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<jats:p>A smectic liquid-crystal phase made from achiral molecules with bent cores was found to have fluid layers that exhibit two spontaneous symmetry-breaking instabilities: polar molecular orientational ordering about the layer normal and molecular tilt. These instabilities combine to form a chiral layer structure with a handedness that depends on the sign of the tilt. The bulk states are either antiferroelectric-racemic, with the layer polar direction and handedness alternating in sign from layer to layer, or antiferroelectric-chiral, which is of uniform layer handedness. Both states exhibit an electric field–induced transition from antiferroelectric to ferroelectric.</jats:p>

<jats:p>Twenty-four molecular dynamics trajectories of chymotrypsin inhibitor 2 provide a direct demonstration of the diversity of unfolding pathways. Comparison with experiments suggests that the transition state region for folding and unfolding occurs early with only 25 percent of the native contacts and that the root-mean-square deviations between contributing structures can be as large as 15 angstroms. Nevertheless, a statistically preferred unfolding pathway emerges from the simulations; disruption of tertiary interactions between the helix and a two-stranded portion of the β sheet is the primary unfolding event. The results suggest a synthesis of the “new” and the classical view of protein folding with a preferred pathway on a funnel-like average energy surface.</jats:p>

<jats:p> The catalytic oxidation of carbon monoxide (CO) on a platinum (111) surface was studied by scanning tunneling microscopy. The adsorbed oxygen atoms and CO molecules were imaged with atomic resolution, and their reactions to carbon dioxide (CO <jats:sub>2</jats:sub> ) were monitored as functions of time. The results allowed the formulation of a rate law that takes the distribution of the reactants in separate domains into account. From temperature-dependent measurements, the kinetic parameters were obtained. Their values agree well with data from macroscopic measurements. In this way, a kinetic description of a chemical reaction was achieved that is based solely on the statistics of the underlying atomic processes. </jats:p>

<jats:p> Films of silicon dioxide (SiO <jats:sub>2</jats:sub> ) were deposited at room temperature by means of catalyzed binary reaction sequence chemistry. The binary reaction SiCl <jats:sub>4</jats:sub> + 2H <jats:sub>2</jats:sub> O → SiO <jats:sub>2</jats:sub> + 4HCl was separated into SiCl <jats:sub>4</jats:sub> and H <jats:sub>2</jats:sub> O half-reactions, and the half-reactions were then performed in an ABAB … sequence and catalyzed with pyridine. The pyridine catalyst lowered the deposition temperature from &gt;600 to 300 kelvin and reduced the reactant flux required for complete reactions from ∼10 <jats:sup>9</jats:sup> to ∼10 <jats:sup>4</jats:sup> Langmuirs. Growth rates of ∼2.1 angstroms per AB reaction cycle were obtained at room temperature for reactant pressures of 15 millitorr and 60-second exposure times with 200 millitorr of pyridine. This catalytic technique may be general and should facilitate the chemical vapor deposition of other oxide and nitride materials. </jats:p>

<jats:p> Dorsoventral patterning of vertebrate and <jats:italic>Drosophila</jats:italic> embryos requires bone morphogenetic proteins (BMPs) and antagonists of BMP activity. The <jats:italic>Drosophila</jats:italic> gene <jats:italic>tolloid</jats:italic> encodes a metalloprotease similar to BMP-1 that interacts genetically with <jats:italic>decapentaplegic</jats:italic> , the <jats:italic>Drosophila</jats:italic> homolog of vertebrate BMP-2/4. Zebrafish embryos overexpressing a zebrafish homolog of <jats:italic>tolloid</jats:italic> were shown to resemble loss-of-function mutations in <jats:italic>chordino</jats:italic> , the zebrafish homolog of the <jats:italic>Xenopus</jats:italic> BMP-4 antagonist Chordin. Furthermore, Chordin was degraded by COS cells expressing Tolloid. These data suggest that Tolloid antagonizes Chordin activity by proteolytically cleaving Chordin. A conserved function for zebrafish and <jats:italic>Drosophila</jats:italic> Tolloid during embryogenesis is proposed. </jats:p>

