2,677 research outputs found

    Degradation of 23S rRNA in Azithromycin-Treated Ribonuclease Mutants of \u3cem\u3eEscherichia coli\u3c/em\u3e.

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    Azithromycin, a macrolide antibiotic, specifically binds to the 50S ribosomal subunit of bacterial ribosomes and inhibits translation. Azithromycin also prevents 50S ribosomal subunit assembly by binding to a 50S ribosomal subunit precursor particle. When exposed to azithromycin, several ribonucleases in wild-type Escherichia coli cells degrade antibiotic-bound 50S precursor particles. Presumably, cells expressing one or more mutated ribonucleases will degrade the antibiotic-bound precursor less efficiently, resulting in increased sensitivity to the antibiotic. To test this, eight ribonucleaseƻdeficient strains of Escherichia coli were grown in the presence or absence of azithromycin. Cell viability, growth rates, and protein synthesis rates were measured. Degradation of 23S rRNA was examined by hybridization with a 23S specific probe. Ribonuclease II and polynucleotide phosphorylase mutants demonstrated hypersensitivity to the antibiotic and showed a greater extent of 23S rRNA accumulation, suggesting that these two ribonucleases are important for 23S rRNA turnover in azithromycin-treated Escherichia coli

    Magnetic buoyancy instabilities in the presence of magnetic flux pumping at the base of the solar convection zone

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    We perform idealized numerical simulations of magnetic buoyancy instabilities in three dimensions, solving the equations of compressible magnetohydrodynamics in a model of the solar tachocline. In particular, we study the effects of including a highly simplified model of magnetic flux pumping in an upper layer (ā€˜the convection zoneā€™) on magnetic buoyancy instabilities in a lower layer (ā€˜the upper parts of the radiative interior ā€“ including the tachoclineā€™), to study these competing flux transport mechanisms at the base of the convection zone. The results of the inclusion of this effect in numerical simulations of the buoyancy instability of both a preconceived magnetic slab and a shear-generated magnetic layer are presented. In the former, we find that if we are in the regime that the downward pumping velocity is comparable with the AlfvĆ©n speed of the magnetic layer, magnetic flux pumping is able to hold back the bulk of the magnetic field, with only small pockets of strong field able to rise into the upper layer. In simulations in which the magnetic layer is generated by shear, we find that the shear velocity is not necessarily required to exceed that of the pumping (therefore the kinetic energy of the shear is not required to exceed that of the overlying convection) for strong localized pockets of magnetic field to be produced which can rise into the upper layer. This is because magnetic flux pumping acts to store the field below the interface, allowing it to be amplified both by the shear and by vortical fluid motions, until pockets of field can achieve sufficient strength to rise into the upper layer. In addition, we find that the interface between the two layers is a natural location for the production of strong vertical gradients in the magnetic field. If these gradients are sufficiently strong to allow the development of magnetic buoyancy instabilities, strong shear is not necessarily required to drive them (cf. previous work by Vasil & Brummell). We find that the addition of magnetic flux pumping appears to be able to assist shear-driven magnetic buoyancy in producing strong flux concentrations that can rise up into the convection zone from the radiative interior

    An Equality Paradign for Preventing Genetic Discrimination

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    On June 26, 2000, scientists announced at a White House news conference that they had completed mapping the human genome sequence, the human race\u27s genetic blueprint. This pronouncement generated tremendous and well-deserved excitement. Genomics, the study and application of genetic information, promises to be an unparalleled tool for improving public health. Genetic testing can identify asymptomatic individuals who are at risk of becoming ill themselves or bestowing illness on their children. As a result, individuals who test positive can take prophylactic measures to slow or stop disease and can also reduce the births of progeny at high risk of compromised health. At the same time, predictive genetic testing threatens unprecedented harm in its potential to engender (and then defend on the grounds of alleged statistical probability) discriminatory treatment in employment. Consequently, scientists most involved in the Human Genome Project and politicians most supportive of it recommend strong legal protections against genetic discrimination. Nevertheless, while the Constitution and the Privacy Act of 19749 provide some protection against the collection, use, and dissemination of genetic information on privacy grounds, effective federal regulations specifically protecting individuals from genetic discrimination in employment are almost nonexistent. Specifically, a single executive order bars federal agencies from discriminating in employment on the basis of genetic information. Despite repeatedly voiced intentions, Congress has yet to pass legislation specifically prohibiting misuse of genetic information in the area of employment, although a five-year-old bill is once more pending. Notably, the Equal Employment Opportunity Commission ( EEOC ) has had mixed initial success in applying the antidiscrimination provisions of the Americans with Disabilities Act ( ADA ) to the realm of genetic discrimination. By contrast, the scope of state statutes varies by jurisdiction. About half of the jurisdictions prohibit workplace ethical acceptability of somatic gene therapy, germ-line therapy, and somatic or germ-line modification)

    Collisional depolarization of state selected (J,M J ) BaO Aā€‰1Ī£+ measured by opticalā€“optical double resonance

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    The opticalā€“optical double resonance (OODR) technique is used to investigate the change in magnetic quantum number (M) a state selected molecule undergoes on collision with other molecules. A first linearly polarized dye laser prepares Aā€‰ 1Ī£+BaO(v = 1) in the J = 1, M = 0 sublevel. The extent of collisional transfer to other M sublevels of both J = 1 and J = 2 is then probed by a second polarized dye laser which induces fluorescence from the Cā€‰ 1Ī£+ state. Elastic collisions (Ī”J = 0) between BaO (Aā€‰ 1Ī£+) and CO2 are observed to change M from 0 to Ā±1 leaving J unchanged. The total elasticMā€changing cross section is ĻƒĪ”M CO2 = 8.4Ā±2.4 ƅ2. Inelastic collisions (Ī”J = +1ā€™ which transfer molecules to j = 2 also cause M changes. with both Ar and CO2 as collision partners. M, the s p a c eā€f i x e d projection of J, is found to be neither conserved nor randomized. Quantum atomā€“diatom collision models with quantization axis along the relative velocity vector are considered. Transition amplitudes in this system are evaluated using the lā€dominant and CS approximations

    Testimony of Damon A. Silvers Deputy Chairman Congressional Oversight Panel ā€œTARP Accountability and Oversight: Achieving Transparencyā€

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    Testimony of Damon A. Silvers

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