Core C1 Research Articles

Looking for evidence of high-mass star formation at core scale in a massive molecular clump

Context. High-mass stars are formed as a result of the fragmentation of massive molecular clumps. However, what it is not clear is whether this fragmentation gives rise to stable prestellar cores massive enough to directly form high-mass stars or leads to prestellar cores of low masses that, by acquiring material from the environment, generate high-mass stars. Several recent observational studies focused on the characterisation of prestellar massive clump candidates. Nevertheless, studies of active massive clumps at different evolutionary stages are still needed to gain a complete understanding of how high-mass stars form. Aims. We present a comprehensive physical and chemical study of the fragmentation and star formation activity towards the massive clump AGAL G338.9188+0.5494, which harbours the extended green object EGO 338.92+0.55(b). The presence of an EGO embedded in a massive clump suggests that high-mass star formation is occurring at clump scale. The main goal of this work is to find evidence of such high-mass star formation, but at core scale. Methods. Using millimetre observations of continuum and molecular lines obtained from the Atacama Large Millimeter Array database at Bands 6 and 7, we study the substructure of the massive clump AGAL G338.9188+0.5494. The angular resolution of the data at Band 7 is about 0″.5, which allows us to resolve structures of about 0.01 pc (~2000 au) at the distance of 4.4 kpc. Results. The continuum emission at 340 GHz reveals that the molecular clump is fragmented into five cores, labelled C1 to C5. The 12CO J = 3−2 emission shows the presence of molecular outflows related to three of them. The molecular outflow related to core C1 is among the most massive (from 0.25 to 0.77 M⊙) and energetic (from 0.4 × 1046 to 1.2 × 1046 erg), considering studies carried out with similar observations towards this type of source. Rotational diagrams for the CH3CN and CH3CCH yield temperatures of about 340 and 72 K, respectively, for the core C1. The different temperatures show that the methyl cyanide would trace a gas layer closer to the protostar than the methyl acetylene, which would trace outermost layers. Using a range of temperatures going from 120 K (about the typical molecular desorption temperature in hot cores) to the temperature derived from CH3CN (about 340 K), the mass of core C1 ranges from 3 to 10 M⊙. The mid-IR 4.5 µm extended emission related to the EGO coincides in position and inclination with the discovered molecular outflow arising from core C1, which indicates that it should be the main source responsible for the 4.5 µm brightness. The average mass and energy of such a molecular outflow is about 0.5 M⊙ and 1046 erg, respectively, which suggest that 10 M⊙ is the most likely mass value for core C1. Additionally, we find that the region is chemically very rich with several complex molecular species. In particular, from an analysis of the CN emission, we find strong evidence that this radical is indirectly tracing the molecular outflows, or, more precisely, the border of the cavity walls carved out by such outflows, and therefore we point out that this is probably one of the first clear detection of CN as a tracer of molecular outflows in star-forming regions.

Diatoms from the cores containing Holocene deposits from the central part of the Volga Delta (Baraniy Bugor region)

In this article we present the study of fossil diatom assemblages in the two cores from the central part of the Volga Delta. In the core C1 from the right bank of the Bolda River diatoms were found in the dark-grey lithological layer consisting of silt. In this layer we distinguish two stages of sedimentation. The first stage corresponds to more stagnant water regime and is represented by prevailing Epithemia adnata (30,0 %) and Aulacoseira granulata (15,7%). These conditions are replaced by more riverine-like ones during the process of sedimentation. The structure of diatom assemblages of the riverine-like conditions is similar to the assemblages from the environments of shallow overgrowing distributary channels in the recent Volga Delta: A. granulata (72%), Stephanodiscus astraea var. intermedia и Aulacoseira italica (4,3 и 3,4% respectively). In the core BB9, taken from the left bank of the Bolda River, we studied the upper part of the sediments, which probably deposed in a bay (liman), and reconstruct low-flow conditions or environments of small rivers.

Assessment of the distribution and ecological risks of heavy metals in coastal sediments in Vietnam's Mong Cai area.

