The structure of Rpf2–Rrs1 explains its role in ribosome biogenesis

The assembly of eukaryotic ribosomes is a hierarchical process involving about 200 biogenesis factors and a series of remodeling steps. The 5S RNP consisting of the 5S rRNA, RpL5 and RpL11 is recruited at an early stage, but has to rearrange during maturation of the pre-60S ribosomal subunit. Rpf2 and Rrs1 have been implicated in 5S RNP biogenesis, but their precise role was unclear. Here, we present the crystal structure of the Rpf2–Rrs1 complex from Aspergillus nidulans at 1.5 Å resolution and describe it as Brix domain of Rpf2 completed by Rrs1 to form two anticodon-binding domains with functionally important tails. Fitting the X-ray structure into the cryo-EM density of a previously described pre-60S particle correlates with biochemical data. The heterodimer forms specific contacts with the 5S rRNA, RpL5 and the biogenesis factor Rsa4. The flexible protein tails of Rpf2–Rrs1 localize to the central protuberance. Two helices in the Rrs1 C-terminal tail occupy a strategic position to block the rotation of 25S rRNA and the 5S RNP. Our data provide a structural model for 5S RNP recruitment to the pre-60S particle and explain why removal of Rpf2–Rrs1 is necessary for rearrangements to drive 60S maturation.     

Directional changes of species spatial dispersion and realized environmental niches drive plant community assembly during early plant succession

Aims Probabilistic models of species co-occurrences predict aggregated intraspecific spatial distributions that might decrease the degree of joint species occurrences and increase community richness. Yet, little is known about the influence of intraspecific aggregation on the co-occurrence of species in natural, species-rich communities. Here, we focus on early plant succession and ask how changes in intraspecific aggregation of colonizing plant species influence the pattern of species co-existence, richness and turnover.     

Effects of the nematofauna on microbial energy and matter transformation rates in European grassland soils

The effect of the nematofauna on the microbiology and soil nitrogen status was studied in 6 major European grassland types (Northern tundra (Abisko, Sweden), Atlantic heath (Otterburn, UK), wet grassland (Wageningen, Netherlands), semi-natural temperate grassland (Linden, Germany), East European steppe (Pusztaszer, Hungary) and Mediterranean garigue (Mt. Vermion, Greece). To extend the range of temperature and humidity experienced locally during the investigation period, soil microclimates were manipulated, and at each site 14 plots were established representing selected combinations of 6 temperature and 6 moisture levels. The investigated soils divided into two groups: mineral grassland soils that were precipitation fed (garigue, wet grassland, seminatural grassland, steppe), and wet organic soils that were groundwater fed (heath, tundra). Effects of the nematofauna on the microflora were found in the mineral soils, where correlations among nematode metabolic activity as calculated from a metabolic model, and microbial activity parameters as indicated by Biolog and ergosterol measurements, were significantly positive. Correlations with bacterial activity were stronger and more consistent. Microbial parameters, in turn, were significantly correlated with the size of the soil nitrogen pools NH4, NO3, and Norganic. Furthermore, model results suggested that there were remarkable direct effects of nematodes on soil nitrogen status. Calculated monthly nematode excretion contributed temporarily up to 27% of soluble soil nitrogen, depending on the site and the microclimate. No significant correlation among nematodes and microbial parameters, or nitrogen pools, were found in the wet organic soils. The data show that the nematofauna can under favourable conditions affect soil nitrogen status in mineral grassland soils both directly by excretion of N, and indirectly by regulating microbial activity. This suggests that the differences in nitrogen availability observed in such natural grasslands partly reflect differences in the activity of their indigenous nematofauna. This revised version was published online in June 2006 with corrections to the Cover Date.     

Efficient internal exon recognition depends on near equal contributions from the 3' and 5' splice sites

Pre-mRNA splicing is carried out by the spliceosome, which identifies exons and removes intervening introns. In vertebrates, most splice sites are initially recognized by the spliceosome across the exon, because most exons are small and surrounded by large introns. This gene architecture predicts that efficient exon recognition depends largely on the strength of the flanking 3' and 5' splice sites. However, it is unknown if the 3' or the 5' splice site dominates the exon recognition process. Here, we test the 3' and 5' splice site contributions towards efficient exon recognition by systematically replacing the splice sites of an internal exon with sequences of different splice site strengths. We show that the presence of an optimal splice site does not guarantee exon inclusion and that the best predictor for exon recognition is the sum of both splice site scores. Using a genome-wide approach, we demonstrate that the combined 3' and 5' splice site strengths of internal exons provide a much more significant separator between constitutive and alternative exons than either the 3' or the 5' splice site strength alone.     

