bluuebunny/crossref_metadata_2025 huggingface dataset:
Photocrosslinking of 5-Iodouracil-Substituted RNA and DNA to Proteins
Authors: Willis Michael C. , Hicke Brian J. , Uhlenbeck Olke C. , Cech Thomas R. , Koch Tad H.
Published: October 2006

5-Iodouracil-substituted RNA and DNA were crosslinked regiospecifically to associated proteins in yields of 70 to 94% of bound nucleic acid. Irradiation of the iodouracil chromophore with monochromatic, long-wavelength ultraviolet radiation (325 nanometers) eliminates excitation of other nucleic acid and protein chromophores. The combination of high crosslinking yields, excellent specificity, and elimination of photodamage to other chromophores represents an important advance toward the precise identification of contacts in nucleoprotein complexes.
Structural Basis of Pilus Subunit Recognition by the PaPd Chaperone
Authors: Kuehn Meta J. , Ogg Derek J. , Kihlberg Jan , Slonim Lynn N. , Flemmer Katarina , Bergfors Terese , Hultgren Scott J.
Published: October 2006

The assembly of different types of virulence-associated surface fibers called pili in Gram-negative bacteria requires periplasmic chaperones. PapD is the prototype member of the periplasmic chaperone family, and the structural basis of its interactions with pilus subunits was investigated. Peptides corresponding to the carboxyl terminus of pilus subunits bound PapD and blocked the ability of PapD to bind to the pilus adhesin PapG in vitro. The crystal structure of PapD complexed to the PapG carboxyl-terminal peptide was determined to 3.0 Å resolution. The peptide bound in an extended conformation with its carboxyl terminus anchored in the interdomain cleft of the chaperone via hydrogen bonds to invariant chaperone residues Arg
8
and Lys
112
. Main chain hydrogen bonds and contacts between hydrophobic residues in the peptide and the chaperone stabilized the complex and may play a role in determining binding specificity. Site-directed mutations in Arg
8
and Lys
112
abolished the ability of PapD to bind pilus subunits and mediate pilus assembly in vivo, an indication that the PapD-peptide crystal structure is a reflection of at least part of the PapD-subunit interaction.
Microtubule Severing by Elongation Factor 1α
Authors: Shiina Nobuyuki , Gotoh Yukiko , Kubomura Nobuko , Iwamatsu Akihiro , Nishida Eisuke
Published: October 2006

An activity that severs stable microtubules is thought to be involved in microtubule reorganization during the cell cycle. Here, a 48-kilodalton microtubule-severing protein was purified from
Xenopus
eggs and identified as translational elongation factor 1α (EF-1α). Bacterially expressed human EF-1α also displayed microtubule-severing activity in vitro and, when microinjected into fibroblasts, induced rapid and transient fragmentation of cytoplasmic microtubule arrays. Thus, EF-1α, an essential component of the eukaryotic translational apparatus, appears to have a second role as a regulator of cytoskeletal rearrangements.
Toxicology and Pharmacological Action ofAnabaena flos-aquaeToxin
Authors: Carmichael Wayne W. , Biggs David F. , Gorham Paul R.
Published: October 2006

Calves, rats, ducks, and goldfish given lethal oral doses of bacteria-free lyophilized cell suspensions of toxicAnabaena flos-aquaedied as a result of respiratory arrest. Experiments with selected animals and pharmacological preparations showed that the main effect of the toxin was production of a sustained postsynaptic depolarizing neuromuscular blockade.
Germ Line Transmission of a Yeast Artificial Chromosome Spanning the Murine α
1
(I) Collagen Locus
Authors: Strauss William M. , Dausman Jessica , Beard Caroline , Johnson Carol , Lawrence Jeanne B. , Jaenisch Rudolf
Published: October 2006

Molecular complementation of mutant phenotypes by transgenic technology is a potentially important tool for gene identification. A technology was developed that allows the transfer of a physically intact yeast artificial chromosome (YAC) into the germ line of the mouse. A purified 150-kilobase YAC encompassing the murine gene
Col1a1
was efficiently introduced into embryonic stem (ES) cells via lipofection. Chimeric founder mice were derived from two transfected ES cell clones. These chimeras transmitted the full length transgene through the germ line, generating two transgenic mouse strains. Transgene expression was visualized as nascent transcripts in interphase nuclei and quantitated by ribonuclease protection analysis. Both assays indicated that the transgene was expressed at levels comparable to the endogenous collagen gene.
Cytoskeletal Role in the Contractile Dysfunction of Hypertrophied Myocardium
Authors: Tsutsui Hiroyuki , Ishihara Kazuaki , Cooper George
Published: October 2006

Cardiac hypertrophy in response to systolic pressure loading frequently results in contractile dysfunction of unknown cause. In the present study, pressure loading increased the microtubule component of the cardiac muscle cell cytoskeleton, which was responsible for the cellular contractile dysfunction observed. The linked microtubule and contractile abnormalities were persistent and thus may have significance for the deterioration of initially compensatory cardiac hypertrophy into congestive heart failure.
Retinal Capillaries: Proliferation of Mural Cells in Vitro
Authors: Buzney Sheldon M. , Frank Robert N. , Robison W. Gerald
Published: October 2006

