bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ribosome recycling factor disassembles the post‐termination ribosomal complex independent of the ribosomal translocase activity of elongation factor G
Authors: Fujiwara Toshinobu , Ito Koichi , Yamami Tohru , Nakamura Yoshikazu 
Published: July 2004

SummaryRibosome recycling factor (RRF) disassembles post‐termination ribosomal complexes in concert with elongation factor EF‐G freeing the ribosome for a new round of polypeptide synthesis. How RRF interacts with EF‐G and disassembles post‐termination ribosomes is unknown. RRF is structurally similar to tRNA and is therefore thought to bind to the ribosomal A site and be translocated by EF‐G during ribosome disassembly as a mimic of tRNA. However, EF‐G variants that remain active in GTP hydrolysis but are defective in tRNA translocation fully activate RRF function in vivo and in vitro. Furthermore, RRF and the GTP form of EF‐G do not co‐occupy the terminating ribosome in vitro; RRF is ejected by EF‐G from the preformed complex. These findings suggest that RRF is not a functional mimic of tRNA and disassembles the post‐termination ribosomal complex independently of the translocation activity of EF‐G.
Yeast genome sequencing: the power of comparative genomics
Authors: Piškur Jure , Langkjær Rikke B. 
Published: July 2004

SummaryFor decades, unicellular yeasts have been general models to help understand the eukaryotic cell and also our own biology. Recently, over a dozen yeast genomes have been sequenced, providing the basis to resolve several complex biological questions. Analysis of the novel sequence data has shown that the minimum number of genes from each species that need to be compared to produce a reliable phylogeny is about 20. Yeast has also become an attractive model to study speciation in eukaryotes, especially to understand molecular mechanisms behind the establishment of reproductive isolation. Comparison of closely related species helps in gene annotation and to answer how many genes there really are within the genomes. Analysis of non‐coding regions among closely related species has provided an example of how to determine novel gene regulatory sequences, which were previously difficult to analyse because they are short and degenerate and occupy different positions. Comparative genomics helps to understand the origin of yeasts and points out crucial molecular events in yeast evolutionary history, such as whole‐genome duplication and horizontal gene transfer(s). In addition, the accumulating sequence data provide the background to use more yeast species in model studies, to combat pathogens and for efficient manipulation of industrial strains.
The SC15 protein of Schizophyllum commune mediates formation of aerial hyphae and attachment in the absence of the SC3 hydrophobin
Authors: Lugones L. G. , De Jong J. F. , De Vries O. M. H. , Jalving R. , Dijksterhuis J. , Wösten H. A. B. 
Published: July 2004

SummaryDisruption of the SC3 gene in the basidiomycete Schizophyllum commune affected not only formation of aerial hyphae but also attachment to hydrophobic surfaces. However, these processes were not completely abolished, indicating involvement of other molecules. We here show that the SC15 protein mediates formation of aerial hyphae and attachment in the absence of SC3. SC15 is a secreted protein of 191 aa with a hydrophilic N‐terminal half and a highly hydrophobic C‐terminal half. It is not a hydrophobin as it lacks the eight conserved cysteine residues found in these proteins. Besides being secreted into the medium, SC15 was localized in the cell wall and the mucilage that binds aerial hyphae together. In a strain in which the SC15 gene was deleted (ΔSC15) formation of aerial hyphae and attachment were not affected. However, these processes were almost completely abolished when the SC15 gene was deleted in the ΔSC3 background. The absence of aerial hyphae in the ΔSC3ΔSC15 strain can be explained by the inability of the strain to lower the water surface tension and to make aerial hyphae hydrophobic.
Light‐to‐dark transitions trigger a transient increase in intracellular Ca2+ modulated by the redox state of the photosynthetic electron transport chain in the cyanobacterium Anabaena sp. PCC7120
Authors: TORRECILLA I. , LEGANÉS F. , BONILLA I. , FERNÁNDEZ‐PIÑAS F. 
Published: July 2004

