bluuebunny/crossref_metadata_2025 huggingface dataset:
p53
Status and the Efficacy of Cancer Therapy in Vivo
Authors: Lowe Scott W. , Bodis Stephan , McClatchey Andrea , Remington Lee , Ruley H. Earl , Fisher David E. , Housman David E. , Jacks Tyler
Published: October 2006

The therapeutic responsiveness of genetically defined tumors expressing or devoid of the p53 tumor suppressor gene was compared in immunocompromised mice. Tumors expressing the p53 gene contained a high proportion of apoptotic cells and typically regressed after treatment with gamma radiation or adriamycin. In contrast, p53-deficient tumors treated with the same regimens continued to enlarge and contained few apoptotic cells. Acquired mutations in p53 were associated with both treatment resistance and relapse in p53-expressing tumors. These results establish that defects in apoptosis, here caused by the inactivation of p53, can produce treatment-resistant tumors and suggest that p53 status may be an important determinant of tumor response to therapy.
Ligands for EPH-Related Receptor Tyrosine Kinases that Require Membrane Attachment or Clustering for Activity
Authors: Davis Samuel , Gale Nicholas W. , Aldrich Thomas H. , Maisonpierre Peter C. , Lhotak Vladimir , Pawson Tony , Goldfarb Mitchell , Yancopoulos George D.
Published: October 2006

The EPH-related transmembrane tyrosine kinases constitute the largest known family of receptor-like tyrosine kinases, with many members displaying specific patterns of expression in the developing and adult nervous system. A family of cell surface-bound ligands exhibiting distinct, but overlapping, specificities for these EPH-related kinases was identified. These ligands were unable to act as conventional soluble factors. However, they did function when presented in membrane-bound form, suggesting that they require direct cell-to-cell contact to activate their receptors. Membrane attachment may serve to facilitate ligand dimerization or aggregation, because antibody-mediated clustering activated previously inactive soluble forms of these ligands.
The Function of KGF in Morphogenesis of Epithelium and Reepithelialization of Wounds
Authors: Werner Sabine , Smola Hans , Liao Xiang , Longaker Michael T. , Krieg Thomas , Hofschneider Peter Hans , Williams Lewis T.
Published: October 2006

The function of keratinocyte growth factor (KGF) in normal and wounded skin was assessed by expression of a dominant-negative KGF receptor transgene in basal keratinocytes. The skin of transgenic mice was characterized by epidermal atrophy, abnormalities in the hair follicles, and dermal hyperthickening. Upon skin injury, inhibition of KGF receptor signaling reduced the proliferation rate of epidermal keratinocytes at the wound edge, resulting in substantially delayed reepithelialization of the wound.
Isolation of Components of the Chloroplast Protein Import Machinery
Authors: Schnell Danny J. , Kessler Felix , Blobel Günter
Published: October 2006

Components of the protein import machinery of the chloroplast were isolated by a procedure in which the import machinery was engaged in vitro with a tagged import substrate under conditions that yielded largely chloroplast envelope-bound import intermediates. Subsequent detergent solubilization of envelope membranes showed that six envelope polypeptides copurified specifically and, apparently, stoichiometrically with the import intermediates. Four of these polypeptides are components of the outer membrane import machinery and are associated with early import intermediates. Two of these polypeptides have been characterized. One is a homolog of the heat shock protein hsp70; the other one is a channel-protein candidate.
Molecular Maps of Red Cell Deformation: Hidden Elasticity and in Situ Connectivity
Authors: Discher D. E. , Mohandas N. , Evans E. A.
Published: October 2006

Fluorescence-imaged micropipette aspiration was used to map redistribution of the proteins and lipids in highly extended human red blood cell membranes. Whereas the fluid bilayer distributed uniformly (± 10 percent), the underlying, solidlike cytoskeleton of spectrin, actin, and protein 4.1 exhibited a steep gradient in density along the aspirated projection, which was reversible on release from deformation. Quantitation of the cytoskeletal protein density gradients showed that skeletal elasticity is well represented by a grafted polymer network with a ratio of surface dilation modulus to shear modulus of approximately 2:1. Fractionally mobile integral proteins, such as band 3, and highly mobile receptors, such as CD59 as well as glycophorin C in protein 4.1-deficient cells, appeared to be squeezed out of areas dense in the underlying network and enriched in areas of network dilation. This complementary segregation demonstrates patterning of cell surface components by cytoskeletal dilation.
Functional Activation of Jak1 and Jak3 by Selective Association with IL-2 Receptor Subunits
Authors: Miyazaki Tadaaki , Kawahara Atsuo , Fujii Hodaka , Nakagawa Yoko , Minami Yasuhiro , Liu Zhao-Jun , Oishi Isao , Silvennoinen Olli , Witthuhn Bruce A. , Ihle James N. , Taniguchi Tadatsugu
Published: October 2006

The interleukin-2 receptor (IL-2R) consists of three subunits: the IL-2Rα, IL-2Rβ, and IL-2Rγ chains, the last of which is also used in the receptors for IL-4, IL-7, and IL-9. Stimulation with IL-2 induces the tyrosine phosphorylation and activation of the Janus kinases Jak1 and Jak3. Jak1 and Jak3 were found to be selectively associated with the "serine-rich" region of IL-2Rβ and the carboxyl-terminal region of IL-2Rγ, respectively. Both regions were necessary for IL-2 signaling. Furthermore, Jak3-negative fibroblasts expressing reconstituted IL-2R became responsive to IL-2 after the additional expression of Jak3 complementary DNA. Thus, activation of Jak1 and Jak3 may be a key event in IL-2 signaling.
A Potential Noninvasive Neurobiological Test for Alzheimer's Disease
Authors: Scinto Leonard F. M. , Daffner Kirk R. , Dressler David , Ransil Bernard I. , Rentz Dorene , Weintraub Sandra , Mesulam Marsel , Potter Huntington
Published: October 2006

