Sites A2 Research Articles

The impact of municipal waste disposal of heavy metals on environmental pollution: A case study for Tonekabon, Iran

unicipal solid waste disposal is considered as one of the most important risks for environmental contamination which necessitates the development of strategies to reduce destructive consequences on the ecosystem as related especially to heavy metal accumulation. This study investigates heavy metal (i.e., As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Zn) accumulation in the Tonekabon region, NW of Iran that is related to city waste disposal and evaluates the environmental impact in the Caspian Sea coastal region. For this purpose, after performing field studies and collecting 50 soil specimens from 5 sites of the study area, geochemical tests (i.e., inductively coupled plasma mass spectrometry, atomic absorption spectroscopy and x-ray fluorescence) were conducted on the soil specimens collected from the 5 sites (named as Sites A1, A2, A3, A4 and A5) and the results were used to estimate the pollution indices (i.e., geo-accumulation index, normalized enrichment factor, contamination factor, and pollution load index). The obtained indices were utilized to assess the eco-toxicological risk level in the landfill site which indicated that the city has been severely contaminated by Cu, Mn, Ni, Pb and Zn. These levels have been developed along the stream towards the nearshore areas indicating uptake of soil degradation. The heavy metal contamination was classified to range from unpolluted to highly polluted, which indicated serious heavy metal pollution in the study area as related to municipal solid waste disposal in Tonekabon.

A specific oligosaccharide-binding site in the alternansucrase catalytic domain mediates alternan elongation

Microbial α-glucans produced by GH70 (glycoside hydrolase family 70) glucansucrases are gaining importance because of the mild conditions for their synthesis from sucrose, their biodegradability, and their current and anticipated applications that largely depend on their molar mass. Focusing on the alternansucrase (ASR) from Leuconostoc citreum NRRL B-1355, a well-known glucansucrase catalyzing the synthesis of both high- and low-molar-mass alternans, we searched for structural traits in ASR that could be involved in the control of alternan elongation. The resolution of five crystal structures of a truncated ASR version (ASRΔ2) in complex with different gluco-oligosaccharides pinpointed key residues in binding sites located in the A and V domains of ASR. Biochemical characterization of three single mutants and three double mutants targeting the sugar-binding pockets identified in domain V revealed an involvement of this domain in alternan binding and elongation. More strikingly, we found an oligosaccharide-binding site at the surface of domain A, distant from the catalytic site and not previously identified in other glucansucrases. We named this site surface-binding site (SBS) A1. Among the residues lining the SBS-A1 site, two (Gln700 and Tyr717) promoted alternan elongation. Their substitution to alanine decreased high-molar-mass alternan yield by a third, without significantly impacting enzyme stability or specificity. We propose that the SBS-A1 site is unique to alternansucrase and appears to be designed to bind alternating structures, acting as a mediator between the catalytic site and the sugar-binding pockets of domain V and contributing to a processive elongation of alternan chains.

Assessing impact of dams on genetic diversity of native fish Mastacembelus armatus in river Yamuna using mitochondrial DNA cytochrome-b sequences as a molecular marker

Several dams have been constructed in Uttarakhand. In the present study an investigation on impact of dams on genetic diversity of native fish species Mastacembelus armatus at the Asan barrage on river Yamuna near Vikasnagar, Uttarakhand in India was done. Partial sequence of mitochondrial Cytochrome-b (Cyto-b) gene was used to determine the genetic variation in the population of Mastacembelus armatus. DNA was extracted from Mastacembelus armatus (n=33) samples, collected from river Yamuna and its tributary Asan from fin and fishes were released back in their habitat. Cytochrome c oxidase I (COI) was used to ascertain the species of fish along with morphometric characters. Analysis of 324 bp mtDNA fragment of Cyto-b revealed the presence of 06 haplotypes with nucleotide diversity, value ranged from 0.0172 to 0.0021 low pair wise Fst value was observed negative (-0.00125) when compared between Asan barrage and Kalsi site. No genetic subdivisions between the population were found after or before the dam sites. Tajima’s D value for river Asan, site A1 Mirzapur (before dam) was -0.1167 (a negative value). Negative Tajima D value can be indicative of recent selective sweep or population expansion after a recent bottleneck and linkage to a swept gene. Our data shows that fragmentation of habitat by dams does not have any impact on the genetic diversity of non-migrating Mastacembelus armatus fish species.