Capillaries from bovine, monkey, and human retinas maintained in tissue culture produced a monolayer of cells. Autoradiographic and electron microscopic evidence indicated that the mural cells (intramural pericytes) were the cells that proliferated. Since intramural pericytes are damaged selectively in diabetes mellitus, their availability in culture will be useful in seeking means to control diabetic retinopathy.
Altered Fluid Transport Across Airway Epithelium in Cystic Fibrosis
Authors: Jiang Canwen , Finkbeiner Walter E. , Widdicombe Jonathan H. , McCray Paul B. , Miller Sheldon S.
Published: October 2006

In cystic fibrosis (CF), absence or dysfunction of a phosphorylation-regulated chloride channel [CF transmembrane conductance regulator (CFTR)] leads to the loss or reduction of chloride secretion into the airways. Active sodium absorption is also increased in CF, and both of these ion transport changes could alter fluid transport across the airways. Under baseline conditions, cultured human airway epithelia from normal individuals absorbed fluid, and this absorption was increased in epithelia from patients with CF. In normal and CF epithelial cultures fluid absorption was inhibited by amiloride. Adenosine 3′,5′-monophosphate stimulated fluid secretion in normal epithelial cultures but not in cultures from individuals with CF. In contrast, fluid secretion induced by nucleotide triphosphates (uridine triphosphate or adenosine triphosphate) was unaltered in cultures of epithelia from patients with CF, suggesting an approach to the treatment of CF.
Long-Range Attractive Force Between Hydrophobic Surfaces Observed by Atomic Force Microscopy
Authors: Tsao Yi-Hua , Evans D. Fennell , Wennerström H.
Published: October 2006

There is evidence from atomic force microscopy for a long-range attractive force between hydrophobic surfaces that is virtually identical to that observed with the surface forces apparatus. This force is present in the nonaqueous solvent ethylene glycol. A possible molecular mechanism involves in-plane polarized domains of solid-like monolayers adsorbed on mica, and a theoretical model has been developed that accounts for many of the observations.
Hyperlipidemia and Atherosclerosis
Authors: Ross Russell , Harker Laurence
Published: October 2006

These studies provide new insight into the complex mechanisms whereby hyperlipidemia causes progressive atherosclerosis. It has been shown that physical injury to the endothelial lining of arteries sets off a process which probably is an attempt at healing the injury but which can lead to atherosclerosis. It has also been found that chemical agents such as homocystine can produce a similar series of events leading to atherosclerosis. These events include focal loss of endothelium, exposure of subendothelial connective tissue, and adherence of platelets followed by release of factors that stimulate intimal smooth muscle proliferation. The present studies indicate that the effects of chronic hyperlipidemia are complex in that the condition results not only in the deposition of lipids in the atheromatous lesions but that it may produce the primary endothelial injury that initiates the process of atherosclerosis as well.
Neuronal Mechanisms of Object Recognition
Authors: Tanaka Keiji
Published: October 2006

Recognition of objects from their visual images is a key function of the primate brain. This recognition is not a template matching between the input image and stored images like the vision in lower animals but is a flexible process in which considerable change in images, resulting from different illumination, viewing angle, and articulation of the object, can be tolerated. Recent experimental findings about the representation of object images in the inferotemporal cortex, a brain structure that is thought to be essential for object vision, are summarized and discussed in relation to the computational frames proposed for object recognition.
Structure at 2.5 Å of a Designed Peptide that Maintains Solubility of Membrane Proteins
Authors: Schafmeister Christian E. , Miercke Larry J. W. , Stroud Robert M.
Published: October 2006

A 24-amino acid peptide designed to solubilize integral membrane proteins has been synthesized. The design was for an amphipathic α helix with a "flat" hydrophobic surface that would interact with a transmembrane protein as a detergent. When mixed with peptide, 85 percent of bacteriorhodopsin and 60 percent of rhodopsin remained in solution over a period of 2 days in their native forms. The crystal structure of peptide alone showed it to form an antiparallel four-helix bundle in which monomers interact, flat surface to flat surface, as predicted.
Nucleosome Disruption by Transcription Factor Binding in Yeast
Authors: Morse Randall H.
Published: October 2006

Studies in vivo and in vitro have shown that the packaging of DNA into chromatin can affect gene expression. Here, binding of the yeast transcriptional activator GAL4 to DNA in chromatin has been investigated in vivo with a yeast episome. A positioned nucleosome that is present in cells grown in glucose and contains a single GAL4 binding site is disrupted by GAL4 binding in galactose. GAL4 can also bind to DNA in chromatin when the carboxyl-terminal activation domain of GAL4 is either masked by GAL80 or is absent. These results show that a transcription factor can bind to its site in vivo in what would appear to be a repressive chromatin structure.
Tethering Ribozymes to a Retroviral Packaging Signal for Destruction of Viral RNA
Authors: Sullenger Bruce A. , Cech Thomas R.
Published: October 2006

Cellular compartmentalization of RNAs is thought to influence their susceptibility to ribozyme cleavage. As a test of this idea, two retroviral vectors—one encoding a hammer-head ribozyme designed to cleave
lacZ
transcripts and another encoding the
lacZ
messenger RNA—were coexpressed inside retroviral packaging cells. Because of the retroviral packaging signal, the ribozyme would be expected to colocalize with the
lacZ
-containing viral genomic RNA but not with the
lacZ
messenger RNA. The ribozyme was found to reduce the titer of infectious virus containing
lacZ
by 90 percent, but had no effect on translation of
lacZ
messenger RNA. These results indicate that sorting gene inhibitors to appropriate intracellular sites may increase their effectiveness.
Active Oxygen Species in the Induction of Plant Systemic Acquired Resistance by Salicylic Acid
Authors: Chen Zhixiang , Silva Herman , Klessig Daniel F.
Published: October 2006