Currently Alzheimer's disease, which affects more than 20 million people worldwide, can only be definitively diagnosed by histological examination of brain tissue obtained at autopsy or biopsy. There is a great need for an early, noninvasive, sensitive, and easily administered diagnostic test of Alzheimer's disease. Here it is reported that patients diagnosed with probable Alzheimer's disease by standard clinical criteria exhibited a marked hypersensitivity in their pupil dilation response to a cholinergic antagonist, tropicamide, placed in their eyes. It was possible to distinguish 18 of 19 individuals (95%) either clinically diagnosed with Alzheimer's disease or classified as suspect Alzheimer's individuals by neuropsychological screening from 30 of 32 normal elderly controls (94%).
Analysis and Expression of a Cloned Pre-T Cell Receptor Gene
Authors: Saint-Ruf Claude , Ungewiss Katharina , Groettrup Marcus , Bruno Ludovica , Fehling Hans Joerg , von Boehmer Harald
Published: October 2006

The T cell antigen receptor (TCR) β chain regulates early T cell development in the absence of the TCRα chain. The developmentally controlled gene described here encodes the pre-TCRα (pTα) chain, which covalently associates with TCRβ and with the CD3 proteins forms a pre-TCR complex that transduces signals in immature thymocytes. Unlike the λ5 pre-B cell receptor protein, the pTα chain is a type I transmembrane protein whose cytoplasmic tail contains two potential phosphorylation sites and a Src homology 3 (SH3)-domain binding sequence. Pre-TCRα transfection experiments indicated that surface expression of the pre-TCR is controlled by additional developmentally regulated proteins. Identification of the pTα gene represents an essential step in the structure-function analysis of the pre-TCR complex.
Interaction of the p53-Regulated Protein Gadd45 with Proliferating Cell Nuclear Antigen
Authors: Smith Martin L. , Chen I.-Tsuen , Zhan Qimin , Bae Insoo , Chen Chaw-Yuan , Gilmer Tona M. , Kastan Michael B , O'Connor Patrick M. , Fornace Albert J.
Published: October 2006

GADD45
is a ubiquitously expressed mammalian gene that is induced by DNA damage and certain other stresses. Like another p53-regulated gene,

p21
WAF1/CIP1

, whose product binds to cyclin-dependent kinases (Cdk's) and proliferating cell nuclear antigen (PCNA),
GADD45
has been associated with growth suppression. Gadd45 was found to bind to PCNA, a normal component of Cdk complexes and a protein involved in DNA replication and repair. Gadd45 stimulated DNA excision repair in vitro and inhibited entry of cells into S phase. These results establish
GADD45
as a link between the p53-dependent cell cycle checkpoint and DNA repair.
How a Protein Binds B
12
: A 3.0 Å X-Ray Structure of B
12
-Binding Domains of Methionine Synthase
Authors: Drennan Catherine Luschinsky , Huang Sha , Drummond James T. , Matthews Rowena G. , Ludwig Martha L.
Published: October 2006

The crystal structure of a 27-kilodalton methylcobalamin-containing fragment of methionine synthase from
Escherichia coli
was determined at 3.0 Å resolution. This structure depicts cobalamin-protein interactions and reveals that the corrin macrocycle lies between a helical amino-terminal domain and an α/β carboxyl-terminal domain that is a variant of the Rossmann fold. Methylcobalamin undergoes a conformational change on binding the protein; the dimethylbenzimidazole group, which is coordinated to the cobalt in the free cofactor, moves away from the corrin and is replaced by a histidine contributed by the protein. The sequence Asp-X-His-X-X-Gly, which contains this histidine ligand, is conserved in the adenosylcobalamin-dependent enzymes methylmalonyl-coenzyme A mutase and glutamate mutase, suggesting that displacement of the dimethylbenzimidazole will be a feature common to many cobalamin-binding proteins. Thus the cobalt ligand, His
759
, and the neighboring residues Asp
757
and Ser
810
, may form a catalytic quartet, Co-His-Asp-Ser, that modulates the reactivity of the B
12
prosthetic group in methionine synthase.
Control of Kinetic Properties of AMPA Receptor Channels by Nuclear RNA Editing
Authors: Lomeli Hilda , Mosbacher Johannes , Melcher Thorsten , Höger Thomas , Geiger Jörg R. P. , Kuner Thomas , Monyer Hannah , Higuchi Miyoko , Bach Alfred , Seeburg Peter H.
Published: October 2006

AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor channels mediate the fast component of excitatory postsynaptic currents in the central nervous system. Site-selective nuclear RNA editing controls the calcium permeability of these channels, and RNA editing at a second site is shown here to affect the kinetic aspects of these channels in rat brain. In three of the four AMPA receptor subunits (GluR-B, -C, and -D), intronic elements determine a codon switch (AGA, arginine, to GGA, glycine) in the primary transcripts in a position termed the R/G site, which immediately precedes the alternatively spliced modules "flip" and "flop." The extent of editing at this site progresses with brain development in a manner specific for subunit and splice form, and edited channels possess faster recovery rates from desensitization.
Suppression of Hyphal Formation in
Candida albicans
by Mutation of a
STE12
Homolog
Authors: Liu Haoping , Köhler Julia , Fink Gerald R.
Published: October 2006