Coastal sediments in the Mong Cai area were collected and analyzed for grain size, heavy metals, total organic carbon, and isotopes (210Pb, 226Ra, δ15N, δ13C) to assess sediment quality. The most common sediments were fine sand in surface sediment, very fine sand in core C1, and very coarse and coarse silt in core C2. The total organic carbon was highest in C2 next to the surface and lowest in C1, with content levels of 1.81%, 0.40%, and 0.31%, respectively. The chronology in C1 was 1877-2019 (142years, 0-5 0cm), with an average sedimentation rate of 0.71cm/year. In C2, the chronology was 1944-2019 (75years, 0-14cm), with an average sedimentation rate of 0.27cm/year. These δ13C and δ15N in the sediment reflect the source of the organic matter mix from the marine and terrigenous sediments. All studied heavy metals were lower than the ISQGs, with the exception of As in C1 and C2, which were higher. C1 showed a decline in As over time, while C2 As levels increased between 1996 and 2019. In terms of heavy metal pollution indexes, the geoaccumulation index (Igeo) showed that C1 and C2 were unpolluted to moderately polluted with As, with Li and Pb in C2; the enrichment factor (EF) was moderately enriched with As; the contamination factor (CF) was moderately contaminated (Pb, Cd, Fe, Mo, and Li) in C2 and C1 (Cd, As, Li) and considerably contaminated (As) in C2. The risk factor (ER) of As showed a moderate potential ecological risk in C2. The degree of contamination (CD) ranged from moderate to considerable (C1, C2), and the ecological risk (RI) was low. Although CD ranged from moderate (C1) to considerable (C2), most contamination was concentrated at the bottom of the cores. RI was low. The Mong Cai sediment quality does not currently affect the coastal area's ecosystem and fauna.

Transformation of sulfur species in lake sediments at Ardley Island and Fildes Peninsula, King George Island, Antarctic Peninsula

In Antarctica, penguins transport sulfur and other bio-elements in the form of guano from marine to terrestrial environments where they become deposited in ornithogenic soils and sediments, including lake or pond systems. Transformation of sulfur species in these terrestrial and aquatic deposits, however, has rarely been studied. Here, we used the cold diffusion method to analyze various sulfur species in a lake deposit of ornithogenic sediment core (C1) and a pristine lake sediment core (C2), collected from Ardley Island and Fildes Peninsula, Antarctic Peninsula, respectively. The total organic carbon, total phosphorus, total nitrogen and various sulfur species in C1 were more fluctuant and much higher than those in C2, indicating a primary source from penguin guano. In core C1, organic sulfur (Org-S) was the main form of sulfur, and sulfate (SO42−) was the main form of inorganic sulfur. The acid volatile sulfur (AVS) in C1 was much higher than pyrite sulfur (CRS). In the pristine lake sediment core C2, Org-S and SO42− were the main sulfur species. CRS was the primary form of reduced inorganic sulfur in C2 sediments in contrast to the AVS in C1, indicating that AVS had been effectively transformed into CRS in C1. Our results demonstrate that the high levels of organic matter in C1 likely limited the transformation of AVS to CRS.

Content of nutrients, trace elements, and ecotoxicity of sediment cores from Ro\u017cn\xf3w reservoir (Southern Poland)

The aims of the study were to investigate the concentration of trace elements, nutrients, and ecotoxicity in bottom sediment cores collected from the silted part of the Rożnów reservoir (Southern Poland). Significant differences in the content of nutrients, trace elements, and ecotoxicity between five sediment cores were found. However, in the vertical distribution, there was no high variability of the above parameters, which means that the intensely suspended matter transported by the Dunajec river is and, at various times, has been homogeneous. Significant correlations between nutrients and trace elements (r = 0.33–0.91, at p ≤ 0.05) point to the same sources of the above-mentioned substances and similar levels of contamination in the sediment cores. However, the PCA results showed that cadmium and phosphorus in the sediment cores had different behaviors than other elements and can be associated mainly with anthropogenic sources. According to the degree of contamination factor, sediment cores fall under the category of considerable contamination of metals. Geochemical factors indicated that nickel, chromium, and cadmium (only sediment core C1) were found to be the cause of significant pollution in the sediment cores. Toxicity assessment found that most of the bottom sediment samples were classified as non-toxic or slightly toxic, only 10% of the sediment samples were toxic for Vibrio fischeri, and 6% of the samples were toxic for Sinapis alba. The two test organisms showed a different sensitivity, and higher toxic responses were recorded for V. fischeri than for S. alba. Cadmium and phosphorus were associated with toxicity for S. alba (r = 0.29–0.58, at p ≤ 0.05), whereas TOC, N, and S, and Ca for stimulation of growth this plants. Trace elements (r = 0.32–0.51, at p ≤ 0.05) and nutrients (S, K, Mg, Na, r = 0.44–0.58, at p ≤ 0.05) were positively correlated with inhibition of luminescence of V. fischeri. The studies of concentration and relation between trace elements, nutrients, and ecotoxicity are important in the ecological risk assessment and describing the quality of sediments with multiple sources contamination.