ABSTRACTLight‐to‐dark transitions represent one of the most crucial environmental stresses that photosynthetic organisms must cope with, since substantial metabolism adaptations are required in order to utilize alternative energy and carbon sources. Although signal transduction systems for changing light regimes are not sufficiently understood, calcium has been implicated in plants as a second messenger in light‐on and light‐off events. Much less is known about light signalling in cyanobacteria, but it has been shown that calcium probably performs similar signalling roles in these organisms and other prokaryotes. Herein it is reported that light‐to‐dark transitions trigger a calcium transient in aequorin expressing Anabaena sp. PCC7120. The magnitude of this transient depends on the fluence rate previously irradiated and can reach a peak height over 2 µm free calcium when the fluence rate of light is around 400 µmol photons s−1 m−2. The use of increasing calcium concentration, ethylene glycol‐bis (β‐aminoethylether) N,N,N′,N′‐tetraacetic acid (EGTA), verapamil and trifluoperazine indicated that these transients are originated by a calcium influx probably through verapamil‐sensitive Ca2+ channels and are probably modulated by calcium‐binding proteins. Experiments with different light spectral qualities and the photosynthetic inhibitors 3‐(3,4 dichlorophenyl)1,1,dimelthylurea (DCMU) and 3,5‐dibromo‐3‐methyl‐b‐isopropyl‐p‐benzoquinone (DBMIB) indicate that the calcium transient triggered by the light‐to‐dark transition is not coupled to a specific photoreceptor but rather to changes in the redox state of photosynthetic electron transport chain components other than the plastoquinone pool.
Diurnal depression of leaf hydraulic conductance in a tropical tree species
Authors: BRODRIBB T. J. , HOLBROOK N. M. 
Published: July 2004

ABSTRACTDiurnal patterns of hydraulic conductance of the leaf lamina (Kleaf) were monitored in a field‐grown tropical tree species in an attempt to ascertain whether the dynamics of stomatal conductance (gs) and CO2 uptake (Aleaf) were associated with short‐term changes in Kleaf. On days of high evaporative demand mid‐day depression of Kleaf to between 40 and 50% of pre‐dawn values was followed by a rapid recovery after 1500 h. Leaf water potential during the recovery stage was less than −1 MPa implying a refilling mechanism, or that loss of Kleaf was not linked to cavitation. Laboratory measurement of the response of Kleaf to Ψleaf confirmed that leaves in the field were operating at water potentials within the depressed region of the leaf ‘vulnerability curve’. Diurnal courses of Kleaf and Ψleaf predicted from measured transpiration, xylem water potential and the Kleaf vulnerability function, yielded good agreement with observed trends in both leaf parameters. Close correlation between depression of Kleaf, gs and Aleaf suggests that xylem dysfunction in the leaf may lead to mid‐day depression of gas exchange in this species.
Reversible decreases in the bulk elastic modulus of mature leaves of deciduousQuercusspecies subjected to two drought treatments
Authors: SAITO T. , TERASHIMA I. 
Published: July 2004

ABSTRACTChanges in leaf water relations under water stress were examined. In experiment 1, water stress was imposed by withholding irrigation to potted seedlings of deciduous oak,Quercus crispulaandQ. serrata. Changes in the pressure–volume (P–V) curve in mature leaves were followed. The leaf water potential at turgor loss (Ψl,tlp) significantly decreased after 13 d of drought treatment. The bulk elastic modulus (ɛ) significantly decreased, which contributed to the maintenance of cell turgor together with the decrease in osmotic potential. In experiment 2, water stress was imposed by notching a branch of aQ. serratatree. After the notching, the daily minimum leaf water potential (Ψl) decreased, and a significant decrease in Ψl,tlpwas observed 15 d after notching. The osmotic potential at water saturation (Ψπ,sat) did not decrease significantly until 25 d after notching whereas,ɛhad already decreased significantly within 15 d after notching and increased promptly after substantial precipitation. It was confirmed thatɛof mature leaves decreased reversibly in water stress. This response ofɛwas more rapid than that of the osmotic potential and, thus, effectively maintained cell turgor when water stress was suddenly imposed on the leaves.
Constitutive and induced resistance to pathogens in Arabidopsis thaliana depends on nitrogen supply
Authors: DIETRICH R. , PLOß K. , HEIL M. 
Published: July 2004