A complementary DNA encoding a salicylic acid (SA)-binding protein has been cloned. Its properties suggest involvement in SA-mediated induction of systemic acquired resistance (SAR) in plants. The sequence of the protein is similar to that of catalases and the protein exhibits catalase activity. Salicylic acid specifically inhibited the catalase activity in vitro and induced an increase in H
2
O
2
concentrations in vivo. H
2
O
2
or compounds, such as SA, that inhibit catalases or enhance the generation of H
2
O
2
, induced expression of defense-related genes associated with SAR. Thus, the action of SA in SAR is likely mediated by elevated amounts of H
2
O
2
.
Mutations in U6 snRNA that Alter Splice Site Specificity: Implications for the Active Site
Authors: Lesser Cammie F. , Guthrie Christine
Published: October 2006

What determines the precise sites of cleavage in the two transesterification reactions of messenger RNA (mRNA) splicing is a major unsolved question. Mutation of the invariant G (guanosine) at position 5 of 5′ splice sites in
Saccharomyces cerevisiae
introns activates cleavage at nearby aberrant sites. A genetic approach was used to test the hypothesis that a base-pairing interaction between the 5′ splice site and the invariant ACAGAG sequence of U6 is a determinant of 5′ splice site choice. Mutations in U6 or the intron (or both) that were predicted to stabilize the interaction suppressed aberrant cleavage and increased normal cleavage. In addition, a mutation in the ACAGAG sequence suppressed mutations of the 3′ splice site dinucleotide. These data can fit a model for the spliceosomal active site comprised of a set of RNA-RNA interactions between the intron, U2 and U6.
Involvement of U6 snRNA in 5′ Splice Site Selection
Authors: Kandels-Lewis Stefanie , Séraphin Bertrand
Published: October 2006

Two models describing the interaction between U6 small nuclear RNA (snRNA) and the 5′ splice site of introns have been proposed on the basis of cross-linking experiments. Here it is shown that a conserved sequence present in U6 snRNA forms base pairs with conserved nucleotides at the 5′ splice junction and that this interaction is involved in 5′ splice site choice. These results demonstrate a specific function for U6 snRNA in splicing and suggest that U6 snRNA has a proofreading role during splice site selection. A model is presented in which this new interaction, in concert with previously described interactions between U6 snRNA, U2 snRNA, and the pre-messenger RNA, would position the branch point near the 5′ splice site for the catalysis of the first splicing step.
From Piecemeal to Configurational Representation of Faces
Authors: Carey Susan , Diamond Rhea
Published: October 2006

Unlike older children and adults, children of less than about 10 years of age remember photographs of faces presented upside down almost as well as those shown upright and are easily fooled by simple disguises. The development at age 10 of the ability to encode orientation-specific configurational aspects of a face may reflect completion of certain maturational changes in the right cerebral hemisphere.
Selective Inhibition of
ras
-Dependent Transformation by a Farnesyltransferase Inhibitor
Authors: Kohl Nancy E. , Mosser Scott D. , deSolms S. Jane , Giuliani Elizabeth A. , Pompliano David L. , Graham Samuel L. , Smith Robert L. , Scolnick Edward M. , Oliff Allen , Gibbs Jackson B.
Published: October 2006

To acquire transforming potential, the precursor of the Ras oncoprotein must undergo farnesylation of the cysteine residue located in a carboxyl-terminal tetrapeptide. Inhibitors of the enzyme that catalyzes this modification, farnesyl protein transfe
ras
e (FPTase), have therefore been suggested as anticancer agents for tumors in which Ras contributes to transformation. The tetrapeptide analog L-731,735 is a potent and selective inhibitor of FPTase in vitro. A prodrug of this compound, L-731,734, inhibited Ras processing in cells transformed with v-
ras
. L-731,734 decreased the ability of v-
ras
-transformed cells to form colonies in soft agar but had no effect on the efficiency of colony formation of cells transformed by either the v-
raf
or v-
mos
oncogenes. The results demonstrate selective inhibition of
ras
-dependent cell transformation with a synthetic organic inhibitor of FPTase.
Colocalization of X-Linked Agammaglobulinemia and X-Linked Immunodeficiency Genes
Authors: Thomas Jeffrey D. , Sideras Paschalis , Smith C. I. Edvard , Vořechovský Igor , Chapman Verne , Paul William E.
Published: October 2006

Mice that bear the X-linked immunodeficiency (
xid
) mutation have a B lymphocyte-specific defect resulting in an inability to make antibody responses to polysaccharide antigens. A backcross of 1114 progeny revealed the colocalization of
xid
with Bruton's agammaglobulinemia tyrosine kinase (
btk
) gene, which is implicated in the human immune deficiency, X-linked agammaglobulinemia. Mice that carry
xid
have a missense mutation that alters a highly conserved arginine near the amino-terminus of the
btk
protein, Btk. Because this region of Btk lies outside any obvious kinase domain, the
xid
mutation may define another aspect of tyrosine kinase function.
Mutation of Unique Region of Bruton's Tyrosine Kinase in Immunodeficient XID Mice
Authors: Rawlings David J. , Saffran Douglas C. , Tsukada Satoshi , Largaespada David A. , Grimaldi J. Christopher , Cohen Lucie , Mohr Randolph N. , Bazan J. Fernando , Howard Maureen , Copeland Neal G. , Jenkins Nancy A. , Witte Owen N.
Published: October 2006

