Semi-annual oscillations in Saturn's low-latitude stratospheric temperatures

Observations of oscillations of temperature and wind in planetary atmospheres provide a means of generalizing models for atmospheric dynamics in a diverse set of planets in the Solar System and elsewhere. An equatorial oscillation similar to one in the Earth's atmosphere has been discovered in Jupiter. Here we report the existence of similar oscillations in Saturn's atmosphere, from an analysis of over two decades of spatially resolved observations of its 7.8-microm methane and 12.2-microm ethane stratospheric emissions, where we compare zonal-mean stratospheric brightness temperatures at planetographic latitudes of 3.6 degrees and 15.5 degrees in both the northern and the southern hemispheres. These results support the interpretation of vertical and meridional variability of temperatures in Saturn's stratosphere as a manifestation of a wave phenomenon similar to that on the Earth and in Jupiter. The period of this oscillation is 14.8 +/- 1.2 terrestrial years, roughly half of Saturn's year, suggesting the influence of seasonal forcing, as is the case with the Earth's semi-annual oscillation.     

Water stress and hybridization between Quercus gambelii and Quercus grisea

The historical and environmental forces involved in determining the geographic location of plant hybrid zones have long been of interest. Often hybrid zones appear to be intimately tied to the environment, yet because many abiotic factors covary it is often difficult to understand which are truly the most important in maintaining the position and structure of a hybrid zone. This study uses empirical data and modeling analyses to examine whether abiotic factors are responsible for the location and structure of an oak ( Quercus ) hybrid zone and, if so, which factors are the most important. Specifically, leaf trait measurements and ecological niche models were used to test the hypothesis that water availability plays a primary role in promoting and maintaining the location of hybridization between 2 species. Leaf trait analyses and ecological niche models both supported the hypothesis that water availability determines the location and structure of the hybrid zone. These findings lend support for the general importance of environmental factors in determining hybrid zone location and structure. Furthermore, they demonstrate how functional trait analyses and predictive ecological niche models can be used in future hybrid zone research.     

Phenol stabilizes more helix in a new symmetrical zinc insulin hexamer

SINCE insulin was first shown by Scott to crystallize in the presence of zinc ions in 1934, a variety of Zn-containing insulin crystals have been grown. The structures of insulin in the related rhombohedral crystals of 2Zn-insulin and 4Zn-insulin have been solved and reveal that the molecule is a hexamer, organized as three dimers, each containing a 2-fold symmetry axis and held together by Zn ions. In 2Zn-insulin the hexamer is nearly symmetrical with the two axial Zn ions and the two molecules of the dimer related closely by a local 2-fold axis. But in 4Zn-insulin the two molecules in the dimer differ remarkably, creating an asymmetric 4Zn-hexamer in which one trimer is essentially equivalent to that in 2Zn-insulin and the other is different by virtue of an additional stretch of N-terminal helix between residues B1 and B8 (refs 6, 7). We report here the structure of a new symmetrical hexamer, in which all six molecules have the B1-B8 helix seen in 4Zn-insulin. Phenol molecules, found bonding specifically to each molecule, evidently stabilize this new helical conformation.     

Ethical Problem Solving and Systems Theory: The Complexity Connection

No matter what the present success in straightening out difficulties and harmonizing conflicts, it is certain that problems will recur in the future in a new form or on a different plane. Indeed, every genuine accomplishment instead of winding up an affair and enclosing it as a jewel in a casket for future contemplation complicates the practical situation. . . . From the side of what has gone before the achievement settles something. From the side of what comes after, it complicates, introducing new problems, unsettling factors. (John Dewey)     

Persistence of Mycobacterium tuberculosis in macrophages and mice requires the glyoxylate shunt enzyme isocitrate lyase

Mycobacterium tuberculosis claims more human lives each year than any other bacterial pathogen. Infection is maintained in spite of acquired immunity and resists eradication by antimicrobials. Despite an urgent need for new therapies targeting persistent bacteria, our knowledge of bacterial metabolism throughout the course of infection remains rudimentary. Here we report that persistence of M. tuberculosis in mice is facilitated by isocitrate lyase (ICL), an enzyme essential for the metabolism of fatty acids. Disruption of the icl gene attenuated bacterial persistence and virulence in immune-competent mice without affecting bacterial growth during the acute phase of infection. A link between the requirement for ICL and the immune status of the host was established by the restored virulence of delta icl bacteria in interferon-gamma knockout mice. This link was apparent at the level of the infected macrophage: Activation of infected macrophages increased expression of ICL, and the delta icl mutant was markedly attenuated for survival in activated but not resting macrophages. These data suggest that the metabolism of M. tuberculosis in vivo is profoundly influenced by the host response to infection, an observation with important implications for the treatment of chronic tuberculosis.     

Effect of immunization with a vaccinia-HIV env recombinant on HIV infection of chimpanzees

Acquired immunodeficiency syndrome (AIDS) is caused by human immunodeficiency virus (HIV) and is now recognized as a worldwide epidemic for which there is no cure or vaccine. Chimpanzees are the only other animals that can be infected by HIV, and therefore the chimpanzee-HIV model system is useful for testing potential HIV vaccines. However, with one exception, there have been no reports of clinical manifestations of AIDS in chimpanzees. We report here results of an HIV vaccine trial in which nine chimpanzees were first immunized with either a recombinant vaccinia virus expressing the envelope glycoproteins of HIV strain LAV-1 (v-env5) or a control recombinant vaccinia virus and were then challenged with a high or low dose of LAV-1. Although HIV-specific antibody and T-cell responses were elicited by immunization, virus was isolated from lymphocytes of all challenged chimpanzees, indicating that immunization did not prevent infection by HIV. Among the animals that received a higher dose of LAV-1, one of two control chimpanzees, but none of the four v-env5-immunized chimpanzees developed substantial and persistent lymphadenopathy.