An Earth-like correspondence between Saturn's auroral features and radio emission.

Saturn is a source of intense kilometre-wavelength radio emissions that are believed to be associated with its polar aurorae, and which provide an important remote diagnostic of its magnetospheric activity. Previous observations implied that the radio emission originated in the polar regions, and indicated a strong correlation with solar wind dynamic pressure. The radio source also appeared to be fixed near local noon and at the latitude of the ultraviolet aurora. There have, however, been no observations relating the radio emissions to detailed auroral structures. Here we report measurements of the radio emissions, which, along with high-resolution images of Saturn's ultraviolet auroral emissions, suggest that although there are differences in the global morphology of the aurorae, Saturn's radio emissions exhibit an Earth-like correspondence between bright auroral features and the radio emissions. This demonstrates the universality of the mechanism that results in emissions near the electron cyclotron frequency narrowly beamed at large angles to the magnetic field.

An intense stratospheric jet on Jupiter.

The Earth's equatorial stratosphere shows oscillations in which the east-west winds reverse direction and the temperatures change cyclically with a period of about two years. This phenomenon, called the quasi-biennial oscillation, also affects the dynamics of the mid- and high-latitude stratosphere and weather in the lower atmosphere. Ground-based observations have suggested that similar temperature oscillations (with a 4-5-yr cycle) occur on Jupiter, but these data suffer from poor vertical resolution and Jupiter's stratospheric wind velocities have not yet been determined. Here we report maps of temperatures and winds with high spatial resolution, obtained from spacecraft measurements of infrared spectra of Jupiter's stratosphere. We find an intense, high-altitude equatorial jet with a speed of approximately 140 m s(-1), whose spatial structure resembles that of a quasi-quadrennial oscillation. Wave activity in the stratosphere also appears analogous to that occurring on Earth. A strong interaction between Jupiter and its plasma environment produces hot spots in its upper atmosphere and stratosphere near its poles, and the temperature maps define the penetration of the hot spots into the stratosphere.

Evidence for supersonic turbulence in the upper atmosphere of Jupiter.

Spectra of the hydrogen Lyman alpha (Ly-alpha) emission line profiles of the jovian dayglow, obtained by the Goddard High Resolution Spectrograph on the Hubble Space Telescope, appear complex and variable on time scales of a few minutes. Dramatic changes occur in the Ly-alpha bulge region at low latitudes, where the line profiles exhibit structures that correspond to supersonic velocities of the order of several to tens of kilometers per second. This behavior, unexpected in a planetary atmosphere, is evidence for the particularly stormy jovian upper atmosphere, not unlike a star's atmosphere.

Auroral signature of comet Shoemaker-Levy 9 in the jovian magnetosphere.

The electrodynamic interaction of the dust and gas comae of comet Shoemaker-Levy 9 with the jovian magnetosphere was unique and different from the atmospheric effects. Early theoretical predictions of auroral-type processes on the comet magnetic field line and advanced modeling of the time-varying morphology of these lines allowed dedicated observations with the Hubble Space Telescope Wide Field Planetary Camera 2 and resulted in the detection of a bright auroral spot. In that respect, this observation of the surface signature of an externally triggered auroral process can be considered as a "magnetospheric active experiment" on Jupiter.

HST far-ultraviolet imaging of Jupiter during the impacts of comet Shoemaker-Levy 9.

Hubble Space Telescope far-ultraviolet images of Jupiter during the Shoemaker-Levy 9 impacts show the impact regions darkening over the 2 to 3 hours after the impact, becoming darker and more extended than at longer wavelengths, which indicates that ultraviolet-absorbing gases or aerosols are more extended, more absorbing, and at higher altitudes than the absorbers of visible light. Transient auroral emissions were observed near the magnetic conjugate point of the K impact site just after that impact. The global auroral activity was fainter than average during the impacts, and a variable auroral emission feature was observed inside the southern auroral oval preceding the impacts of fragments Q1 and Q2.

A remarkable auroral event on jupiter observed in the ultraviolet with the hubble space telescope.

