Bacteriophage PBS1 of Bacillus subtilis was rapidly adsorbed on montmorillonite (M) and kaolinite (K), and adsorption was maximal after 30min on both clays. There was no correlation between adsorption and the cation exchange capacity of the clays. Studies with sodium metaphosphate (a polyanion that interacts with positively charged sites on clay) indicated that positively charged sites on K were primarily responsible for the adsorption of the phage, whereas other mechanisms appeared to be involved in adsorption of the phage on M. X-ray diffraction and electron microscopic analyses showed that the phage partially intercalated M. Survival of the phage was increased by adsorption on the clays, and adsorbed phage maintained its ability to transduce bacterial cells for at least 30 days (the longest time studied) after the preparation of the clay-phage complexes. Electron microscopic observations indicated that transduction by the clay-phage complexes was primarily the result of the phage detaching from the clays in the presence of host cells.
Pectate lyase A is a virulence factor secreted by the plantpathogenic bacteria Erwinia chrysanthemi. The enzyme cleaves the glycosidic bond of pectate polymers by a calcium-dependent -elimination mechanism. The crystal structure of pectate lyase A from E. chrysanthemi EC16 has been determined in two crystal forms, monoclinic C2 to 1.8 A Ê and rhombohedral R3 to 2.1 A Ê . The protein structure is compared with two other pectate lyase isoforms from E. chrysanthemi EC16, pectate lyase C and pectate lyase E. Pectate lyase A is unique as it is the only acidic pectate lyase and has end products that are signi®cantly more varied in length in comparison to those of the other four major pectate lyase isozymes. Differences and similarities in polypeptide trace, size and volume of the active-site groove and surface electrostatics are discussed.
Gallium nitride (GaN) has been known for some time'. The first U.S. Government research funding began in 1970 with substantial increases in 1982 and again in 1993 and 1995. While the biggest initial commercial interest is in visible light emission, there will be substantial commercial and governmental use of ultra violet (UV) applications as well. It is, however, in the microwave and the millimeter wave spectrum where GaN will engender new systems enabling applications. It is here where anticipated hlly digital signal synthesis and beam steering technology will require broadband, linear, efficient amplifiers with moderate power levels; GaN currently appears to be the most promising candidate semiconductor for SUCR amplifiers.K-i for T = 300 -700 K and at a rate of+7.75 x K-' for T = 700 -900 K.' GaN
Recent advances in imaging and stereotactic techniques have resulted in wider application of interstitial brachytherapy (IBT) for brain tumors. The advantages of brachytherapy alone or in combination with teletherapy have been detailed, and may be responsible for increasing survival time. We report the preliminary results of 20 patients who underwent CT stereotactic IBT for malignant brain tumors. Despite both old and recent evidence about the effïcacy of IBT, concerns remain about the proper grade neoplasm, the target, the dose, and the timing for treatment. Current usage of IBT should be limited to centers with both stereotactic and radiotherapeutic expertise, and where the risks and benefïts are being investigated.
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