bluuebunny/crossref_metadata_2025 huggingface dataset:
Expanding the Scope of RNA Catalysis
Authors: Prudent James R. , Uno Tetsuo , Schultz Peter G.
Published: October 2006

The basic notions of transition state theory have been exploited in the past to generate highly selective catalysts from the vast library of antibody molecules in the immune system. These same ideas were used to isolate an RNA molecule, from a large library of RNAs, that catalyzes the isomerization of a bridged biphenyl. The RNA-catalyzed reaction displays Michaelis-Menten kinetics with a catalytic rate constant (
k
cat
) of 2.8 × 10
-5
per minute and a Michaelis constant (
K
m
) of 542 μM; the reaction is competitively inhibited by the planar transition state analog with an inhibition constant (
K
i
) value of ∼7 μM. This approach may provide a general strategy for expanding the scope of RNA catalysis beyond those reactions in which the substrates are nucleic acids or nucleic acid derivatives.
Maternal Rescue of Transforming Growth Factor-β 1 Null Mice
Authors: Letterio John J. , Geiser Andrew G. , Kulkarni Ashok B. , Roche Nanette S. , Sporn Michael B. , Roberts Anita B.
Published: October 2006

Maternal sources of transforming growth factor-β1 (TGF-β1) are shown here to contribute to the normal appearance and perinatal survival of TGF-β1 null newborn mice. Labeled TGF-β1 crossed the placenta and was recovered intact from various tissues after oral administration to mouse pups. TGFβ-1 protein was also detected in cells recovered from breast milk. In immunohistochemical analyses, TGF-β1 null embryos and null newborn pups born to TGF-β1 heterozygotes stained positive for TGF-β1, whereas those born to a null female were negative and had severe cardiac abnormalities. These results suggest an important role for maternal sources of TGF-β1 during development and, more generally, provide evidence for maternal rescue of targeted gene disruption in the fetus.
Implications of
FRA16A
Structure for the Mechanism of Chromosomal Fragile Site Genesis
Authors: Nancarrow J. K. , Kremer E. , Holman K. , Eyre H. , Doggett N. A. , Le Paslier D. , Callen D. F. , Sutherland G. R. , Richards R. I.
Published: October 2006

Fragile sites are chemically induced nonstaining gaps in chromosomes. Different fragile sites vary in frequency in the population and in the chemistry of their induction. DNA sequences encompassing and including the rare, autosomal, folate-sensitive fragile site,
FRA16A
, were isolated by positional cloning. The molecular basis of
FRA16A
was found to be expansion of a normally polymorphic p(CCG)

n

repeat. This repeat was adjacent to a CpG island that was methylated in fragile site-expressing individuals. The
FRA16A
locus in individuals who do not express the fragile site is not a site of DNA methylation (imprinting), which suggests that the methylation associated with fragile sites may be a consequence and not a cause of their genesis.
Receptor and Ligand Domains for Invasion of Erythrocytes by
Plasmodium falciparum
Authors: Sim B. K. L. , Chitnis C. E. , Wasniowska K. , Hadley T. J. , Miller L. H.
Published: October 2006

A 175-kilodalton erythrocyte binding protein, EBA-175, of the parasite
Plasmodium falciparum
mediates the invasion of erythrocytes. The erythrocyte receptor for EBA-175 is dependent on sialic acid. The domain of EBA-175 that binds erythrocytes was identified as region II with the use of truncated portions of EBA-175 expressed on COS cells. Region II, which contains a cysteine-rich motif, and native EBA-175 bind specifically to glycophorin A, but not to glycophorin B, on the erythrocyte membrane. Erythrocyte recognition of EBA-175 requires both sialic acid and the peptide backbone of glycophorin A. The identification of both the receptor and ligand domains may suggest rational designs for receptor blockade and vaccines.
Changes of Induction and Competence During the Evolution of Vulva Development in Nematodes
Authors: Sommer Ralf J. , Sternberg Paul W.
Published: October 2006

In
Caenorhabditis
, the vulva is formed in the central body region from three of six equivalent cells and is induced by the gonad. In some nematodes, however, the vulva is located in the posterior body region. Vulval development has been analyzed in three such genera. The same precursor cells give rise to the vulva in
Caenorhabditis
and in the posterior vulva species, but in the latter the cells first migrate posteriorly. In two such species, the vulva is not induced by the gonad, but instead relies on intrinsic properties of precursor cells. Thus, evolution of organ position involves changes in induction and competence.
Lack of Evidence for the Dichotomy of T
H
1 and T
H
2 Predominance in HIV-Infected Individuals
Authors: Graziosi Cecilia , Pantaleo Giuseppe , Gantt Kira R. , Fortin Jean-Pierre , Demarest James F. , Cohen Oren J. , Sékaly Rafick P. , Fauci Anthony S.
Published: October 2006

A switch from a T helper 1 (T
H
1) cytokine phenotype to a T
H
2 phenotype has been proposed as a critical element in the progression of human immunodeficiency virus (HIV) disease. Here, constitutive cytokine expression was analyzed in unfractionated and sorted cell populations isolated from peripheral blood and lymph nodes of HIV-infected individuals at different stages of disease. Expression of interleukin-2 (IL-2) and IL-4 was barely detectable (or undetectable) regardless of the stage of disease. CD8
+
cells expressed large amounts of interferon γ and IL-10, and the levels of these cytokines remained stably high throughout the course of infection. Furthermore, similar patterns of cytokine expression were observed after stimulation in vitro of purified CD4+ T cell populations obtained from HIV-infected individuals at different stages of disease. These results indicate that a switch from the T
H
1 to the T
H
2 cytokine phenotype does not occur during the progression of HIV disease.
Crystal Structure of P22 Tailspike Protein: Interdigitated Subunits in a Thermostable Trimer
Authors: Steinbacher Stefan , Seckler Robert , Miller Stefan , Steipe Boris , Huber Robert , Reinemer Peter
Published: October 2006