A
Candida albicans
gene (
CPH1
) was cloned that encodes a protein homologous to
Saccharomyces cerevisiae
Ste12p, a transcription factor that is the target of the pheromone response mitogen-activated protein kinase cascade.
CPH1
complements both the mating defect of
ste12
haploids and the filamentous growth defect of
ste12
/
ste12
diploids.
Candida albicans
strains without a functional
CPH1
gene (
cph1
/
cph1
) show suppressed hyphal formation on solid medium. However,
cph1
/
cph1
strains can still form hyphae in liquid culture and in response to serum. Thus, filamentous growth may be activated in
C. albicans
by the same signaling kinase cascade that activates Ste12p in
S. cerevisiae
; however, alternative pathways may exist in
C. albicans
.
Identification of Herpesvirus-Like DNA Sequences in AIDS-Sssociated Kaposi's Sarcoma
Authors: Chang Yuan , Cesarman Ethel , Pessin Melissa S. , Lee Frank , Culpepper Janice , Knowles Daniel M. , Moore Patrick S.
Published: October 2006

Representational difference analysis was used to isolate unique sequences present in more than 90 percent of Kaposi's sarcoma (KS) tissues obtained from patients with acquired immunodeficiency syndrome (AIDS). These sequences were not present in tissue DNA from non-AIDS patients, but were present in 15 percent of non-KS tissue DNA samples from AIDS patients. The sequences are homologous to, but distinct from, capsid and tegument protein genes of the Gammaherpesvirinae, herpesvirus saimiri and Epstein-Barr virus. These KS-associated herpesvirus-like (KSHV) sequences appear to define a new human herpesvirus.
Suppression of Odorant Responses by Odorants in Olfactory Receptor Cells
Authors: Kurahashi Takashi , Lowe Graeme , Gold Geoffrey H.
Published: October 2006

Odorants activate an inward current in vertebrate olfactory receptor cells. Here it is shown, in receptor cells from the newt, that odorants can also suppress this current, by a mechanism that is distinct from inhibition and adaptation. Suppression provides a simple explanation for two seemingly unrelated phenomena: the anomalously long latency of olfactory transduction and the existence of an "off response" at the end of a prolonged stimulus. Suppression may influence the perception of odorants by masking odorant responses and by sharpening the odorant specificities of single cells.
Induction of an Olfactory Memory by the Activation of a Metabotropic Glutamate Receptor
Authors: Kaba Hideto , Hayashi Yasunori , Higuchi Takashi , Nakanishi Shigetada
Published: October 2006

Female mice form an olfactory memory of male pheromones at mating; exposure to the pheromones of a strange male after that mating will block pregnancy. The formation of this memory is mediated by the accessory olfactory system, in which an increase in norepinephrine after mating reduces inhibitory transmission of γ-aminobutyric acid from the granule cells to the mitral cells. This study shows that the activation of mGluR2, a metabotropic glutamate receptor that suppresses the γ-aminobutyric acid inhibition of the mitral cells, permits the formation of a specific olfactory memory without the occurrence of mating by infusion of mGluR2 agonists into the female's accessory olfactory bulb. This memory faithfully reflects the memory formed at mating.
Crystal Structure of a p53 Tumor Suppressor-DNA Complex: Understanding Tumorigenic Mutations
Authors: Cho Yunje , Gorina Svetlana , Jeffrey Philip D. , Pavletich Nikola P.
Published: October 2006

Mutations in the p53 tumor suppressor are the most frequently observed genetic alterations in human cancer. The majority of the mutations occur in the core domain which contains the sequence-specific DNA binding activity of the p53 protein (residues 102-292), and they result in loss of DNA binding. The crystal structure of a complex containing the core domain of human p53 and a DNA binding site has been determined at 2.2 angstroms resolution and refined to a crystallographic R factor of 20.5 percent. The core domain structure consists of a β sandwich that serves as a scaffold for two large loops and a loop-sheet-helix motif. The two loops, which are held together in part by a tetrahedrally coordinated zinc atom, and the loop-sheet-helix motif form the DNA binding surface of p53. Residues from the loop-sheet-helix motif interact in the major groove of the DNA, while an arginine from one of the two large loops interacts in the minor groove. The loops and the loop-sheet-helix motif consist of the conserved regions of the core domain and contain the majority of the p53 mutations identified in tumors. The structure supports the hypothesis that DNA binding is critical for the biological activity of p53, and provides a framework for understanding how mutations inactivate it.
Mitotic Regulation of Microtubule Cross-Linking Activity of CENP-E Kinetochore Protein
Authors: Liao Hong , Li Gang , Yen Tim J.
Published: October 2006

CENP-E is a kinesin-like protein that is transiently bound to kinetochores during early mitosis, becomes redistributed to the spindle midzone at anaphase, and is degraded after cytokinesis. At anaphase, CENP-E may cross-link the interdigitating microtubules in the spindle midzone through a motor-like binding site at the amino terminus and a 99-amino acid carboxyl-terminal domain that bound microtubules in a distinct manner. Phosphorylation of the carboxyl terminus by the mitotic kinase maturation promoting factor (MPF) inhibited microtubule-binding activity before anaphase. Thus, MPF suppresses the microtubule cross-linking activity of CENP-E until anaphase, when its activity is lost.
Engineered Biosynthesis of a Complete Macrolactone in a Heterologous Host
Authors: Kao Camilla M. , Katz Leonard , Khosla Chaitan
Published: October 2006

