Showing 731 - 740 of 2039 Items
Disruption of topoisomerase II perturbs pairing in Drosophila cell culture
Date: 2007-09-01
Creator: Benjamin R. Williams
Jack R. Bateman
Natasha D. Novikov
C. Ting Wu
Access: Open access
- Homolog pairing refers to the alignment and physical apposition of homologous chromosomal segments. Although commonly observed during meiosis, homolog pairing also occurs in nonmeiotic cells of several organisms, including humans and Drosophila. The mechanism underlying nonmeiotic pairing, however, remains largely unknown. Here, we explore the use of established Drosophila cell lines for the analysis of pairing in somatic cells. Using fluorescent in situ hybridization (FISH), we assayed pairing at nine regions scattered throughout the genome of Kc167 cells, observing high levels of homolog pairing at all six euchromatic regions assayed and variably lower levels in regions in or near centromeric heterochromatin. We have also observed extensive pairing in six additional cell lines representing different tissues of origin, different ploidies, and two different species, demonstrating homolog pairing in cell culture to be impervious to cell type or culture history. Furthermore, by sorting Kc167 cells into G1, S, and G2 subpopulations, we show that even progression through these stages of the cell cycle does not significantly change pairing levels. Finally, our data indicate that disrupting Drosophila topoisomerase II (Top2) gene function with RNAi and chemical inhibitors perturbs homolog pairing, suggesting Top2 to be a gene important for pairing. Copyright Ā© 2007 by the Genetics Society of America.
A record of atmospheric halocarbons during the twentieth century from polar firn air
Date: 1999-06-24
Creator: James H. Butler
Mark Battle
Michael L. Bender
Stephen A. Montzka
Andrew D., Clarke
Eric S. Saltzman
Cara M. Sucher
Jeffrey P. Severinghaus
James W. Elkins
Access: Open access
- Measurements of trace gases in air trapped in polar firn (unconsolidated snow) demonstrate that natural sources of chlorofluorocarbons, halons, persistent chlorocarbon solvents and sulphur hexafluoride to the atmosphere are minimal or non-existent. Atmospheric concentrations of these gases, reconstructed back to the late nineteenth century, are consistent with atmospheric histories derived from anthropogenic emission rates and known atmospheric lifetimes. The measurements confirm the predominance of human activity in the atmospheric budget of organic chlorine, and allow the estimation of atmospheric histories of halogenated gases of combined anthropogenic and natural origin. The pre-twentieth-century burden of methyl chloride was close to that at present, while the burden of methyl bromide was probably over half of today's value.
Ocean primary production derived from satellite data: An evaluation with atmospheric oxygen measurements
Date: 1999-06-01
Creator: Yves Balkanski
Patrick Monfray
Mark Battle
Martin Heimann
Access: Open access
- Recently, very precise measurements have detected the seasonal variability in the atmospheric O2/N2 ratio at several sites in the northern and southern hemispheres. In this paper, we derive marine primary productivity (PP) from satellite ocean color data. To infer air-sea oxygen fluxes, a simple one-dimensional diagnostic model of ocean biology has been developed that depends on only two parameters: a time delay between organic production and oxidation (set to 2 weeks) and an export scale length (50 m). This model gives a global net community production of 4.3 mol C m-2 yr-1 in the euphotic zone and 3.2 mol C m-2 yr-1 in the mixed layer. This last value corresponds to a global f ratio (net community production (NCP)/PP) at the base of the mixed layer of 0.37. The air-sea fluxes derived from this model are then used at the base of a three-dimensional atmospheric model to compare the atmospheric seasonal cycle of O2/N2 at five sites: Cape Grim (40.6S, 144.6E), Baring Head (41.3S, 174.8E), Mauna Loa (19.5N,154.8W), La Jolla (32.9N, 117.3W), and Barrow (71.3N, 156.6W). The agreement between model and observations is very encouraging. We infer from the agreement that the seasonal variations in O2/N2 are largely controlled by the photosynthesis rate but also by the remineralization linked to the deepening and shoaling of the mixed layer. Lateral ventilation to high latitudes may also be an important factor controlling the amplitude of the seasonal cycle.
Identification of the determinants for the specific recognition of single-strand telomeric DNA by Cdc13
Date: 2006-01-24
Creator: Aimee M. Eldridge
Wayne A. Halsey
Deborah S. Wuttke
Access: Open access
- The single-strand overhang present at telomeres plays a critical role in mediating both the capping and telomerase regulation functions of telomeres. The telomere end-binding proteins, Cdc13 in Saccharomyces cerevisiae, Pot1 in higher eukaryotes, and TEBP in the ciliated protozoan Oxytricha nova, exhibit sequence-specific binding to their respective single-strand overhangs. S. cerevisiae telomeres are composed of a heterogeneous mixture of GT-rich telomeric sequence, unlike in higher eukaryotes which have a simple repeat that is maintained with high fidelity. In yeast, the telomeric overhang is recognized by the essential protein Cdc13, which coordinates end-capping and telomerase activities at the telomere. The Cdc13 DNA-binding domain (Cdc13-DBD) binds these telomere sequences with high affinity (3 pM) and sequence specificity. To better understand the basis for this remarkable recognition, we have investigated the binding of the Cdc13-DBD to a series of altered DNA substrates. Although an 11-mer of GT-rich sequence is required for full binding affinity, only three of these 11 bases are recognized with high specificity. This specificity differs from that observed in the other known telomere end-binding proteins, but is well suited to the specific role of Cdc13 at yeast telomeres. These studies expand our understanding of telomere recognition by the Cdc13-DBD and of the unique molecular recognition properties of ssDNA binding. Ā© 2006 American Chemical Society.
