ABSTRACT
We report the characterization of a soft x-ray plasma source generated by a long-pulse XeCl excimer laser system. The output energy is 4 J at a wavelength of 308 nm in a 100-ns pulse. The intensity of radiation on target is estimated to be 4 × 1012 W cm-2. X-ray emission spectra of the plasma have been recorded using a double focusing spatial resolution spectrometer with a spherical mica crystal. From these measurements, the plasma temperature and electron density have been estimated. Various applications of such a plasma source have been investigated. First images of whole intact living cells from our system, imaged using the technique of soft x-ray contact microscopy, utilizing x rays in the "water window" region (280-530 eV), are shown. The suitability of the source for other applications, for example, x-ray lithography and radiation damage studies, to living cells are discussed. Possible improvements to the x-ray source for the various applications are proposed.
ABSTRACT
An investigation has been made on structure modifications of E. coli ribosomes following EDTA treatment. When completely deprived of magnesium, the small subunit sediments at 16S while the large one, in the same conditions, shows two components at 17S and 21S. Unfolding causes in both subunits an increase in radius of gyration without substantial change in molecular weight, as shown by light scattering measurements. The occurence of the slower 17S component besides the 21S one has to be connected with a fraction of the large subunit population which presents nucleolytic breaks in its RNA chain. These breaks do not cause fragmentation of the unfolded subunit but lead to a more open configuration sedimenting at lower velocity.
Subject(s)
Escherichia coli , Ribosomes , Edetic Acid/pharmacology , Magnesium , Molecular Conformation , Molecular Weight , RNA, Ribosomal , Ribosomes/drug effects , UltracentrifugationABSTRACT
The light scattering technique has been used to measure the molecular weight of Escherichia coli ribosomes. The 30S, 50S, and 70S components have been isolated and purified. The refractive index increment dn/dc was found to have the same value, (0.20 +/-0.01) cm(3)/g, for the three species. The molecular weights are (1.0 +/-0.1).10(6), (1.7 +/-0.1).10(6), and (2.9 +/-0.3).10(6) daltons respectively. Some information about the dimensions in solution (radius of gyration) and the interaction constant (second virial coefficient) have been obtained, and their significance is discussed.
Subject(s)
Light , Ribosomes , Buffers , Escherichia coli/cytology , Mathematics , Methods , Molecular Weight , Pancreas/enzymology , Proteins/analysis , RNA, Viral/analysis , Ribonucleases , Ribosomes/analysis , Scattering, Radiation , Sucrose , UltracentrifugationSubject(s)
Antibody Formation , Coliphages/immunology , Spleen/immunology , Amines , Animals , Biphenyl Compounds , Centrifugation, Density Gradient , Erythrocytes/immunology , Hemolysis , Immune Sera , Immunoglobulin G , Immunoglobulin M/biosynthesis , Injections, Intravenous , Mercaptoethanol/pharmacology , Rabbits , SheepABSTRACT
Phenotypic repair by streptomycin has been studied in amber mutants of phage T4 on su- strains, as has the interference of SmR mutations with amber suppressors. The repair seems not to be specific; however a temporal specificity of streptomycin action has been demonstrated by means of pulse experiments. The dependence of the efficiency of suppression upon experimental condition is also reported.