Heavy metal fractionation in core sediments and potential biological risk assessment from Chilika lagoon, Odisha state, India

The distribution and fractionation of heavy metals in the sediment cores from five locations and their impacts on ecological health of Chilika lagoon were investigated. The heavy metals Cu, Zn, Pb, Cd, Co, Ni, Mn and Fe were determined in the cores. In general the average concentration of heavy metals in different cores are found in the following order Fe > Mn > Cu > Pb > Zn > Ni > Co > Cd. The cores (C1, C3 and C5) collected near the major fishing villages and jetties have higher metal concentration when compared with cores collected from relatively pristine regions. Correlations between the trace metals and Organic Carbon (OC), Total Nitrogen (TN), Total Phosphorus (TP) and silty clay fraction, suggests that these elements and grain size play a role in controlling the abundance of heavy metals in the sediments. Metals like Pb, Cu, Zn are positively correlated to OC, TN and TP and grain size. Significant enrichment for Pb (EF = 5–20) and moderately significant enrichments for Cu (EF = 2–5) is observed in almost all the cores. Co and Ni are moderately enriched in cores C1 and C2. Extremely severe enrichment for Cd (EF > 40) is observed in core C1. Runoff from the agricultural fields, untreated sewage discharge and boat traffic are the major heavy metal sources. Roadway runoff, fuel discharge and atmospheric deposition are the dominant source of elevated Pb levels. The fractionation profiles of metals in different cores found them to be associated mostly with residual phase followed by Fe-Mn oxides and organic bound metals. Risk Assessment Code (RAC) reveals significant pollution by Mn in almost all the cores, whereas Pb, Cu and Zn are also present in bioavailable form to some extent in the sediments. In general, Fe-Mn oxides and organic bound metal fraction phases would contribute metals accumulation into the food-chain (i.e plant and fishery resources) consumed by the population create human health hazards.

Trace metal contamination by phosphogypsum discharge in surface and core sediments of the Gabes coast area (SE of Tunisia)

The purpose of the present study is to ascertain the extent of the effect that phosphate fertilizer industrial waste has on the surface and bottom sediments of the Ghannouch-Gabes coast, off the Tunisian Mediterranean Sea. To achieve this, 44 surface sediments and 3 core sediments were studied for mineralogy, trace metals (Cd, Cu, Pb, and Zn), F, CaO, and SO3. For all the analyzed elements, the spatial distribution in surface sediments showed that the area located between the commercial and the fishing port of Gabes is the most polluted zone. The ranking of metal contents was found to be Zn > Cd > Cu > Pb. The vertical distribution of trace metals indicated that the highest levels were found in the uppermost segment of the sediment cores compared to the lower depth subsurface due to a continuous input of phosphogypsum (PG) release and confirmed that the area between the two harbors suffered from several types of pollutants compared to reference core C1, collected from other non-industrialized areas. This spatial and vertical distribution is probably due to the harbor piers which acted as barriers and limited the dispersion of PG discharge. The contamination factor, the geoaccumulation index, and the pollution load index were determined. The results obtained confirm the anthropogenic impact on the levels of metal, on the fluorine, calcium, and sulfate concentrations in the area, located between the commercial harbor of Ghannouch and the fishing harbor of Gabes, whereas the concentrations of elements analyzed tends to decrease on both sides of this sector. Statistical analyses (principal component analysis) showed trace metals, fluoride, sulfate, and a large amount of calcium resulting from the same anthropogenic source.