The tailspike protein (TSP) of
Salmonella typhimurium
phage P22 is a part of the apparatus by which the phage attaches to the bacterial host and hydrolyzes the O antigen. It has served as a model system for genetic and biochemical analysis of protein folding. The x-ray structure of a shortened TSP (residues 109 to 666) was determined to a 2.0 angstrom resolution. Each subunit of the homotrimer contains a large parallel β helix. The interdigitation of the polypeptide chains at the carboxyl termini is important to protrimer formation in the folding pathway and to thermostability of the mature protein.
High-Resolution Structure of the Oligomerization Domain of p53 by Multidimensional NMR
Authors: Clore G. Marius , Omichinski James G. , Sakaguchi Kazuyasu , Zambrano Nicola , Sakamoto Hiroshi , Appella Ettore , Gronenborn Angela M.
Published: October 2006

The three-dimensional structure of the oligomerization domain (residues 319 to 360) of the tumor suppressor p53 has been solved by multidimensional heteronuclear magnetic resonance (NMR) spectroscopy. The domain forms a 20-kilodalton symmetric tetramer with a topology made up from a dimer of dimers. The two primary dimers each comprise two antiparallel helices linked by an antiparallel β sheet. One β strand and one helix are contributed from each monomer. The interface between the two dimers forming the tetramer is mediated solely by helix-helix contacts. The overall result is a symmetric, four-helix bundle with adjacent helices oriented antiparallel to each other and with the two antiparallel β sheets located on opposing faces of the molecule. The tetramer is stabilized not only by hydrophobic interactions within the protein core but also by a number of electrostatic interactions. The implications of the structure of the tetramer for the biological function of p53 are discussed.
Potential Role of Human Cytomegalovirus and p53 Interaction in Coronary Restenosis
Authors: Speir Edith , Modali Rama , Huang Eng-Shang , Leon Martin B. , Shawl Fayaz , Finkel Toren , Epstein Stephen E.
Published: October 2006

A subset of patients who have undergone coronary angioplasty develop restenosis, a vessel renarrowing characterized by excessive proliferation of smooth muscle cells (SMCs). Of 60 human restenosis lesions examined, 23 (38 percent) were found to have accumulated high amounts of the tumor suppressor protein p53, and this correlated with the presence of human cytomegalovirus (HCMV) in the lesions. SMCs grown from the lesions expressed HCMV protein IE84 and high amounts of p53. HCMV infection of cultured SMCs enhanced p53 accumulation, which correlated temporally with IE84 expression. IE84 also bound to p53 and abolished its ability to transcriptionally activate a reporter gene. Thus, HCMV, and IE84-mediated inhibition of p53 function, may contribute to the development of restenosis.
Importance of Peptide Amino and Carboxyl Termini to the Stability of MHC Class I Molecules
Authors: Bouvier Marlène , Wiley Don C.
Published: October 2006

An influenza virus matrix peptide in which either the charged amino or carboxyl terminus was substituted by methyl groups promoted folding of the class I human histocompatibility antigen (HLA-A2). A peptide modified at both termini did not promote stable folding. The thermal stability of HLA-A2 complexed with peptides that did not have either terminus was ∼22°C lower than that of the control peptide, whereas matrix peptide in which both anchor positions were substituted by alanines had its stability decreased by only 5.5°C. Thus, the conserved major histocompatibility complex class I residues at both ends of the peptide binding site form energetically important sites for binding the termini of short peptides.
Adaptive Mutation by Deletions in Small Mononucleotide Repeats
Authors: Rosenberg Susan M. , Longerich Simonne , Gee Pauline , Harris Reuben S.
Published: October 2006

Adaptive reversion of a +1 frameshift mutation in
Escherichia coli
, which requires homologous recombination functions, is shown here to occur by -1 deletions in regions of small mononucleotide repeats. This pattern makes improbable recombinational mechanisms for adaptive mutation in which blocks of sequences are transferred into the mutating gene, and it supports mechanisms that use DNA polymerase errors. The pattern appears similar to that of mutations found in yeast cells and in hereditary colon cancer cells that are deficient in mismatch repair. These results suggest a recombinational mechanism for adaptive mutation that functions through polymerase errors that persist as a result of a deficiency in post-synthesis mismatch repair.
The Three-Dimensional Crystal Structure of the Catalytic Core of Cellobiohydrolase I from
Trichoderma reesei
Authors: Divne Christina , Ståhlberg Jerry , Reinikainen Tapani , Ruohonen Laura , Pettersson Göran , Knowles Jonathan K. C. , Teeri Tuula T. , Jones T. Alwyn
Published: October 2006

Cellulose is the major polysaccharide of plants where it plays a predominantly structural role. A variety of highly specialized microorganisms have evolved to produce enzymes that either synergistically or in complexes can carry out the complete hydrolysis of cellulose. The structure of the major cellobiohydrolase, CBHI, of the potent cellulolytic fungus
Trichoderma reesei
has been determined and refined to 1.8 angstrom resolution. The molecule contains a 40 angstrom long active site tunnel that may account for many of the previously poorly understood macroscopic properties of the enzyme and its interaction with solid cellulose. The active site residues were identified by solving the structure of the enzyme complexed with an oligosaccharide,
o
-iodobenzyl-1-thio-β-cellobioside. The three-dimensional structure is very similar to a family of bacterial β-glucanases with the main-chain topology of the plant legume lectins.
Association of Polyomavirus Middle Tumor Antigen with 14-3-3 Proteins
Authors: Pallas David C. , Fu Haian , Haehnel Leda C. , Weller Wendy , Collier R. John , Roberts Thomas M.
Published: October 2006