Macrocyclic polyketides have been subjects of great interest in synthetic and biosynthetic chemistry because of their structural complexity and medicinal activities. With expression of the entire 6-deoxyerythronolide B synthase (DEBS) (10,283 amino acids) in a heterologous host, substantial quantities of 6-deoxyerythronolide B (6dEB), the aglycone of the macrolide antibiotic erythromycin, and 8,8a-deoxyoleandolide, a 14-membered lactone ring identical to 6dEB except for a methyl group side chain in place of an ethyl unit, were synthesized in
Streptomyces coelicolor
. The biosynthetic strategy utilizes a genetic approach that facilitates rapid structural manipulation of DEBS or other modular polyketide synthases (PKSs), including those found in actinomycetes with poorly developed genetic methods. From a technological viewpoint, this approach should allow the rational design of biosynthetic products and may eventually lead to the generation of diverse polyketide libraries by means of combinatorial cloning of naturally occurring and mutant PKS modules.
The High-Resolution Crystal Structure of a Parallel-Stranded Guanine Tetraplex
Authors: Laughlan Gerard , Murchie Alastair I. H. , Norman David G. , Moore Madeleine H. , Moody Peter C. E. , Lilley David M. J. , Luisi Ben
Published: October 2006

Repeat tracts of guanine bases found in DNA and RNA can form tetraplex structures in the presence of a variety of monovalent cations. Evidence suggests that guanine tetraplexes assume important functions within chromosomal telomeres, immunoglobulin switch regions, and the human immunodeficiency virus genome. The structure of a parallel-stranded tetraplex formed by the hexanucleotide d(TG
4
T) and stabilized by sodium cations was determined by x-ray crystallography to 1.2 angstroms resolution. Sharply resolved sodium cations were found between and within planes of hydrogen-bonded guanine quartets, and an ordered groove hydration was observed. Distinct intra- and intermolecular stacking arrangements were adopted by the guanine quartets. Thymine bases were exclusively involved in making extensive lattice contacts.
14-3-3 Protein Homologs Required for the DNA Damage Checkpoint in Fission Yeast
Authors: Ford Jon C. , al-Khodairy Fahad , Fotou Eleftheria , Sheldrick Katherine S. , Griffiths Dominic J. F. , Carr Antony M.
Published: October 2006

During the cell cycle, DNA is replicated and segregated equally into two daughter cells. The DNA damage checkpoint ensures that DNA damage is repaired before mitosis is attempted. Genetic studies of the fission yeast
Schizosaccharomyces pombe
have identified two genes,
rad24
and
rad25
, that are required for this checkpoint. These genes encode 14-3-3 protein homologs that together provide a function that is essential for cell proliferation. In addition,
S. pombe
rad24
null mutants, and to a lesser extent
rad25
null mutants, enter mitosis prematurely, which indicates that 14-3-3 proteins have a role in determining the timing of mitosis.
Direct Cortical Representation of Drawing
Authors: Schwartz Andrew B.
Published: October 2006

How the intention to act results in movement is a fundamental question of brain organization. Recent work has shown that this operation involves the cooperative interaction of large neuronal populations. A population vector method, by transforming neuronal activity to the spatial domain, was used to visualize the motor cortical representation of the hand's trajectory made by rhesus monkeys as they drew spirals. Hand path was accurately reflected by a series of population vectors calculated throughout the task. A psychophysical rule relating speed to curvature, the "power law," was found in this cortical representation. The relative timing between each population vector and the corresponding portion of the movement was variable. The population vectors only preceded the movement in a predictive manner in portions of the spiral where the radius of curvature was greater than 6 centimeters. These results show that the movement trajectory is an important determinant of motor cortical activity and that this aspect of motor cortical activity may contribute only to discrete portions of the drawing movement.
Variable Gearing During Locomotion in the Human Musculoskeletal System
Authors: Carrier David R. , Heglund Norman C. , Earls Kathleen D.
Published: October 2006

Human feet and toes provide a mechanism for changing the gear ratio of the ankle extensor muscles during a running step. A variable gear ratio could enhance muscle performance during constant-speed running by applying a more effective prestretch during landing, while maintaining the muscles near the high-efficiency or high-power portion of the force-velocity curve during takeoff. Furthermore, during acceleration, variable gearing may allow muscle contractile properties to remain optimized despite rapid changes in running speed. Force-plate and kinematic analyses of running steps show low gear ratios at touchdown that increase throughout the contact phase.
Dependence on REM Sleep of Overnight Improvement of a Perceptual Skill
Authors: Karni Avi , Tanne David , Rubenstein Barton S. , Askenasy Jean J. M. , Sagi Dov
Published: October 2006

Several paradigms of perceptual learning suggest that practice can trigger long-term, experience-dependent changes in the adult visual system of humans. As shown here, performance of a basic visual discrimination task improved after a normal night's sleep. Selective disruption of rapid eye movement (REM) sleep resulted in no performance gain during a comparable sleep interval, although non-REM slow-wave sleep disruption did not affect improvement. On the other hand, deprivation of REM sleep had no detrimental effects on the performance of a similar, but previously learned, task. These results indicate that a process of human memory consolidation, active during sleep, is strongly dependent on REM sleep.
Stimulation of RNA Polymerase II Elongation by Chromosomal Protein HMG-14
Authors: Ding Han-Fei , Rimsky Sylvie , Batson Susan C. , Bustin Michael , Hansen Ulla
Published: October 2006

The high-mobility group protein 14 (HMG-14) is a non-histone chromosomal protein that is preferentially associated with transcriptionally active chromatin. To assess the effect of HMG-14 on transcription by RNA polymerase II, in vivo-assembled chromatin with elevated amounts of HMG-14 was obtained. Here it is shown that HMG-14 enhanced transcription on chromatin templates but not on DNA templates. This protein stimulated the rate of elongation by RNA polymerase II but not the level of initiation of transcription. These findings suggest that the association of HMG-14 with nucleosomes is part of the cellular process involved in the generation of transcriptionally active chromatin.
An Osmosensing Signal Transduction Pathway in Mammalian Cells
Authors: Galcheva-Gargova Zoya , Dérijard Benoit , Wu I-Huan , Davis Roger J.
Published: October 2006