Environmental assessment of a mangrove protected area in the southeast Gulf of Mexico through sediment core analysis

Three sediment cores were collected from different regions of the mangrove adjacent to Carmen Island, in Terminos Lagoon, to examine the influence that natural processes, the oil industry and urban development exert upon the mangrove environment. Textural and chemical characteristics were evaluated in each core. The variations among them reflect the different dynamic and depositional conditions for each site. Core C1, located near Puerto Real inlet, presents higher averages of grave l (16%), silt (32.6%), clay (1.48%), organic carbon (4.42%), carbonates (49.9%), CaO (28.96%), MgO (1.7%), P2O5 (0.99%) and Cu (4.46 mg/kg), some of these elements linked to the abundance of organisms in the area. Located in a channel with high sand content formed by an ancient delta, core C2 presents the highest average concentration of Al2O3 (4.39%), Fe2O3 (1.1%), MnO (0.02%), TiO2 (0.17%), Zn (14.8 mg/kg), Ni (16.9 mg/kg), Cr (293 mg/kg), V (12.3 mg/kg) and Cd (0.14 mg/kg), indicating high concentration of terrigenous sediments associated with heavy minerals. Situated in the lagoon border close to Carmen City, core C3 presents the highest sand (88.3%), SiO2 (64.5%), K2O (1.1%) and Pb (2.2 mg/kg) concentration. The location of this core makes it more susceptible to the dynamic processes that take place in the lagoon. The chemical differences observed in C2 are linked to the construction of Federal Highway 180. The drought that affected the basin during El Nino (1997–1998) produced a decrease in the rivers flow and a diminution of terrigenous sediments supply to Terminos Lagoon that is mainly observed in C3.

Ecological risk and contamination history of heavy metals in the Andong tidal flat, Hangzhou Bay, China

ABSTRACTIn this study, we collected two sediment cores (C1 and C2) from the Andong tidal flat, Hangzhou Bay, and studied the temporal variations of heavy metals in the cores. Vertical distributions of heavy metals were almost unchanged in both the cores before 2000. After 2000, however, the heavy metal concentrations increased dramatically, suggesting that the sediments have been affected by enhanced human pollution in the recent decade. In the core C1, the sediments were severely polluted by Pb, moderately to considerably polluted by Cr and Zn, and low to moderately polluted by other heavy metals. The core C2 was relatively unpolluted before 2000 and low to moderately polluted after 2000. Multi-statistical analyses indicated that the core C1 was additionally contaminated by local human activities such as wastewater discharge and the Hangzhou Bay Bridge. The heavy metals in the core C2, however, were largely contributed by the Yangtze River and controlled by sedimentation process. The calculated sedimentary flux (4–8 g m−2 a−1) of heavy metals generally increased with time. It was closely related to the wastewater discharge in adjacent areas. This study reconstructed the local heavy metal pollution history and provides important information for environmental protection and policy making.

Magnetic field geometry of the large globule CB 34

We report the results of optical polarimetric observations of a Bok globule CB34 to study magnetic field structure on large scales ($10^5-10^6$ AU), which is combined with archival sub-mm observations to characterize the magnetic field structure of CB34 on small scales ($10^4 - 10^5$ AU). The optical polarization measurements indicate that the magnetic field in the globule is constrained to a maximum radius of $10^5$AU around the core, out to densities not smaller than $10^4$cm$^{-3}$. Our study is mainly concentrated on two submillimeter cores C1 and C2 of CB34. The direction of magnetic field of core C2 is found to be nearly perpendicular to the CO outflow direction of the globule. The magnetic field of core C1 is almost aligned with the minor axis of the core which is typical for magnetically dominated star formation models. The mean value of offset between the minor axis of core C2 and the outflow direction is found to be $14^\circ$ which suggests that the direction of the outflow is almost aligned with the minor axis of core C2. The magnetic field strength in the plane-of-sky for cores C1 and C2 is estimated to be $\approx 34\mu$G and $\approx 70\mu$G.