Synergistic defects in pre-rRNA processing from mutations in the U3-specific protein Rrp9 and U3 snoRNA

U3 snoRNA and the associated Rrp9/U3-55K protein are essential for 18S rRNA production by the SSU-processome complex. U3 and Rrp9 are required for early pre-rRNA cleavages at sites A0, A1 and A2, but the mechanism remains unclear. Substitution of Arg 289 in Rrp9 to Ala (R289A) specifically reduced cleavage at sites A1 and A2. Surprisingly, R289 is located on the surface of the Rrp9 β-propeller structure opposite to U3 snoRNA. To understand this, we first characterized the protein-protein interaction network of Rrp9 within the SSU-processome. This identified a direct interaction between the Rrp9 β-propeller domain and Rrp36, the strength of which was reduced by the R289A substitution, implicating this interaction in the observed processing phenotype. The Rrp9 R289A mutation also showed strong synergistic negative interactions with mutations in U3 that destabilize the U3/pre-rRNA base-pair interactions or reduce the length of their linking segments. We propose that the Rrp9 β-propeller and U3/pre-rRNA binding cooperate in the structure or stability of the SSU-processome. Additionally, our analysis of U3 variants gave insights into the function of individual segments of the 5′-terminal 72-nt sequence of U3. We interpret these data in the light of recently reported SSU-processome structures.

A geographical information system based multi-criteria decision-making approach for location analysis and evaluation of urban photovoltaic charging station: A case study in Beijing

The integration of photovoltaic (PV) power generation system and electric vehicle (EV) charging station can effectively promote the local consumption of renewable energy and reduce the indirect carbon emissions of EV. This paper aims to provide a practical model for location decision of PV charging station (PVCS) which combines geographic information system (GIS) with multi-criteria decision making (MCDM) methods. To verify the feasibility and practicality, an empirical study was conducted in Beijing. First, seven suitable areas were selected preliminarily by suitability analysis of GIS. This stage focused on traffic flow and road distribution. Second, MCDM methods were used to further evaluation. At this stage, a comprehensive evaluation index system of natural, economic, technical and social criteria was established. Interval number, triangular fuzzy number and hesitant fuzzy linguistic term set were utilized to collect and describe evaluation information. Then, the subjective and objective weights of the criteria were calculated by best-worst method and mixed information entropy method, respectively. Finally, the TODIM (an acronym in Portuguese of interactive and MCDM) method was used to rank the alternatives. The ranking results illustrated that alternative sites A3 and A7 are outstanding. Moreover, dual sensitivity analysis and comparative analysis proved the stability and reliability of the model. Scenario analysis expanded the application scope of TODIM method, which also showed that it is necessary to express decision preferences by setting different recession coefficients. This study can provide support for the layout of PVCS in urban, and enrich the application fields of GIS and MCDM methods.

Hedonic shopping rent valuation by one-to-one neuromarketing and neutrosophic PROMETHEE method

One-to-one marketing emphasises personalised client fulfilment, explicitly as per personal interests. It is client-centred. The integration of quantitative and qualitative criteria can assess marketing value. Calculations relevant to marketing employ quantitative (objective, structured) and qualitative (subjective, unstructured) data. Regardless, globally, assessment of marketing value rarely includes criteria of the emotional and physiological states of potential buyers along with their valence and arousal and their affective attitudes. Upon evaluating these parameters, the implementation of the one-to-one marketing process would be more accurate and more effective. The purpose of this research was to determine the hedonic value by applying the Neutrosophic PROMETHEE Method used in one-to-one marketing including the data gathered during the VINERS Project on the emotional and physiological states, valence and arousal and affective attitudes of potential buyers. The hypothesis posed in this research is that the sales site rental price; customer satisfaction; indicators of economy, aesthetics and attractiveness; social and psychological data on customers and indicators of the purchasing process and emotional factors all interrelate with hedonic value. The hypothesis proposed during the time of research proved correct with the application of the neutrosophic PROMETHEE method. The results gained by this research permit asserting that seeking to increase the effectiveness of one-to-one marketing, it is necessary to analyse the emotional and physiological states, valence and arousal and the affective attitudes of potential buyers. The purpose of a case study was to determine the hedonic value of Sales Site a1 on Pilies St. 1 and Sales Site a2on Lukiškių Square during the Kaziuko Fair in Vilnius.

