Evaporation effects as reflected in freshwaters and ostracod calcite from modern environments in Central and Northeast Yakutia (East Siberia,Russia)

Taxonomical and geochemical investigations on freshwater ostracods from 15 waters in Central and Northeast (NE) Yakutia have been undertaken in order to estimate their potential usefulness in palaeoenvironmental reconstructions based on regional fossil records. Higher variability in environmental factors such as pH, electrical conductivity, and ionic content was observed in thermokarst-affected lakes in Central Yakutia than in NE Yakutia lakes. Species diversity of freshwater ostracods reached up to eight taxa per lake, mostly dominated by Candona weltneri Hartwig 1899, in Central Yakutia, whereas in NE Yakutian waters the diversity was lower and Candona muelleri jakutica Pietrzeniuk 1977 or Fabaeformiscandona inaequivalvis (Sars 1898) had highest frequencies. Coupled analyses of stable isotopes (δ¹⁸O, δ¹³C) and element ratios (Sr/Ca, Mg/Ca) were performed on both host waters and ostracod calcite, aiming to estimate the modern relationships. Correlations between host waters and ostracod calcite of single species were found for δ¹⁸O, δ¹³C and Sr/Ca and Mg/Ca ratios. The relationships between δ¹⁸O, Mg/Ca and Sr/Ca ratios and electrical conductivity (salinity) as an expression of solute concentrations in the waters mainly controlled by evaporation are more complicated but evident, and may be useful in future interpretation of geochemical data from fossil Siberian ostracods. Handling editor: K. Martens     

AcrS/EnvR represses expression of the acrAB multidrug efflux genes in Escherichia coli

The acrS regulatory gene is located upstream of the acrEF multidrug efflux system genes. However, the roles of AcrS in regulation of drug efflux pumps have not been clearly understood. Here we show that AcrS represses other multidrug efflux genes, acrAB, which encode a major efflux system in Escherichia coli.     

SoxAX cytochromes, a new type of heme copper protein involved in bacterial energy generation from sulfur compounds

SoxAX cytochromes are essential for the function of the only confirmed pathway for bacterial thiosulfate oxidation, the so-called "Sox pathway," in which they catalyze the initial formation of a S-S bond between thiosulfate and the SoxYZ carrier protein. Our work using the Starkeya novella diheme SoxAX protein reveals for the first time that in addition to two active site heme groups, SoxAX contains a mononuclear Cu(II) center with a distorted tetragonal geometry and three to four nitrogen ligands, one of which is a histidine. The Cu(II) center enhanced SoxAX activity in a newly developed, glutathione-based assay system that mimics the natural reaction of SoxAX with SoxYZ. EPR spectroscopy confirmed that the SoxAX Cu(II) center is reduced by glutathione. At pH 7 a K(m) (app) of 0.19+/-0.028 mm and a k(cat) (app) of 5.7+/-0.25s(-1) were determined for glutathione. We propose that SoxAX cytochromes are a new type of heme-copper proteins, with SoxAX-mediated S-S bond formation involving both the copper and heme centers.     

SiPaGene: A new repository for instant online retrieval, sharing and meta-analyses of GeneChip® expression data

Background

Staphylothermus marinus is an anaerobic, sulfur-reducing peptide fermenter of the archaeal phylum Crenarchaeota. It is the third heterotrophic, obligate sulfur reducing crenarchaeote to be sequenced and provides an opportunity for comparative analysis of the three genomes.

Results

The 1.57 Mbp genome of the hyperthermophilic crenarchaeote Staphylothermus marinus has been completely sequenced. The main energy generating pathways likely involve 2-oxoacid:ferredoxin oxidoreductases and ADP-forming acetyl-CoA synthases. S. marinus possesses several enzymes not present in other crenarchaeotes including a sodium ion-translocating decarboxylase likely to be involved in amino acid degradation. S. marinus lacks sulfur-reducing enzymes present in the other two sulfur-reducing crenarchaeotes that have been sequenced – Thermofilum pendens and Hyperthermus butylicus. Instead it has three operons similar to the mbh and mbx operons of Pyrococcus furiosus, which may play a role in sulfur reduction and/or hydrogen production. The two marine organisms, S. marinus and H. butylicus, possess more sodium-dependent transporters than T. pendens and use symporters for potassium uptake while T. pendens uses an ATP-dependent potassium transporter. T. pendens has adapted to a nutrient-rich environment while H. butylicus is adapted to a nutrient-poor environment, and S. marinus lies between these two extremes.

Conclusion

The three heterotrophic sulfur-reducing crenarchaeotes have adapted to their habitats, terrestrial vs. marine, via their transporter content, and they have also adapted to environments with differing levels of nutrients. Despite the fact that they all use sulfur as an electron acceptor, they are likely to have different pathways for sulfur reduction.     