Production and decay of D1 (2420)0 and D2* (2460)0
Date: 1994-06-30
Creator: P. Avery
A. Freyberger
J. Rodriguez
R. Stephens
S., Yang
J. Yelton
D. Cinabro
S. Henderson
T. Liu
M. Saulnier
R. Wilson
H. Yamamoto
T. Bergfeld
B. I. Eisenstein
G. Gollin
B. Ong
M. Palmer
M. Selen
J. J. Thaler
K. W. Edwards
M. Ogg
B. Spaan
A. Bellerive
D. I. Britton
E. R.F. Hyatt
D. B. MacFarlane
P. M. Patel
A. J. Sadoff
R. Ammar
S. Ball
P. Baringer
Access: Open access
- We have investigated D+ Ļ- and D*+ Ļ- final states and observed the two established L = 1 charmed mesons, the D1 (2420)0 with mass 2421-2-2+1+2 MeV/c2 and width 20-5-3+6+3 MeV/c2 and the D2* (2460)0 with mass 2465 Ā± 3 Ā± 3 MeV/c2 and width 28-7-6+8+6 MeV/c2. Properties of these final states, including their decay angular distributions and spin-parity assignments, have been studied. We identify these two mesons as the jlight = 3 2 doublet predicted by HQET. We also obtain constraints on Īs/ (Īs + ĪD) as a function of the cosine of the relative phase of the two amplitudes in the D1 (2420)0 decay. Ā© 1994.
A structural role for arginine in proteins: Multiple hydrogen bonds to backbone carbonyl oxygens
Date: 1994-01-01
Creator: C. L. Borders
John A. Broadwater
Paula A. Bekeny
Johanna E. Salmon
Ann S., Lee
Aimee M. Eldridge
Virginia B. Pett
Access: Open access
- We propose that arginine side chains often play a previously unappreciated general structural role in the maintenance of tertiary structure in proteins, wherein the positively charged guanidinium group forms multiple hydrogen bonds to backbone carbonyl oxygens. Using as a criterion for a āstructuralā arginine one that forms 4 or more hydrogen bonds to 3 or more backbone carbonyl oxygens, we have used molecular graphics to locate arginines of interest in 4 proteins: Arg 180 in Thermus thermophilus manganese superoxide dismutase, Arg 254 in human carbonic anhydrase II, Arg 31 in Streptomyces rubiginosus xylose isomerase, and Arg 313 in Rhodospirillum rubrum ribuloseā1,5ābisphosphate carboxylase/oxygenase. Arg 180 helps to mold the active site channel of superoxide dismutase, whereas in each of the other enzymes the structural arginine is buried in the āmantleā (i.e., inside, but near the surface) of the protein interior well removed from the active site, where it makes 5 hydrogen bonds to 4 backbone carbonyl oxygens. Using a more relaxed criterion of 3 or more hydrogen bonds to 2 or more backbone carbonyl oxygens, arginines that play a potentially important structural role were found in yeast enolase, Bacillus stearothermophilus glyceraldehydeā3āphosphate dehydrogenase, bacteriophage T4 and human lysozymes, Enteromorpha prolifera plastocyanin, HIVā1 protease, Trypanosoma brucei brucei and yeast triosephosphate isomerases, and Escherichia coli trp aporepressor (but not trp repressor or the trp repressor/operator complex). In addition to helping form the active site funnel in superoxide dismutase, the structural arginines found in this study play such diverse roles as stapling together 3 strands of backbone from different regions of the primary sequence, and tying Ī±āhelix to Ī±āhelix, Ī²turn to Ī²āturn, and subunit to subunit. Copyright Ā© 1994 The Protein Society
A structural role for arginine in proteins: Multiple hydrogen bonds to backbone carbonyl oxygens
Date: 1994-01-01
Creator: C. L. Borders
John A. Broadwater
Paula A. Bekeny
Johanna E. Salmon
Ann S., Lee
Aimee M. Eldridge
Virginia B. Pett
Access: Open access
- We propose that arginine side chains often play a previously unappreciated general structural role in the maintenance of tertiary structure in proteins, wherein the positively charged guanidinium group forms multiple hydrogen bonds to backbone carbonyl oxygens. Using as a criterion for a āstructuralā arginine one that forms 4 or more hydrogen bonds to 3 or more backbone carbonyl oxygens, we have used molecular graphics to locate arginines of interest in 4 proteins: Arg 180 in Thermus thermophilus manganese superoxide dismutase, Arg 254 in human carbonic anhydrase II, Arg 31 in Streptomyces rubiginosus xylose isomerase, and Arg 313 in Rhodospirillum rubrum ribuloseā1,5ābisphosphate carboxylase/oxygenase. Arg 180 helps to mold the active site channel of superoxide dismutase, whereas in each of the other enzymes the structural arginine is buried in the āmantleā (i.e., inside, but near the surface) of the protein interior well removed from the active site, where it makes 5 hydrogen bonds to 4 backbone carbonyl oxygens. Using a more relaxed criterion of 3 or more hydrogen bonds to 2 or more backbone carbonyl oxygens, arginines that play a potentially important structural role were found in yeast enolase, Bacillus stearothermophilus glyceraldehydeā3āphosphate dehydrogenase, bacteriophage T4 and human lysozymes, Enteromorpha prolifera plastocyanin, HIVā1 protease, Trypanosoma brucei brucei and yeast triosephosphate isomerases, and Escherichia coli trp aporepressor (but not trp repressor or the trp repressor/operator complex). In addition to helping form the active site funnel in superoxide dismutase, the structural arginines found in this study play such diverse roles as stapling together 3 strands of backbone from different regions of the primary sequence, and tying Ī±āhelix to Ī±āhelix, Ī²turn to Ī²āturn, and subunit to subunit. Copyright Ā© 1994 The Protein Society