To carry out its transformation function, the middle tumor antigen (MT) of murine polyomavirus associates with a number of cellular proteins involved in regulation of cell proliferation, including pp60
c-Src
, phosphatidylinositol 3-kinase, protein phosphatase 2A, Src homologous and collagen protein and growth factor receptor-binding protein 2. Here, two additional MT-associated proteins were identified as members of the 14-3-3 family of proteins. Yeast homologs of 14-3-3 proteins have recently been shown to play a role in the timing of mitosis. Thus, regulation of 14-3-3 protein function by MT may contribute to the development of neoplasia.
Reactivation of Hippocampal Ensemble Memories During Sleep
Authors: Wilson Matthew A. , McNaughton Bruce L.
Published: October 2006

Simultaneous recordings were made from large ensembles of hippocampal "place cells" in three rats during spatial behavioral tasks and in slow-wave sleep preceding and following these behaviors. Cells that fired together when the animal occupied particular locations in the environment exhibited an increased tendency to fire together during subsequent sleep, in comparison to sleep episodes preceding the behavioral tasks. Cells that were inactive during behavior, or that were active but had non-overlapping spatial firing, did not show this increase. This effect, which declined gradually during each post-behavior sleep session, may result from synaptic modification during waking experience. Information acquired during active behavior is thus re-expressed in hippocampal circuits during sleep, as postulated by some theories of memory consolidation.
Neutrophil and B Cell Expansion in Mice That Lack the Murine IL-8 Receptor Homolog
Authors: Cacalano Grace , Lee James , Kikly Kristine , Ryan Ann M. , Pitts-Meek Sharon , Hultgren Bruce , Wood William I. , Moore Mark W.
Published: October 2006

Interleukin-8 (IL-8) is a proinflammatory cytokine that specifically attracts and activates human neutrophils. A murine gene with a high degree of homology to the two known human IL-8 receptors was cloned and then deleted from the mouse genome by homologous recombination in embryonic stem (ES) cells. These mice, although outwardly healthy, had lymphadenopathy, resulting from an increase in B cells, and splenomegaly, resulting from an increase in metamyelocytes, band, and mature neutrophils. Thus, this receptor may participate in the expansion and development of neutrophils and B cells. This receptor was the major mediator of neutrophil migration to sites of inflammation and may provide a potential therapeutic target in inflammatory disease.
Control of Topographic Retinal Axon Branching by Inhibitory Membrane-Bound Molecules
Authors: Roskies Adina L. , O'Leary Dennis D. M.
Published: October 2006

Retinotopic map development in nonmammalian vertebrates appears to be controlled by molecules that guide or restrict retinal axons to correct locations in their targets. However, the retinotopic map in the superior colliculus (SC) of the rat is developed instead by a topographic bias in collateral branching and arborization. Temporal retinal axons extending across alternating membranes from the topographically correct rostral SC or the incorrect caudal SC of embryonic rats preferentially branch on rostral membranes. Branching preference is due to an inhibitory phosphatidylinositol-linked molecule in the caudal SC. Thus, position-encoding membrane-bound molecules may establish retinotopic maps in mammals by regulating axon branching, not by directing axon growth.
On the Probability of Finding a Water Molecule in a Nonpolar Cavity
Authors: Wolfenden Richard , Radzicka Anna
Published: October 2006

Measurements of solubility and vapor pressure indicate that the cost of making a cavity in a nonpolar solvent that is large enough to accommodate a single water molecule is just balanced by the attraction between the water molecule and the walls of the cavity. As a result of this unexpected coincidence, the equilibrium constant for entry of an isolated water molecule from the vapor phase into cyclohexane is almost exactly unity at room temperature. Molecules smaller than water prefer the vapor phase, whereas molecules larger than water prefer cyclohexane. In equilibrium with liquid water, the tendency of single water molecules to enter small nonpolar cavities, such as may be present in mutant proteins, is expected to be vanishingly small.
Activation of a Cerebellar Output Nucleus During Cognitive Processing
Authors: Kim S.-G. , Uğurbil K. , Strick P. L.
Published: October 2006

Magnetic resonance imaging was used to examine the involvement of the dentate nucleus of the cerebellum in cognitive operations. All seven people examined displayed a large bilateral activation in the dentate during their attempts to solve a pegboard puzzle. The area activated was three to four times greater than that activated during simple movements of the pegs. These results provide support for the concept that the computational power of the cerebellum is applied not only to the control of movement but also to cognitive functions.
Ribosomal Heterogeneity from Chromatin Diminution in
Ascaris lumbricoides
Authors: Etter A. , Bernard V. , Kenzelmann M. , Tobler H. , Müller F.
Published: October 2006

The genome of
Ascaris lumbricoides
encodes both germline- and soma-specific proteins homologous to the eukaryotic small ribosomal protein (Rp) S19. The two
Ascaris
homologs differ by 24 amino acid substitutions and are both components of the small ribosomal subunits. In oocytes, the germline RpS19 homolog (RpS19G) predominates. During chromatin diminution, however, the gene is eliminated from all presomatic cells, and RpS19G is replaced by the product of the somatic gene (RpS19S). Chromatin diminution in
A. lumbricoides
causes a change in the protein composition of ribosomes during development and represents an alternative means of gene regulation.
Transformation of Mammalian Cells by Constitutively Active MAP Kinase Kinase
Authors: Mansour Sam J. , Matten Wayne T. , Hermann April S. , Candia Julian M. , Rong Sing , Fukasawa Kenji , Vande Woude George F. , Ahn Natalie G.
Published: October 2006