The cytoplasmic tyrosine kinase, Bruton's tyrosine kinase (Btk, formerly bpk or atk), is crucial for B cell development. Loss of kinase activity results in the human immunodeficiency, X-linked agammaglobulinemia, characterized by a failure to produce B cells. In the murine X-linked immunodeficiency (XID), B cells are present but respond abnormally to activating signals. The Btk gene,
btk
, was mapped to the
xid
region of the mouse X chromosome by interspecific backcross analysis. A single conserved residue within the amino terminal unique region of Btk was mutated in XID mice. This change in
xid
probably interferes with normal B cell signaling mediated by Btk protein interactions.
A Function of Lung Surfactant Protein SP-B
Authors: Longo M. L. , Bisagno A. M. , Zasadzinski J. A.N. , Bruni R. , Waring A. J.
Published: October 2006

The primary function of lung surfactant is to form monolayers at the alveolar interface capable of lowering the normal surface tension to near zero. To accomplish this process, the surfactant must be capable of maintaining a coherent, tightly packed monolayer that avoids collapse during expiration. The positively charged amino-terminal peptide SP-B1-25 of lung surfactant-specific protein SP-B increases the collapse pressure of an important component of lung surfactant, palmitic acid (PA), to nearly 70 millinewtons per meter. This alteration of the PA isotherms removes the driving force for "squeeze-out" of the fatty acids from the primarily dipalmitoylphosphatidylcholine monolayers of lung surfactant. An uncharged mutant of SP-B1-25 induced little change in the isotherms, suggesting that a specific charge interaction between the cationic peptide and the anionic lipid is responsible for the stabilization. The effect of SP-B1-25 on fatty acid isotherms is remarkably similar to that of simple poly-cations, suggesting that such polymers might be useful as components of replacement surfactants for the treatment of respiratory distress syndrome.
Direct Colorimetric Detection of a Receptor-Ligand Interaction by a Polymerized Bilayer Assembly
Authors: Charych Deborah H. , Nagy Jon O. , Spevak Wayne , Bednarski Mark D.
Published: October 2006

Detection of receptor-ligand interactions is generally accomplished by indirect assays such as enzyme-linked immunosorbent assay. A direct colorimetric detection method based on a polydiacetylene bilayer assembled on glass microscope slides has been developed. The bilayer is composed of a self-assembled monolayer of octadecylsilane and a Langmuir-Blodgett monolayer of polydiacetylene. The polydiacetylene layer is functionalized with an analog of sialic acid, the receptor-specific ligand for the influenza virus hemagglutinin. The sialic acid ligand serves as a molecular recognition element and the conjugated polymer backbone signals binding at the surface by a chromatic transition. The color transition is readily visible to the naked eye as a blue to red color change and can be quantified by visible absorption spectroscopy. Direct colorimetric detection by polydiacetylene films offers new possibilities for diagnostic applications and screening for new drug candidates or binding ligands.
Interaction of Activated EGF Receptors with Coated Pit Adaptins
Authors: Sorkin Alexander , Carpenter Graham
Published: October 2006

The epidermal growth factor (EGF) receptor interacts with plasma membrane-associated adapter proteins during endocytosis through coated pits. Almost 50 percent of the total pool of α-adaptins was coimmunoprecipitated with the EGF receptor when A-431 cells were treated with EGF at 37°C, but not at 4°C. Partial proteolysis of α-adaptin suggested that the amino-terminal domain is the region that associates with the EGF receptor. The extent of receptor-adaptin association was increased in cells depleted of potassium to block endocytosis. These data suggest that receptor-adaptin association occurs in intact cells before coated pits are fully assembled.
Rat Annexin V Crystal Structure: Ca
2+
-Induced Conformational Changes
Authors: Concha N. O. , Head J. F. , Kaetzel M. A. , Dedman J. R. , Seaton B. A.
Published: October 2006

Annexins are a family of calcium- and phospholipid-binding proteins implicated in mediating membrane-related processes such as secretion, signal transduction, and ion channel activity. The crystal structure of rat annexin V was solved to 1.9 angstrom resolution by multiple isomorphous replacement. Unlike previously solved annexin V structures, all four domains bound calcium in this structure. Calcium binding in the third domain induced a large relocation of the calcium-binding loop regions, exposing the single tryptophan residue to the solvent. These alterations in annexin V suggest a role for domain 3 in calcium-triggered interaction with phospholipid membranes.
A UV-Sensitive Mutant of
Arabidopsis
Defective in the Repair of Pyrimidine-Pyrimidinone(6-4) Dimers
Authors: Britt A. B. , Chen J. J. , Wykoff D. , Mitchell D.
Published: October 2006

