Genome sequence of the human malaria parasite Plasmodium falciparum

The parasite Plasmodium falciparum is responsible for hundreds of millions of cases of malaria, and kills more than one million African children annually. Here we report an analysis of the genome sequence of P. falciparum clone 3D7. The 23-megabase nuclear genome consists of 14 chromosomes, encodes about 5,300 genes, and is the most (A + T)-rich genome sequenced to date. Genes involved in antigenic variation are concentrated in the subtelomeric regions of the chromosomes. Compared to the genomes of free-living eukaryotic microbes, the genome of this intracellular parasite encodes fewer enzymes and transporters, but a large proportion of genes are devoted to immune evasion and host-parasite interactions. Many nuclear-encoded proteins are targeted to the apicoplast, an organelle involved in fatty-acid and isoprenoid metabolism. The genome sequence provides the foundation for future studies of this organism, and is being exploited in the search for new drugs and vaccines to fight malaria.     

Changes with hypertension and maturation in the response of stomach fundus to acetylcholine

The purpose of these experiments was to compare the contractile response to ACh of stomach fundal strips from hypertensive (SHR) and normotensive (WKY) rats during the development of hypertension. The results indicate that the reactivity to ACh is the same in fundal strips from young SHR and WKY rats; however, with maturation strips from WKY rats undergo a reduction in responsiveness which does not occur in the SHR. Therefore, strips from older SHR rats are more reactive to ACh than are those from age matched WKY rats.     

Present status of underwater medicine. Review of some challenging problems

Zusammenfassung Es wird eine Übersicht über den gegenwärtigen Stand der Unterwassermedizin gegeben. Besondere Berücksichtigung finden die in jüngster Zeit durchgeführten Forschungen, die die Grundlage für eine Erweiterung der Grenzen des Tieftauchens bereiteten, wie z.B. der 1972 durchgeführte Rekordtauchgang der Comex Gruppe, bei dem eine Tiefe von 2001 Fuss (610 m) in der Kammer erreicht wurde. Nach den in diesem Experiment erhobenen Befunden können ausgewählte und trainierte Taucher in einer Tiefe von 1400 Fuss (427 m) noch gut arbeiten und leben, wenn sie eine Helium-Sauerstoffmischung atmen. Die Ursachen des «Nervösen Hochdruck-Syndromes», sowie die kritische Volumentherorie vonMiller ⁶ als ein Erklärungsversuch für das Fehlen der narkotischen Wirkung von Helium unter hohem Druck im Vergleich zu Stickstoff werden diskutiert.

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This paper was presented in part at the XXI International Congress of Aviation and Space Medicine, September 19, 1973 in Munich (Germany, Fed. Rep.).     

Calcium transients in aequorin-injected frog cardiac muscle.

The Ca2+ -sensitive bioluminescent protein aequorin was microinjected into cells of frog atrial trabeculae to study intracellular calcium transients associated with excitation-contraction coupling. The amplitude of the aequorin signal increased with extracellular Ca2+ concentration and stimulus frequency, but decreased with stretch. Isoprenaline and acetylstrophanthidin both increased the amplitude, but had strikingly different effects on the time course of the signal.     

Visual unpatterned input determines the occurrence of reward-contingent positive variation

Résumé Des chats porteurs d'électrodes corticales Ag-AgCl non polarisables et de lentilles de contact translucides, ont été entraînés, dans obscurité, à presser un levier pour obtenir 0,8 ml de lait. Ils montrent des périodes d'activité lente de haut voltage, c'est-à-dire un phénomène ECoG connu comme synchronisation de post-reinforcement sur le cortex pariéto-occipital. Quand cette synchronisation associée à la variation positive de contingent est supprimée dans l'obscurité, ces phénomènes dépendent de l'influx de la lumière diffuse et non de la perception visuelle.

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Supported by PHS grant No. NB 06385 to T.J.M., and by the training grants No. GM 81 to J.L.Y., J.T.H. and No. MH 8396 to J.H.R.     

Diatom carbon export enhanced by silicate upwelling in the northeast Atlantic

Diatoms are unicellular or chain-forming phytoplankton that use silicon (Si) in cell wall construction. Their survival during periods of apparent nutrient exhaustion enhances carbon sequestration in frontal regions of the northern North Atlantic. These regions may therefore have a more important role in the 'biological pump' than they have previously been attributed, but how this is achieved is unknown. Diatom growth depends on silicate availability, in addition to nitrate and phosphate, but northern Atlantic waters are richer in nitrate than silicate. Following the spring stratification, diatoms are the first phytoplankton to bloom. Once silicate is exhausted, diatom blooms subside in a major export event. Here we show that, with nitrate still available for new production, the diatom bloom is prolonged where there is a periodic supply of new silicate: specifically, diatoms thrive by 'mining' deep-water silicate brought to the surface by an unstable ocean front. The mechanism we present here is not limited to silicate fertilization; similar mechanisms could support nitrate-, phosphate- or iron-limited frontal regions in oceans elsewhere.     

The deterministic nature of earthquake rupture

Understanding the earthquake rupture process is central to our understanding of fault systems and earthquake hazards. Multiple hypotheses concerning the nature of fault rupture have been proposed but no unifying theory has emerged. The conceptual hypothesis most commonly cited is the cascade model for fault rupture. In the cascade model, slip initiates on a small fault patch and continues to rupture further across a fault plane as long as the conditions are favourable. Two fundamental implications of this domino-like theory are that small earthquakes begin in the same manner as large earthquakes and that the rupture process is not deterministic--that is, the size of the earthquake cannot be determined until the cessation of rupture. Here we show that the frequency content of radiated seismic energy within the first few seconds of rupture scales with the final magnitude of the event. We infer that the magnitude of an earthquake can therefore be estimated before the rupture is complete. This finding implies that the rupture process is to some degree deterministic and has implications for the physics of the rupture process.