Two sets of ultraviolet images of the Jovian north aurora were obtained with the Faint Object Camera on board the Hubble Space Telescope. The first series shows an intense discrete arc in near corotation with the planet. The maximum apparent molecular hydrogen emission rate corresponds to an electron precipitation of approximately 1 watt per square meter, which is about 30,000 times larger than the solar heating by extreme ultraviolet radiation. Such a particle heating rate of the auroral upper atmosphere of Jupiter should cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours after initial observation, the discrete arc had decreased in brightness by more than one order of magnitude. The time scale and magnitude of the change in the ultraviolet aurora leads us to suggest that the discrete Jovian auroral precipitation is related to large-scale variations in the current system, as is the case for Earth's discrete aurorae.

The low-frequency source of Saturn's kilometric radiation.

Understanding how auroral radio emissions are produced by magnetized bodies requires in situ measurements within their source region. Saturn's kilometric radiation (SKR) has been widely used as a remote proxy of Saturn's magnetosphere. We present wave and plasma measurements from the Cassini spacecraft during its ring-grazing high-inclination orbits, which passed three times through the high-altitude SKR emission region. Northern dawn-side, narrow-banded radio sources were encountered at frequencies of 10 to 20 kilohertz, within regions of upward currents mapping to the ultraviolet auroral oval. The kilometric waves were produced on the extraordinary mode by the cyclotron maser instability from 6- to 12-kilo-electron volt electron beams and radiated quasi-perpendicularly to the auroral magnetic field lines. The SKR low-frequency sources appear to be strongly controlled by time-variable magnetospheric electron densities.

Deletion and insertion mutants of HBsAg particles.

We have found previously that hybrid 22-nm HBsAg particles can be created by insertion of short antigenic sequences into the HBV major envelope protein. We have now performed a detailed deletion mutagenesis of the S gene of HBV encoding HBsAg. Deletion of the 51 C-terminal amino acids including most of the third and all of the fourth hydrophobic domain of the S protein did not affect particle assembly and secretion. However, secretion of 22-nm particles was abolished by minor deletions in the N-terminal region. Insertion and deletion/substitution mutants carrying a poliovirus epitope at the N-terminus and the preS1 region at the C-terminus have been characterized.

Titan's atmospheric temperatures, winds, and composition.

Temperatures obtained from early Cassini infrared observations of Titan show a stratopause at an altitude of 310 kilometers (and 186 kelvin at 15 degrees S). Stratospheric temperatures are coldest in the winter northern hemisphere, with zonal winds reaching 160 meters per second. The concentrations of several stratospheric organic compounds are enhanced at mid- and high northern latitudes, and the strong zonal winds may inhibit mixing between these latitudes and the rest of Titan. Above the south pole, temperatures in the stratosphere are 4 to 5 kelvin cooler than at the equator. The stratospheric mole fractions of methane and carbon monoxide are (1.6 +/- 0.5) x 10(-2) and (4.5 +/- 1.5) x 10(-5), respectively.

Temperatures, winds, and composition in the saturnian system.

Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites.

Resurgence in quasiclassical scattering.

In quasiclassical spectral theory, "resurgence" means that long periodic orbits can be expressed by short ones in such a way that the spectral determinant is real. The question has thus long been posed whether long scattering orbits can be expressed by short orbits in such a way as to make the quasiclassical scattering matrix unitary. We here find a resurgent and manifestly Hermitean expression for Wigner's R matrix, implying a unitary scattering matrix. The result is particularly important if the average resonance width is comparable with the average resonance spacing.

Role for calnexin and N-linked glycosylation in the assembly and secretion of hepatitis B virus middle envelope protein particles.

Unlike those of the S and the L envelope proteins, the functional role of the related M protein in the life cycle of the hepatitis B virus (HBV) is less understood. We now demonstrate that a single N glycan, specific for M, is required for efficient secretion of M empty envelope particles. Moreover, this glycan mediates specific association of M with the chaperone calnexin. Conversely, the N glycan, common to all three envelope proteins, is involved neither in calnexin binding nor in subviral particle release. As proper folding and trafficking of M need the assistance of the chaperone, the glycan-dependent association of M with calnexin may thus play a crucial role in the assembly of HBV. Beyond being modified by N glycosylation, M is modified by O glycosylation occurring within its amino acid sequence at positions 27 to 47. The O glycans, however, were found to be dispensable for secretion of M but may rather support viral infectivity. Surprisingly, nonglycosylated M localizes exclusively to the cytosol, either for degradation or for a yet-unknown function.