Preferred selenium incorporation and unexpected interlayer bonding in the layered structure of Sb2Te3− x Se x

Abstract We have performed a detailed structural analysis of several crystals from the Sb2Te3 − x Se x solid solution (with x = 0–1.55) using a combination of single-crystal and powder X-ray diffraction and high-resolution scanning transmission electron microscope imaging combined with energy-dispersive X-ray spectroscopic mapping. The experimental study was supported by quantum-chemical calculations. All compounds crystallize in the rhombohedral tetradymite structure type in which the atoms occupy three symmetrically independent crystallographic sites; the two chalcogenide sites A1 and A2, and the antimony site Sb. They form quintuple A2–Sb–A1–Sb–A2 layers perpendicular to the [001] direction, held together via A2–A2 chalcogenide-chalcogenide interactions. The results of our experimental study show unambiguously, and in agreement with quantum-chemical calculations, a preferred incorporation of selenium into the A2 position inside the layers. An unexpected increase of the van-der-Waals inter-layer distances is observed for low Se contents (x < 1) and discussed with the help of DFT calculations.

The system thorium-palladium-boron: A DFT study on the stability and properties of Th2Pd15B5

Phase relations in the Th-Pd-B system were determined via electron microprobe and X-ray powder diffraction analyses of ∼20 ternary alloys. Phase equilibria are dominated by the two high-melting thorium borides ThB4, Th1-yB6 and one ternary compound, namely τ1-Th2Pd14+xB5, with a structure deriving from the Sc4Ni29B10-type. Th1-yB6 is the binary starting point of a continuous solid solution up to ThPd0.53B4.28 closely corresponding to the superconducting phase Th1-yPdxB6-2x (x ≤ 0.65; 0 ≤ y ≤ 0.22 at x = 0; TC = 21 K), which was described by Zandbergen et al. in 1995 for x = 0.65 from high resolution electron microscopy. All thorium-rich palladium compounds from 0 to 75 at.% Pd form stable two-phase equilibria with ThB4 without any significant mutual solid solubilities. The solubility of Th in βB has been determined for the first time from a single crystal X-ray study of ThB99: Th atoms occupy sites A1 (occ. = 13%), D (occ. = 11%), and a rather small amount of 2.9% resides in site 18f (Dd-hole).To shed light on the physical properties of the ternary compound, DFT (density functional theory) calculations were performed for two idealized representatives of the τ1-phase, namely for Th2Pd14B5 and Th2Pd15B4. The calculations cover ionic relaxation, electron density of states, band structure and Fermi surfaces, elastic constants (computed via the linear response method) and the phonon density of states. Furthermore the thermodynamic stability (energy of formation) as well as the phonon contribution of the thermodynamic properties, such as the specific heat have been calculated clearly indicating Th2Pd15B4 as the composition thermodynamically more stable than Th2Pd14B5. At the Fermi energy the Pd-d contribution is dominant for both structures, but the number of states is higher for Th2Pd15B4 with DOS(EF) = 13 states/eV/f.u. than for Th2Pd14B5 with DOS(EF) = 8.5 states/eV/f.u. The corresponding Sommerfeld constants, γe = DOS(EF)kBπ2/3 = 30.55 mJ/molK2 for Th2Pd15B4 and 19.98 mJ/molK2 for Th2Pd14B5, clearly indicate metallic behavior of the τ1-phase. In addition, mechanical properties were measured for Th2Pd15B5 and compared with calculated values and data from the literature. Th2Pd15B5 on account of its high content of Pd is only slightly harder than the rather soft and almost ductile binary Pd-borides.

Structural and functional analysis of Utp24, an endonuclease for processing 18S ribosomal RNA.