Mitogen-activated protein (MAP) kinase kinase (MAPKK) activates MAP kinase in a signal transduction pathway that mediates cellular responses to growth and differentiation factors. Oncogenes such as
ras
,
src
,
raf
, and
mos
have been proposed to transform cells by prolonging the activated state of MAPKK and of components downstream in the signaling pathway. To test this hypothesis, constitutively active MAPKK mutants were designed that had basal activities up to 400 times greater than that of the unphosphorylated wild-type kinase. Expression of these mutants in mammalian cells activated AP-1-regulated transcription. The cells formed transformed foci, grew efficiently in soft agar, and were highly tumorigenic in nude mice. These findings indicate that constitutive activation of MAPKK is sufficient to promote cell transformation.
Dependence of Enhancer-Mediated Transcription of the Immunoglobulin μ Gene on Nuclear Matrix Attachment Regions
Authors: Forrester William C. , van Genderen Courtney , Jenuwein Thomas , Grosschedl Rudolf
Published: October 2006

Transcription of the immunoglobulin μ heavy chain locus is regulated by an intronic enhancer that is flanked on both sides by nuclear matrix attachment regions (MARs). These MARs have now been shown to be essential for transcription of a rearranged μ gene in transgenic B lymphocytes, but they were not required in stably transfected tissue culture cells. Normal rates of transcriptional initiation at a variable region promoter and the formation of an extended deoxyribonuclease I (DNase I)—sensitive chromatin domain were dependent on MARs, although DNase I hypersensitivity at the enhancer was detected in the absence of MARs. Thus, transcriptional activation of the μ gene during normal lymphoid development requires a synergistic collaboration between the enhancer and flanking MARs.
Catalysis of ATP-Dependent Homologous DNA Pairing and Strand Exchange by Yeast RAD51 Protein
Authors: Sung Patrick
Published: October 2006

The
RAD51
gene of
Saccharomyces cerevisiae
is required for genetic recombination and DNA double-strand break repair. Here it is demonstrated that RAD51 protein pairs circular viral single-stranded DNA from φX 174 or M13 with its respective homologous linear double-stranded form. The product of synapsis between these DNA partners is further processed by RAD51 to yield nicked circular duplex DNA, which indicates that RAD51 can catalyze strand exchange. The pairing and strand exchange reaction requires adenosine triphosphate, a result consistent with the presence of a DNA-dependent adenosine triphosphatase activity in RAD51 protein. Thus, RAD51 is a eukaryotic recombination protein that can catalyze the strand exchange reaction.
Lattice Location oif Trace Elements Within Minerals and at Their Surfaces with X-Ray Standing Waves
Authors: Qian Yonglin , Sturchio Neil C. , Chiarello Ronald P. , Lyman Paul F. , Lee Tien-Lin , Bedzyk Michael J
Published: October 2006

The x-ray standing waves generated by dynamical Bragg diffraction were used to directly measure lattice locations of trace elements within and at the surface of a mineral single crystal. These high-precision measurements were made on natural Iceland spar calcite cleaved along the (101̅4) plane and reacted with a dilute aqueous lead solution. Within the bulk crystal, naturally occurring trace manganese was found within (101̅4) planes, consistent with its substitution for calcium. At the crystal surface, sorbed lead was found to be highly ordered and mostly within (101̅4) planes. This demonstrates a powerful application of synchrotron radiation in the earth and environmental sciences.
Requirement of Transcription Factor PU.1 in the Development of Multiple Hematopoietic Lineages
Authors: Scott Edward W. , Simon M. Celeste , Anastasi John , Singh Harinder
Published: October 2006

The transcription factor PU.1 is a hematopoietic-specific member of theetsfamily. Mice carrying a mutation in thePU.1locus were generated by gene targeting. Homozygous mutant embryos died at a late gestational stage. Mutant embryos produced normal numbers of megakaryocytes and erythroid progenitors, but some showed an impairment of erythroblast maturation. An invariant consequence of the mutation was a multilineage defect in the generation of progenitors for B and T lymphocytes, monocytes, and granulocytes. Thus, the developmental programs of lymphoid and myeloid lineages require a common genetic function likely acting at the level of a multipotential progenitor.
Analysis of Sequence Transfers Resembling Gene Conversion in a Mouse Antibody Transgene
Authors: Xu Bo , Selsing Erik
Published: October 2006

The role of gene conversion in murine immunoglobulin gene diversification is unclear. An antibody gene construct designed to provide the homologous donor and acceptor sequences required for conversion mechanisms was produced and used to generate transgenic mice. When these transgenic mice were immunized, DNA sequence transfers between tandem transgene VDJ regions were detectable and resembled gene conversion events. There is a strong link between these conversion-like sequence transfers and transgene somatic hypermutation, suggesting that both processes might occur at the same stage of B cell differentiation.
Activation of the Sphingomyelin Cycle Through the Low-Affinity Neurotrophin Receptor
Authors: Dobrowsky Rick T. , Werner Mark H. , Castellino Alexander M. , Chao Moses V. , Hannun Yusuf A.
Published: October 2006