The osmotic balance between the cytoplasmic and extracellular compartments of cells is critical for the control of cell volume. A mammalian protein kinase, Jnk, which is a distant relative of the mitogen-activated protein kinase group, was activated by phosphorylation on threonine and tyrosine in osmotically shocked cells. The activation of Jnk may be relevant to the biological response to osmotic shock because the expression of human Jnk in the yeast
Saccharomyces cerevisiae
rescued a defect in growth on hyper-osmolar media. These data indicate that related protein kinases may mediate osmosensing signal transduction in yeast and mammalian cells.
T Cell Receptor-MHC Class I Peptide Interactions: Affinity, Kinetics, and Specificity
Authors: Corr Maripat , Slanetz Alfred E. , Boyd Lisa F. , Jelonek Marie T. , Khilko Sergei , al-Ramadi Basel K. , Kim Young Sang , Maher Stephen E. , Bothwell Alfred L. M. , Margulies David H.
Published: October 2006

The critical discriminatory event in the activation of T lymphocytes bearing αβ T cell receptors (TCRs) is their interaction with a molecular complex consisting of a peptide bound to a major histocompatibility complex (MHC)-encoded class I or class II molecule on the surface of an antigen-presenting cell. The kinetics of binding were measured of a purified TCR to molecular complexes of a purified soluble analog of the murine MHC class I molecule H-2L
d
(sH-2L
d
) and a synthetic octamer peptide p2CL in a direct, real-time assay based on surface plasmon resonance. The kinetic dissociation rate of the MHC-peptide complex from the TCR was rapid (2.6 × 10
-2
second
-1
, corresponding to a half-time for dissociation of approximately 27 seconds), and the kinetic association rate was 2.1 × 10
5
M
-1
second
-1
. The equilibrium constant for dissociation was approximately 10
-7
M. These values indicate that TCRs must interact with a multivalent array of MHC-peptide complexes to trigger T cell signaling.
Inhibition of NF-κB by Sodium Salicylate and Aspirin
Authors: Kopp Elizabeth , Ghosh Sankar
Published: October 2006

The transcription factor nuclear factor-κB (NF-κB) is critical for the inducible expression of multiple cellular and viral genes involved in inflammation and infection including interleukin-1 (IL-1), IL-6, and adhesion molecules. The anti-inflammatory drugs sodium salicylate and aspirin inhibited the activation of NF-κB, which further explains the mechanism of action of these drugs. This inhibition prevented the degradation of the NF-κB inhibitor, IκB, and therefore NF-κB was retained in the cytosol. Sodium salicylate and aspirin also inhibited NF-κB-dependent transcription from the Igκ enhancer and the human immunodeficiency virus (HIV) long terminal repeat (LTR) in transfected T cells.
Oscillations of Membrane Current and Excitability Driven by Metabolic Oscillations in Heart Cells
Authors: O'Rourke Brian , Ramza Brian M. , Marban Eduardo
Published: October 2006

Periodic changes in membrane ionic current linked to intrinsic oscillations of energy metabolism were identified in guinea pig cardiomyocytes. Metabolic stress initiated cyclical activation of adenosine triphosphate-sensitive potassium current and concomitant suppression of depolarization-evoked intracellular calcium transients. The oscillations in membrane current and excitation-contraction coupling were linked to oscillations in the oxidation state of pyridine nucleotides but were not driven by pacemaker currents or alterations in the concentration of cytosolic calcium. Interventions that altered the rate of glucose metabolism modulated the oscillations, suggesting that the rhythms originated at the level of glycolysis. The energy-driven oscillations in potassium currents produced cyclical changes in the cardiac action potential and thus may contribute to the genesis of arrhythmias during metabolic compromise.
Crystal Structure of a Catalytic Antibody with a Serine Protease Active Site
Authors: Zhou G. Wayne , Guo Jincan , Huang Wei , Fletterick Robert J. , Scanlan Thomas S.
Published: October 2006

The three-dimensional structure of an unusually active hydrolytic antibody with a phosphonate transition state analog (hapten) bound to the active site has been solved to 2.5 Å resolution. The antibody (17E8) catalyzes the hydrolysis of norleucine and methionine phenyl esters and is selective for amino acid esters that have the natural α-carbon L configuration. A plot of the pH-dependence of the antibody-catalyzed reaction is bell-shaped with an activity maximum at pH 9.5; experiments on mechanism lend support to the formation of a covalent acyl-antibody intermediate. The structural and kinetic data are complementary and support a hydrolytic mechanism for the antibody that is remarkably similar to that of the serine proteases. The antibody active site contains a Ser-His dyad structure proximal to the phosphorous atom of the bound hapten that resembles two of the three components of the Ser-His-Asp catalytic triad of serine proteases. The antibody active site also contains a Lys residue to stabilize oxyanion formation, and a hydrophobic binding pocket for specific substrate recognition of norleucine and methionine side chains. The structure identifies active site residues that mediate catalysis and suggests specific mutations that may improve the catalytic efficiency of the antibody. This high resolution structure of a catalytic antibody-hapten complex shows that antibodies can converge on active site structures that have arisen through natural enzyme evolution.
Requirement of a Critical Period of Transcription for Induction of a Late Phase of LTP
Authors: Nguyen Peter V. , Abel Ted , Kandel Eric R.
Published: October 2006

