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<jats:p> A scanning probe microscope was used to induce local, nonvolatile field effects in epitaxial, ferroelectric Pb(Zr <jats:sub>0.52</jats:sub> Ti <jats:sub>0.48</jats:sub> )O <jats:sub>3</jats:sub> /SrRuO <jats:sub>3</jats:sub> heterostructures. Field-effected regions with linewidths as small as 3500 angstroms were written by locally switching the polarization field of the Pb(Zr <jats:sub>0.52</jats:sub> Ti <jats:sub>0.48</jats:sub> )O <jats:sub>3</jats:sub> layer; the electronic density of the underlying metallic SrRuO <jats:sub>3</jats:sub> layer was modified and the sheet resistance was changed by up to 300 ohms per square. This procedure is completely reversible and allows submicrometer electronic features to be written directly in two dimensions, with no external electrical contacts or lithographic steps required. </jats:p>

<jats:p>Transmission electron microscope observations of the Allende carbonaceous chondrite provided evidence of widespread hydrous phases replacing enstatite in chondrules. Calcic amphibole and talc occur in thin (less than 0.3 micrometer) crosscutting veins and as alteration products of primary chondrule glass in contraction cracks within the enstatite. In addition, talc and disordered biopyriboles were found replacing enstatite grains along cracks and fractures. Although rare hydrous phases have been reported in calcium- and aluminum-rich inclusions in the Allende meteorite, these observations suggest that aqueous fluids played a much more significant role in the mineralogical and geochemical evolution of Allende than has previously been thought.</jats:p>

<jats:p>Data from the Galileo orbiter suggest that two of Jupiter’s moons, Io and Ganymede, have intrinsic magnetic fields. The magnetic field of Jupiter alters the nature of the magnetohydrodynamic processes generating these intrinsic fields. Such an imposed field allows appreciable internal fields to be generated in cases where convection cannot otherwise maintain a dynamo. The dipole moment of the internal field can then become aligned with the background field, as is observed for Io and Ganymede. Io might not have a self-sustained intrinsic field in the absence of the ambient jovian field; Ganymede is almost certainly operating as a dynamo in its own right.</jats:p>

<jats:p>Single-molecule atomic force microscopy (AFM) was used to investigate the mechanical properties of titin, the giant sarcomeric protein of striated muscle. Individual titin molecules were repeatedly stretched, and the applied force was recorded as a function of the elongation. At large extensions, the restoring force exhibited a sawtoothlike pattern, with a periodicity that varied between 25 and 28 nanometers. Measurements of recombinant titin immunoglobulin segments of two different lengths exhibited the same pattern and allowed attribution of the discontinuities to the unfolding of individual immunoglobulin domains. The forces required to unfold individual domains ranged from 150 to 300 piconewtons and depended on the pulling speed. Upon relaxation, refolding of immunoglobulin domains was observed.</jats:p>

<jats:p>Titin, a giant filamentous polypeptide, is believed to play a fundamental role in maintaining sarcomeric structural integrity and developing what is known as passive force in muscle. Measurements of the force required to stretch a single molecule revealed that titin behaves as a highly nonlinear entropic spring. The molecule unfolds in a high-force transition beginning at 20 to 30 piconewtons and refolds in a low-force transition at ∼2.5 piconewtons. A fraction of the molecule (5 to 40 percent) remains permanently unfolded, behaving as a wormlike chain with a persistence length (a measure of the chain’s bending rigidity) of 20 angstroms. Force hysteresis arises from a difference between the unfolding and refolding kinetics of the molecule relative to the stretch and release rates in the experiments, respectively. Scaling the molecular data up to sarcomeric dimensions reproduced many features of the passive force versus extension curve of muscle fibers.</jats:p>

