Dyes in History and Archaeology 41: Reflections on the Conference and Its Assembly of Articles

Editorial: no abstract availabl

Gene expression level influences amino acid usage, but not codon usage, in the tsetse fly endosymbiont Wigglesworthia

Author Posting. © Society for General Mircobiology, 2003. This article is posted here by permission of Society for General Mircobiology for personal use, not for redistribution. The definitive version was published in Microbiology 149 (2003): 2585-2596, doi:10.1099/mic.0.26381-0.Wigglesworthia glossinidia brevipalpis, the obligate bacterial endosymbiont of the tsetse fly Glossina brevipalpis, is characterized by extreme genome reduction and AT nucleotide composition bias. Here, multivariate statistical analyses are used to test the hypothesis that mutational bias and genetic drift shape synonymous codon usage and amino acid usage of Wigglesworthia. The results show that synonymous codon usage patterns vary little across the genome and do not distinguish genes of putative high and low expression levels, thus indicating a lack of translational selection. Extreme AT composition bias across the genome also drives relative amino acid usage, but predicted high-expression genes (ribosomal proteins and chaperonins) use GC-rich amino acids more frequently than do low-expression genes. The levels and configuration of amino acid differences between Wigglesworthia and Escherichia coli were compared to test the hypothesis that the relatively GC-rich amino acid profiles of high-expression genes reflect greater amino acid conservation at these loci. This hypothesis is supported by reduced levels of protein divergence at predicted high-expression Wigglesworthia genes and similar configurations of amino acid changes across expression categories. Combined, the results suggest that codon and amino acid usage in the Wigglesworthia genome reflect a strong AT mutational bias and elevated levels of genetic drift, consistent with expected effects of an endosymbiotic lifestyle and repeated population bottlenecks. However, these impacts of mutation and drift are apparently attenuated by selection on amino acid composition at high-expression genes.This work was made possible by support to J. J. W. from the NIH (R01 GM62626-01) and NSF (DEB 0089455), and the Josephine Bay Paul and C. Michael Paul Foundation

Preparation and topology of the Mediator middle module

Mediator is the central coactivor complex required for regulated transcription by RNA polymerase (Pol) II. Mediator consists of 25 subunits arranged in the head, middle, tail and kinase modules. Structural and functional studies of Mediator are limited by the availability of protocols for the preparation of recombinant modules. Here, we describe protocols for obtaining pure endogenous and recombinant complete Mediator middle module from Saccharomyces cerevisiae that consists of seven subunits: Med1, 4, 7, 9, 10, 21 and 31. Native mass spectrometry reveals that all subunits are present in equimolar stoichiometry. Ion-mobility mass spectrometry, limited proteolysis, light scattering and small-angle X-ray scattering all indicate a high degree of intrinsic flexibility and an elongated shape of the middle module. Protein–protein interaction assays combined with previously published data suggest that the Med7 and Med4 subunits serve as a binding platform to form the three heterodimeric subcomplexes, Med7N/21, Med7C/31 and Med4/9. The subunits, Med1 and Med10, which bridge to the Mediator tail module, bind to both Med7 and Med4