The precursor ribosomal RNA is processed by multiple steps of nucleolytic cleavage to generate mature rRNAs. Utp24 is a PIN domain endonuclease in the early 90S precursor of small ribosomal subunit and is proposed to cleave at sites A1 and A2 of pre-rRNA. Here we determine the crystal structure of Utp24 from Schizosaccharomyces pombe at 2.1 angstrom resolution. Utp24 structurally resembles the ribosome assembly factor Utp23 and both contain a Zn-finger motif. Functional analysis in Saccharomyces cerevisiae shows that depletion of Utp24 disturbs the assembly of 90S and abolishes cleavage at sites A0, A1 and A2. The 90S assembled with inactivated Utp24 is arrested at a post-A0-cleavage state and contains enriched nuclear exosome for degradation of 5' ETS. Despite of high sequence conservation, Utp24 from other organisms is unable to form an active 90S in S. cerevisiae, suggesting that Utp24 needs to be precisely positioned in 90S. Our study provides biochemical and structural insight into the role of Utp24 in 90S assembly and activity.

Crystal structure and electronic properties of Sr-substituted barium disilicide Ba1-xSrxSi2 for solar cells: Computational and experimental studies

The effects of Sr substitution in BaSi2, a promising photoabsorber for thin-film solar cells, were examined computationally and experimentally. The calculations showed that Ba0.5Sr0.5Si2 with Sr atoms at the A1 site (A1-Sr-BSS) is more stable than that with Sr atoms at the A2 site (A2-Sr-BSS). Both materials are indirect bandgap semiconductors. The indirect and direct bandgaps of A1-Sr-BSS are larger than those of BaSi2, while those of A2-Sr-BSS are smaller. The indirect bandgap of A1-Sr-BSS is 0.01 eV higher than that of BaSi2, while that of A2-Sr-BSS is 0.06 eV lower. This trend is attributable to the difference in the electronic properties around the conduction band minimum, which is determined by the type of atoms (Ba or Sr) that occupy the A1 site. Single-crystal X-ray diffraction and diffuse reflectance measurements of Ba1-xSrxSi2 (0.0 ≤ x ≤ 0.8) revealed that the Ba atoms at the crystallographic site A1 are preferentially substituted by Sr atoms and that the bandgap, Eg, decreases with x (1.24 eV at x = 0 and 1.15 eV at x = 0.65). The preferential occupation of the A1 site by Sr atoms is consistent with the computational result that A1-Sr-BSS is more stable than A2-Sr-BSS. However, the experimentally observed decrease in Eg with x is closer to the decrease of −0.06 eV in the indirect bandgap of A2-Sr-BSS than to the 0.01 eV increase in the case of A1-Sr-BSS. The reason for this discrepancy is discussed.

Structural and functional analysis of ribosome assembly factor Efg1.

Ribosome biogenesis in eukaryotes is a complicated process that involves association and dissociation of numerous assembly factors and snoRNAs. The yeast small ribosomal subunit is first assembled into 90S pre-ribosomes in an ordered and dynamic manner. Efg1 is a protein with no recognizable domain that is associated with early 90S particles. Here, we determine the crystal structure of Efg1 from Chaetomium thermophilum at 3.3 Å resolution, revealing a novel elongated all-helical structure. Efg1 is not located in recently determined cryo-EM densities of 90S likely due to its low abundance in mature 90S. Genetic analysis in Saccharomyces cerevisiae shows that the functional core of Efg1 contains two helical hairpins composed of highly conserved residues. Depletion of Efg1 blocks 18S rRNA processing at sites A1 and A2, but not at site A0, and production of small ribosomal subunits. Efg1 is initially recruited by the 5′ domain of 18S rRNA. Its absence disturbs the assembly of the 5′ domain and inhibits release of U14 snoRNA from 90S. Our study shows that Efg1 is required for early assembly and reorganization of the 5′ domain of 18S rRNA.

The complete structure of the small-subunit processome.

The small-subunit processome represents the earliest stable precursor of the eukaryotic small ribosomal subunit. Here we present the cryo-EM structure of the Saccharomyces cerevisiae small-subunit processome at an overall resolution of 3.8 Å, which provides an essentially complete near-atomic model of this assembly. In this nucleolar superstructure, 51 ribosome-assembly factors and two RNAs encapsulate the 18S rRNA precursor and 15 ribosomal proteins in a state that precedes pre-rRNA cleavage at site A1. Extended flexible proteins are employed to connect distant sites in this particle. Molecular mimicry and steric hindrance, as well as protein- and RNA-mediated RNA remodeling, are used in a concerted fashion to prevent the premature formation of the central pseudoknot and its surrounding elements within the small ribosomal subunit.