The role of the low-affinity neurotrophin receptor (p75
NTR
) in signal transduction is undefined. Nerve growth factor can activate the sphingomyelin cycle, generating the putative-lipid second messenger ceramide. In T9 glioma cells, addition of a cell-permeable ceramide analog mimicked the effects of nerve growth factor on cell growth inhibition and process formation. This signaling pathway appears to be mediated by p75
NTR
in T9 cells and NIH 3T3 cells overexpressing p75
NTR
. Expression of an epidermal growth factor receptor-p75
NTR
chimera in T9 cells imparted to epidermal growth factor the ability to activate the sphingomyelin cycle. These data demonstrate that p75
NTR
is capable of signaling independently of the
trk
neurotrophin receptor (p140

trk

) and that ceramide may be a mediator in neurotrophin biology.
Nitric Oxide Activation of Poly(ADP-Ribose) Synthetase in Neurotoxicity
Authors: Zhang Jie , Dawson Valina L. , Dawson Ted M. , Snyder Solomon H.
Published: October 2006

Poly(adenosine 5′-diphosphoribose) synthetase (PARS) is a nuclear enzyme which, when activated by DNA strand breaks, adds up to 100 adenosine 5′-diphosphoribose (ADP-ribose) units to nuclear proteins such as histones and PARS itself. This activation can lead to cell death through depletion of β-nicotinamide adenine dinucleotide (the source of ADP-ribose) and adenosine triphosphate. Nitric oxide (NO) stimulated ADP-ribosylation of PARS in rat brain. Benzamide and other derivatives, which inhibit PARS, blocked
N
-methyl-D-aspartate- and NO-mediated neurotoxicity with relative potencies paralleling their ability to inhibit PARS. Thus, NO appeared to elicit neurotoxicity by activating PARS.
An Interleukin-4-Induced Transcription Factor: IL-4 Stat
Authors: Hou Jinzhao , Schindler Ulrike , Henzel William J. , Ho Tze Chun , Brasseur Mike , McKnight Steven L.
Published: October 2006

Interleukin-4 (IL-4) is an immunomodulatory cytokine secreted by activated T lymphocytes, basophils, and mast cells. It plays an important role in modulating the balance of T helper (Th) cell subsets, favoring expansion of the Th2 lineage relative to Th1. Imbalance of these T lymphocyte subsets has been implicated in immunological diseases including allergy, inflammation, and autoimmune disease. IL-4 may mediate its biological effects, at least in part, by activating a tyrosine-phosphorylated DNA binding protein. This protein has now been purified and its encoding gene cloned. Examination of the primary amino acid sequence of this protein indicates that it is a member of the signal transducers and activators of transcription (Stat) family of DNA binding proteins, hereby designated IL-4 Stat. Study of the inhibitory activities of phosphotyrosine-containing peptides derived from the intracellular domain of the IL-4 receptor provided evidence for direct coupling of receptor and transcription factor during the IL-4 Stat activation cycle. Such observations indicate that IL-4 Stat has the same functional domain for both receptor coupling and dimerization.
Regulation of Alternative Splicing in Vivo by Overexpression of Antagonistic Splicing Factors
Authors: Cáceres Javier F. , Stamm Stefan , Helfman David M. , Krainer Adrian R.
Published: October 2006

The opposing effects of SF2/ASF and heterogeneous nuclear ribonucleoprotein (hnRNP) A1 influence alternative splicing in vitro. SF2/ASF or hnRNP A1 complementary DNAs were transiently overexpressed in HeLa cells, and the effect on alternative splicing of several cotransfected reporter genes was measured. Increased expression of SF2/ASF activated proximal 5′ splice sites, promoted inclusion of a neuron-specific exon, and prevented abnormal exon skipping. Increased expression of hnRNP A1 activated distal 5′ splice sites. Therefore, variations in the intracellular levels of antagonistic splicing factors influence different modes of alternative splicing in vivo and may be a natural mechanism for tissue-specific or developmental regulation of gene expression.
Molecular Determinants of State-Dependent Block of Na
+
Channels by Local Anesthetics
Authors: Ragsdale David S. , McPhee Jancy C. , Scheuer Todd , Catterall William A.
Published: October 2006

Sodium ion (Na
+
) channels, which initiate the action potential in electrically excitable cells, are the molecular targets of local anesthetic drugs. Site-directed mutations in transmembrane segment S6 of domain IV of the Na
+
channel α subunit from rat brain selectively modified drug binding to resting or to open and inactivated channels when expressed in
Xenopus
oocytes. Mutation F1764A, near the middle of this segment, decreased the affinity of open and inactivated channels to 1 percent of the wild-type value, resulting in almost complete abolition of both the use-dependence and voltage-dependence of drug block, whereas mutation N1769A increased the affinity of the resting channel 15-fold. Mutation I1760A created an access pathway for drug molecules to reach the receptor site from the extracellular side. The results define the location of the local anesthetic receptor site in the pore of the Na
+
channel and identify molecular determinants of the state-dependent binding of local anesthetics.
Thymus-Neuroendocrine Interactions in Extrathymic T Cell Development
Authors: Wang Jin , Klein John R.
Published: October 2006

Studies of the development of murine intestinal intraepithelial lymphocytes (IELs) have yielded markedly different results depending on the experimental system used. In athymic radiation chimeras, IELs consist of all subsets found in euthymic mice; adult mice that were athymic at birth have only IELs that are positive for T cell receptor γδ and CD8αα. These differences are resolved by the finding that administration of the neuropeptide thyrotropin-releasing hormone to adult mice thymectomized as neonates leads to the development of all IEL T cells. Thus, a neuroendocrine signal initiated by the thymus during fetal or neonatal life appears to be required for subsequent extrathymic maturation of gut αβ T cells.
Complementation by SR Proteins of Pre-mRNA Splicing Reactions Depleted of U1 snRNP
Authors: Crispino John D. , Blencowe Benjamin J. , Sharp Phillip A.
Published: October 2006