Repeated high-frequency trains of stimuli induce long-term potentiation (LTP) in the CA1 region that persists for up to 8 hours in hippocampal slices and for days in intact animals. This long time course has made LTP an attractive model for certain forms of long-term memory in the mammalian brain. A hallmark of long-term memory in the intact animal is a requirement for transcription, and thus whether the late phase of LTP (L-LTP) requires transcription was investigated here. With the use of different inhibitors, it was found in rat hippocampal slices that the induction of L-LTP [produced either by tetanic stimulation or by application of the cyclic adenosine monophosphate (cAMP) analog Sp-cAMPS (Sp-cyclic adenosine 3′,5′-monophosphorothioate)] was selectively prevented when transcription was blocked immediately after tetanization or during application of cAMP. As with behavioral memory, this requirement for transcription had a critical time window. Thus, the late phase of LTP in the CA1 region requires transcription during a critical period, perhaps because cAMP-inducible genes must be expressed during this period.
Arrest of Motor Neuron Disease in
wobbler
Mice Cotreated with CNTF and BDNF
Authors: Mitsumoto Hiroshi , Ikeda Ken , Klinkosz Bogdan , Cedarbaum Jesse M. , Wong Vivien , Lindsay Ronald M.
Published: October 2006

Ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) each promote the survival and differentiation of developing motor neurons, but do so through distinct cellular signaling pathways. Administration of either factor alone has been shown to slow, but not to arrest, progression of motor neuron dysfunction in
wobbler
mice, an animal model of motor neuron disease. Because CNTF and BDNF are known to synergize in vitro and in ovo, the efficacy of CNTF and BDNF cotreatment was tested in the same animal model. Subcutaneous injection of the two factors on alternate days was found to arrest disease progression in
wobbler
mice for 1 month, as measured by several behavioral, physiological, and histological criteria.
Fossil Evidence for Early Hominid Tool Use
Authors: Susman Randall L.
Published: October 2006

Although several Plio-Pleistocene hominids are found in association with stone and bone tools, it has been generally assumed that at any one time the hominid with the largest brain was the toolmaker. Fossils recovered over the last decade suggest that early hominids subsequent to 2.5 million years ago all might have used tools and occupied "cultural" niches. A test for humanlike precision grasping (the enhanced ability to manipulate tools) is proposed and applied to australopithecines and early
Homo
. The results indicate that tools were likely to have been used by all early hominids at around 2.0 million years ago. The earliest australopithecines, which predate the appearance of stone tools in the archaeological record, do not show signs of advanced precision grasping.
Detection of Endogenous Malondialdehyde-Deoxyguanosine Adducts in Human Liver
Authors: Chaudhary Ajai K. , Nokubo Munetaka , Reddy G. Ramachandra , Yeola Suresh N. , Morrow Jason D. , Blair lan A. , Marnett Lawrence J.
Published: October 2006

Endogenous DNA adducts may contribute to the etiology of human genetic disease and cancer. One potential source of endogenous DNA adducts is lipid peroxidation, which generates mutagenic carbonyl compounds such as malondialdehyde. A sensitive mass spectrometric method permitted detection and quantitation of the major malondialdehyde-DNA adduct, a pyrimidopurinone derived from deoxyguanosine. DNA from disease-free human liver was found to contain 5400 adducts per cell, a frequency comparable to that of adducts formed by exogenous carcinogens.
Nanosecond Dynamics of the R→T Transition in Hemoglobin: Ultraviolet Raman Studies
Authors: Rodgers K. R. , Spiro T. G.
Published: October 2006

Pulse-probe transient Raman spectroscopy, with probe excitation at 230 nanometers, reveals changes in signals arising from tyrosine and tryptophan residues of the hemoglobin molecule as it moves from the relaxed (R) to the tense (T) state after photodeligation. Signals associated with intersubunit contacts in the T state develop in about 10 microseconds but are preceded by quite different signals, which reach maximum amplitude in about 50 nanoseconds. These signals involve the interior tryptophan residues that bridge the A and E helices by means of H bonds between the indole rings and serine or threonine side chains. Alterations of the H bond strengths, as a result of interhelix motions, can account for the signals. A model is proposed here in which loss of the ligand from the heme binding pocket is concerted with inward motion of the adjacent E helix; this motion, along with a complementary motion of the proximal F helix, transmits the energy associated with heme deligation to the subunit interfaces, leading to the T state rearrangement.
Coaxially Stacked RNA Helices in the Catalytic Center of the
Tetrahymena
Ribozyme
Authors: Murphy Felicia L. , Wang Yuh-Hwa , Griffith Jack D. , Cech Thomas R.
Published: October 2006

Coaxial stacking of helical elements is a determinant of three-dimensional structure in RNA. In the catalytic center of the
Tetrahymena
group I intron, helices P4 and P6 are part of a tertiary structural domain that folds independently of the remainder of the intron. When P4 and P6 were fused with a phosphodiester linkage, the resulting RNA retained the detailed tertiary interactions characteristic of the native P4-P6 domain and even required lower magnesium ion concentrations for folding. These results indicate that P4 and P6 are coaxial in the P4-P6 domain and, therefore, in the native ribozyme. Helix fusion could provide a general method for identifying pairs of coaxially stacked helices in biological RNA molecules.
Molecular Evidence That the Myxozoan Protists Are Metazoans
Authors: Smothers James F. , von Dohlen Carol D. , Smith Laurens H. , Spall Richard D.
Published: October 2006

The evolutionary origins of the protistan phylum, Myxozoa, have long been questioned. Although these obligate parasites are like protozoans in many features, several aspects of their ontogeny and morphology have implied a closer relationship to metazoan lineages. Phylogenetic analyses of 18
S
ribosomal RNA sequences from myxozoans and other eukaryotes, with the use of parsimony, distance, and maximum-likelihood methods, support the hypothesis that myxozoans are closely related to the bilateral animals. These results suggest that the Myxozoa, long considered an assemblage of protozoans, should be considered a metazoan phylum.
The Basal Ganglia and Adaptive Motor Control
Authors: Graybiel Ann M. , Aosaki Toshihiko , Flaherty Alice W. , Kimura Minoru
Published: October 2006