Die Nervenendigugen in der Statocyste von Sepia

Ohne Zusammenfassung Mit 42 Textabbildungen     

Post-Fledging Dispersal of King Penguins (Aptenodytes patagonicus) from Two Breeding Sites in the South Atlantic

Most studies concerning the foraging ecology of marine vertebrates are limited to breeding adults, although other life history stages might comprise half the total population. For penguins, little is known about juvenile dispersal, a period when individuals may be susceptible to increased mortality given their naïve foraging behaviour. Therefore, we used satellite telemetry to study king penguin fledglings (n = 18) from two sites in the Southwest Atlantic in December 2007. The two sites differed with respect to climate and proximity to the Antarctic Polar Front (APF), a key oceanographic feature generally thought to be important for king penguin foraging success. Accordingly, birds from both sites foraged predominantly in the vicinity of the APF. Eight king penguins were tracked for periods greater than 120 days; seven of these (three from the Falkland Islands and four from South Georgia) migrated into the Pacific. Only one bird from the Falkland Islands moved into the Indian Ocean, visiting the northern limit of the winter pack-ice. Three others from the Falkland Islands migrated to the eastern coast of Tierra del Fuego before travelling south. Derived tracking parameters describing their migratory behaviour showed no significant differences between sites. Nevertheless, generalized linear habitat modelling revealed that juveniles from the Falkland Islands spent more time in comparatively shallow waters with low sea surface temperature, sea surface height and chlorophyll variability. Birds from South Georgia spent more time in deeper waters with low sea surface temperature and sea surface height, but high concentrations of chlorophyll. Our results indicate that inexperienced king penguins, irrespective of the location of their natal site in relation to the position of the APF, develop their foraging skills progressively over time, including specific adaptations to the environment around their prospective breeding site.     

Myocardial GLP-1 Receptor Activation in the Presence of Glucose: Strong Partners

International Journal of Peptide Research and Therapeutics - Glucagon-like peptide 1 (GLP-1) receptor agonists increase the intracellular calcium levels of atrial cardiomyocytes in a protein kinase...     

Structure of Shigella IpgB2 in Complex with Human RhoA: IMPLICATIONS FOR THE MECHANISM OF BACTERIAL GUANINE NUCLEOTIDE EXCHANGE FACTOR MIMICRY*

A common theme in bacterial pathogenesis is the manipulation of eukaryotic cells by targeting the cytoskeleton. This is in most cases achieved either by modifying actin, or indirectly via activation of key regulators controlling actin dynamics such as Rho-GTPases. A novel group of bacterial virulence factors termed the WXXXE family has emerged as guanine nucleotide exchange factors (GEFs) for these GTPases. The precise mechanism of nucleotide exchange, however, has remained unclear. Here we report the structure of the WXXXE-protein IpgB2 from Shigella flexneri and its complex with human RhoA. We unambiguously identify IpgB2 as a bacterial RhoA-GEF and dissect the molecular mechanism of GDP release, an essential prerequisite for GTP binding. Our observations uncover that IpgB2 induces conformational changes on RhoA mimicking DbI- but not DOCK family GEFs. We also show that dissociation of the GDP·Mg²⁺ complex is preceded by the displacement of the metal ion to the α-phosphate of the nucleotide, diminishing its affinity to the GTPase. These data refine our understanding of the mode of action not only of WXXXE GEFs but also of mammalian GEFs of the DH/PH family.     

Resilience and alternative equilibria in a mire plant community after experimental disturbance by volcanic ash

Following disturbance events vegetation can either be resilient and return to its original state, or there can be shifts in vegetation composition and abundance patterns that may indicate alternative equilibiria. We conducted a long‐term field experiment that simulated impact by aerially transported volcanic ejecta (tephra) in a Sphagnum‐dominated plant community in order to test the effects of this type of large‐scale disturbance. Sixty plots of 1.4 × 1.4 m were established at Sarobetsu mire in northern Hokkaido, Japan and subjected to seven treatments (including the control) with natural tephra or ground glass shards differing in grain size, layer thickness and season of application. Water chemistry and vegetation were surveyed before tephra application and during five and eight years after the perturbation, respectively. Leaching of ions from fine‐grained glass shards caused a sustained increase of soil water pH and electric conductivity. Under coarser materials water quality differed little from the control, but a short‐lived peak of potassium suggested that mechanisms like nutrient release from decomposing plant material may influence water chemistry after volcanic disturbance. The perturbation initially reduced the cover of the dominant functional group (Sphagnum mosses) in all treatments; vascular plants were less affected. All species were able to recover by growing through the tephra, and open tephra surfaces were colonized by ubiquitous cryptogams, but not by spermatophytes. In contrast to the overall resilient behaviour of the vegetation, in some plots that received natural tephra an alternative state with high cover of the dwarf shrub Myrica gale developed. The patterns indicated that physical and chemical properties of the tephra determined the initial effects on plants, but that stochastic processes contributed to subsequent succession. These are likely to have effects on ecosystem functioning, e.g. hydrological processes and carbon sequestration.