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<jats:p> To test proposals for the origin of oxygen absorption bands in the visible reflectance spectrum of Ganymede, the reflectance of condensed films of pure oxygen (O <jats:sub>2</jats:sub> ) and O <jats:sub>2</jats:sub> -water mixtures and the evolution of O <jats:sub>2</jats:sub> from the films as a function of temperature were determined. Absorption band shapes and positions for oxygen at 26 kelvin were similar to those reported for Ganymede, whereas those for the mixtures were slightly shifted. The band intensity dropped by more than two orders of magnitude when the ice mixture was warmed to 100 kelvin, although about 20 percent of the O <jats:sub>2</jats:sub> remained trapped in the ice, which suggested that at these temperatures O <jats:sub>2</jats:sub> molecules dissolve in the ice rather than aggregate in clusters or bubbles. The experiments suggest that the absorption bands in Ganymede's spectrum were not produced in the relatively warm surface of the satellite but in a much colder source. Solid O <jats:sub>2</jats:sub> may exist in a cold subsurface layer or in an atmospheric haze. </jats:p>

<jats:p> A leucine-rich nuclear export signal (NES) allows rapid export of proteins from cell nuclei. Microinjection studies revealed a role for the guanosine triphosphatase (GTPase) Ran in NES-mediated export. Nuclear injection of a Ran mutant (Thr <jats:sup>24</jats:sup> → Asn) blocked protein export but not import, whereas depletion of the Ran nucleotide exchange factor RCC1 blocked protein import but not export. However, injection of Ran GTPase-activating protein (RanGAP) into RCC1-depleted cell nuclei inhibited export. Coinjection with Ran mutants insensitive to RanGAP prevented this inhibition. Therefore, NES-mediated protein export appears to require a Ran-GTP complex but does not require Ran-dependent GTP hydrolysis. </jats:p>

<jats:p> Transport of macromolecules into and out of nuclei, essential steps in gene expression, are potential points of control. The matrix protein (M protein) of vesicular stomatitis virus (VSV) was shown to block transport of RNAs and proteins between the nucleus and cytoplasm of <jats:italic>Xenopus laevis</jats:italic> oocytes. The pattern of inhibition indicated that M protein interfered with transport that is dependent on the <jats:underline>ra</jats:underline> s-like <jats:underline>n</jats:underline> uclear guanosine triphosphatase (GTPase) Ran-TC4 and its associated factors. This inhibition of nuclear transport by M protein explains several observations about the effects of VSV infection on host cell gene expression and suggests that RNA export is closely coupled to protein import. </jats:p>

<jats:p> The avian sarcoma virus 16 (ASV 16) is a retrovirus that induces hemangiosarcomas in chickens. Analysis of the ASV 16 genome revealed that it encodes an oncogene that is derived from the cellular gene for the catalytic subunit of phosphoinositide 3-kinase (PI 3-kinase). The gene is referred to as v- <jats:italic>p3k</jats:italic> , and like its cellular counterpart c- <jats:italic>p3k</jats:italic> , it is a potent transforming gene in cultured chicken embryo fibroblasts (CEFs). The products of the viral and cellular <jats:italic>p3k</jats:italic> genes have PI 3-kinase activity. CEFs transformed with either gene showed elevated levels of phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate and activation of Akt kinase. </jats:p>

<jats:p>Kaposi's sarcoma–associated herpesvirus (KSHV) was found in the bone marrow dendritic cells of multiple myeloma patients but not in malignant plasma cells or bone marrow dendritic cells from normal individuals or patients with other malignancies. In addition the virus was detected in the bone marrow dendritic cells from two out of eight patients with monoclonal gammopathy of undetermined significance (MGUS), a precursor to myeloma. Viral interleukin-6, the human homolog of which is a growth factor for myeloma, was found to be transcribed in the myeloma bone marrow dendritic cells. KSHV may be required for transformation from MGUS to myeloma and perpetuate the growth of malignant plasma cells.</jats:p>

<jats:p>Gene flow and morphological divergence were measured among 12 populations of a common species of rainforest passerine. Populations in the forest and the ecotone (the transition zone between the African rainforest and savanna) are morphologically divergent, despite high gene flow, and morphological differences between habitats are as large as those found between related species. In contrast to past theories of rainforest speciation, which emphasize geographic isolation, these results suggest that natural selection may play an important role in generating rainforest biodiversity. Because ecotone habitats may be a source of evolutionary novelty, greater attention should be paid to their conservation in order to preserve the processes that may be important to maintain rainforest diversity.</jats:p>

<jats:p> The source of increasing viremia that characterizes the latter stages of human immunodeficiency virus (HIV) disease has remained a paradox because it occurs at a time when lymphoid tissue is quantitatively and qualitatively impaired, and the patients' CD4 T lymphocytes are steadily declining. Here, macrophages, both infected and uninfected with common opportunistic pathogens of HIV disease such as <jats:italic>Mycobacterium avium</jats:italic> complex and <jats:italic>Pneumocystis carinii</jats:italic> , were identified as highly productive sources of HIV in coinfected lymph nodes. These observations indicate that tissue macrophages are not only infected with HIV, but that common pathogens of HIV disease can dramatically increase their production of virus. Thus, prevention or successful treatment of opportunistic coinfections, or both, potentially benefits the patient twofold by limiting the pathology caused by opportunistic infection and by controlling induction of HIV replication. </jats:p>

<jats:p>Bactericidal/permeability-increasing protein (BPI), a potent antimicrobial protein of 456 residues, binds to and neutralizes lipopolysaccharides from the outer membrane of Gram-negative bacteria. At a resolution of 2.4 angstroms, the crystal structure of human BPI shows a boomerang-shaped molecule formed by two similar domains. Two apolar pockets on the concave surface of the boomerang each bind a molecule of phosphatidylcholine, primarily by interacting with their acyl chains; this suggests that the pockets may also bind the acyl chains of lipopolysaccharide. As a model for the related plasma lipid transfer proteins, BPI illuminates a mechanism of lipid transfer for this protein family.</jats:p>

<jats:p> The plant hormone auxin regulates plant physiology by modulating the interaction of transcription factors with auxin response elements (AuxREs) of the affected genes. A transcription factor, Auxin Response Factor 1 (ARF1), that binds to the sequence TGTCTC in AuxREs was cloned from <jats:italic>Arabidopsis</jats:italic> by using a yeast one-hybrid system. ARF1 has an amino-terminal DNA-binding domain related to the carboxyl terminus of the maize transactivator Viviparous-1. Sequence requirements for ARF1 binding in vitro are identical to those that confer auxin responsiveness in vivo. The carboxyl terminus of ARF1 contains two motifs found in the Aux/IAA class of proteins and appears to mediate protein-protein interactions. </jats:p>

<jats:p>A new type of inhalation aerosol, characterized by particles of small mass density and large size, permitted the highly efficient delivery of inhaled therapeutics into the systemic circulation. Particles with mass densities less than 0.4 gram per cubic centimeter and mean diameters exceeding 5 micrometers were inspired deep into the lungs and escaped the lungs' natural clearance mechanisms until the inhaled particles delivered their therapeutic payload. Inhalation of large porous insulin particles resulted in elevated systemic levels of insulin and suppressed systemic glucose levels for 96 hours, whereas small nonporous insulin particles had this effect for only 4 hours. High systemic bioavailability of testosterone was also achieved by inhalation delivery of porous particles with a mean diameter (20 micrometers) approximately 10 times that of conventional inhaled therapeutic particles.</jats:p>