Isotopic evidence for Mesoarchaean anoxia and changing atmospheric sulphur chemistry

The evolution of the Earth's atmosphere is marked by a transition from an early atmosphere with very low oxygen content to one with an oxygen content within a few per cent of the present atmospheric level. Placing time constraints on this transition is of interest because it identifies the time when oxidative weathering became efficient, when ocean chemistry was transformed by delivery of oxygen and sulphate, and when a large part of Earth's ecology changed from anaerobic to aerobic. The observation of non-mass-dependent sulphur isotope ratios in sedimentary rocks more than approximately 2.45 billion years (2.45 Gyr) old and the disappearance of this signal in younger sediments is taken as one of the strongest lines of evidence for the transition from an anoxic to an oxic atmosphere around 2.45 Gyr ago. Detailed examination of the sulphur isotope record before 2.45 Gyr ago also reveals early and late periods of large amplitude non-mass-dependent signals bracketing an intervening period when the signal was attenuated. Until recently, this record has been too sparse to allow interpretation, but collection of new data has prompted some workers to argue that the Mesoarchaean interval (3.2-2.8 Gyr ago) lacks a non-mass-dependent signal, and records the effects of earlier and possibly permanent oxygenation of the Earth's atmosphere. Here we focus on the Mesoarchaean interval, and demonstrate preservation of a non-mass-dependent signal that differs from that of preceding and following periods in the Archaean. Our findings point to the persistence of an anoxic early atmosphere, and identify variability within the isotope record that suggests changes in pre-2.45-Gyr-ago atmospheric pathways for non-mass-dependent chemistry and in the ultraviolet transparency of an evolving early atmosphere.     

Myofibrillar ATPase activities of red and white myotomal muscles of marine fish

Zusammenfassung Die Ca⁺⁺-und nicht-Ca⁺⁺-abhängige ATPase-Aktivität von isolierten Myofibrillen der roten und weissen Muskeln von drei Meerfischen wurde gemessen und festgestellt, dass die weissen Muskeln eine höhere Aktivität besitzen.

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I. A. Johnston was in receipt of a Science Research Council Research Studentship.

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This work was also supported by a Natural Environment Research Council grant to Dr.G. Goldspink.     

Histamine formation in rats bearing the walker mammary carcinosarcoma

Zusammenfassung Die Geschwindigkeit der Histaminbildung wurde bei Ratten von experimentellem Walker Carcinosarcom kontrolliert. Bei Parabiosen konnte gezeigt werden, dass der Faktor, welcher diese Histaminbildung auslöst, mit dem Blutstrom übertragen wird.

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This study was supported by U.S. Public Health Service grant No. 5RO1 HDOO255-06 to Prof.G. Kahlson, whose interest is gratefully acknowledged. Merck, Sharp and Dohme, Rahway, N.J., USA, kindly gave the -methylhistidine.     

Three-dimensional atomic-scale structure of size-selected gold nanoclusters

An unambiguous determination of the three-dimensional structure of nanoparticles is challenging. Electron tomography requires a series of images taken for many different specimen orientations. This approach is ideal for stable and stationary structures. But ultrasmall nanoparticles are intrinsically structurally unstable and may interact with the incident electron beam, constraining the electron beam density that can be used and the duration of the observation. Here we use aberration-corrected scanning transmission electron microscopy, coupled with simple imaging simulation, to determine with atomic resolution the size, three-dimensional shape, orientation and atomic arrangement of size-selected gold nanoclusters that are preformed in the gas phase and soft-landed on an amorphous carbon substrate. The structures of gold nanoclusters containing 3096 atoms can be identified with either Ino-decahedral, cuboctahedral or icosahedral geometries. Comparison with theoretical modelling of the system suggests that the structures are consistent with energetic considerations. The discovery that nanoscale gold particles function as active and selective catalysts for a variety of important chemical reactions has provoked much research interest in recent years. We believe that the detailed structure information we provide will help to unravel the role of these nanoclusters in size- and structure-specific catalytic reactions. We note that the technique will be of use in investigations of other supported ultrasmall metal cluster systems.     

Proteolytic turnover of the Gal4 transcription factor is not required for function in vivo

Transactivator-promoter complexes are essential intermediates in the activation of eukaryotic gene expression. Recent studies of these complexes have shown that some are quite dynamic in living cells owing to rapid and reversible disruption of activator-promoter complexes by molecular chaperones, or a slower, ubiquitin-proteasome-pathway-mediated turnover of DNA-bound activator. These mechanisms may act to ensure continued responsiveness of activators to signalling cascades by limiting the lifetime of the active protein-DNA complex. Furthermore, the potency of some activators is compromised by proteasome inhibition, leading to the suggestion that periodic clearance of activators from a promoter is essential for high-level expression. Here we describe a variant of the chromatin immunoprecipitation assay that has allowed direct observation of the kinetic stability of native Gal4-promoter complexes in yeast. Under non-inducing conditions, the complex is dynamic, but on induction the Gal4-promoter complexes 'lock in' and exhibit long half-lives. Inhibition of proteasome-mediated proteolysis had little or no effect on Gal4-mediated gene expression. These studies, combined with earlier data, show that the lifetimes of different transactivator-promoter complexes in vivo can vary widely and that proteasome-mediated turnover is not a general requirement for transactivator function.