Carotid plaque elasticity estimation using ultrasound elastography, MRI, and inverse FEA – A numerical feasibility study

The material properties of atherosclerotic plaques govern the biomechanical environment, which is associated with rupture-risk. We investigated the feasibility of noninvasively estimating carotid plaque component material properties through simulating ultrasound (US) elastography and in vivo magnetic resonance imaging (MRI), and solving the inverse problem with finite element analysis. 2D plaque models were derived from endarterectomy specimens of nine patients. Nonlinear neo-Hookean models (tissue elasticity C1) were assigned to fibrous intima, wall (i.e., media/adventitia), and lipid-rich necrotic core. Finite element analysis was used to simulate clinical cross-sectional US strain imaging. Computer-simulated, single-slice in vivo MR images were segmented by two MR readers. We investigated multiple scenarios for plaque model elasticity, and consistently found clear separations between estimated tissue elasticity values. The intima C1 (160 kPa scenario) was estimated as 125.8 ± 19.4 kPa (reader 1) and 128.9 ± 24.8 kPa (reader 2). The lipid-rich necrotic core C1 (5 kPa) was estimated as 5.6 ± 2.0 kPa (reader 1) and 8.5 ± 4.5 kPa (reader 2). A scenario with a stiffer wall yielded similar results, while realistic US strain noise and rotating the models had little influence, thus demonstrating robustness of the procedure. The promising findings of this computer-simulation study stimulate applying the proposed methodology in a clinical setting.

Historical levels of heavy metals reconstructed from sedimentary record in the Hejiang River, located in a typical mining region of Southern China

Historical levels of Pb, Zn, Cd, Cr, Cu, Ni, As, Fe, Al and Mn were found in C1 and C2 sediment cores from the Hejiang River, which is located in a typical mining region of Southern China, the levels date back approximately 57 and 83years. Temporal variations in the core C1 around the mining peaked in the 1960s, after which they exhibited a decreasing trend, which reflects successful government management. Historical events such as the Pacific War and China’s first 5-year economic plan were recorded in core C2, which was collected from the downstream portion of the Hejiang River. Enrichment factors (EF), geo-accumulation (Igeo), and excess flux indicate that severe contamination occurred during the period between 1956 and 1985 due to the release of high amounts of mining waste from human activities around the core C1 region. The highest EF value was displayed by As (67); this was followed by Pb (64), Cd (39), and Zn (35). In contrast, the core C2 sediments exhibited minor pollution because of dilution from tributaries (the Fu River and the Daning River) that do not flow through the mined area and because C2 was farther from the source of the metals. The results of the risk assessment codes (RAC) for both cores indicate that Cd posed a high risk to the local environment. Principal component analysis (PCA) and correlation analysis (CA) revealed that accumulation of heavy metals was mainly due to mining pollution.

High-Resolution Profiles of Dissolved Reactive Phosphorus in the Porewaters of Lake Sediments Assessed by DGT Technique

The technique of DGT (diffusive gradients in thin films) was applied to obtain high-resolution vertical profiles of dissolved reactive phosphorus (DRP) in sediment porewater of Lake Chaohu, a shallow eutrophication lake. Three kinds of DGT probes (with three thicknesses of diffusive gel: 0.38 mm, 0.78 mm and 1.18 mm) measured vertical concentration and induced flux from solid to solution phase which had intricate variations with depth. The results indicated that higher concentrations and induced fluxes of DRP were achieved by using DGT probe with thicker diffusion layer (CDGT1.18 > CDGT0.78 > CDGT0.38) and relatively stable DRP concentration profiles using DGT probes with 0.78 mm diffusive gel were obtained in each sediment core. The DRP concentrations displayed a clear gradient from Core C1 to Core C3 in sediment porewaters due to different sources and exchange degrees of reactive phosphorus. Compared to the concentrations obtained by the centrifugation technique, the concentrations of DRP resulting from the DGT technique were higher because some dissolved reactive phosphorus compounds have always been neglected using conventional centrifugation method.

