Quantitation of the common components of deoxyribonucleic acids by mass spectrometry: application to the analysis of DNAs of unusual composition

A mass spectral method for the quantitation of the percentages of deoxyadenosine, deoxyguanosine, deoxycytidine, and thymidine in intact DNAs has been devised. Standard curves for each nucleoside have been constructed which are based upon the observation that a direct correlation exists between the heights (% deflection) of diagnostic peaks from these nucleosides in a mass spectrum and the published percent composition of specific DNAs. Analyses of DNA from Clostridiumperfringens, Micrococcusluteus, Escherichiacoli, Bacillussubtilis, Pseudomonasfluorescens, Drosophilamelanogaster, salmon sperm, and bacteriophage lambda were used to determine standard curves. The validity of the method was demonstrated by comparison of the results from the mass spectral procedure with results from the chemical analyses of the DNAs from calf thymus and wheat germ. Analysis of ØX-174 DNA yielded values consistent with the published values obtained via sequence analysis and indicated that the method is applicable to both single and double-stranded DNAs. Results from T2 DNA, which contains no cytidine, exhibited artificially high values for adenosine, guanosine and thymidine with concomitant alteration in the A/T and G/C molar ratios. Such skewed results are useful in predicting the presence of modified nucleosides. The extreme sensitivity of the method has been exploited in the analysis of subnanogram quantities of restriction endonuclease fragments from DNA

A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator

International audienceThe European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created