An inhibitor of DNA topoisomerase I from Xenopus laevis ovaries

A novel, heat-resistant and Pronase-sensitive, inhibitor of eukaryotic DNA topoisomerase I has been purified from Xenopus laevis ovaries. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the most purified fraction revealed three bands with apparent molecular masses of 25, 28.5, and 33.5 kDa. The 25- and 33.5-kDa peptides recovered from an SDS-PAGE gel inhibited X. laevis DNA topoisomerase I. The purified inhibitor was specific to DNA topoisomerase I and did not inhibit other DNA enzymes tested. The inhibitor blocked the catalytic activity of DNA topoisomerase I by interacting with the enzyme, rather than by competing for binding sites on substrate DNA. Binding of DNA topoisomerase I to substrate DNA was blocked by the inhibitor, as was the cleavage reaction catalyzed by DNA topoisomerase I. Inhibition of DNA topoisomerase I was relieved by divalent cations Ca2+, Mg2+, or Mn2+.     

Ultrasound‐activated Knoevenagel condensation of malononitrile with carbonylic compounds catalysed by alkaline‐doped saponites

α,β‐Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline‐promoted clays (Li⁺‐ and Cs⁺‐exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent‐free procedure, α,β‐unsaturated nitriles have been produced in very high yields (97%) when the Cs⁺‐saponite is used as catalyst. Copyright © 2004 Society of Chemical Industry     

89-GHz fT room-temperature silicon MOSFETs

The authors report the implementation of deep-submicrometer Si MOSFETs that at room temperature have a unity-current-gain cutoff frequency (f_T) of 89 GHz, for a drain-to-source bias of 1.5 V, a gate-to-source bias of 1 V, a gate oxide thickness of 40 Å, and a channel length of 0.15 μm. The fabrication procedure is mostly conventional, except for the e-beam defined gates. The speed performance is achieved through an intrinsic transit time of only 1.8 ps across the active device region     

Application of a general health policy model in the American health care crisis

There is near consensus that the US health care system requires reform. Only a quarter of the American public has faith in the current system. Health care was one of the major issues considered in the 1992 US presidential election and the search for innovative solutions has transcended administrations.     

Uniform Polarization Scattering With Fiber-Coil-Based Polarization Controllers

A detailed study of fiber-coil-based polarization controllers (PCs) is performed. First, a method to deterministically calculate the PC configuration in order to transform between any two states of polarization is presented. In a second stage, the case in which the configuration angles are randomly changed is studied. The cases of a single PC and of the system obtained with the concatenation of several PCs are analyzed. For both cases, a general expression for the variance of the Stokes parameters is obtained. Using this expression, it is demonstrated that it is possible to achieve uniform polarization scattering using a concatenation of fiber-coil-based PCs. Finally, it is shown that fiber-coil-based PCs can be used to emulate both first- and second-order polarization-mode dispersions