ABSTRACTKnowledge about the induced pathogen resistance of plants is rapidly increasing, but little information exists on its dependence on abiotic growing conditions. Arabidopsis thaliana plants that had been cultivated under different nitrogen regimes were treated with BION®, a chemical resistance elicitor. The activities of three enzyme classes functionally involved in resistance (chitinase, chitosanase and peroxidase) were quantified over 8 d following treatment as resistance markers. Constitutive levels of three markers and the induced level of peroxidase and chitinase activity were significantly lower under limiting nitrogen supply. Under such conditions the increase of chitosanase activity after resistance induction was severely delayed, although the induced maximum activity of chitosanase was not significantly affected. Total soluble protein content decreased during the first 12 h after resistance elicitation. Thereafter, the induced plants cultivated under high N conditions reached higher protein contents than controls, whereas N‐limited induced plants continuously had reduced protein contents. A plant's investment in resistance‐related compounds can be severely constrained under limiting nitrogen supply.
Facies and basin architecture of the Late Carboniferous Salvan‐Dorénaz continental basin (Western Alps, Switzerland/France)
Authors: Capuzzo Nicola , Wetzel Andreas 
Published: July 2004

AbstractThe Salvan‐Dorénaz Basin formed during the Late Palaeozoic within the Aiguilles‐Rouges crystalline basement (Western Alps) as an asymmetric, intramontane graben elongated in a NE–SW direction and bounded by active faults. At least 1700 m of fluvial, alluvial fan and volcanic deposits provide evidence for a strong tectonic influence on deposition with long‐term, average subsidence rates of > 0·2 mm yr−1. The early basin fill was associated with coarse‐grained alluvial fans that were dominated by braided channels (unit I). These issued from the south‐western margin of the basin. The fans then retreated to a marginal position and were overlain by muddy floodplain deposits of an anastomosed fluvial system (unit II) that drained towards the NE. Deposition of thick muds resulted from a reduction in the axial fluvial gradient caused by accelerated tectonic subsidence. Overlying sand‐rich meandering river deposits (unit III) document a reversal in the drainage direction from the NE to the SW caused by synsedimentary tectonism, reflecting large‐scale topographic reorganization in this part of the Variscides with subsidence now preferentially in the W and SW and uplift in the E and NE. Coarse‐grained alluvial fan deposits (unit IV) repeatedly prograded into, and retreated from, the basin as documented by coarsening‐upward cycles tens of metres thick reflecting smaller scale tectonic cycles. Volcanism was active throughout the evolution of the basin, and U/Pb isotopic dating of the volcanic deposits restricts the time of basin development to the Late Carboniferous (308–295 Ma).40Ar/39Ar ages of detrital white mica indicate rapid tectonic movements and exhumation of the nearby basement. In unit I, youngest ages are close to that of the host sediment, but the age spectrum is wide. In unit II, high subsidence and/or sedimentation rates coincide with very narrow age spectra, indicating small, homogeneous catchment areas. In unit III, age spectra became wider again and indicate growing catchment areas.
Stratigraphic evolution of an aeolian erg margin system: the Permian Cedar Mesa Sandstone, SE Utah, USA
Authors: Mountney Nigel P. , Jagger Alison 
Published: July 2004