Plants are continually subjected to ultraviolet-B (UV-B) irradiation (290 to 320 nanometers) as a component of sunlight, which induces a variety of types of damage to the plant DNA. Repair of the two major DNA photoproducts was analyzed in wild-type
Arabidopsis thaliana
and in a mutant derivative whose growth was sensitive to UV-B radiation. In wild-type seedlings, repair of cyclobutane pyrimidine dimers occurred more slowly in the dark than in the light; repair of this photoproduct was not affected in the mutant. Repair, in the dark, of pyrimidine-pyrimidinone(6-4) dimers was defective in the UV-sensitive mutant.
Phosphorylation and Modulation of a Kainate Receptor (GluR6) by cAMP-Dependent Protein Kinase
Authors: Wang Lu-Yang , Taverna Franco A. , Huang Xi-Ping , MacDonald John F. , Hampson David R.
Published: October 2006

Ligand-gated ion channels gated by glutamate constitute the major excitatory neurotransmitter system in the mammalian brain. The functional modulation of GluR6, a kainate-activated glutamate receptor, by adenosine 3′,5′-monophosphate-dependent protein kinase A (PKA) was examined with receptors expressed in human embryonic kidney cells. Kainate-evoked currents underwent a rapid desensitization that was blocked by lectins. Kainate currents were potentiated by intracellular perfusion of PKA, and this potentiation was blocked by co-application of an inhibitory peptide. Site-directed mutagenesis was used to identify the site or sites of phosphorylation on GluR6. Although mutagenesis of two serine residues, Ser
684
and Ser
666
, was required for complete abolition of the PKA-induced potentiation, Ser
684
may be the preferred site of phosphorylation in native GluR6 receptor complexes. These results indicate that glutamate receptor function can be directly modulated by protein phosphorylation and suggest that a dynamic regulation of excitatory receptors could be associated with some forms of learning and memory in the mammalian brain.
Sea Urchin Egg Receptor for Sperm: Sequence Similarity of Binding Domain and hsp70
Authors: Foltz Kathleen R. , Partin Jacqueline S. , Lennarz William J.
Published: October 2006

Fertilization depends on cell surface recognition proteins that interact and thereby mediate binding and subsequent fusion of the sperm and egg. Overlapping complementary DNA's encoding the egg plasma membrane receptor for sperm from the sea urchin
Strongylocentrotus purpuratus
were cloned and sequenced. Analysis of the deduced primary structure suggests that the receptor is a transmembrane protein with a short cytoplasmic domain. This domain showed no sequence similarity to known protein sequences. In contrast, the extracellular, sperm binding domain of the receptor did show sequence similarity to the heat shock protein 70 (hsp70) family of proteins. Recombinant protein representing this portion of the receptor bound to the sperm protein, bindin, and also inhibited fertilization in a species-specific manner; beads coated with the protein became specifically bound to acrosome-reacted sperm. These data provide a basis for detailed investigations of molecular interactions that occur in gamete recognition and egg activation.
Redundant Mechanisms of Calcium-Induced Calcium Release Underlying Calcium Waves During Fertilization of Sea Urchin Eggs
Authors: Galione Antony , McDougall Alex , Busa William B. , Willmott Nick , Gillot Isabelle , Whitaker Michael
Published: October 2006

Propagating Ca
2+
waves are a characteristic feature of Ca
2+
-linked signal transduction pathways. Intracellular Ca
2+
waves are formed by regenerative stimulation of Ca
2+
release from intracellular stores by Ca
2+
itself. Mechanisms that rely on either inositol trisphosphate or ryanodine receptor channels have been proposed to account for Ca
2+
waves in various cell types. Both channel types contributed to the Ca
2+
wave during fertilization of sea urchin eggs. Alternative mechanisms of Ca
2+
release imply redundancy but may also allow for modulation and diversity in the generation of Ca
2+
waves.
A Putative ATP-Activated Na
+
Channel Involved in Sperm-Induced Fertilization
Authors: Kupitz Yuval , Atlas Daphne
Published: October 2006

Extracellular application of adenosine triphosphate (ATP) to defolliculated
Xenopus laevis
oocytes activated a saturating inward current with a maximal amplitude
E
max
of 2.4 ± 0.2 microamperes and an apparent Michaelis constant of 197.6 micromolar. The current was carried predominantly by sodium ions and potently inhibited by amiloride, guanosine triphosphate (GTP), and its nonhydrolyzable analogs guanosine 5′-[β,γ-imido]triphosphate (GppNHp) and guanosine 5′-
O
-(3-thiotriphosphate). Likewise, in vitro fertilization using mature eggs and
Xenopus
sperm was inhibited by amiloride, GTP, and GppNHp. Hence, an ATP receptor on the egg membrane may be the recipient target for ATP originating in sperm, suggesting that an ATP-induced increase in sodium permeability mediates the initial sperm to egg signal in the fertilization process.
Repair of DNA Methylphosphotriesters Through a Metalloactivated Cysteine Nucleophile
Authors: Myers Lawrence C. , Terranova Michael P. , Ferentz Ann E. , Wagner Gerhard , Verdine Gregory L.
Published: October 2006

The
Escherichia coli
Ada protein repairs methylphosphotriesters in DNA by direct, irreversible methyl transfer to one of its own cysteines. Upon methyl transfer, Ada acquires the ability to bind specific DNA sequences and thereby to induce genes that confer resistance to methylating agents. The amino-terminal domain of Ada, which comprises the methylphosphotriester repair and sequence-specific DNA binding elements, contains a tightly bound zinc ion. Analysis of the zinc binding site by cadmium-113 nuclear magnetic resonance and site-directed mutagenesis revealed that zinc participates in the autocatalytic activation of the active site cysteine and may also function as a conformational switch.
Rod Photoreceptors Detect Rapid Flicker
Authors: Conner J. D. , MacLeod Donald I. A.
Published: October 2006