Dual topology of the hepatitis B virus large envelope protein: determinants influencing post-translational pre-S translocation.

The large (L) envelope protein of the hepatitis B virus (HBV) has the peculiar capacity to form two transmembrane topologies via an as yet uncharacterized process of partial post-translational translocation of its pre-S domain across membranes. In view of a current model that predicts an HBV-specific channel generated during virion envelope assembly to enable pre-S translocation, we have examined parameters influencing L topogenesis by using protease protection analysis of wild-type and mutant L proteins synthesized in transfected cells. We demonstrate that contrary to expectation, all determinants, thought to be responsible for channel formation, are dispensable for pre-S reorientation. In particular, we observed that this process does not require (i) the helper function of the HBV S (small) and M (middle) envelope proteins, (ii) covalent dimer formation of envelope chains, or (iii) either of the three amphipathic transmembrane segments of L. Rather, the most hydrophobic transmembrane segment 2 of L was identified as a vital topogenic determinant, essential and sufficient for post-translational pre-S translocation. Cell fractionation studies revealed that pre-S refolding and thus the dual topology of L is established at the endoplasmic reticulum (ER) membrane rather than at a post-ER compartment as originally supposed. Together our data provide evidence to suggest that the topological reorientation of L is facilitated by a host cell transmembrane transport machinery such as the ER translocon.

DNA-mediated immunization to hepatitis B virus envelope proteins: preS antigen secretion enhances the humoral response.

In order to design optimized DNA vectors as genetic vaccines against infections with the hepatitis B virus (HBV) we investigated if secretion or retention of the viral antigens has an influence on the quality and quantity of the humoral immune response. Intramuscular injection of plasmid DNA encoding the HBV large L envelope protein, known to be retained within host cells, induced only a weak response in mice whereas a vector expressing the secretion-competent small S envelope protein elicited strong and sustained immunity. Immunization with rearranged envelope genes further demonstrated that secretion affects the magnitude of the immune response. In situ expression of modified small and middle envelope genes carrying C-terminally attached epitopes are derived from the preS1 region of L generated high titers of preS1- and preS2-specific antibodies, unless antigen secretion was blocked. Accessibility of preS antigens to B-cells that can be achieved by generating extracellular forms of the envelope proteins is thus critical to elicit humoral responses. Such DNA constructs carrying preS1 determinants are promising candidates for the development of multivalent HBV vaccines.

[Variations in activity and sexual dimorphism of central nervous neurons in the rat in the course of postnatal development]. / Aktivitätsschwankungen und Sexualdimorphismus zentralnervöser Neurone der Ratte im Verlauf der postnatalen Entwicklung.

Processes of growth and differentiation of the neurons are based on adequate metabolic activities of the karyoplasm and cytoplasm and measurable at the volume of the cell nucleus. Furthermore, they are affected by metabolic activities related to special neuronal functions. Studies of neurons related to the Nuclei arcuatus, amygdaloideus medialis, amygdaloideus corticalis and amygdaloideus basolateralis (Pars lateralis of the Nucleus amygdaloideus basalis) as well as to the external granular layer (Lamina granularis externa, Lamina II) of the parietal cortex of female and male Wistar rats resulted in distinct karyovolumetrically verifiable variations of the neuronal activities during the postnatal development (between the 5th and 60th day after birth). The variations of the neuronal activities are characterized by their nuclear specifity and indicate a significant sexual dimorphism, which also is of nuclear specifity. The nuclear specifity of the neuronal activity and the variations of the activities are understood as a total of differentiated developmental rhythms and performances of the studied neurons during the postnatal development. The sexual dimorphism, reflected in the nuclear cell volume resp. in the neuronal activity, is finally related to the sexual specificity of the differentiation of the central nervous system.

Differential Response in the Water Status of Immature and Mature Fronds of the Ostrich Fern (Matteuccia struthiopteris [L.] Todaro) to a Mild Water Stress.

Experiments were conducted in growth chambers to examine the effect of a mild water stress (-200 kilopascals polyethylene glycol) on frond elongation and water status of the ostrich fern (Matteuccia struthiopteris [L.] Todaro). Measurements were taken for two days, starting one day after the application of polyethylene glycol. Total water potential in control (well-watered) plants was always significantly higher in immature fronds than in mature fronds. The osmotic potential in mature fronds was always significantly lower (about 800 kilopascals) than in immature fronds in both control and stressed plants. In immature fronds, the stress decreased elongation and total water and pressure potentials, while in mature fronds it increased total water and pressure potentials. The decreases in total and pressure potentials in immature fronds were approximately equal to the increases in mature fronds.