AbstractThe Permian Cedar Mesa Sandstone of south‐east Utah is a predominantly aeolian succession that exhibits a complex spatial variation in sedimentary architecture which, in terms of palaeogeographic setting, reflects a transition from a dry erg centre, through a water table‐controlled aeolian‐dominated erg margin, to an outer erg margin subject to periodic fluvial incursion. The erg margin succession represents a wet aeolian system, accumulation of which was controlled by progressive water table rise coupled with ongoing dune migration and associated changes in the supply and availability of sediment for aeolian transport. Variation in the level of the water table relative to the depositional surface determined the nature of interdune sedimentary processes, and a range of dry, damp and wet (flooded) interdune elements is recognized. Variations in the geometry of these units reflect the original morphology and the migratory behaviour of spatially isolated dry interdune hollows in the erg centre, locally interconnected damp and/or wet interdune ponds in the aeolian‐dominated erg margin and fully interconnected, fluvially flooded interdune corridors in the outer erg margin. Relationships between aeolian dune and interdune units indicate that dry, damp and wet interdune sedimentation occurred synchronously with aeolian bedform migration. Temporal variation in the rates of water‐table rise and bedform migration determined the angle of climb of the erg margin succession, such that accumulation rates increased during periods of rapidly rising water table, whereas sediment bypassing (zero angle of climb) occurred in the aftermath of flood events in response to periods of elevated but temporarily static water table. During these periods in the outer erg margin, the expansion of fluvially flooded interdunes in front of non‐climbing but migrating dunes resulted in the amalgamation of laterally adjacent interdunes and the generation of regionally extensive bypass (flood) supersurfaces. A spectrum of genetic depositional models is envisaged that accounts for the complex spatial and temporal evolution of the Cedar Mesa erg margin succession.
Depositional controls on Palaeoproterozoic iron formation accumulation, Gogebic Range, Lake Superior region, USA
Authors: Pufahl Peir K. , Fralick Philip W. 
Published: July 2004

AbstractShallowing‐upward, decametre‐scale, Palaeoproterozoic iron formation cycles in northern Wisconsin record the combined effects of tectonism and changing oceanographic conditions on a storm‐dominated shelf. Cycles consist of a lower unit of laminated, Fe‐ and Si‐rich chemical mudstone that is transitional into an upper unit dominated by trough cross‐stratified chert grainstone. Grainstone lenses become progressively thicker upwards in cycles with the largest at cycle tops, where they are sharply overlain by a unit of slumped chemical mudstone. The cycles developed through progradation when offshore‐directed storm currents transported chert sand intraclasts that were formed in nearshore settings into middle and distal shelf environments. Abrupt subsidence events, probably resulting from normal faulting associated with extensional tectonism, repeatedly terminated chert grainstone accumulation and may also have generated the slumped units at cycle boundaries. The episodic storm currents are also interpreted to have transported biologically oxygenated waters from the shallow‐water, inner shelf into otherwise anoxic bottom waters of the strongly stratified distal shelf. The consequence of such transport and mixing was rapid deposition of chemical mud, mainly as precipitated Fe‐oxide. In many cases, the resultant decrease in Fe2+ in the water column, together with pelagic inorganic precipitation of SiO2 and rainout of terrigenous clays, resulted in submillimetre‐ to millimetre‐thick, chemically graded laminae. The concomitant decreasing Fe2+/Mn2+ ratio also led to increasing Mn‐compound precipitation and enrichment in the upper portions of some chemically graded layers.
Differentiating the effect of episodic tectonism and eustatic sea‐level fluctuations in foreland basins filled by alluvial fans and axial deltaic systems: insights from a three‐dimensional stratigraphic forward model
Authors: Clevis Quintijn , De Boer Poppe L. , Nijman Wouter 
Published: July 2004

AbstractMany studies of foreland basins have recognized a hierarchical organization in the stacking of sequences deposited by axial‐deltaic and alluvial fan systems. The hierarchy is often explained in terms of the competing control of eustasy and pulsed tectonic subsidence and the different frequencies at which these processes operate. Unravelling the relative contributions of tectonic and eustatic controls on the sequence stacking pattern is a fundamental question in foreland basin analysis, yet this is difficult because of the lack of independent stratigraphic evidence. In this study, a three‐dimensional numerical model is presented, which aids in the interpretation of alluvial successions in foreland basins filled by transverse and axial depositional systems, under conditions of variable tectonism and eustatic sea‐level change. The tectono‐sedimentary model is capable of simulating the hierarchical stratigraphic response to both eustatic and tectonic forcing, and is of higher resolution than previous models of foreland basin filling. Numerical results indicate that the onset of tectonic activity is reflected by rapid retrogradation of both depositional systems and by widespread flooding and onlap of carbonate sediments. Syntectonic fluvial patterns on the axial‐deltaic plain are dominated by bifurcating channels, swiftly relocating in response to the general rise in relative sea level induced by flexural subsidence. The resulting surface morphology of the axial delta is convex upwards. Syntectonic eustatic sea‐level fluctuations result in parasequence‐scale packages of retrograding and prograding fan and delta sediments bounded by minor flooding surfaces and type 2 sequence boundaries. Incised channels are rare within the syntectonic parasequences and are formed only during phases of tectonic quiescence when eustatic falls are no longer compensated by the subsidence component in the rise in relative sea level. Suites of amalgamating, axial channels corresponding to multiple eustatic falls delineate the resulting type 1 unconformities. Coarse‐grained, incised‐channel fills are found in the zone between the alluvial fan fringes and the convex‐upward body of the axial delta, as the axial streams tend to migrate towards this zone of maximum accommodation.
Shallow slides and pockmark swarms in the Eivissa Channel, western Mediterranean Sea
Authors: Lastras G. , Canals M. , Urgeles R. , Hughes‐Clarke J. E. , Acosta J. 
Published: July 2004

