Catálogo de publicaciones - revistas

<jats:p>Images of comet C/1996 B2 (Hyakutake) taken during its close approach to Earth show differences in the distribution of gas and dust in the inner coma and reveal two arc-shaped molecular resonant emission features. The morphology of these features, as well as the apparent decoupling gas from dust in the inner coma, suggest that an extended region of icy grains surrounds the nucleus of Hyakutake and contributes substantially to the production of volatiles. Model simulations suggest the same conclusion and indicate that the brighter arc is explainable by the presence of a trailing condensation of ice-bearing granules with a rate of volatile production approximately 23 percent of that of the nucleus.</jats:p>

<jats:p> Mice lacking the gene encoding the receptor for prostaglandin F <jats:sub>2α</jats:sub> (FP) developed normally but were unable to deliver normal fetuses at term. Although these FP-deficient mice showed no abnormality in the estrous cycle, ovulation, fertilization, or implantation, they did not respond to exogenous oxytocin because of the lack of induction of oxytocin receptor (a proposed triggering event in parturition), and they did not show the normal decline of serum progesterone concentrations that precedes parturition. Ovariectomy at day 19 of pregnancy restored induction of the oxytocin receptor and permitted successful delivery in the FP-deficient mice. These results indicate that parturition is initiated when prostaglandin F <jats:sub>2α</jats:sub> interacts with FP in ovarian luteal cells of the pregnant mice to induce luteolysis. </jats:p>

<jats:p>In the early months of life, infants acquire information about the phonetic properties of their native language simply by listening to adults speak. The acoustic properties of phonetic units in language input to young infants in the United States, Russia, and Sweden were examined. In all three countries, mothers addressing their infants produced acoustically more extreme vowels than they did when addressing adults, resulting in a “stretching” of vowel space. The findings show that language input to infants provides exceptionally well-specified information about the linguistic units that form the building blocks for words.</jats:p>

<jats:p> Heterotrimeric guanine nucleotide-binding protein (G protein)–coupled receptors are phosphorylated by kinases that mediate agonist-dependent receptor deactivation. Although many receptor kinases have been isolated, the corresponding phosphatases, necessary for restoring the ground state of the receptor, have not been identified. <jats:italic>Drosophila</jats:italic> RDGC (retinal degeneration C) is a phosphatase required for rhodopsin dephosphorylation in vivo. Loss of RDGC caused severe defects in the termination of the light response as well as extensive light-dependent retinal degeneration. These phenotypes resulted from the hyperphosphorylation of rhodopsin because expression of a truncated rhodopsin lacking the phosphorylation sites restored normal photoreceptor function. These results suggest the existence of a family of receptor phosphatases involved in the regulation of G protein–coupled signaling cascades. </jats:p>

<jats:p>Type II DNA topoisomerases catalyze the interconversion of DNA topoisomers by transporting one DNA segment through another. The steady-state fraction of knotted or catenated DNA molecules produced by prokaryotic and eukaryotic type II topoisomerases was found to be as much as 80 times lower than at thermodynamic equilibrium. These enzymes also yielded a tighter distribution of linking number topoisomers than at equilibrium. Thus, topoisomerases do not merely catalyze passage of randomly juxtaposed DNA segments but control a global property of DNA, its topology. The results imply that type II topoisomerases use the energy of adenosine triphosphate hydrolysis to preferentially remove the topological links that provide barriers to DNA segregation.</jats:p>

<jats:p> The c-Jun amino-terminal kinase (JNK) is a member of the stress-activated group of mitogen-activated protein (MAP) kinases that are implicated in the control of cell growth. A murine cytoplasmic protein that binds specifically to JNK [the JNK interacting protein-1 (JIP-1)] was characterized and cloned. JIP-1 caused cytoplasmic retention of JNK and inhibition of JNK-regulated gene expression. In addition, JIP-1 suppressed the effects of the JNK signaling pathway on cellular proliferation, including transformation by the <jats:italic>Bcr-Abl</jats:italic> oncogene. This analysis identifies JIP-1 as a specific inhibitor of the JNK signal transduction pathway and establishes protein targeting as a mechanism that regulates signaling by stress-activated MAP kinases. </jats:p>

<jats:p> In the Gramineae, the cyclic hydroxamic acids 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) form part of the defense against insects and microbial pathogens. Five genes, <jats:italic>Bx1</jats:italic> through <jats:italic>Bx5</jats:italic> , are required for DIBOA biosynthesis in maize. The functions of these five genes, clustered on chromosome 4, were demonstrated in vitro. <jats:italic>Bx1</jats:italic> encodes a tryptophan synthase α homolog that catalyzes the formation of indole for the production of secondary metabolites rather than tryptophan, thereby defining the branch point from primary to secondary metabolism. <jats:italic>Bx2</jats:italic> through <jats:italic>Bx5</jats:italic> encode cytochrome P450–dependent monooxygenases that catalyze four consecutive hydroxylations and one ring expansion to form the highly oxidized DIBOA. </jats:p>