EXPLORING THE CENTRAL SUB-PARSEC REGION OF THE γ-RAY BRIGHT RADIO GALAXY 3C 84 WITH VLBA AT 43 GHz IN THE PERIOD OF 2002-2008

Following the discovery of a new radio component right before the GeV γ-ray detection since 2008 August by the Fermi Gamma-ray Space Telescope, we present a detailed study of the kinematics and light curve on the central sub-parsec scale of 3C 84 using the archival Very Long Baseline Array 43 GHz data covering the period between 2002 January and 2008 November. We find that the new component C3, previously reported by the observations with the Very Long Baseline Interferometer Exploration of Radio Astrometry, was already formed in 2003. The flux density of C3 increases moderately until 2008, and then it becomes brighter rapidly after 2008. The radio core, C1, also shows a similar trend. The apparent speed of C3 with reference to the core C1 shows moderate acceleration from 0.10c to 0.47c between 2003 November and 2008 November, but is still sub-relativistic. We further try to fit the observed broadband spectrum by the one-zone synchrotron self-Compton model using the measured apparent speed of C3. The fit can reproduce the observed γ-ray emission, but does not agree with the observed radio spectral index between 22 and 43 GHz.

The Sedimentary Environment of Current Estuary and Abandoned Estuary at the Modern Yellow River Delta

Based upon statistics of sediment parameters and sediment moving modes from probability cumulative distribution curves, and combined with topography and hydrodynamics, the sedimentary environment at the intertidal flats of Qing 8 estuary (1996-now) and Diaokou estuary (1964-1976) at the Yellow River Delta was discussed in depth in present study. The results demonstrated that sediment grain size parameters can clearly reveal hydrodynamic condition of the sedimentary environment. Core C1 at current estuary was divided into four layers. The corresponding hydrodynamic conditions from top to bottom varied from strong to fluctuating between strong and weak, and finally to weak. Meanwhile, Core A1 at abandoned estuary can be divided into three layers and corresponding hydrodynamics from top to bottom changed from fairly strong to rather strong. Furthermore, the sedimentary facies of two cores were identified and they depended on water and sediment discharge from the Yellow River.

Antibody to C1 Domain of Factor VIII Alters Interaction of Factor Xase Complex with Factor X.

The role of the C1 domain in function of factor VIII has not been clearly defined. In contrast, functional interactions have been identified for the three A domains and the C2 domain. We hypothesized that the C1 domain of factor VIII participates in both phospholipid binding and interaction with factor X and/or factor IXa. We evaluated inhibition of the factor Xase complex by LE2E9, a human inhibitor IgG4k mAb against C1. We utilized altered catalytic activity of the factor Xase complex in a defined assay to report the inhibition by LE2E9. Inhibition by LE2E9 was also evaluated when soluble phosphatidylserine replaced vesicles to support the factor Xase complex and when Gla-domainless factor X was the substrate. The deglycosylated form of LE2E9 was also evaluated to better define the mechanism through which LE2E9 exerts its effect. We found that LE2E9 bound to factor VIIIa with an apparent KD of 0.5 nM. The apparent affinity of factor VIIIa for sonicated phospholipid vesicles of phosphatidylserine:phosphatidylethanolamine:phosphatidylcholine 4:20:76 increased 3-fold in the presence of LE2E9. The apparent affinity of factor VIIIa for factor IXa was not significantly changed. The KM of the factor VIIIa-factor IXa complex was 20 ± 2 nM with LE2E9 vs. 40 ± 2 nM without. LE2E9 decreased the Vmax by 77 ± 6% indicating that the affinity of factor X for the factor Xase complex is increased while the rate of cleavage is decreased. When Gla-domainless factor X was used as the substrate for the factor Xase complex, LE2E9 did not inhibit activity indicating that inhibition occurs via an interaction that involves the factor X Gla domain. When the factor VIIIa-factor IX complex was supported by dihexanoyl phosphatidylserine rather than phospholipid vesicles the inhibition of Vmax was 47% indicating that the inhibitory effect does not require a phospholipid bilayer. Deglycosylated LE2E9 did not significantly change the KM but decreased the Vmax by 22% while both antibodies bound to factor VIII with the same affinity. These results suggest that LE2E9 inhibition relates largely to interaction of a carbohydrate moiety with factor VIII or factor X rather than binding the core C1 epitope. We conclude that LE2E9 decreases the KM, and the Vmax for the factor VIIIa-factor IXa complex, but only when the factor X Gla domain is present. These results suggest that in the factor Xase complex the C1 domain of factor VIII is intimately associated with the Gla domain of factor X and that interaction between these domains enhances the kcat for the factor VIIIa-factor IXa complex.

