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- Buchan, K. L., et al.
(författare)
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Comparing the drift of Laurentia and baltica in the Proterozoic : the importance of key palaeomagnetic poles
- 2000
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Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 319:3, s. 167-198
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Tidskriftsartikel (refereegranskat)abstract
- Key palaeomagnetic poles are defined as those which pass basic reliability criteria and are precisely and accurately dated. They allow a more rigorous analysis of Precambrian continental drift and continental reconstructions than the traditional apparent polar wander path (APWP) approach using mostly non-key poles. Between ca. 2.45 and 2.00 Ga in the early Palaeoproterozoic, key poles define the drift of the Archaean Superior craton of Laurentia, yielding a result that is quite unlike the drift interpreted in earlier studies using the APWP method. There are no early Palaeoproterozoic key poles for the other Archaean cratons that amalgamated to form Laurentia and Baltica prior to 1.8 Ga, so that a rigorous test of early Palaeoproterozoic reconstruction models is not possible. Key poles from Laurentia between ca. 1.46 and 1.267 Ga and Baltica between 1.63 and 1.265 Ga help to define, in a preliminary fashion, the early Mesoproterozoic drift of the two shields. The key pole age match at ca. 1.265 Ga is consistent with Baltica located adjacent to eastern Greenland, and geological considerations suggest that the most reasonable fit aligns the Labradorian belt of Laurentia with the Gothian belt of Baltica. Although there is limited support from non-key poles and key poles that are not matched in age for such a fit as early as ca. 1.8 Ga, no rigorous assessment will be possible until a match in key pole ages is achieved. In the late Mesoproterozoic to Neoproterozoic, Laurentia's drift is reasonably well documented by seven key poles between 1.235 and 0.73 Ga. There are no key poles in this period from Baltica, however, so that a ≈90° clockwise rotation of Baltica relative to Laurentia between 1.265 and 1.0 Ga, widely used in the literature, cannot be confirmed.
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- Bylund, Göran O., et al.
(författare)
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Characterization of mutations in the metY-nusA-infB operon that suppress the slow growth of a DeltarimM mutant
- 2001
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Ingår i: Journal of Bacteriology. - : American Society for Microbiology. - 0021-9193 .- 1098-5530. ; 183:20, s. 6095-6106
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Tidskriftsartikel (refereegranskat)abstract
- The RimM protein in Escherichia coli is associated with free 30S ribosomal subunits but not with 70S ribosomes. A DeltarimM mutant shows a sevenfold-reduced growth rate and a reduced translational efficiency, probably as a result of aberrant assembly of the ribosomal 30S subunits. The slow growth and translational deficiency can be partially suppressed by increased synthesis of the ribosome binding factor RbfA. Here, we have identified 14 chromosomal suppressor mutations that increase the growth rate of a DeltarimM mutant by increasing the expression of rbfA. Nine of these mutations were in the nusA gene, which is located upstream from rbfA in the metY-nusA-infB operon; three mutations deleted the transcriptional terminator between infB and rbfA; one was an insertion of IS2 in infB, creating a new promoter for rbfA; and one was a duplication, placing a second copy of rbfA downstream from a promoter for the yhbM gene. Two of the nusA mutations were identical, while another mutation (nusA98) was identical to a previously isolated mutation, nusA11, shown to decrease termination of transcription. The different nusA mutations were found to increase the expression of rbfA by increasing the read-through of two internal transcriptional terminators located just downstream from the metY gene and that of the internal terminator preceding rbfA. Induced expression of the nusA(+) gene from a plasmid in a nusA(+) strain decreased the read-through of the two terminators just downstream from metY, demonstrating that one target for a previously proposed NusA-mediated feedback regulation of the metY-nusA-infB operon expression is these terminators. All of the nusA mutations produced temperature-sensitive phenotypes of rimM(+) strains. The nusA gene has previously been shown to be essential at 42 degrees C and below 32 degrees C. Here, we show that nusA is also essential at 37 degrees C.
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- Nilsson, S. L., et al.
(författare)
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Phosphate buffers in capillary electrophoresis/mass spectrometry using atmospheric pressure photo ionization and electrospray ionization
- 2003
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Ingår i: Rapid Communication in mass spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 17:20, s. 2267-2272
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Tidskriftsartikel (refereegranskat)abstract
- Capillary electrophoresis (CE) has been combined with atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) for mass spectrometric (MS) detection. Separation conditions using potassium phosphate buffer and ammonium formate buffer have been compared for analysis of eleven pharmaceutical bases. The results showed improvements in separation efficiency and peak symmetry when phosphate buffer was used. The low flow in CE may enable utilization of these advances with MS detection. Compared with ESI, the APPI technique provided a cluster-free background. The enhanced signal-to-noise ratio in the total ion current (TIC) and the reduced spectral background indicated that the APPI process is less affected by non-volatile salts in the CE buffers. This results in a wider range of choice of CE buffers in CE/MS analysis when APPI is the ionization method.
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