Individual small nuclear ribonucleoproteins (snRNPs) U1, U2, and U4/U6 were removed from nuclear extracts of HeLa cells by antisense affinity depletion. Addition of a highly purified preparation of SR proteins fully restored splicing activity in reactions depleted of U1 snRNP but did not reconstitute splicing in reactions depleted of the other snRNPs. Affinity selection experiments revealed that spliceosomes lacking U1 snRNA formed in the U1 snRNP-depleted reactions reconstituted with SR proteins. Thus, high concentrations of SR proteins facilitate the assembly of precursor messenger RNA (pre-mRNA) into a spliceosome in the absence of interactions with U1 snRNP.
Enhanced Aggressive Behavior in Mice Lacking 5-HT
1B
Receptor
Authors: Saudou Frédéric , Amara Djamel Aït , Dierich Andrée , LeMeur Marianne , Ramboz Sylvie , Segu Louis , Buhot Marie-Christine , Hen René
Published: October 2006

The neuromodulator serotonin (5-hydroxytryptamine, 5-HT) has been associated with mood disorders such as depression, anxiety, and impulsive violence. To define the contribution of 5-HT receptor subtypes to behavior, mutant mice lacking the 5-HT
1B
receptor were generated by homologous recombination. These mice did not exhibit any obvious developmental or behavioral defects. However, the hyperlocomotor effect of the 5-HT
1A/1B
agonist RU24969 was absent in mutant mice, indicating that this effect is mediated by 5-HT
1B
receptors. Moreover, when confronted with an intruder, mutant mice attacked the intruder faster and more intensely than did wild-type mice, suggesting the participation of 5-HT
1B
receptors in aggressive behavior.
Premature Microtubule-Dependent Cytoplasmic Streaming in
cappuccino
and
spire
Mutant Oocytes
Authors: Theurkauf William E.
Published: October 2006

Embryonic axis specification in
Drosophila melanogaster
is achieved through the asymmetric subcellular localization of morphogenetic molecules within the oocyte. The
cappuccino
and
spire
loci are required for both posterior and dorsoventral patterning. Time-lapse confocal microscopic analyses of living egg chambers demonstrated that these mutations induce microtubule reorganization and the premature initiation of microtubule-dependent ooplasmic streaming. As a result, microtubule organization is altered and bulk ooplasm rapidly streams during the developmental stages in which morphogens are normally localized. These changes in oocyte cytoarchitecture and dynamics appear to disrupt axial patterning of the embryo.
Requirement for CD8 β Chain in Positive Selection of CD8-Lineage T Cells
Authors: Nakayama Kei-ichi , Nakayama Keiko , Negishi Izumi , Kuida Keisuke , Louie Marjorie C. , Kanagawa Osami , Nakauchi Hiromitsu , Loh Dennis Y.
Published: October 2006

CD8 is either an αα homodimer or an αβ heterodimer, although most peripheral CD8-lineage T cells express only the CD8αβ heterodimer. The physiological function of CD8β was elucidated with mice that were chimeric for the homozygous disruption of the
CD8β
gene. The
CD8β
-/-
T cells developed normally to CD4
+
CD8
+
stage, but did not efficiently differentiate further, which resulted in few peripheral CD8
+
T cells. The number of peripheral CD8
+
T cells was restored by transfer of an exogenous
CD8β
gene into CD8β-deficient T cells. Thus, CD8β is necessary for the maturation of CD8
+
T cells.
Premature p34
cdc2
Activation Required for Apoptosis
Authors: Shi Lianfa , Nishioka Walter K. , Th'ng John , Bradbury E. Morton , Litchfield David W. , Greenberg Arnold H.
Published: October 2006

Activation of the serine-threonine kinase p34
cdc2
at an inappropriate time during the cell cycle leads to cell death that resembles apoptosis. Premature activation of p34
cdc2
was shown to be required for apoptosis induced by a lymphocyte granule protease. The kinase was rapidly activated and tyrosine dephosphorylated at the initiation of apoptosis. DNA fragmentation and nuclear collapse could be prevented by blocking p34
cdc2
activity with excess peptide substrate, or by inactivating p34
cdc2
in a temperature-sensitive mutant. Premature p34
cdc2
activation may be a general mechanism by which cells induced to undergo apoptosis initiate the disruption of the nucleus.
Selection of Guide Sequences That Direct Efficient Cleavage of mRNA by Human Ribonuclease P
Authors: Yuan Yan , Altman Sidney
Published: October 2006

Any RNA, when in a complex with another oligoribonucleotide known as an external guide sequence (EGS), can become a substrate for ribonuclease P. Simulation of evolution in vitro was used to select EGSs that bind tightly to a target substrate messenger RNA and that increase the efficiency of cleavage of the target by human ribonuclease P to a level equal to that achieved with natural substrates. The most efficient EGSs form transfer RNA precursor-like structures with the target RNA, in which the analog of the anticodon stem has been disrupted, an indication that selection for the optimal substrate for ribonuclease P yields an RNA structure different from that of present-day transfer RNA precursors.
Suppression of Ras-Induced Transformation of NIH 3T3 Cells by Activated Gα
S
Authors: Chen Jianghao , Iyengar Ravi
Published: October 2006

Conversion of external signals into proliferative responses may be mediated by interactions between signaling pathways that control cell proliferation. Interactions between Gα
s
, the α subunit of the heterotrimeric guanine nucleotide binding protein that stimulates adenylyl cyclase, and Ras, an important element in growth factor signaling, were studied. Expression of activated Gα
s
in NIH 3T3 cells increased intracellular concentrations of adenosine 3′,5′-monophosphate (cAMP) and inhibited H-Ras-stimulated DNA synthesis and mitogen-activated protein kinase activity. Activated Gα
s
and 8-Br-cAMP suppressed H-Ras-induced transformation of NIH 3T3 cells. Apparently, Gα
s
inhibits proliferative signals from Ras by stimulating cAMP production and activating protein kinase A.
Modulation of Cortical Motor Output Maps During Development of Implicit and Explicit Knowledge
Authors: Pascual-Leone Alvaro , Grafman Jordan , Hallett Mark
Published: October 2006

