Is E37, a major polypeptide of the inner membrane from plastid envelope,an S-adenosyl methionine-dependent methyltransferase?

Using antibodies raised against E37, one of the major polypeptides of the inner membrane from the chloroplast envelope, it has been demonstrated that a single immunologically related polypeptide was present in total protein extracts from various higher plants (monocots and dicots), in photosynthetic and non-photosynthetic tissues from young spinach plantlets, as well as in the cytoplasmic membrane from the cyanobacteria Synechococcus . This ubiquitous distribution of E37 strongly suggests that this protein plays an envelope-specific function common to all types of plastids. Comparison of tobacco and spinach E37 amino acid sequences deduced from the corresponding cDNA demonstrates that consensus motifs for S-adenosyl methionine-dependent methyltransferases are located in both sequences. This hypothesis was confirmed using a biochemical approach. It was demonstrated that E37, together with two minor spinach chloroplast envelope polypeptides of 32 and 39 kDa, can be specifically photolabeled with [³H]-S-adenosyl methionine upon UV-irradiation. Identification of E37 as a photolabeled polypeptide was established by immunoprecipitation. Furthermore, photolabeling of the three envelope polypeptides was specifically inhibited by very low concentration of S-adenosyl homocysteine, thus providing evidence for the presence within these proteins of S-adenosyl methionine- and S-adenosyl homocysteine-binding sites that were closely associated. Taken as a whole these results strongly suggest that E37 is an ubiquitous plastid envelope protein that probably has an S-adenosyl methionine-dependent methyltransferase activity. The 32 and 39 kDa envelope polypeptides probably have a similar methyltransferase activity.     

Site of synthesis of geranylgeraniol derivatives in intact spinach chloroplasts

Chloroplasts isolated from fully developed spinach leaves and incubated in the presence of isopentenyl pyrophosphate were able to synthesize rapidly geranylgeranyl chlorophyll a and geranylgeraniol.The biosynthesis of the geranylgeraniol derivatives from isopentenyl pyrophosphate is a compartimentalized process. The membrane fractions (thylakoid and envelope membranes) were essentially unable to synthesize geranylgeraniol, geranylgeranyl pyrophosphate and geranylgeranyl chlorophyll a. When stromal and thylakoid fractions were combined the capacity to synthesize geranylgeranyl chlorophyll a and geranylgeraniol was restored. When stromal and envelope membrane fractions were combined the capacity to synthesize geranylgeranyl pyrophosphate and geranylgeraniol was restored. The products of the reaction were discharged inside the lipid phase of the membranes.     

Where to Dig for Fossils: Combining Climate-Envelope,Taphonomy and Discovery Models

Fossils represent invaluable data to reconstruct the past history of life, yet fossil-rich sites are often rare and difficult to find. The traditional fossil-hunting approach focuses on small areas and has not yet taken advantage of modelling techniques commonly used in ecology to account for an organism’s past distributions. We propose a new method to assist finding fossils at continental scales based on modelling the past distribution of species, the geological suitability of fossil preservation and the likelihood of fossil discovery in the field, and apply it to several genera of Australian megafauna that went extinct in the Late Quaternary. Our models predicted higher fossil potentials for independent sites than for randomly selected locations (mean Kolmogorov-Smirnov statistic = 0.66). We demonstrate the utility of accounting for the distribution history of fossil taxa when trying to find the most suitable areas to look for fossils. For some genera, the probability of finding fossils based on simple climate-envelope models was higher than the probability based on models incorporating current conditions associated with fossil preservation and discovery as predictors. However, combining the outputs from climate-envelope, preservation, and discovery models resulted in the most accurate predictions of potential fossil sites at a continental scale. We proposed potential areas to discover new fossils of Diprotodon, Zygomaturus, Protemnodon, Thylacoleo, and Genyornis, and provide guidelines on how to apply our approach to assist fossil hunting in other continents and geological settings.     

Purification and properties of stringent factor.

The stringent factor from Escherichia coli is the product of the relA locus. It is the enzyme that catalyzes the synthesis of pppGpp and ppGpp eliciting a pyrophosphate transfer from ATP to the 3'--OH of GTP (or GDP). This protein is responsible for the synthesis of pppGpp and ppGpp in stringent strains in response to an amino acid starvation. In vitro it catalyzes the synthesis of these guanosine compounds in either a ribosome-dependent reaction that requires a particular conformation of the ribosome i.e. the presence of an uncharged tRNA recognizing a codon in the acceptor (A) site of the ribosome or in a ribosome-independent reaction at temperatures under 30 degrees in the presence of only buffer, salts, and substrates. Here we report the purification of the stringent factor to near homogeneity. It is a monomeric protein with a molecular weight of 75,000. The properties of the ribosome-independent reaction are studied and it is shown that the presence of certain acidic proteins, such as the 50 S ribosomal proteins L7 and L12 or casein, or 20% methanol or both stimulates the reaction by creating an environment that together with the low temperature further stabilizes the stringent factor.     

Free Edges in Epithelial Cell Sheets Stimulate Epidermal Growth Factor Receptor Signaling

The ability of epithelia to migrate and cover wounds is essential to maintaining their functions as physical barriers. Wounding induces many cues that may affect the transition to motility, including the immediate mechanical perturbation, release of material from broken cells, new interactions with adjacent extracellular matrix, and breakdown of physical separation of ligands from their receptors. Depending on the exact nature of wounds, some cues may be present only transiently or insignificantly. In many epithelia, activation of the epidermal growth factor receptor (EGFR) is a central event in induction of motility, and we find that its continuous activation is required for progression of healing of wounds in sheets of corneal epithelial cells. Here, we examine the hypothesis that edges, which are universally and continuously present in wounds, are a cue. Using a novel culture model we find that their presence is sufficient to cause activation of the EGFR and increased motility of cells in the absence of other cues. Edges that are bordered by agarose do not induce activation of the EGFR, indicating that activation is not due to loss of any specific type of cell–cell interaction but rather due to loss of physical constraints.     

Semi-intact CHO and endothelial cells: a tool to probe the control of integrin activity?

An in vitro assay has been developed using semi-intact cells, made with the bacterial toxin streptolysin O, in order to measure integrin activity in relation to the cytosol environment. In this assay, the cytosolic content can easily be modified while the receptor binding activity is measured by monitoring the interaction of specific radiolabeled substrates with the cell surface. Using two different cell types, i.e., wild-type Chinese hamster ovary cells and human endothelial cells in culture, it has been shown that the binding activities of the fibronectin and fibrinogen receptors become cytosol-dependent on perforated cells. Furthermore, this control depends on micromolar concentrations of intracellular calcium, suggesting that calcium or calcium binding protein(s) may play a key role in controlling integrin activity.     

Observations on the life history of Limnodrilus hoffmeisteri (Annelida,Tubificidae) from the Little Calumet River in temperate North America

The reproductive period for L. hoffmeisteri as observed in the Little Calumet River (41°34′22″N. 87°28′30Prime;W) occurs from early fall through late spring. The period is marked by the development of the reproductive organs in the early fall months, followed by the development of sperm products within the sperm sac. The female organs appear to mature in middle to late winter with the appearance of nutritive granules followed by the developing eggs in early spring. This cycle is completed in early to late spring with the appearance of cocoons containing developing embryos. It is also apparent that a low level of reproductive activity occurs throughout the rest of the year. This is usually observed in worms with developed sperm sacs and sperm products, having matured penis and some developed egg sacs with nutritive granules. Eggs have not been observed during this low level of reproductive activity.