Phosphorylation of elF-4E and initiation of protein synthesis in P19 embryonal carcinoma cells

Mitogenic stimulation of protein synthesis is accompanied by an increase in elF-4E phosphorylation. The effect on protein synthesis by induction of differentiation is less well known. We treated P19 embryonal carcinoma cells with the differentiating agent retinoic acid and found that protein synthesis increased during the first hour of addition. However, the phosphorylation state, as well as the turnover of phosphate on elF-4E, remained unchanged. Apparently, the change in protein synthesis after RA addition is regulated by another mechanism than elF-4E phosphorylation. By using P19 cells overexpressing the EGF receptor, we show that the signal transduction pathway that leads to phosphorylation of elF-4E is present in P19 cells; the EGF-induced change in phosphorylation of elF-4E in these cells is likely to be regulated by a change in elF-4E phosphatase activity. These results suggest that the onset of retinoic acid-induced differentiation is triggered by a signal transduction pathway which involves changes in protein synthesis, but not elF-4E phosphorylation. © 1995 Wiley-Liss, Inc.     

The mantle, ink sac, ink, arm hooks and soft body debris associated with the shells in Late Triassic coleoid cephalopod Phragmoteuthis from the Austrian Alps

Fragmentarily preserved shells – mainly pro-ostraca, in several cases also phragmocones – occurring together with arm hooks and the ink sac of the Carnian (Late Triassic) coleoid cephalopod Phragmoteuthis bisinuata (Bronn) from Lunz (Austria) are examined with the scanning electron microscope and energy-dispersive spectrometer. The pro-ostracum bears black, shiny, pitch-like sheets. The black sheets, the ink sac content and the arm hooks have a granular ultrastructure of 0.1–1 μm grain size. The arm hooks and black sheets are micro-laminated; each lamina consists of fibres. The ink consists of an agglomerate of grains. On the ventral (internal) side of the pro-ostracum, the black sheets occasionally bear agglomerates of homogeneous, ink-like material along with heterogeneous structures. The pro-ostracum has crystal-shaped units with lamello-columnar ultrastructure of the inner layer and plate ultrastructure of the outer layer. This resembles the Late Triassic Lunzoteuthis [Doguzhaeva, L.A., Mutvei, H., Summesberger, H., 2005a. A Late Triassic coleoid from the Austrian Alps: the pro-ostracum viewpoint. In: Kostak, M., Marek, J. (Eds.), Proceedings of the 2nd International Symposium on Coleoid Cephalopods Through Time. Short Papers/Abstracts Vol. Prague, 26–29 September, 2005, pp. 55–59] and Early Jurassic Belemnotheutis [Doguzhaeva, L.A., Donovan, D.T., Mutvei, H., 2005b. The rostrum, conotheca and pro-ostracum in the Jurassic coleoid Belemnotheutis Pearce from Wiltshire, England. In: Kostak, M., Marek, J. (Eds.), Proceedings of the 2nd International Symposium on Coleoid Cephalopods Through Time. Short Papers/Abstracts Vol. Prague, 26–29 September, 2005, pp. 45–49]. The black sheets, the material on their inner surface, the ink and the arm hooks consist of carbon, occasionally with minor amounts of sulfur. The shell is of calcium carbonate.Based on their organic composition, position in the shell and lamello-fibrillar ultrastructure, the black sheets are considered to be remains of the mantle, sometimes with ink sac and soft body debris. The carbon composition and granular ultrastructure of arm hooks, ink, and soft tissue remains indicate that the non-mineralized structures are pseudomorphosed by carbon (carbonization), possibly due to C-accumulating bacteria.     

Predictive Computational Models of Substrate Binding by a Nucleoside Transporter

Transporters play a vital role in both the resistance mechanisms of existing drugs and effective targeting of their replacements. Melarsoprol and diamidine compounds similar to pentamidine and furamidine are primarily taken up by trypanosomes of the genus Trypanosoma brucei through the P2 aminopurine transporter. In standardized competition experiments with [³H]adenosine, P2 transporter inhibition constants (K_i) have been determined for a diverse dataset of adenosine analogs, diamidines, Food and Drug Administration-approved compounds and analogs thereof, and custom-designed trypanocidal compounds. Computational biology has been employed to investigate compound structure diversity in relation to P2 transporter interaction. These explorations have led to models for inhibition predictions of known and novel compounds to obtain information about the molecular basis for P2 transporter inhibition. A common pharmacophore for P2 transporter inhibition has been identified along with other key structural characteristics. Our model provides insight into P2 transporter interactions with known compounds and contributes to strategies for the design of novel antiparasitic compounds. This approach offers a quantitative and predictive tool for molecular recognition by specific transporters without the need for structural or even primary sequence information of the transport protein.     

Plants increase silicon content as a response to nitrogen or phosphorus limitation: a case study with Holcus lanatus

Plant and Soil - Silicon (Si) has been shown to beneficially affect plant performance under stressful environmental conditions, such as water or nutrient deficiency. Here we tested the effects of...