Protein-primed and de novo initiation of RNA synthesis by norovirus 3Dpol

Noroviruses (Caliciviridae) are RNA viruses with a single-stranded, positive-oriented polyadenylated genome. To date, little is known about the replication strategy of norovirus, a so-far noncultivable virus. We have examined the initiation of replication of the norovirus genome in vitro, using the active norovirus RNA-dependent RNA polymerase (3D(pol)), homopolymeric templates, and synthetic subgenomic or antisubgenomic RNA. Initiation of RNA synthesis on homopolymeric templates as well as replication of subgenomic polyadenylated RNA was strictly primer dependent. In this context and as observed for other enteric RNA viruses, i.e., poliovirus, a protein-primed initiation of RNA synthesis after elongation of the VPg by norovirus 3D(pol) was postulated. To address this question, norovirus VPg was expressed in Escherichia coli and purified. Incubation of VPg with norovirus 3D(pol) generated VPg-poly(U), which primed the replication of subgenomic polyadenylated RNA. In contrast, replication of antisubgenomic RNA was not primer dependent, nor did it depend on a leader sequence, as evidenced by deletion analysis of the 3' termini of subgenomic and antisubgenomic RNA. On nonpolyadenylated RNA, i.e., antisubgenomic RNA, norovirus 3D(pol) initiated RNA synthesis de novo and terminated RNA synthesis by a poly(C) stretch. Interestingly, on poly(C) RNA templates, norovirus 3D(pol) initiated RNA synthesis de novo in the presence of high concentrations of GTP. We propose a novel model for initiation of replication of the norovirus genome by 3D(pol), with a VPg-protein-primed initiation of replication of polyadenylated genomic RNA and a de novo initiation of replication of antigenomic RNA.     

Sexual dimorphism in esterified steroid levels in the gastropod Marisa cornuarietis: the effect of xenoandrogenic compounds

Molluscs can conjugate a variety of steroids to form fatty acid esters. In this work, the freshwater ramshorn snail Marisa cornuarietis was used to investigate sex differences in endogenous levels of esterified steroids. Testosterone and estradiol were mainly found in the esterified form in the digestive gland/gonad complex of M. cornuarietis, and males had higher levels of esterified steroids than females (4-10-fold). Additionally, the ability of several xenobiotics, namely tributyltin (TBT), methyltestosterone (MT) and fenarimol (FEN) to interfere with the esterification of testosterone and estradiol was investigated. All three compounds induced imposex - appearance of male sexual characteristics in females. Exposure to TBT led to a decrease in both esterified testosterone (60-85%) and estradiol (16-53%) in females after 100 days exposure, but had no effect on males. Exposure to FEN and MT did not alter levels of esterified steroids in males or in females, although exposed females developed imposex after 150 days exposure. The decrease in esterified steroids by TBT could not be directly linked with a decrease in microsomal acyl-CoA:testosterone acyltransferase (ATAT) activity, which catalyzes the esterification of steroids. In fact, ATAT activity was marginally induced in organisms exposed to TBT for 50 days (1.3-fold), and significantly induced in males and females exposed to MT for 50 days (1.8- and 1.5-fold, respectively), whereas no effect on ATAT activity was observed after 150 days exposure.     

Increased ethanol resistance and consumption in Eps8 knockout mice correlates with altered actin dynamics

Dynamic modulation of the actin cytoskeleton is critical for synaptic plasticity, abnormalities of which are thought to contribute to mental illness and addiction. Here we report that mice lacking Eps8, a regulator of actin dynamics, are resistant to some acute intoxicating effects of ethanol and show increased ethanol consumption. In the brain, the N-methyl-D-aspartate (NMDA) receptor is a major target of ethanol. We show that Eps8 is localized to postsynaptic structures and is part of the NMDA receptor complex. Moreover, in Eps8 null mice, NMDA receptor currents and their sensitivity to inhibition by ethanol are abnormal. In addition, Eps8 null neurons are resistant to the actin-remodeling activities of NMDA and ethanol. We propose that proper regulation of the actin cytoskeleton is a key determinant of cellular and behavioral responses to ethanol.     

Synthesis, biological evaluation and molecular modelling studies of novel ACD- and ABD-ring steroidomimetics as inhibitors of CYP17

Two novel classes of non-steroidal substrate mimetics were synthesised and examined for their potency as inhibitors of human CYP17. Selected compounds were tested for inhibition of hepatic CYP enzymes 3A4, 1A2, 2C9 and 2C19. The most promising compound 15 showed a good inhibition of the target enzyme (31% and 66% at 0.2 and 2 microM, respectively), and little inhibition of the most important hepatic enzyme CYP3A4 (6% and 19% inhibition at 0.2 and 2 microM, respectively) and the key enzyme of glucocorticoid biosynthesis CYP11B1 (3% and 23% inhibition at 0.2 and 2 microM, respectively). Docking studies revealed that this compound does not assume the same binding mode as steroidal ligands.