<jats:p> The inositol 1,4,5-trisphosphate (IP <jats:sub>3</jats:sub> ) receptor is a calcium ion channel involved in the release of free Ca <jats:sup>2+</jats:sup> from intracellular stores. For analysis of the role of IP <jats:sub>3</jats:sub> -induced Ca <jats:sup>2+</jats:sup> release (IICR) on patterning of the embryonic body, monoclonal antibodies that inhibit IICR were produced. Injection of these blocking antibodies into the ventral part of early <jats:italic>Xenopus</jats:italic> embryos induced modest dorsal differentiation. A close correlation between IICR blocking potencies and ectopic dorsal axis induction frequency suggests that an active IP <jats:sub>3</jats:sub> -Ca <jats:sup>2+</jats:sup> signal may participate in the modulation of ventral differentiation. </jats:p>

<jats:p> The crystal structure of G <jats:sub>s</jats:sub> <jats:sub>α</jats:sub> , the heterotrimeric G protein α subunit that stimulates adenylyl cyclase, was determined at 2.5 Å in a complex with guanosine 5′- <jats:italic>O</jats:italic> -(3-thiotriphosphate) (GTPγS). G <jats:sub>s</jats:sub> <jats:sub>α</jats:sub> is the prototypic member of a family of GTP-binding proteins that regulate the activities of effectors in a hormone-dependent manner. Comparison of the structure of G <jats:sub>s</jats:sub> <jats:sub>α</jats:sub> ·GTPγS with that of G <jats:sub>i</jats:sub> <jats:sub>α</jats:sub> ·GTPγS suggests that their effector specificity is primarily dictated by the shape of the binding surface formed by the switch II helix and the α3-β5 loop, despite the high sequence homology of these elements. In contrast, sequence divergence explains the inability of regulators of G protein signaling to stimulate the GTPase activity of G <jats:sub>s</jats:sub> <jats:sub>α</jats:sub> . The βγ binding surface of G <jats:sub>s</jats:sub> <jats:sub>α</jats:sub> is largely conserved in sequence and structure to that of G <jats:sub>i</jats:sub> <jats:sub>α</jats:sub> , whereas differences in the surface formed by the carboxyl-terminal helix and the α4-β6 loop may mediate receptor specificity. </jats:p>

<jats:p> A Sonic hedgehog (Shh) response element was identified in the chicken ovalbumin upstream promoter–transcription factor II (COUP-TFII) promoter that binds to a factor distinct from <jats:italic>Gli</jats:italic> , a gene known to mediate Shh signaling. Although this binding activity is specifically stimulated by Shh-N (amino-terminal signaling domain), it can also be unmasked with protein phosphatase treatment in the mouse cell line P19, and induction by Shh-N can be blocked by phosphatase inhibitors. Thus, Shh-N signaling may result in dephosphorylation of a target factor that is required for activation of COUP-TFII–, Islet1-, and Gli response element–dependent gene expression. This finding identifies another step in the Shh-N signaling pathway. </jats:p>

<jats:p>It is now commonly accepted that planning and execution of movements are based on distributed processing by neuronal populations in motor cortical areas. It is less clear, though, how these populations organize dynamically to cope with the momentary computational demands. Simultaneously recorded activities of neurons in the primary motor cortex of monkeys during performance of a delayed-pointing task exhibited context-dependent, rapid changes in the patterns of coincident action potentials. Accurate spike synchronization occurred in relation to external events (stimuli, movements) and was commonly accompanied by discharge rate modulations but without precise time locking of the spikes to these external events. Spike synchronization also occurred in relation to purely internal events (stimulus expectancy), where firing rate modulations were distinctly absent. These findings indicate that internally generated synchronization of individual spike discharges may subserve the cortical organization of cognitive motor processes.</jats:p>

<jats:p> Light-regulated translation of chloroplast messenger RNAs (mRNAs) requires <jats:italic>trans-</jats:italic> acting factors that interact with the 5′ untranslated region (UTR) of these mRNAs. Chloroplast polyadenylate-binding protein (cPABP) specifically binds to the 5′-UTR of the <jats:italic>psbA</jats:italic> mRNA and is essential for translation of this mRNA. A protein disulfide isomerase that is localized to the chloroplast and copurifies with cPABP was shown to modulate the binding of cPABP to the 5′-UTR of the <jats:italic>psbA</jats:italic> mRNA by reversibly changing the redox status of cPABP through redox potential or adenosine 5′-diphosphate–dependent phosphorylation. This mechanism allows for a simple reversible switch regulating gene expression in the chloroplast. </jats:p>