AbstractFour slides, the Ana, Joan, Nuna and Jersi slides, have been imaged on the seafloor along the Balearic margin of the Eivissa Channel in the western Mediterranean. They have areas of up to 16 km2 and occur in water depths ranging between 600 and 900 m. Volumes range from 0·14 to 0·4 km3. Their headwall scarps, internal architecture and associated deposits are characterized using a combination of swath bathymetry data and very high‐resolution seismic reflection profiles. In general, they show horseshoe‐shaped headwall scarps and distinct depositional lobes with positive relief. Internally, the slide bodies are mostly composed of transparent seismic facies. Chaotic facies are observed at the toe of some of the slides, and blocks of coherent stratified facies embedded in the slide deposit have also been identified. The reflection profiles demonstrate that the four slides share the same slip horizon, which corresponds to a distinctive continuous, high‐amplitude reflector. Furthermore, the geometry of the headwall scars of the Nuna and Ana slides reveals evidence of pockmarks, and fluid escape features are also present further upslope. This indicates a possible link between fluid escape features and destabilization of the upper sediment layers. In addition, these well‐characterized slides demonstrate the pitfalls associated with calculating the volume of the slide masses using headwall scarp heights and the assumed preslide seafloor topography in the absence of seismic data. The internal structure also demonstrates that transport distances within the slides are generally low and poorly characterized by headwall scarp to slide toe lengths.
Implementing a rural programme of prevention of mother‐to‐child transmission of HIV in Zimbabwe: first 18 months of experience
Authors: Perez Freddy , Mukotekwa Tarisai , Miller Anna , Orne‐Gliemann Joanna , Glenshaw Monica , Chitsike Inam , Dabis François 
Published: July 2004

SummaryObjective  To report on activities and lessons learned during the first 18 months of a rural programme of prevention of mother‐to‐child transmission of HIV (PMTCT) in Zimbabwe.Methods  The PMTCT services were introduced in Murambinda Mission Hospital (120 beds), Buhera, in 2001. Programme strategies consisted in recruiting counselling staff, training health professionals, improving mother–child health (MCH) facilities and conducting information, education and communication activities within the community to address HIV/AIDS awareness and stigma. The following components were implemented within MCH services: voluntary counselling and testing of HIV using rapid testing, nevirapine short regimen proposed to all HIV‐infected mothers identified and their newborns, support to exclusive breastfeeding for 6‐ and 18‐month mother–child follow‐up. Routine monitoring data collected from August 2001 to February 2003 were used to estimate programme uptake.Results  Of 2471 pregnant women using antenatal services, 2298 were pre‐test counselled, the acceptance of HIV testing reached 92.9%. Of the women who decided to take an HIV test, 1588 (74.3%) returned to collect their result. Overall HIV prevalence was 20.4% (n = 437); 326 of the HIV‐positive women were counselled and 104 (24%) received complete mother–child antiretroviral prophylaxis.Conclusions  Acceptability of HIV testing after counselling has remained above 90% since the onset of the programme. Collection of test results and mother–child follow‐up are among the most challenging activities of the programme. A district approach and community participation are critical to develop PMTCT programmes in rural settings, even with reasonably good MCH services.