It is widely believed that human rods cannot detect rapid flicker. With rod-isolation techniques, however, light-adapted rods detect flicker frequencies as high as 28 hertz, and the function relating rod critical flicker frequency to stimulus intensity contains two distinct branches. Human rod vision may, therefore, depend on two independent mechanisms.
Reading Disability: An Information-Processing Analysis
Authors: Morrison Frederick J. , Giordani Bruno , Nagy Jill
Published: October 2006

In a task designed to separate perceptual processes from memory, 12-year-old children with reading disabilities showed no perceptual deficits as compared to their peers. However, they exhibited major deficiencies in memory skills for both labelable and nonlabelable visual information. Reading-disabled children in this age group appear to suffer from a basic information-processing deficiency.
A Traveling-Wave Amplifier Model of the Cochlea
Authors: Hubbard Allyn
Published: October 2006

A two-mode model of the cochlea that uses active intermode feedback has been developed that quantitatively accounts for the motion of the basilar membrane in response to single tones and qualitatively accounts for cochlear emission phenomena. In contrast to existing single-mode models, this model amplifies the mechanical traveling wave in spatially localized cochlear regions where an approximate match occurs between the traveling-wave velocities of each of the two traveling-wave lines or modes.
Identification of a Whitefly Species by Genomic and Behavioral Studies
Authors: Perring Thomas M. , Cooper Arthur D. , Rodriguez Russell J. , Farrar Charles A. , Bellows Tom S.
Published: October 2006

An introduced whitefly species, responsible for over a half billion dollars in damage to U.S. agricultural production in 1991, is morphologically indistinguishable from
Bemisia tabaci
(Gennadius). However, with the use of polymerase chain reaction-based DNA differentiation tests, allozymic frequency analyses, crossing experiments, and mating behavior studies, the introduced whitefly is found to be a distinct species. Recognition of this new species, the silverleaf whitefly, is critical in the search for management options.
Sequence-Specific Binding of Transfer RNA by Glyceraldehyde-3-Phosphate Dehydrogenase
Authors: Singh Ravinder , Green Michael R.
Published: October 2006

A transfer RNA (tRNA) binding protein present in HeLa cell nuclear extracts was purified and identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Studies with mutant tRNAs indicated that GAPDH recognizes both sequence and structural features in the RNA. GAPDH discriminated between wild-type tRNA and two tRNA mutants that are defective in nuclear export, which suggests that the protein may participate in RNA export. The cofactor nicotinamide adenine dinucleotide disrupted complex formation between tRNA and GAPDH and thus may share a common binding site with the RNA. Indirect immunofluorescence experiments showed that GAPDH is present in the nucleus as well as in the cytoplasm.
Tumor Suppression in
Xiphophorus
by an Accidentally Acquired Promoter
Authors: Adam Dieter , Dimitrijevic Nicola , Schartl Manfred
Published: October 2006

Melanoma formation in the teleost
Xiphophorus
is caused by a dominant genetic locus,
Tu
. This locus includes the
Xmrk
oncogene, which encodes a receptor tyrosine kinase. Tumor induction is suppressed in wild-type fish by a tumor suppressor locus, R. Molecular genetic analyses revealed that the
Tu
locus emerged by nonhomologous recombination of the
Xmrk
proto-oncogene with a previously uncharacterized sequence,
D
. This event generated an additional copy of
Xmrk
with a new promoter. Suppression of the new
Xmrk
promoter by
R
in parental fish and its deregulation in hybrids explain the genetics of melanoma formation in
Xiphophorus
.
Existence of a Flat Phase in Red Cell Membrane Skeletons
Authors: Schmidt Christoph F. , Svoboda Karel , Lei Ning , Petsche Irena B. , Berman Lonny E. , Safinya Cyrus R. , Grest Gary S.
Published: October 2006

Biomolecular membranes display rich statistical mechanical behavior. They are classified as liquid in the absence of shear elasticity in the plane of the membrane and tethered (solid) when the neighboring molecules or subunits are connected and the membranes exhibit solid-like elastic behavior in the plane of the membrane. The spectrin skeleton of red blood cells was studied as a model tethered membrane. The static structure factor of the skeletons, measured by small-angle x-ray and light scattering, was fitted with a structure factor predicted with a model calculation. The model describes tethered membrane sheets with free edges in a flat phase, which is a locally rough but globally flat membrane configuration. The fit was good for large scattering vectors. The membrane roughness exponent, ζ, defined through h α L
ζ
, where h is the average amplitude of out-of-plane fluctuations and L is the linear membrane dimension, was determined to be 0.65 ± 0.10. Computer simulations of model red blood cell skeletons also showed this flat phase. The value for the roughness exponent, which was determined from the scaling properties of membranes of different sizes, was consistent with that from the experiments.
Requirement for a GTPase-Activating Protein in Vesicle Budding from the Endoplasmic Reticulum
Authors: Yoshihisa Tohru , Barlowe Charles , Schekman Randy
Published: October 2006