Multi-colony calibrations of coral Ba/Ca with a contemporaneous in situ seawater barium record
Date: 2016-04-15
Creator: MichĆØle LaVigne
AndrƩa G. Grottoli
James E. Palardy
Robert M. Sherrell
Access: Open access
- The coral skeleton barium to calcium ratio (Ba/Ca ), a proxy for seawater barium concentrations (Ba ), has been interpreted as a tracer of upwelling based on the characteristic "nutrient like" depth profile of Ba . However, in some tropical regions, such as the Gulf of PanamĆ”, substantial influence of terrestrial runoff inputs and differences between the vertical distribution of Ba and that of the major nutrients (nitrate and phosphate) in the upper water column can complicate the interpretation of Ba/Ca as an upwelled nutrient proxy. In the Gulf of PanamĆ”, contemporaneous Ba/Ca records from multiple colonies of Porites lobata, Pavona gigantea, and Pavona clavus corals record a nearly twofold change in surface water Ba as a 20-70% increase in skeletal Ba/Ca with excellent correlation among Ba/Ca records from co-located colonies (r = 0.86-0.99). These results provide, for the first time, an absolute calibration of the coral Ba proxy with a contemporaneous Ba record. Compiling the Ba/Ca records from three co-located colonies of each species into taxon-specific composite regressions reveals strong statistically significant correlations with the Ba time-series record (p < 0.001). Differences among taxa in regression slope, y-intercept, and average distribution coefficient, as well as a demonstration of the application of the P. clavus calibration to a previously published Ba/Ca record, emphasize the necessity of using taxon-specific calibrations to reconstruct changes in Ba with accuracy. These results support the application of Ba/Ca to reconstruct past changes in absolute Ba concentrations, adding an important tool to the collection of geochemical proxies for reconstructing surface ocean biogeochemical processes in the past. coral SW SW SW coral coral SW SW coral SW coral SW coral SW
Unidirectional Transition Waves in Bistable Lattices
Date: 2016-06-13
Creator: Neel Nadkarni
Andres F. Arrieta
Christopher Chong
Dennis M. Kochmann
Chiara, Daraio
Access: Open access
- We present a model system for strongly nonlinear transition waves generated in a periodic lattice of bistable members connected by magnetic links. The asymmetry of the on-site energy wells created by the bistable members produces a mechanical diode that supports only unidirectional transition wave propagation with constant wave velocity. We theoretically justify the cause of the unidirectionality of the transition wave and confirm these predictions by experiments and simulations. We further identify how the wave velocity and profile are uniquely linked to the double-well energy landscape, which serves as a blueprint for transition wave control.
Associations Between Mode of Birth and Neuropsychological Development in Children Aged 4 Years: Results from a Birth Cohort Study
Date: 2021-12-01
Creator: Lea TakƔcs
Samuel P. Putnam
Catherine Monk
Hannah G. Dahlen
Charlene, Thornton
FrantiŔek BartoŔ
Anastasia Topalidou
Lilian L. Peters
Access: Open access
- The aim of this prospective longitudinal study was to examine the association between Cesarean section (CS) and child development and behavior. The sample consisted of 256 children who were born at term without serious perinatal pathologies. Their development and behavior was assessed at the age of four using Ages and Stages Questionnaire (ASQ-3), Childrenās Behavior Questionnaire and Strength and Difficulties Questionnaire. Multivariate linear regression analyses were conducted to assess the association between CS and child outcomes. CS was associated with better scores in the Problem Solving domain of the ASQ in the whole sample. After stratifying by child sex, the positive association between CS and the Problem Solving domain was significant in boys, while no association was found in girls. Girls were rated less optimally in the Gross Motor domain of the ASQ when born via CS. Mode of birth was not associated with behavioral outcomes.