The neural effects of palytoxinThe neural effects of palytoxin

Palytoxin, the most potent known marine toxin, has been demonstrated to produce acute neurological disturbances in several animal species and, possibly, even in humans. However, the effects of palytoxin on excitable membranes have not been well characterised or explained. Palytoxin occurs within the same ecosystem in which other seafood toxins such as ciguatoxin, saxitoxin and brevetoxins are found. Also, several reports suggest that, occasionally, palytoxin may contribute to the ciguatera syndrome. As these other toxins are known to affect the sodium ion channel, either by activation or inactivation, evidence that palytoxin may also affect this structure was sought. The studies performed on the ventral coccygeal nerve of the rat tail, subsequent to an intraperitoneal injection of palytoxin, demonstrated a significant slowing of mixed nerve and motor conduction velocities and a reduction in the amplitude of the mixed nerve and motor action potentials. However, palytoxin exerted no effect on the latency of the shortest F-wave response. In the palytoxin-treated group, the absolute and relative refractory periods were prolonged. Palytoxin also appeared to induce a significant prolongation of the supernormal period of nerve excitability. The response of the palytoxin-treated ventral coccygeal nerve to repetitive stimulation demonstrated no consistent abnormality. These studies lend indirect support to the proposition that at least one action of palytoxin is that of an alteration in the excitability of neural tissue by inducing persistent sodium ion channel activation. Lignocaine, administered via the intraperitoneal route, was demonstrated to reverse many of the electrophysiological disturbances and, particularly, the prolonged supernormal period, in palytoxin-treated rats. These results suggest that prior activation of sodium ion channels by palytoxin may be blocked by lignocaine. Ethanol, administered via the intraperitoneal route, was observed to reverse many of the electrophysiological disturbances recorded in the palytoxin-treated rats, however, the supernormal period remained prolonged, yet not particularly enhanced or diminished in magnitude. Ouabain, administered via the intraperitoneal route, also reversed many of the electrophysiological disturbances induced in palytoxin-treated rats. However, in these animals, the palytoxin-induced supernormal period remained prolonged, yet not exaggerated or diminished in magnitude. These results suggest that membrane excitability may occur independently of, or with, the (Na+,K+)A TPase mechanism. The effect of palytoxin on mammalian nerve tissue appeared to be modified at a lower temperature. Mixed nerve and motor conduction, F-wave responses, absolute and relative refractory period and supernormal period studies were performed on palytoxin-treated animals at 25°C. The only significant abnormalities were a prolongation of the relative refractory period and of the supernormal period. This study suggests that, at least, in mammalian nerve tissue, this toxin is less active at a lower ambient temperature. In terms of central studies, in palytoxin-treated rats the brainstem auditory evoked response was not significantly altered although there was significant prolongation of the corticospinal evoked response. This finding suggests that palytoxin is capable of crossing the blood-brain barrier and, then, exerting an effect on central nerve membranes. These results are similar to those induced by ciguatoxin in the ventral coccygeal nerve of the rat. Both toxins produce slowing of the mixed nerve and motor conduction velocities, a reduction in the amplitude of the mixed nerve and motor action potentials and a prolongation of the refractory period and supernormal period. Lignocaine abolishes the supernormal period induced by both toxins. At a temperature of 25°C, both toxins produce reduced electrophysiological effects, in comparison with those produced at 37°C. Ciguatoxin is known to bind to and to activate or open sodium ion channels. These studies suggest that at least one action of palytoxin may be that of a similar activation of sodium ion channels. With reference to these studies and to the fact that both toxins occur within the same ecosystem, palytoxin could potentially contribute, on occasions, to the ciguatera syndrome

Woodpeckers of the world /

no.4 (1982

Characteristics of Particles in Pyrolysis Oil

Particles filtered out of pyrolysis oil produced through fast pyrolysis of stem wood, willow, reed canary grass, bark, and forest residue were characterized using scanning electron microscopy and energy-dispersive spectroscopy with the aim of identifying particle categories and discussing transport mechanisms of particles and inorganics into the oil. Particles filtered out of both the condensed and the aerosol fractions of the oil displayed three types of morphology: (i) char-like structures (1–15 μm), (ii) spheres (100 nm to 1 μm), and (iii) irregularly shaped residue (50–500 nm). The char-like structures were identified as char. The spheres and irregularly shaped residue shared morphology and composition with tar balls and organic particles with inorganic inclusions. These particles could have formed either during the fast pyrolysis stage or through precipitation from the oil during storage. All particles consisted mainly of C and O but also small amounts of inorganics. The particles from the aerosol fraction of the oil had higher inorganics content than the particles from the condensed fraction. The results were discussed, and suggested transport mechanisms of inorganics into particles were presented