The binding and hydrolysis of guanosine triphosphate (GTP) by the small GTP-binding protein Sar1p is required to form transport vesicles from the endoplasmic reticulum (ER) in
Saccharomyces cerevisiae
. Experiments revealed that an interaction between Sar1p and the Sec23p subunit of an oligomeric protein is also required for vesicle budding. The isolated Sec23p subunit and the oligomeric complex stimulated guanosine triphosphatase (GTPase) activity of Sar1p 10- to 15-fold but did not activate two other small GTP-binding proteins involved in vesicle traffic (Ypt1p and ARF). Activation of GTPase was inhibited by an antibody to Sec23p but not by an antibody that inhibits the budding activity of the other subunit of the Sec23p complex. Also, activation was thermolabile in pure samples of Sec23p that were isolated from two independent sec23 mutant strains. It appears that Sec23p represents a new class of GTPase-activating protein because its sequence shows no similarity to any known member of this family.
Force of Single Kinesin Molecules Measured with Optical Tweezers
Authors: Kuo Scot C. , Sheetz Michael P.
Published: October 2006

Isometric forces generated by single molecules of the mechanochemical enzyme kinesin were measured with a laser-induced, single-beam optical gradient trap, also known as optical tweezers. For the microspheres used in this study, the optical tweezers was spring-like for a radius of 100 nanometers and had a maximum force region at a radius of ∼150 nanometers. With the use of biotinylated microtubules and special streptavidin-coated latex microspheres as handles, microtubule translocation by single squid kinesin molecules was reversibly stalled. The stalled microtubules escaped optical trapping forces of 1.9 ± 0.4 piconewtons. The ability to measure force parameters of single macromolecules now allows direct testing of molecular models for contractility.
Decreased Expression of Myotonin-Protein Kinase Messenger RNA and Protein in Adult Form of Myotonic Dystrophy
Authors: Fu Ying-Hui , Friedman David L. , Richards Stephen , Pearlman Joel A. , Gibbs Richard A. , Pizzuti Antonio , Ashizawa Tetsuo , Perryman M. Benjamin , Scarlato Guglielmo , Fenwick Raymond G. , Caskey C. Thomas
Published: October 2006

The myotonic dystrophy mutation has recently been identified; however, the molecular mechanism of the disease is still unknown. The sequence of the myotonin-protein kinase gene was determined, and messenger RNA spliced forms were identified in various tissues. Antisera were developed for analytical studies. Quantitative reverse transcription-polymerase chain reaction and radioimmunoassay were used to demonstrate that decreased levels of the messenger RNA and protein expression are associated with the adult form of myotonic dystrophy.
Structure of DNA Polymerase I Klenow Fragment Bound to Duplex DNA
Authors: Beese Lorena S. , Derbyshire Victoria , Steitz Thomas A.
Published: October 2006

Klenow fragment of
Escherichia coli
DNA polymerase I, which was cocrystallized with duplex DNA, positioned 11 base pairs of DNA in a groove that lies at right angles to the cleft that contains the polymerase active site and is adjacent to the 3′ to 5′ exonuclease domain. When the fragment bound DNA, a region previously referred to as the "disordered domain" became more ordered and moved along with two helices toward the 3′ to 5′ exonuclease domain to form the binding groove. A single-stranded, 3′ extension of three nucleotides bound to the 3′ to 5′ exonuclease active site. Although this cocrystal structure appears to be an editing complex, it suggests that the primer strand approaches the catalytic site of the polymerase from the direction of the 3′ to 5′ exonuclease domain and that the duplex DNA product may bend to enter the cleft that contains the polymerase catalytic site.
Knotting of a DNA Chain During Ring Closure
Authors: Shaw Stanley Y. , Wang James C.
Published: October 2006

The formation of knotted species on random ring closure of two DNAs that are 5.6 kilobase pairs (kbp) and 8.6 kbp in length was measured, and these data were used to calculate the effective DNA helix diameter as a function of sodium ion and magnesium ion concentration. In the presence of more than 50 mM magnesium ion, interactions between DNA segments appear to be attractive rather than repulsive. The free energy of formation of relaxed trefoil and figure-eight DNA knots and of supercoiled trefoil DNA knots was also evaluated.
Sequences and Structures Required for Recombination Between Virus-Associated RNAs
Authors: Cascone Pamela J. , Haydar Tarik F. , Simon Anne E.
Published: October 2006

RNA recombination has been described for a number of viruses in the plant and animal kingdoms, but the mechanisms of selection of recombination sites are poorly understood. The nonrandom recombination between two subviral RNAs associated with turnip crinkle virus was used to study the requirement for specific sequences and structures in the generation of recombinant molecules. Single-base mutations that disrupted either the stem or the loop of one of the two computer-predicted stem-loop structures eliminated detectable recombinant molecules. However, recombinants were detected if compensatory mutations were generated that re-formed a stable hairpin structure. These results provide evidence for the necessity of specific structures in the formation of recombinant molecules in this system.
Genetic Mapping of a Locus Predisposing to Human Colorectal Cancer
Authors: Peltomäki Päivi , Aaltonen Lauri A. , Sistonen Pertti , Pylkkänen Lea , Mecklin Jukka-Pekka , Järvinen Heikki , Green Jane S. , Jass Jeremy R. , Weber James L. , Leach Fredrick S. , Petersen Gloria M. , Hamilton Stanley R. , de la Chapelle Albert , Vogelstein Bert
Published: October 2006