The ribosome biogenesis factor yUtp23/hUTP23 coordinates key interactions in the yeast and human pre-40S particle and hUTP23 contains an essential PIN domain.

Two proteins with PIN endonuclease domains, yUtp24(Fcf1)/hUTP24 and yUtp23/hUTP23 are essential for early pre-ribosomal (r)RNA cleavages at sites A0, A1/1 and A2/2a in yeast and humans. The yUtp24/hUTP24 PIN endonuclease is proposed to cleave at sites A1/1 and A2/2a, but the enzyme cleaving at site A0 is not known. Yeast yUtp23 contains a degenerate, non-essential PIN domain and functions together with the snR30 snoRNA, while human hUTP23 is associated with U17, the human snR30 counterpart. Using in vivo RNA–protein crosslinking and gel shift experiments, we reveal that yUtp23/hUTP23 makes direct contacts with expansion sequence 6 (ES6) in the 18S rRNA sequence and that yUtp23 interacts with the 3΄ half of the snR30 snoRNA. Protein–protein interaction studies further demonstrated that yeast yUtp23 and human hUTP23 directly interact with the H/ACA snoRNP protein yNhp2/hNHP2, the RNA helicase yRok1/hROK1(DDX52), the ribosome biogenesis factor yRrp7/hRRP7 and yUtp24/hUTP24. yUtp23/hUTP23 could therefore be central to the coordinated integration and release of ES6 binding factors and likely plays a pivotal role in remodeling this pre-rRNA region in both yeast and humans. Finally, studies using RNAi-rescue systems in human cells revealed that intact PIN domain and Zinc finger motifs in human hUTP23 are essential for 18S rRNA maturation.

Assessment and Measurement of Atmospheric Pollution (Particulate Matter) Around Zawiya City-Libya

Total air suspended particulates (TSP) samples were collected over glass fiber filter and determined gravimetrically. The contents on the glass filter was digested in HF-HCl-HNO3 mixture and the trace elemental analysis of Al, Fe, Mn, and Pb were performed using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) technique, which offers many advantages such as low detection limits, wide linear calibration range and no matrix interference in addition to simultaneous multi-element determination. The filter with TSP was weighted, dissolved in HF-HCl-HNO3 acid mixture and the trace element such as Al, Fe, Mn and Pb were determined using (ICP-OES) technique. This work was carried out at four sites around Zawia city. Three sampling location were selected on sites of heavy traffics and industrial activities. These sites were (A1) at the center of Zawia city; (A2) near the power station and the refinery; (A3) nearby the main coastal road and (A4 control) at zone where there are no industrial activities or any obvious source of pollution. These samples were collected during Summer, Autumn, Spring, and Winter. The daily variation of TSP during this period showed the lowest value 70 µg/m3 in January (Winter), and the highest value 587.121 µg/m3. This value is relatively high compared with EU limit values (300 µg/m3), USEPA (150 µg/m3), and WHO (150-230 µg/ m3). The mean monthly variation of TSP showed the lowest measured result of 78.28 ± 0.08 µg/m3 in January and the highest value 306 µg/m3 in May. Seasonal variation of TSP showed high results during Spring season which is 239.44 µg/m3 and all other seasons showed lower values of 131.19 µg/m3, 198.28 µg/m3 and 159.85 µg/m3 for Winter, Autumn, and Summer, respectively compared with Spring season. The trace elements levels in TSP were Al>Fe>Pb>Mn. The concentration of Al, Fe, Mn and Pb are lower in site A4 and Al and higher in sites A3 and A2 due to heavy traffic and industrial activities. The meteorological parameters over the study area showed some factors such as wind speed, humidity and temperature that may affect TSP concentrations.

