Structures and mechanisms of tRNA methylation by METTL1-WDR4.

Specific, regulated modification of RNAs is important for proper gene expression1,2. tRNAs are rich with various chemical modifications that affect their stability and function3,4. 7-Methylguanosine (m7G) at tRNA position 46 is a conserved modification that modulates steady-state tRNA levels to affect cell growth5,6. The METTL1-WDR4 complex generates m7G46 in humans, and dysregulation of METTL1-WDR4 has been linked to brain malformation and multiple cancers7-22. Here we show how METTL1 and WDR4 cooperate to recognize RNA substrates and catalyse methylation. A crystal structure of METTL1-WDR4 and cryo-electron microscopy structures of METTL1-WDR4-tRNA show that the composite protein surface recognizes the tRNA elbow through shape complementarity. The cryo-electron microscopy structures of METTL1-WDR4-tRNA with S-adenosylmethionine or S-adenosylhomocysteine along with METTL1 crystal structures provide additional insights into the catalytic mechanism by revealing the active site in multiple states. The METTL1 N terminus couples cofactor binding with conformational changes in the tRNA, the catalytic loop and the WDR4 C terminus, acting as the switch to activate m7G methylation. Thus, our structural models explain how post-translational modifications of the METTL1 N terminus can regulate methylation. Together, our work elucidates the core and regulatory mechanisms underlying m7G modification by METTL1, providing the framework to understand its contribution to biology and disease.

On the genesis of the Earth's magnetism.

Few areas of geophysics are today progressing as rapidly as basic geomagnetism, which seeks to understand the origin of the Earth's magnetism. Data about the present geomagnetic field pours in from orbiting satellites, and supplements the ever growing body of information about the field in the remote past, derived from the magnetism of rocks. The first of the three parts of this review summarizes the available geomagnetic data and makes significant inferences about the large scale structure of the geomagnetic field at the surface of the Earth's electrically conducting fluid core, within which the field originates. In it, we recognize the first major obstacle to progress: because of the Earth's mantle, only the broad, slowly varying features of the magnetic field within the core can be directly observed. The second (and main) part of the review commences with the geodynamo hypothesis: the geomagnetic field is induced by core flow as a self-excited dynamo. Its electrodynamics define 'kinematic dynamo theory'. Key processes involving the motion of magnetic field lines, their diffusion through the conducting fluid, and their reconnection are described in detail. Four kinematic models are presented that are basic to a later section on successful dynamo experiments. The fluid dynamics of the core is considered next, the fluid being driven into motion by buoyancy created by the cooling of the Earth from its primordial state. The resulting flow is strongly affected by the rotation of the Earth and by the Lorentz force, which alters fluid motion by the interaction of the electric current and magnetic field. A section on 'magnetohydrodynamic (MHD) dynamo theory' is devoted to this rotating magnetoconvection. Theoretical treatment of the MHD responsible for geomagnetism culminates with numerical solutions of its governing equations. These simulations help overcome the first major obstacle to progress, but quickly meet the second: the dynamics of Earth's core are too complex, and operate across time and length scales too broad to be captured by any single laboratory experiment, or resolved on present-day computers. The geophysical relevance of the experiments and simulations is therefore called into question. Speculation about what may happen when computational power is eventually able to resolve core dynamics is given considerable attention. The final part of the review is a postscript to the earlier sections. It reflects on the problems that geodynamo theory will have to solve in the future, particularly those that core turbulence presents.

Identification of nonregulated pollutants in North Sea-produced water discharges.

Produced water collected from oil and gas platforms on the United Kingdom Continental Shelf was characterized for nonregulated pollutants through an effects-directed analysis procedure. Produced water samples were characterized for the presence of aryl hydrocarbon receptor (AhR) and estrogen receptor (ER) agonists using the dioxin-responsive, chemical-activated luciferase gene expression assay (DR-CALUX) and yeast estrogen screen (YES) bioassays. The AhR and ER agonists were then isolated by normal-phase, high-performance liquid chromatography and identified using gas chromatography coupled to mass spectrometry in a number of formats. The identified compounds were cross-referenced with those compounds routinely analyzed and regarded by the Oslo and Paris (OSPAR) Commission for the North East Atlantic as priority hazardous substances. The occurrence in produced water of a number of nonregulated compounds with demonstrable potential environmental effects is presented, to our knowledge for the first time. These include persistent organic contaminants, such as hexachlorobenzene, decachlorobiphenyl, and octachlorodibenzofuran.