Heterogeneous nuclear ribonucleoprotein particle A/B proteins and the control of alternative splicing of the mammalian heterogeneous nuclear ribonucleoprotein particle A1 pre-mRNA.

Mammalian pre-messenger RNAs (pre-mRNAs) interact with a distinct set of proteins to form heterogeneous nuclear ribonucleoprotein particles (hnRNPs). More than 25 different hnRNP proteins have been found associated with these complexes (Pinol-Roma et al. 1988; Dreyfuss et al. 1993). The core hnRNP proteins A1, A2, B1, B2, C1, and C2 are the most abundant species and are expressed in actively growing cells to levels that are comparable to core histones (Beyer et al. 1977; Kiledjian et al. 1994). Although several observations support the notion that core hnRNP proteins participate in pre-mRNA processing, the question of whether these proteins act in a sequence-independent or a sequence-specific manner is still a matter of debate (Abdul-Manan and Williams 1996; Abdul-Manan et al. 1996; McAfee et al. 1997). Early investigations have suggested that hnRNP proteins associate randomly with many different types of pre-mRNAs and ribopolymers to form particles sharing common structures and sedimentation properties (McKnight and Miller 1979; Lamb and Daneholt 1979; Pullman and Martin 1983; Thomas et al. 1983; Wilk et al. 1983). While the great abundance of core hnRNP proteins in the nucleus of growing cells (approximately 0.2 mM in a HeLa cell nucleus) can be taken as an argument in favor of generic RNA binding activity, it is unclear what fraction of this population of hnRNP proteins is free to interact with a nascent RNA sequence that exits the RNA polymerase II transcription complex. More recently, the use of antibodies recognizing individual hnRNP proteins has revealed that some hnRNP proteins can be deposited nonrandomly on nascent pre-mRNAs (Pinol-Roma et al. 1989; Matunis et al. 1993; Wurtz et al. 1996), suggesting that binding can be sequence-specific. Given the high abundance of hnRNP proteins and their ability to bind to many types of sequences with a range of affinities (Cobianchi et al. 1988; Conway et al. 1988; Pinol-Roma et al. 1988; LeStourgeon et al. 1990; Casas-Finet et al. 1993; Abdul-Manan and Williams 1996; Abdul-Manan et al. 1996), it has remained unclear to what extent the functions of core hnRNP proteins in nuclear RNA processing always depend on their ability to bind RNA in a sequence-specific manner.

Chloromethane: tetrahydrofolate methyl transfer by two proteins from Methylobacterium chloromethanicum strain CM4.

The cmuA and cmuB genes are required for growth of Methylobacterium chloromethanicum strain CM4 with chloromethane as the sole carbon source. While CmuB was previously shown to possess methylcobalamin:tetrahydrofolate methyltransferase activity, sequence analysis indicated that CmuA represented a novel and so far unique two-domain methyltransferase/corrinoid-binding protein involved in methyl transfer from chloromethane to a corrin moiety. CmuA was purified from wild-type M. chloromethanicum strain CM4 and characterized as a monomeric, cobalt-containing and zinc-containing enzyme of molecular mass 67 kDa with a bound vitamin B12 cofactor. In combination, CmuA and CmuB proteins catalyze the in vitro transfer of the methyl group of chloromethane to tetrahydrofolate, thus affording a direct link between chloromethane dehalogenation and core C1 metabolism of Methylobacterium. Chloromethane dehalogenase activity in vitro is limited by CmuB, as formation of methyltetrahydrofolate from chloromethane displays apparent Michaelis-Menten kinetics with respect to methylated CmuA, with an apparent Km of 0.27 microM and a Vmax of 0.45 U x mg(-1). This contrasts with sequence-related systems for methyl transfer from methanogens, which involve methyltransferase and corrinoid protein components in well-defined stoichiometric ratios.

The phytoliths in Core C1 from the Okinawa Trough

The phytoliths in Core C1 from the Okinawa Trough