Biomonitoring of Mucheke and Shagashe Rivers in Masvingo, Zimbabwe Using Macro-Invertebrates as Indicators of Water Quality

The traditional way of assessing water quality of water bodies is through measurement of biological, physical and chemical parameters. However, such assessments only reflect the concentration of pollutants at the time of sampling not periodic pollution events. The goal of the study was to evaluate the river health using the macro-invertebrates that are found within the Mucheke and Shagashe rivers of Masvingo City as water quality monitors. The South African Scoring System (SASS 5) was used to score using the sensitivity of macro-invertebrates to levels of pollution in the two river systems. The data collection process was carried in April 2017 at four sampling sites using the kick sampling method and results validated by testing the physical, chemical and biological characteristics of the water and comparing them with the macro-invertebrates score. Results showed that the mean sensitivity score of macro-invertebrates showed variations depending on the selected site. Sample sites B2 and A2 downstream of the two river systems show high levels pollution tolerant macro-invertebrates as compared to sites A1 and B1 that are on the upper course and have more of pollution sensitive macro-invertebrates. On validation, to a large extent the levels of pollution indicated by macro-invertebrates were found to be congruent to the levels of pollution indicated by the physical, chemical and biological parameters. The research concludes that the presence of specific types of macro-invertebrates can be used to assess the levels of pollution in Mucheke and Shagashe rivers of Masvingo City.

Examination of factors dominating the sediment-water diffusion flux of DDT-related compounds measured by passive sampling in an urbanized estuarine bay

The fate of hydrophobic organic compounds in aquatic environment are largely determined by their exchange at sediment-water interface, which is highly dynamic and subject to rapidly evolving environmental conditions. In turn, environmental conditions may be governed by both physicochemical parameters and anthropogenic events. To examine the importance of various impact factors, passive sampling devices were deployed at the seafloor of Hailing Bay, an urbanized estuarine bay in Guangdong Province of South China to measure the sediment-water diffusion fluxes of several metabolites of dichlorodiphenyltrichloroethane (DDT), p,p′-DDE, p,p′-DDD and o,p′-DDD. The physicochemical properties of water (temperature, pH, salinity and dissolved oxygen) and surface sediment (sediment organic matter, physical composition, pH, water content, colony forming unit and catalase activity) were also measured. The results showed that the diffusion fluxes of o,p′-DDD, p,p′-DDD and p,p′-DDE at sites A1 and A2 near a fishing boat maintenance facility ranged from 0.42 to 4.73 ng m−2 d−1 (from sediment to overlying water), whereas those at offshore sites varied between −0.03 and −3.02 ng m−2 d−1 (from overlying water to sediment), implicating A1 and A2 as the sources of the target compounds. The distribution patterns of the diffusion fluxes of the target compounds were different from those of water and sediment parameters (water temperature, salinity, sediment texture, pH, colony forming unit and catalase activity) at six sampling sites. This finding suggested that none of these parameters were critical in dictating the sediment-water diffusion fluxes. Besides, decreases in the contents of kerogen and black carbon by 6.7% and 11% would enhance the diffusion fluxes of the target compounds by 11–14% and 12–23%, respectively, at site A1, indicating that kerogen and black carbon were the key factors in mediating the sediment–water diffusion fluxes of DDT-related compounds in field environments.

Role of the yeast ribosomal protein L16 in ribosome biogenesis.

Most ribosomal proteins play essential roles in ribosome synthesis and function. In this study, we have analysed the contribution of yeast ribosomal protein L16 to ribosome biogenesis. We show that in vivo depletion of the essential L16 protein results in a deficit in 60S subunits and the appearance of half-mer polysomes. This phenotype is likely due to the instability and rapid turnover of early and intermediate pre-60S particles, as evidenced by the reduced steady-state levels of 27SBS and 7SL /S pre-rRNA, and the low amounts of de novo synthesized 27S pre-rRNA and 25S rRNA. Additionally, depletion of L16 blocks nucleocytoplasmic export of pre-60S particles. Moreover, we show that L16 assembles in the nucleolus and binds to early 90S preribosomal particles. Many evolutionarily conserved ribosomal proteins possess extra eukaryote-specific amino- or carboxy-terminal extensions and/or internal loops. Here, we have also investigated the role of the eukaryote-specific carboxy-terminal extension of L16. Progressive truncation of this extension recapitulates, albeit to a lesser extent, the growth and ribosome biogenesis defects of the L16 depletion. We conclude that L16 assembly is a prerequisite to properly stabilize rRNA structures within early pre-60S particles, thereby favouring efficient 27S pre-rRNA processing within the internal transcribed spacer 1 at sites A3 and B1 . Upon depletion of L16, the lack of this stabilization aborts early pre-60S particle assembly and subjects these intermediates to turnover.

