-M_* systems in the sample. However, the outflows typically carry sufficient energy to reach distances of >50 kpc, and may therefore be a viable source of cool material for the massive circumgalactic medium observed around bright galaxies at z~0. [abridged]
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evidence for ubiquitous collimated galactic scale outflows along the star Forming Sequence at z 0 5
The Astrophysical Journal, 2014Co-Authors: Kate H. R. Rubin, David C. Koo, Andrew C. Phillips, Crystal L. Martin, Xavier J Prochaska, L. O. WinstromAbstract:We analyze Mg II λλ2796, 2803 and Fe II λλ2586, 2600 absorption profiles in individual spectra of 105 galaxies at 0.3 50° (edge-on). Combined with the comparatively weak dependence of wind detection rate on intrinsic galaxy properties, this implies that biconical outflows are ubiquitous in normal, star-Forming galaxies at z ~ 0.5. We find that wind velocity is correlated with galaxy M * at 3.4σ significance, while outflow equivalent width is correlated with SFR at 3.5σ significance, suggesting hosts with higher SFR launch more material and/or generate a larger velocity spread for the absorbing clouds. Assuming the gas is driven into halos with isothermal density profiles, the wind velocities (~200-400 km s–1) permit escape from the halo potentials only for the lowest-M * systems in the sample. However, the gas carries sufficient energy to reach distances 50 kpc, and may therefore be a viable source of material for the massive, cool circumgalactic medium around bright galaxies at z ~ 0.
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PHYSICAL PROPERTIES OF EMISSION-LINE GALAXIES AT z similar to 2 FROM NEAR-INFRARED SPECTROSCOPY WITH MAGELLAN FIRE
The Astrophysical Journal, 2014Co-Authors: Daniel Masters, Crystal L. Martin, Patrick Mccarthy, Brian Siana, Mathew Malkan, Bahram Mobasher, Hakim Atek, Alaina Henry, Marc Rafelski, Nimish P. HathiAbstract:We present results from near-infrared spectroscopy of 26 emission-line galaxies at z similar to 2.2 and z similar to 1.5 obtained with the Folded-port InfraRed Echellette (FIRE) spectrometer on the 6.5 m Magellan Baade telescope. The sample was selected from the WFC3 Infrared Spectroscopic Parallels survey, which uses the near-infrared grism of the Hubble Space Telescope Wide Field Camera 3 (WFC3) to detect emission-line galaxies over 0.3 less than or similar to z less than or similar to 2.3. Our FIRE follow-up spectroscopy (R similar to 5000) over 1.0-2.5 mu m permits detailedmeasurements of the physical properties of the z similar to 2 emission-line galaxies. Dust-corrected star formation rates for the sample range from similar to 5-100 M-circle dot yr(-1) with a mean of 29 M-circle dot yr(-1). We derive a median metallicity for the sample of 12 + log(O/H) = 8.34 or similar to 0.45 Z(circle dot). The estimated stellar masses range from similar to 10(8.5)-10(9.5) M-circle dot, and a clear positive correlation between metallicity and stellar mass is observed. The average ionization parameter measured for the sample, log U approximate to -2.5, is significantly higher than what is found for most star-Forming galaxies in the local universe, but similar to the values found for other star-Forming galaxies at high redshift. We derive composite spectra from the FIRE sample, from which we measure typical nebular electron densities of similar to 100-400 cm(-3). Based on the location of the galaxies and composite spectra on diagnostic diagrams, we do not find evidence for significant active galactic nucleus activity in the sample. Most of the galaxies, as well as the composites, are offset diagram toward higher [O III]/H beta at a given [N II]/H alpha, in agreement with other observations of z greater than or similar to 1 star-Forming galaxies, but composite spectra derived from the sample do not show an appreciable offset from the local star-Forming Sequence on the [O III]/H beta versus [S II]/H alpha diagram. We infer a high nitrogen-to-oxygen abundance ratio from the composite spectrum, which may contribute to the offset of the high-redshift galaxies from the local star-Forming Sequence in the [O III]/H beta versus [N II]/H alpha diagram. We speculate that the elevated nitrogen abundance could result from substantial numbers of Wolf-Rayet stars in starbursting galaxies at z similar to 2.
Karen M. Vasquez - One of the best experts on this subject based on the ideXlab platform.
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118 DNA structure-induced genetic instability in mammals
Journal of Biomolecular Structure and Dynamics, 2013Co-Authors: Guliang Wang, Laura A. Christensen, Karen M. VasquezAbstract:Naturally occurring repetitive DNA Sequences can adopt alternative (i.e. non-B) DNA secondary structures, and often co-localize with chromosomal breakpoint “hotspots,” implicating non-B DNA in translocation-related cancer etiology. We have found that Sequences capable of adopting H-DNA and Z-DNA structures are intrinsically mutagenic in mammals. For example, an endogenous H-DNA-Forming Sequence from the human c-MYC promoter and a model Z-DNA-Forming CpG repeat induced genetic instability in mammalian cells, largely in the form of deletions resulting from DNA double-strand breaks (Wang & Vasquez, 2004; Wang et al., 2006). Characterization of the mutants revealed microhomologies at the breakpoints, consistent with a microhomology-mediated end-joining repair of the double-strand breaks (Kha et al., 2010). We have constructed transgenic mutation-reporter mice containing these human H-DNA- and Z-DNA-Forming Sequences to determine their effects on genomic instability in a chromosomal context in a living organis...