The excitability of the human motor cortex during the development of implicit and declarative knowledge of a motor task was examined. During a serial reaction time test, subjects developed implicit knowledge of the test sequence, which was reflected by diminishing response times. Motor cortical mapping with transcranial magnetic stimulation revealed that the cortical output maps to the muscles involved in the task became progressively larger until explicit knowledge was achieved, after which they returned to their baseline topography. These results illustrate the rapid functional plasticity of cortical outputs associated with learning and with the transfer of knowledge from an implicit to explicit state.
Differential Adhesion of Cells to Enantiomorphous Crystal Surfaces
Authors: Hanein Dorit , Geiger Benjamin , Addadi Lia
Published: October 2006

Interactions during cell adhesion to external surfaces may reach the level of discrimination of molecular chirality. Cultured epithelial cells interact differently with the {011} faces of the (
R
,
R
) and (
S
,
S
) calcium tartrate tetrahydrate crystals. In a modified version of the classical Pasteur experiment, the enantiomorphous crystals were sorted out from a 1:1 mixture by the selective adhesion of cells to the (
R
,
R
) crystals. This stereospecificity results from molecular recognition between chiral components on the cell surface and the structured crystal surface. Crystals may allow experimental differentiation between distinct stages in cell substrate contacts, providing mechanistic information not readily attainable on conventional heterogeneous surfaces.
DNA Repair Rates Mapped Along the Human
PGK1
Gene at Nucleotide Resolution
Authors: Gao Shuwei , Drouin Régen , Holmquist Gerald P.
Published: October 2006

The repair of cyclobutane pyrimidine dimers (CPDs), DNA lesions induced by ultraviolet light, was studied at nucleotide resolution. Human fibroblasts were irradiated with ultraviolet light and allowed to repair. The DNA was enzymatically cleaved at the CPDs, and the induced breaks along the promoter and exon 1 of the
PGK1
gene were mapped by ligation-mediated polymerase chain reaction. Repair rates within the nontranscribed strand varied as much as 15-fold, depending on nucleotide position. Preferential repair of the transcribed strand began just downstream of the transcription start site but was most pronounced beginning at nucleotide +140 in exon 1. The promoter contained two slowly repaired regions that coincided with two transcription factor binding sites.
Dependence on p75 for Innervation of Some Sympathetic Targets
Authors: Lee Kuo-Fen , Bachman Kathy , Landis Story , Jaenisch Rudolf
Published: October 2006

The low-affinity neurotrophin receptor p75 binds all neurotrophins with similar affinity. For elucidation of its function, mice bearing a null mutation in the p75 locus were generated. Examination of sympathetic innervation of target tissues revealed that pineal glands lacked innervation and sweat gland innervation was absent or reduced in particular footpads. The absence of adult innervation reflects the failure of axons to reach these targets during development rather than a target deficit. These results indicate that p75 facilitates development of specific populations of sympathetic neurons, for which it may support axon growth.
Negative Feedback Defining a Circadian Clock: Autoregulation of the Clock Gene
frequency
Authors: Aronson Benjamin D. , Johnson Keith A. , Loros Jennifer J. , Dunlap Jay C.
Published: October 2006

The
frequency
(
frq
) locus of Neurospora crassa was originally identified in searches for loci encoding components of the circadian clock. The
frq
gene is now shown to encode a central component in a molecular feedback loop in which the product of
frq
negatively regulated its own transcript, which resulted in a daily oscillation in the amount of
frq
transcript. Rhythmic messenger RNA expression was essential for overt rhythmicity in the organism and no amount of constitutive expression rescued normal rhythmicity in
frq
loss-of-function mutants. Step reductions in the amount of FRQ-encoding transcript set the clock to a specific and predicted phase. These results establish
frq
as encoding a central component in a circadian oscillator.
Loss of Circadian Behavioral Rhythms and
per
RNA Oscillations in the
Drosophila
Mutant
timeless
Authors: Sehgal Amita , Price Jeffrey L. , Man Bernice , Young Michael W.
Published: October 2006

Eclosion, or emergence of adult flies from the pupa, and locomotor activity of adults occur rhythmically in
Drosophila melanogaster
, with a circadian period of about 24 hours. Here, a clock mutation,
timeless
(
tim
), is described that produces arrhythmia for both behaviors. The effects of
tim
on behavioral rhythms are likely to involve products of the X chromosome-linked clock gene
period
(
per
), because
tim
alters circadian oscillations of
per
RNA. Genetic mapping places
tim
on the left arm of the second chromosome between
dumpy
(
dp
) and
decapentaplegic
(
dpp
).
Activation of Phosphatidylinositol-3′ Kinase by Src-Family Kinase SH3 Binding to the p85 Subunit
Authors: Pleiman Christopher M. , Hertz W. Marc , Cambier John C.
Published: October 2006