The PIN domain endonuclease Utp24 cleaves pre-ribosomal RNA at two coupled sites in yeast and humans

During ribosomal RNA (rRNA) maturation, cleavages at defined sites separate the mature rRNAs from spacer regions, but the identities of several enzymes required for 18S rRNA release remain unknown. PilT N-terminus (PIN) domain proteins are frequently endonucleases and the PIN domain protein Utp24 is essential for early cleavages at three pre-rRNA sites in yeast (A0, A1 and A2) and humans (A0, 1 and 2a). In yeast, A1 is cleaved prior to A2 and both cleavages require base-pairing by the U3 snoRNA to the central pseudoknot elements of the 18S rRNA. We found that yeast Utp24 UV-crosslinked in vivo to U3 and the pseudoknot, placing Utp24 close to cleavage at site A1. Yeast and human Utp24 proteins exhibited in vitro endonuclease activity on an RNA substrate containing yeast site A2. Moreover, an intact PIN domain in human UTP24 was required for accurate cleavages at sites 1 and 2a in vivo, whereas mutation of another potential site 2a endonuclease, RCL1, did not affect 18S production. We propose that Utp24 cleaves sites A1/1 and A2/2a in yeast and human cells.

The PIN domain endonuclease Utp24 cleaves pre-ribosomal RNA at two coupled sites in yeast and humans

During ribosomal RNA (rRNA) maturation, cleavages at defined sites separate the mature rRNAs from spacer regions, but the identities of several enzymes required for 18S rRNA release remain unknown. PilT N-terminus (PIN) domain proteins are frequently endonucleases and the PIN domain protein Utp24 is essential for early cleavages at three pre-rRNA sites in yeast (A0, A1 and A2) and humans (A0, 1 and 2a). In yeast, A1 is cleaved prior to A2 and both cleavages require base-pairing by the U3 snoRNA to the central pseudoknot elements of the 18S rRNA. We found that yeast Utp24 UV-crosslinked in vivo to U3 and the pseudoknot, placing Utp24 close to cleavage at site A1. Yeast and human Utp24 proteins exhibited in vitro endonuclease activity on an RNA substrate containing yeast site A2. Moreover, an intact PIN domain in human UTP24 was required for accurate cleavages at sites 1 and 2a in vivo, whereas mutation of another potential site 2a endonuclease, RCL1, did not affect 18S production. We propose that Utp24 cleaves sites A1/1 and A2/2a in yeast and human cells.

Spatial and seasonal distributions of soil sulfur in two marsh wetlands with different flooding frequencies of the Yellow River Delta, China

Soil samples from 0 to 100cm depth were collected in eight sampling sites (Sites A1, B1, C1 and D1; Sites A2, B2, C2 and D2) respectively along two 250-m length of sampling zones (Zone N and Zone S) from the Yellow River channel to a tidal creek in the short-term flooding and seasonal flooding wetland of the Yellow River Delta of China in fall of 2007 and spring of 2008 to investigate spatial and seasonal distribution patterns of total sulfur (TS) and their influencing factors. Our results showed that TS contents in both seasons in surface soil in Zone N increased with increasing distances away from the Yellow River channel except for Site D1 in fall. However, TS contents in both seasons in surface soil in Zone S showed a tendency of increasing and then decreasing with increasing distances away from the Yellow River channel. Relative to spring, the mean TS contents in surface soils were slightly higher in fall in Zone N, whereas an opposite tendency was observed in Zone S. The mean TS stocks were obviously higher in fall with 934.36g/m2 and 877.77g/m2 compared to those in spring with 729.85g/m2 and 696.78g/m2 in Zone N and Zone S, respectively. TS contents and stock generally declined with depth along soil profiles with one accumulation peaks at a soil increment of 40–60cm. Topsoil concentration factors also indicated that TS had shallower distribution in soil profiles. Soil total carbon (TC), total nitrogen (TN), soil organic matter (SOM), salinity and silt exerted positive loadings on TS, while soil pH and depth exhibited a negative correlation with TS content.