Hepatitis B virus large envelope protein interacts with gamma2-adaptin, a clathrin adaptor-related protein.

For the outcome of a hepatitis B virus (HBV) infection, the viral L envelope protein with its pre-S domain performs pivotal functions by mediating attachment of HBV to liver cells, envelopment of viral capsids, release of (sub)viral particles, regulation of supercoiled DNA amplification, and transcriptional transactivation. To assess its multiple functions and host-protein assistance involved, we initiated a two-hybrid screen using the L-specific pre-S1 domain as bait. With this approach, we have identified gamma2-adaptin, a putative member of the clathrin adaptor proteins responsible for protein sorting and trafficking, as a specific binding partner of L protein. Evidence for a physical interaction between L protein and gamma2-adaptin was also demonstrated by affinity chromatography and coimmunoprecipitation, and the binding sites were mapped to the L-specific pre-S1 domain and the gamma2-adaptin-specific ear domain. The specificity of the interaction was further sustained by the failure of gamma1-adaptin, a closely related gamma2-adaptin homologue, to associate with L protein. Analysis of an L mutant protein indicates that the L-gamma2-adaptin interaction strictly depends on the pre-S1 domain of transmembrane L protein oriented to the cytosol and thus appears to occur in the cytosolic environment. Interestingly, coexpression of the two interacting partners in transfected cells resulted in recruitment of gamma2-adaptin by L protein onto cis-Golgi-like structures, strongly indicating that the association is physiologically relevant. Together, the results suggest a role for gamma2-adaptin in L-mediated processes of viral biogenesis and/or pathogenesis, such as facilitating and guiding HBV assembly.

Novel transmembrane topology of the hepatitis B virus envelope proteins.

The small (S), middle (M) and large (L) envelope proteins of the hepatitis B virus (HBV) are initially synthesized as multispanning membrane proteins of the endoplasmic reticulum membrane. We now demonstrate that all envelope proteins synthesized in transfected cells or in a cell-free system adopt more than one transmembrane orientation. The L protein disposes its N-terminal preS domain both to the cytoplasmic and the luminal side of the membrane. This unusual topology does not depend on interaction with the viral nucleocapsid, but is preserved in secreted empty envelope particles. Pulse-chase analysis suggests a novel process of post-translational translocation leading to the non-uniform topology. Analysis of L deletion mutants indicates that the block to co-translational translocation can be attributed to a specific sequence within preS, suggesting that translocation of L may be regulated. Additional topological heterogeneity is displayed in the S region of the envelope proteins and in the S protein itself, as assayed in a cell-free system. S proteins integrated into microsomal membranes exhibit both a luminal and a cytoplasmic orientation of the internal hydrophilic region carrying the major antigenic determinants. This may explain the unusual partial glycosylation of the HBV envelope proteins.

A carboxyl-terminal cysteine residue is required for palmitic acid binding and biological activity of the ras-related yeast YPT1 protein.

The Saccharomyces cerevisiae YPT1 gene codes for a ras-like, guanine nucleotide-binding protein which is essential for cell viability. The functional significance of two consecutive cysteines at the very carboxyl-terminal end of this protein and in ypt homologues of other eukaryotic species was examined. YPT1 gene mutations were generated that either led to substitutions by serine or the deletion of one or both C-terminal cysteines. The consequences of the mutations were checked in cells after replacing the wild type with the mutant genes. It was found that as long as one of the cysteines was retained, the protein was fully functional. The YPT1 protein could be labelled with [3H]palmitic acid that appeared to be bound in an ester linkage. The wild-type protein was evenly distributed between soluble and membrane-associated proteins, the palmitoylated form was predominantly in the crude membrane fraction. The mutant protein lacking the C-terminal cysteines was not palmitoylated and was exclusively found in the soluble fraction. The extension by three residues, -Val-Leu-Ser, generating a ras-typical C-terminal end, did not interfere with the mutant YPT1 protein's function although it resulted in a reduced labelling with palmitic acid.