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Inhibitory effect of a short Z-DNA Forming Sequence on transcription elongation by T7 RNA polymerase
Nucleic acids research, 2008Co-Authors: Jennifer V. Ditlevson, Guliang Wang, Karen M. Vasquez, Silvia Tornaletti, Boris P. Belotserkovskii, Virginia Teijeiro, Philip C. HanawaltAbstract:DNA Sequences capable of Forming unusual secondary structures can be a source of genomic instability. In some cases that instability might be affected by transcription, as recently shown for the Z-DNA Forming Sequence (CG)14, which causes genomic instability both in mammalian cells and in bacteria, and this effect increases with its transcription. We have investigated the effect of this (CG)14 Sequence on transcription with T7 RNA polymerase in vitro. We detected partial transcription blockage within the Sequence; the blockage increased with negative supercoiling of the template DNA. This effect was not observed in a control selfcomplementary Sequence of identical length and base composition as the (CG)14 Sequence, when the purine–pyrimidine alternation required for Z-DNA formation was disrupted. These findings suggest that the inhibitory effect on T7 transcription results from Z-DNA formation in the (CG)14 Sequence rather than from an effect of the Sequence composition or from hairpin formation in either the DNA or the RNA product.
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A triplex-Forming Sequence from the human c-MYC promoter interferes with DNA transcription.
The Journal of biological chemistry, 2007Co-Authors: Boris P. Belotserkovskii, Guliang Wang, Karen M. Vasquez, Silvia Tornaletti, Erandi K. De Silva, Philip C. HanawaltAbstract:Naturally occurring DNA Sequences that are able to form unusual DNA structures have been shown to be mutagenic, and in some cases the mutagenesis induced by these Sequences is enhanced by their transcription. It is possible that transcription-coupled DNA repair induced at sites of transcription arrest might be involved in this mutagenesis. Thus, it is of interest to determine whether there are correlations between the mutagenic effects of such noncanonical DNA structures and their ability to arrest transcription. We have studied T7 RNA polymerase transcription through the Sequence from the nuclease-sensitive element of the human c-MYC promoter, which is mutagenic in mammalian cells (Wang, G., and Vasquez, K. M. (2004) Proc. Natl. Acad. Sci. U. S. A. 101, 13448-13453). This element has two mirror-symmetric homopurine-homopyrimidine blocks that potentially can form either DNA triplex (H-DNA) or quadruplex structures. We detected truncated transcription products indicating partial transcription arrest within and closely downstream of the element. The arrest required negative supercoiling and was much more pronounced when the pyrimidine-rich strand of the element served as the template. The exact positions of arrest sites downstream from the element depended upon the downstream flanking Sequences. We made various nucleotide substitutions in the wild-type Sequence from the c-MYC nuclease-sensitive element that specifically destabilize either the triplex or the quadruplex structure. When these substitutions were ranked for their effects on transcription, the results implicated the triplex structure in the transcription arrest. We suggest that transcription-induced triplex formation enhances pre-existing weak transcription pause sites within the flanking Sequences by creating steric obstacles for the transcription machinery.
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Z-DNA-Forming Sequences generate large-scale deletions in mammalian cells
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: Guliang Wang, Laura A. Christensen, Karen M. VasquezAbstract:Spontaneous chromosomal breakages frequently occur at genomic hot spots in the absence of DNA damage and can result in translocation-related human disease. Chromosomal breakpoints are often mapped near purine-pyrimidine Z-DNA-Forming Sequences in human tumors. However, it is not known whether Z-DNA plays a role in the generation of these chromosomal breakages. Here, we show that Z-DNA-Forming Sequences induce high levels of genetic instability in both bacterial and mammalian cells. In mammalian cells, the Z-DNA-Forming Sequences induce double-strand breaks nearby, resulting in large-scale deletions in 95% of the mutants. These Z-DNA-induced double-strand breaks in mammalian cells are not confined to a specific Sequence but rather are dispersed over a 400-bp region, consistent with chromosomal breakpoints in human diseases. This observation is in contrast to the mutations generated in Escherichia coli that are predominantly small deletions within the repeats. We found that the frequency of small deletions is increased by replication in mammalian cell extracts. Surprisingly, the large-scale deletions generated in mammalian cells are, at least in part, replication-independent and are likely initiated by repair processing cleavages surrounding the Z-DNA-Forming Sequence. These results reveal that mammalian cells process Z-DNA-Forming Sequences in a strikingly different fashion from that used by bacteria. Our data suggest that Z-DNA-Forming Sequences may be causative factors for gene translocations found in leukemias and lymphomas and that certain cellular conditions such as active transcription may increase the risk of Z-DNA-related genetic instability.
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Naturally occurring H-DNA-Forming Sequences are mutagenic in mammalian cells
Proceedings of the National Academy of Sciences of the United States of America, 2004Co-Authors: Guliang Wang, Karen M. VasquezAbstract:Naturally occurring DNA Sequences can form noncanonical structures such as H-DNA, which are abundant and regulate the expression of several disease-linked genes. Here, we show that H-DNA-Forming Sequences are intrinsically mutagenic in mammalian cells. This finding suggests that DNA is a causative factor in mutagenesis and not just the end product. By using the endogenous H-DNA-Forming Sequence found in the human c-myc promoter, mutation frequencies in a reporter gene were increased ≈20-fold over background in COS-7 cells. H-DNA-induced double-strand breaks (DSBs) were detected near the H-DNA locus. The structures of the mutants revealed microhomologies at the breakpoints, consistent with a nonhomologous end-joining repair of the DSBs. These results implicate H-DNA-induced DSBs in c-myc gene translocations in diseases such as Burkitt's lymphoma and t(12;15) BALB/c plasmacytomas, where most breakpoints are found near the H-DNA-Forming site. Thus, our findings suggest that H-DNA is a source of genetic instability resulting from DSBs and demonstrate that naturally occurring DNA Sequences are mutagenic in mammals, perhaps contributing to genetic evolution and disease.