The basal ganglia are neural structures within the motor and cognitive control circuits in the mammalian forebrain and are interconnected with the neocortex by multiple loops. Dysfunction in these parallel loops caused by damage to the striatum results in major defects in voluntary movement, exemplified in Parkinson's disease and Huntington's disease. These parallel loops have a distributed modular architecture resembling local expert architectures of computational learning models. During sensorimotor learning, such distributed networks may be coordinated by widely spaced striatal interneurons that acquire response properties on the basis of experienced reward.
A Comprehensive Human Linkage Map with Centimorgan Density
Authors: Murray Jeffrey C. , Buetow Kenneth H. , Weber James L. , Ludwigsen Susan , Scherpbier-Heddema Titia , Manion Frank , Quillen John , Sheffield Val C. , Sunden Sara , Duyk Geoffrey M. , Weissenbach Jean , Gyapay Gabor , Dib Colette , Morrissette Jean , Lathrop G. Mark , Vignal Alain , White Ray , Matsunami Norisada , Gerken Steven , Mells Roberta , Albertsen Hans , Plaetke Rosemarie , Odelberg Shannon , Ward David , Dausset Jean , Cohen Daniel , Cann Howard
Published: October 2006

In the last few years there have been rapid advances in developing genetic maps for humans, greatly enhancing our ability to localize and identify genes for inherited disorders. Through the collaborative efforts of three large groups generating microsatellite markers and the efforts of the 110 CEPH collaborators, a comprehensive human linkage map is presented here. It consists of 5840 loci, of which 970 are uniquely ordered, covering 4000 centimorgans on the sex-averaged map. Of these loci, 3617 are polymerase chain reaction-formatted short tandem repeat polymorphisms, and another 427 are genes. The map has markers at an average density of 0.7 centimorgan, providing a resource for ready transference to physical maps and achieving one of the first goals of the Human Genome Project—a comprehensive, high-density genetic map.
Localization of a Breast Cancer Susceptibility Gene,
BRCA2
, to Chromosome 13q12-13
Authors: Wooster Richard , Neuhausen Susan L. , Mangion Jonathan , Quirk Yvette , Ford Deborah , Collins Nadine , Nguyen Kim , Seal Sheila , Tran Thao , Averill Diane , Fields Patty , Marshall Gill , Narod Steven , Lenoir Gilbert M. , Lynch Henry , Feunteun Jean , Devilee Peter , Cornelisse Cees J. , Menko Fred H. , Daly Peter A. , Ormiston Wilma , McManus Ross , Pye Carole , Lewis Cathryn M. , Cannon-Albright Lisa A. , Peto Julian , Ponder Bruce A. J. , Skolnick Mark H. , Easton Douglas F. , Goldgar David E. , Stratton Michael R.
Published: October 2006

A small proportion of breast cancer, in particular those cases arising at a young age, is due to the inheritance of dominant susceptibility genes conferring a high risk of the disease. A genomic linkage search was performed with 15 high-risk breast cancer families that were unlinked to the
BRCA1
locus on chromosome 17q21. This analysis localized a second breast cancer susceptibility locus,
BRCA2
, to a 6-centimorgan interval on chromosome 13q12-13. Preliminary evidence suggests that
BRCA2
confers a high risk of breast cancer but, unlike
BRCA1
, does not confer a substantially elevated risk of ovarian cancer.
Mediation of c-Myc-Induced Apoptosis by p53
Authors: Hermeking Heiko , Eick Dirk
Published: October 2006

The cellular proto-oncogene c-
myc
is involved in cell proliferation and transformation but is also implicated in the induction of programmed cell death (apoptosis). The same characteristics have been described for the tumor suppressor gene
p53
, the most commonly mutated gene in human cancer. In quiescent mouse fibroblasts expressing wild-type p53 protein, activation of c-Myc was found to induce apoptosis and cell cycle reentry, preceded by stabilization of p53. In contrast, in quiescent p53-null fibroblasts, activation of c-Myc induced cell cycle reentry but not apoptosis. These results suggest that p53 mediates apoptosis as a safeguard mechanism to prevent cell proliferation induced by oncogene activation.
Extension of Life-Span by Overexpression of Superoxide Dismutase and Catalase in
Drosophila melanogaster
Authors: Orr William C. , Sohal Rajindar S.
Published: October 2006

The hypothesis that oxygen free radicals are causally involved in the aging process was tested by a study of the effects of simultaneous overexpression of copper-zinc superoxide dismutase and catalase. As compared to diploid controls, transgenic flies carrying three copies of each of these genes exhibited as much as a one-third extension of life-span, a longer mortality rate doubling time, a lower amount of protein oxidative damage, and a delayed loss in physical performance. Results provide direct support for the free radical hypothesis of aging.
Replacement of Diseased Mouse Liver by Hepatic Cell Transplantation
Authors: Rhim Jonathan A. , Sandgren Eric P. , Degen Jay L. , Palmiter Richard D. , Brinster Ralph L.
Published: October 2006

Adult liver has the unusual ability to fully regenerate after injury. Although regeneration is accomplished by the division of mature hepatocytes, the replicative potential of these cells is unknown. Here, the replicative capacity of adult liver cells and their medical usefulness as donor cells for transplantation were investigated by transfer of adult mouse liver cells into transgenic mice that display an endogenous defect in hepatic growth potential and function. The transplanted liver cell populations replaced up to 80 percent of the diseased recipient liver. These findings demonstrate the enormous growth potential of adult hepatocytes, indicating the feasibility of liver cell transplantation as a method to replace lost or diseased hepatic parenchyma.
Heat-Inducible Degron: a Method for Constructing Temperature-Sensitive Mutants
Authors: Dohmen R. Jürgen , Wu Peipei , Varshavsky Alexander
Published: October 2006