Analysis, fate studies and monitoring of the antifungal agent clotrimazole in the aquatic environment.

The analysis and presence of clotrimazole, an antifungal agent with logK(OW) > 4, was thoroughly studied in the aquatic environment. For that reason analytical methods based on gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry were developed and validated to quantify clotrimazole with limits of quantification down to 5 and 1 ng/L, respectively. Both methods were compared in an intercalibration exercise. The complete mass-spectrometric fragmentation pattern could be elucidated with the aid of quadrupole time of flight mass spectrometry. Since clotrimazole tends to adsorb to laboratory glassware, studies on its adsorption behaviour were made to ensure the appropriate handling of water samples, e.g. pH, storage time, pretreatment of sampling vessels or material of the vials used for final extracts. The phenomena of adsorption to suspended matter were investigated while analysing different waste-water samples. Application of the methods in various investigated wastewater and surface water samples demonstrated that clotrimazole could only be detected in the low nanogram per litre range of anthropogenic influenced unfiltered water samples after acidification to pH 2.

Analysis of OSPAR priority pharmaceuticals using high-performance liquid chromatography-electrospray ionisation tandem mass spectrometry.

The occurrence and potential adverse effects of pharmaceutical compounds in the aquatic environment have received much scientific interest. Presented are analytical methodologies for the determination of 10 of the pharmaceuticals listed on the Oslo and Paris Commission for the protection of the Marine Environment of the North East Atlantic (OSPAR) hazardous substances website. In addition to these 10 substances, the chemical fluoxetine (Prozac) was also investigated. The performance characteristics of a combined solid phase extraction (SPE) isolation and high-performance liquid chromatography-electrospray ionisation tandem mass spectrometry (HPLC-ESI-MS/MS) procedure have been determined. Extraction efficiencies were obtained for a variety of SPE sorbents, following this initial investigation. Strata-X (Phenomenex, UK) was selected for further development. The extraction method performed satisfactorily for the majority of the 11 compounds analysed, with recoveries of over 60% for most of the compounds and relative standard deviations of between 4 and 13%. The recoveries of chloroquine and closantel were below 50% but the method provides semi-quantitative information regarding the occurrence of these compounds. Separation of the analytes was made using a C18 Luna analytical column (Phenomenex, UK) and mass spectra were obtained using an ion trap mass spectrometer operated in both positive and negative electrospray ionisation modes. Limits of detection for all compounds ranged from 1 to 20 ng/l, making the method suitable for low level environmental analysis. Of the selected surface water and treated sewage effluent samples (n = 6) analysed, chlorpromazine, fluoxetine and miconazole were detected in concentrations ranging from 7 to 34 ng/l. The chemicals determined using this procedure fall into a variety of pharmaceutical classes including antipsychotics and tranquilisers resulting in an analytical method that contains compounds from diverse chemical classes.

The occurrence of selected pharmaceuticals in wastewater effluent and surface waters of the lower Tyne catchment.

This paper presents the results of a survey of the wastewater effluent and surface waters of the lower river Tyne, UK. Samples were analysed by reversed-phase high-performance liquid chromatography-electrospray tandem mass spectrometry following solid phase extraction, for the presence of 13 pharmaceuticals selected from the priority lists of the UK Environment Agency and the Oslo and Paris Commission (OSPAR). The pharmaceutical compounds measured were acetyl-sulfamethoxazole, clofibric acid, clotrimazole, dextropropoxyphene, diclofenac, erythromycin, ibuprofen, mefenamic acid, paracetamol, propranolol, sulfamethoxazole, tamoxifen and trimethoprim. Of the wastewater treatment works (WTW) samples (n=9) analysed, all compounds except sulfamethoxazole and acetyl-sulfamethoxazole were detected at concentrations ranging from 11 to 69,570 ng l(-1) (in raw effluent). In the surface water samples (n=18), clotrimazole, dextropropoxyphene, erythromycin, ibuprofen, propranolol, tamoxifen and trimethoprim were detected at concentrations ranging from 4 to 2370 ng l(-1). Results of this study show that various pharmaceutical compounds are effectively reduced during their passage through a tertiary wastewater treatment works, whilst others are sufficiently persistent to occur in estuarine systems.