Catálogo de publicaciones - revistas

<jats:p>The inability to use light intensity to represent negative values limits the potential of optical computing. The protein bacteriorhodopsin, an optically switchable bistable material, was used to represent an image as a local concentration of one of its two states. Light of one wavelength increased this concentration and represented positive intensity, whereas light of a different wavelength decreased the concentration and represented negative intensity. Optical subtraction was demonstrated by performing the mathematical operation of a difference of Gaussians. The electro-optical characteristics of bacteriorhodopsin films portend a variety of practical applications for this system.</jats:p>

<jats:p> The metallointercalator Rh(phi) <jats:sub>2</jats:sub> DMB <jats:sup>3+</jats:sup> (phi, 9,10-phenanthrenequinone diimine; DMB, 4,4′-dimethyl-2,2′-bipyridine) catalyzed the repair of a thymine dimer incorporated site-specifically in a 16-base pair DNA duplex by means of visible light. This repair could be accomplished with rhodium noncovalently bound to the duplex and at long range (16 to 26 angstroms), with the rhodium intercalator tethered to either end of the duplex assembly. This long-range repair was mediated by the DNA helix. Repair efficiency did not decrease with increasing distance between intercalated rhodium and the thymine dimer, but it diminished with disruption of the intervening π-stack. </jats:p>

<jats:p> The <jats:italic>DED1</jats:italic> gene, which encodes a putative RNA helicase, has been implicated in nuclear pre-messenger RNA splicing in the yeast <jats:italic>Saccharomyces cerevisiae</jats:italic> . It is shown here by genetic and biochemical analysis that translation, rather than splicing, is severely impaired in two newly isolated <jats:italic>ded1</jats:italic> conditional mutants. Preliminary evidence suggests that the protein Ded1p may be required for the initiation step of translation, as is the distinct DEAD-box protein, eukaryotic initiation factor 4A (eIF4A). The <jats:italic>DED1</jats:italic> gene could be functionally replaced by a mouse homolog, <jats:italic>PL10</jats:italic> , which suggests that the function of Ded1p in translation is evolutionarily conserved. </jats:p>

<jats:p>The blue-light photoreceptor photoactive yellow protein (PYP) undergoes a self-contained light cycle. The atomic structure of the bleached signaling intermediate in the light cycle of PYP was determined by millisecond time-resolved, multiwavelength Laue crystallography and simultaneous optical spectroscopy. Light-induced trans-to-cis isomerization of the 4-hydroxycinnamyl chromophore and coupled protein rearrangements produce a new set of active-site hydrogen bonds. An arginine gateway opens, allowing solvent exposure and protonation of the chromophore's phenolic oxygen. Resulting changes in shape, hydrogen bonding, and electrostatic potential at the protein surface form a likely basis for signal transduction. The structural results suggest a general framework for the interpretation of protein photocycles.</jats:p>

<jats:p>Protein dephosphorylation by phosphatase PP1 plays a central role in mediating the effects of insulin on glucose and lipid metabolism. A PP1C-targeting protein expressed in 3T3-L1 adipocytes (called PTG, for protein targeting to glycogen) was cloned and characterized. PTG was expressed predominantly in insulin-sensitive tissues. In addition to binding and localizing PP1C to glycogen, PTG formed complexes with phosphorylase kinase, phosphorylase a, and glycogen synthase, the primary enzymes involved in the hormonal regulation of glycogen metabolism. Overexpression of PTG markedly increased basal and insulin-stimulated glycogen synthesis in Chinese hamster ovary cells overexpressing the insulin receptor, which do not express endogenous PTG. These results suggest that PTG is critical for glycogen metabolism, possibly functioning as a molecular scaffold.</jats:p>

<jats:p> Telomeres are essential for chromosome stability, but their functions at specific cell-cycle stages are unknown. Telomeres are now shown to have a role in chromosome separation during mitosis. In telomeric DNA mutants of <jats:italic>Tetrahymena thermophila</jats:italic> , created by expression of a telomerase RNA with an altered template sequence, division of the germline nucleus was severely delayed or blocked in anaphase. The mutant chromatids failed to separate completely at the midzone, becoming stretched to up to twice their normal length. These results suggest a physical block in mutant telomere separation. </jats:p>

<jats:p>Human immunodeficiency virus-type 1 (HIV-1) infection is characterized by a chronic state of immune hyperactivation in patients. Infection of human peripheral blood lymphocytes with HIV-1 in vitro resulted in increased interleukin-2 (IL-2) secretion in response to T cell activation via the CD3 and CD28 receptors. Expression of the HIV-1 transactivator Tat recapitulated this phenotype and was associated with increased IL-2 secretion in response to costimulation with CD3 plus CD28. IL-2 superinduction by Tat occurred at the transcriptional level, was mediated by the CD28-responsive element in the IL-2 promoter, and was exclusively dependent on the 29 amino acids encoded by the second exon of Tat.</jats:p>

<jats:p> Protozoan parasites of the phylum Apicomplexa contain three genetic elements: the nuclear and mitochondrial genomes characteristic of virtually all eukaryotic cells and a 35-kilobase circular extrachromosomal DNA. In situ hybridization techniques were used to localize the 35-kilobase DNA of <jats:italic>Toxoplasma gondii</jats:italic> to a discrete organelle surrounded by four membranes. Phylogenetic analysis of the <jats:italic>tufA</jats:italic> gene encoded by the 35-kilobase genomes of coccidians <jats:italic>T. gondii</jats:italic> and <jats:italic>Eimeria tenella</jats:italic> and the malaria parasite <jats:italic>Plasmodium falciparum</jats:italic> grouped this organellar genome with cyanobacteria and plastids, showing consistent clustering with green algal plastids. Taken together, these observations indicate that the Apicomplexa acquired a plastid by secondary endosymbiosis, probably from a green alga. </jats:p>