A temperature-sensitive (
ts
) mutant retains the function of a gene at a low (permissive) temperature but not at a high (nonpermissive) temperature. Arg-DHFR, a dihydrofolate reductase bearing an amino-terminal (N-terminal) arginine, is long-lived in the yeast
Saccharomyces cerevisiae
, even though arginine is a destabilizing residue in the N-end rule of protein degradation. A
ts
derivative of Arg-DHFR was identified that is long-lived at 23°C but rapidly degraded by the N-end rule pathway at 37°C. Fusions of
ts
Arg-DHFR to either Ura3 or Cdc28 of
S. cerevisiae
confer
ts
phenotypes specific for these gene products. Thus, Arg-DHFR
ts
is a heat-inducible degradation signal that can be used to produce
ts
mutants without a search for
ts
mutations.
Global Form and Singularity: Modeling the Blind Spot's Role in Lateral Geniculate Morphogenesis
Authors: Lee Daeyeol , Malpeli Joseph G.
Published: October 2006

Optic nerve terminals segregate by functional class into distinct layers in the lateral geniculate nucleus, the thalamic relay nucleus of the visual system. In the rhesus monkey, the number of geniculate layers changes abruptly from six posteriorly (central vision) to four anteriorly (peripheral vision). The plane of transition between these patterns passes through small laminar gaps corresponding to the perceptual blind spot caused by the exit of the optic nerve from the eyeball. However, this plane of transition has no apparent functional link to the blind spot. A thermodynamic model of geniculate morphogenesis supports the hypothesis that the blind spot traps the transition in its stereotypic position by introducing a singularity in an otherwise smooth gradient in forces guiding the development of geniculate morphogenesis. This relation suggests that small-scale anomalies may be important in the determination of large-scale patterns in biological structure.
Crystal Structure of Human Protein Tyrosine Phosphatase 1B
Authors: Barford David , Flint Andrew J. , Tonks Nicholas K.
Published: October 2006

Protein tyrosine phosphatases (PTPs) constitute a family of receptor-like and cytoplasmic signal transducing enzymes that catalyze the dephosphorylation of phosphotyrosine residues and are characterized by homologous catalytic domains. The crystal structure of a representative member of this family, the 37-kilodalton form (residues 1 to 321) of PTP1B, has been determined at 2.8 Å resolution. The enzyme consists of a single domain with the catalytic site located at the base of a shallow cleft. The phosphate recognition site is created from a loop that is located at the amino-terminus of an α helix. This site is formed from an 11-residue sequence motif that is diagnostic of PTPs and the dual specificity phosphatases, and that contains the catalytically essential cysteine and arginine residues. The position of the invariant cysteine residue within the phosphate binding site is consistent with its role as a nucleophile in the catalytic reaction. The structure of PTP1B should serve as a model for other members of the PTP family and as a framework for understanding the mechanism of tyrosine dephosphorylation.
The 2.9 Å Crystal Structure of
T. thermophilus
Seryl-tRNA Synthetase Complexed with tRNA

Ser
Authors: Biou Valérie , Yaremchuk Anna , Tukalo Michael , Cusack Stephen
Published: October 2006

The crystal structure of
Thermus thermophilus
seryl-transfer RNA synthetase, a class 2 aminoacyl-tRNA synthetase, complexed with a single tRNA
Ser
molecule was solved at 2.9 Å resolution. The structure revealed how insertion of conserved base G20b from the D loop into the core of the tRNA determines the orientation of the long variable arm, which is a characteristic feature of most serine specific tRNAs. On tRNA binding, the antiparallel coiled-coil domain of one subunit of the synthetase makes contacts with the variable arm and TψC loop of the tRNA and directs the acceptor stem of the tRNA into the active site of the other subunit. Specificity depends principally on recognition of the shape of tRNA
Ser
through backbone contacts and secondarily on sequence specific interactions.
Autonomy and Nonautonomy in Cell Fate Specification of Muscle in the
Caenorhabditis elegans
Embryo: a Reciprocal Induction
Authors: Schnabel Ralf
Published: October 2006

EMS, a blastomere of the
Caenorhabditis elegans
embryo, produces body wall muscle cell-autonomously in isolation. Within the embryonic context, however, the specification of body wall muscle derived from EMS depends on inductive interactions between its daughter MS and ABa descendants that are required to overcome inhibitory interactions with other cells. The inductive events between the MS and ABa descendants are reciprocal, specifying subsequent fates in both lineages. Both induction events are blocked by mutations in the gene
glp-1
, known to encode a Notch-like transmembrane receptor protein.
Block in Nuclear Localization of
period
Protein by a Second Clock Mutation,
timeless
Authors: Vosshall Leslie B. , Price Jeffrey L. , Sehgal Amita , Saez Lino , Young Michael W.
Published: October 2006

In wild-type
Drosophila
, the
period
protein (PER) is found in nuclei of the eyes and brain, and PER immunoreactivity oscillates with a circadian rhythm. The studies described here indicate that the nuclear localization of PER is blocked by
timeless
(
tim
), a second chromosome mutation that, like
per
null mutations, abolishes circadian rhythms. PER fusion proteins without a conserved domain (PAS) and some flanking sequences are nuclear in
tim
mutants. This suggests that a segment of PER inhibits nuclear localization in
tim
mutants. The
tim
gene may have a role in establishing rhythms of PER abundance and nuclear localization in wild-type flies.