Engagement of antigen receptor complexes induces rapid activation of Src-family kinases and association with phosphatidylinositol-3′ kinase (PI-3 kinase). Here it was found that the Src homology 3 (SH3) domain of Lyn and Fyn bound to a proline-rich region (residues 84 to 99) within the 85-kilodalton subunit (p85) of PI-3 kinase. The binding of SH3 to the purified kinase led to a five- to sevenfold increase in the specific activity of PI-3 kinase. Ligand-induced receptor stimulation activated PI-3 kinase, and this activation was blocked by a peptide containing residues 84 to 99 of p85. These data demonstrate a mechanism for PI-3 kinase activation and show that binding of SH3 domains to proline-rich target sequences can regulate enzymatic activity.
Mutation of a
mutL
Homolog in Hereditary Colon Cancer
Authors: Papadopoulos Nickolas , Nicolaides Nicholas C. , Wei Ying-Fei , Ruben Steven M. , Carter Kenneth C. , Rosen Craig A. , Haseltine William A. , Fleischmann Robert D. , Fraser Claire M. , Adams Mark D. , Venter J. Craig , Hamilton Stanley R. , Petersen Gloria M. , Watson Patrice , Lynch Henry T. , Peltomäki Päivi , Mecklin Jukka-Pekka , de la Chapelle Albert , Kinzler Kenneth W. , Vogelstein Bert
Published: October 2006

Some cases of hereditary nonpolyposis colorectal cancer (HNPCC) are due to alterations in a
mutS
-related mismatch repair gene. A search of a large database of expressed sequence tags derived from random complementary DNA clones revealed three additional human mismatch repair genes, all related to the bacterial
mutL
gene. One of these genes (
hMLH1
) resides on chromosome 3p21, within 1 centimorgan of markers previously linked to cancer susceptibility in HNPCC kindreds. Mutations of
hMLH1
that would disrupt the gene product were identified in such kindreds, demonstrating that this gene is responsible for the disease. These results suggest that defects in any of several mismatch repair genes can cause HNPCC.
Langmuir-Blodgett films
Authors: Zasadzinski J. A. , Viswanathan R. , Madsen L. , Garnaes J. , Schwartz D. K.
Published: October 2006

The controlled transfer of organized monolayers of amphiphilic molecules from the air-water interface to a solid substrate was the first molecular-scale technology for the creation of new materials. However, the potential benefits of the technology envisioned by Langmuir and Blodgett in the 1930s have yet to be fully realized. Problems of reproducibility and defects and the lack of basic understanding of the packing of complex molecules in thin films have continued to thwart practical applications of Langmuir-Blodgett films and devices made from such films. However, modern high-resolution x-ray diffraction and scanning probe microscopy have proven to be ideal tools to resolve many of the basic questions involving thin organic films. Here, studies are presented of molecular order and organization in thin films of fatty acid salts, the prototypical system of Katharine Blodgett. Even these relatively simple systems present liquid, hexatic, and crystalline order; van der Waals and strained layer epitaxy on various substrates; wide variations in crystal symmetry and interfacial area with counterions; modulated superstructures; and coexisting lattice structures. The wide variety of possible structures presents both a challenge and an opportunity for future molecular design of organic thin-film devices.
Genetic Mapping of Quantitative Trait Loci for Growth and Fatness in Pigs
Authors: Andersson Leif , Haley Chris S. , Ellegren Hans , Knott Sara A. , Johansson Maria , Andersson Kjell , Andersson-Eklund Lena , Edfors-Lilja Inger , Fredholm Merete , Hansson Ingemar , Håkansson Jan , Lundström Kerstin
Published: October 2006

The European wild boar was crossed with the domesticated Large White pig to genetically dissect phenotypic differences between these populations for growth and fat deposition. The most important effects were clustered on chromosome 4, with a single region accounting for a large part of the breed difference in growth rate, fatness, and length of the small intestine. The study is an advance in genome analyses and documents the usefulness of crosses between divergent outbred populations for the detection and characterization of quantitative trait loci. The genetic mapping of a major locus for fat deposition in the pig could have implications for understanding human obesity.
Requirement of Human Renal Water Channel Aquaporin-2 for Vasopressin-dependent Concentration of Urine
Authors: Deen Peter M. T. , Verdijk Marian A. J. , Knoers Nine V. A. M. , Wieringa Bé , Monnens Leo A. H. , van Os Carel H. , van Oost Bernard A.
Published: October 2006

Concentration of urine in mammals is regulated by the antidiuretic hormone vasopressin. Binding of vasopressin to its V2 receptor leads to the insertion of water channels in apical membranes of principal cells in collecting ducts. In nephrogenic diabetes insipidus (NDI), the kidney fails to concentrate urine in response to vasopressin. A male patient with an autosomal recessive form of NDI was found to be a compound heterozygote for two mutations in the gene encoding aquaporin-2, a water channel. Functional expression studies in
Xenopus
oocytes revealed that each mutation resulted in nonfunctional water channel proteins. Thus, aquaporin-2 is essential for vasopressin-dependent concentration of urine.
Neural Mechanisms for Forming a Perceptual Decision
Authors: Salzman C. Daniel , Newsome William T.
Published: October 2006

Cognitive and behavioral responses to environmental stimuli depend on an evaluation of sensory signals within the cerebral cortex. The mechanism by which this occurs in a specific visual task was investigated with a combination of physiological and psychophysical techniques. Rhesus monkeys discriminated among eight possible directions of motion while directional signals were manipulated in visual area MT. One directional signal was generated by a visual stimulus and a second signal was introduced by electrically stimulating neurons that encoded a specific direction of motion. The decisions made by the monkeys in response to the two signals allowed a distinction to be made between two possible mechanisms for interpreting directional signals in MT. The monkeys tended to cast decisions in favor of one or the other signal, indicating that the signals exerted independent effects on performance and that an interactive mechanism such as vector averaging of the two signals was not operative. Thus, the data suggest a mechanism in which monkeys chose the direction encoded by the largest signal in the representation of motion direction, a "winner-take-all" decision process.