<jats:p> <jats:italic>Magnaporthe grisea</jats:italic> is a fungal pathogen with two mating types, <jats:italic>MAT1-1</jats:italic> and <jats:italic>MAT1-2</jats:italic> , that forms a specialized cell necessary for pathogenesis, the appressorium. <jats:italic>Saccharomyces cerevisiae</jats:italic> α-factor pheromone blocked appressorium formation in a mating type–specific manner and protected plants from infection by <jats:italic>MAT1-2</jats:italic> strains. Experiments with α-factor analogs suggest that the observed activity is due to a specific interaction of α-factor with an <jats:italic>M. grisea</jats:italic> receptor. Culture filtrates of a <jats:italic>MAT1-1</jats:italic> strain contained an activity that inhibited appressorium formation of mating type <jats:italic>MAT1-2</jats:italic> strains. These findings provide evidence that a pheromone response pathway exists in <jats:italic>M. grisea</jats:italic> that can be exploited for plant protection. </jats:p>

<jats:p>Prion diseases are transmissible neurodegenerative conditions characterized by the accumulation of protease-resistant forms of the prion protein (PrP), termed PrPres, in the brain. Insoluble PrPres tends to aggregate into amyloid fibrils. The anthracycline 4′-iodo-4′-deoxy-doxorubicin (IDX) binds to amyloid fibrils and induces amyloid resorption in patients with systemic amyloidosis. To test IDX in an experimental model of prion disease, Syrian hamsters were inoculated intracerebrally either with scrapie-infected brain homogenate or with infected homogenate coincubated with IDX. In IDX-treated hamsters, clinical signs of disease were delayed and survival time was prolonged. Neuropathological examination showed a parallel delay in the appearance of brain changes and in the accumulation of PrPres and PrP amyloid.</jats:p>

<jats:p> The human malaria parasite <jats:italic>Plasmodium falciparum</jats:italic> exports an interconnected network of tubovesicular membranes (the TVM) that extends from the parasite’s vacuolar membrane to the periphery of the red cell. Here it is shown that extracellular solutes such as Lucifer yellow enter the TVM and are delivered to the parasite. Blocking the assembly of the network blocked the delivery of exogenous Lucifer yellow, nucleosides, and amino acids to the parasite without inhibiting secretion of plasmodial proteins. These data suggest that the TVM is a transport network that allows nutrients efficient access to the parasite and could be used to deliver antimalarial drugs directly into the parasite. </jats:p>

<jats:p> Cell surface oligosaccharides can be engineered to display unusual functional groups for the selective chemical remodeling of cell surfaces. An unnatural derivative of <jats:italic>N</jats:italic> -acetylmannosamine, which has a ketone group, was converted to the corresponding sialic acid and incorporated into cell surface oligosaccharides metabolically, resulting in the cell surface display of ketone groups. The ketone group on the cell surface can then be covalently ligated under physiological conditions with molecules carrying a complementary reactive functional group such as the hydrazide. Cell surface reactions of this kind should prove useful in the introduction of new recognition epitopes, such as peptides, oligosaccharides, or small organic molecules, onto cell surfaces and in the subsequent modulation of cell-cell or cell–small molecule binding events. The versatility of this technology was demonstrated by an example of selective drug delivery. Cells were decorated with biotin through selective conjugation to ketone groups, and selectively killed in the presence of a ricin A chain–avidin conjugate. </jats:p>

<jats:p> In many organisms, pattern formation in the embryo develops from the polarized distributions of messenger RNAs (mRNAs) in the egg. In <jats:italic>Xenopus</jats:italic> , the mRNA encoding Vg1, a growth factor involved in mesoderm induction, is localized to the vegetal cortex of oocytes. A protein named Vera was shown to be involved in Vg1 mRNA localization. Vera cofractionates with endoplasmic reticulum (ER) membranes, and endogenous Vg1 mRNA is associated with a subcompartment of the ER. Vera may promote mRNA localization in <jats:italic>Xenopus</jats:italic> oocytes by mediating an interaction between the Vg1 3′ untranslated region and the ER subcompartment. </jats:p>