Genetic linkage analysis was used to determine whether a specific chromosomal locus could be implicated in families with a history of early onset cancer but with no other unique features. Close linkage of disease to anonymous microsatellite markers on chromosome 2 was demonstrated in two large kindreds. The pairwise lod scores for linkage to marker D2S123 in these kindreds were 6.39 and 1.45 at zero recombination, and multipoint linkage with flanking markers resulted in lod scores of 6.47 and 6.01. These results prove the existence of a genetically determined predisposition to colorectal cancer that has important ramifications for understanding and preventing this disease.
Secondary and Tertiary Structural Effects on Protein NMR Chemical Shifts: an ab Initio Approach
Authors: de Dios Angel C. , Pearson John G. , Oldfield Eric
Published: October 2006

Recent theoretical developments permit the prediction of
1
H,
13
C,
15
N, and
19
F nuclear magnetic resonance chemical shifts in proteins and offer new ways of analyzing secondary and tertiary structure as well as for probing protein electrostatics. For
13
C, φ, ψ torsion angles dominate shielding for Cα and Cβ, but the addition of hydrogen bonding and electrostatics gives even better accord with experiment. For
15
N
H
, side chain (χ
1
) torsion angles are also important, as are nearest neighbor sequence effects, whereas for
1
H
N
, hydrogen bonding is particularly significant. For
19
F, weak or long-range electrostatic fields dominate
19
F shielding nonequivalencies. The ability to predict chemical shifts in proteins from known or test structures opens new avenues to structure refinement or determination, especially for condensed systems.
Denervated Skeletal Muscle Fibers Develop Discrete Patches of High Acetylcholine Receptor Density
Authors: Ko P. K. , Anderson M. J. , Cohen M. W.
Published: October 2006

Denervated skeletal muscle fibers of mice develop discrete patches of high acetylcholine receptor density. The patches vary in size from less than 1 micrometer up to 30 micrometers, depending on the muscle and the period of denervation. Within the patches the acetylcholine receptor density is some 20 times greater than elsewhere along the muscle fiber and probably approaches that in the subsynaptic membrane.
Mercury Emissions from Geothermal Power Plants
Authors: Robertson D. E. , Crecelius E. A. , Fruchter J. S. , Ludwick J. D.
Published: October 2006

Geothermal steam used for power production contains significant quantities of volatile mercury. Much of this mercury escapes to the atmosphere as elemental mercury vapor in cooling tower exhausts. Mercury emissions from geothermal power plants, on a per megawatt (electric) basis, are comparable to releases from coal-fired power plants.
Synthetic Peptides Form Ion Channels in Artificial Lipid Bilayer Membranes
Authors: Kennedy Stephen J. , Roeske Roger W. , Freeman Alan R. , Watanabe August M. , Besche Henry R.
Published: October 2006

Ion permeability of cell membranes is considered to be mediated by ion channels. The synthesis and testing of four peptides having the sequence (Leu-Ser-Leu-Gly)n and expected to form β
12
6,6
-helical ion channels in lipid bilayer membranes is reported. The two peptides capable of forming helices four turns in length have been demonstrated to form ion channels in an artificial lipid bilayer membrane system. The ion selectivity of the channels is consistent with the predicted β
12
-helical model in which ions traversing the channel are coordinated by serine hydroxyl groups arrayed in the interior of the channel.
Freeze-Fractured Purple Membrane Particles: Protein Content
Authors: Fisher Knute A. , Stoeckenius Walther
Published: October 2006

Optical diffraction and image reconstruction can be used to correlate the electron microscope image of the biological membrane with its electron density projection. Such correlation shows that a single purple membrane particle contains 9 to 12 protein molecules—63 to 84 transmembrane alpha helices—a complexity two to ten times greater than that previously suggested for membrane particles.
Toxicity of Mild Prenatal Carbon Monoxide Exposure
Authors: Fechter Laurence D. , Annau Zoltan
Published: October 2006

Rats prenatally exposed to a low concentration of carbon monoxide which results in carboxyhemoglobin levels equivalent to those maintained by human cigarette smokers, show reduced birth weight and decreased weight gain. Neuro-behavioral and biochemical testing of the offspring reveals lower behavioral activity levels through the preweaning period, altered central catecholamine activity, and reduction in total brain protein at birth.
A Developmental Theory of Environmental Enrichment
Authors: Cummins R. A. , Livesey P. J. , Evans J. G. M. , Walsh R. N.
Published: October 2006

The differential brain development induced by sensory enrichment or deprivation is most apparent in rats with low brain weights. These differences are hypothesized to represent the retarded development of environment-dependent neurons in the isolated animals.
Complexes of Stannous Fluoride and Other Group IVB Dihalides with Mammalian Hemoproteins
Authors: Dahl Alan R. , Hodgson Ernest
Published: October 2006

Stannous fluoride, the widely used anticaries toothpaste additive, and other tin and germanium dihalides form complexes with hemoproteins such as hepatic cytochrome P-450, hemoglobin, and peroxidase. These complexes are characterized by visible spectra closely similar in shape, molar absorptivity, and absorbance maxima to those obtained with analogous complexes of carbon monoxide. Evidence is presented that the observed complexes are formed with uncharged MX
2
or LMX
2
moieties (where L is a neutral Lewis base, M is a metal, and X is a halogen) acting as π-acceptor ligands.
Trichromatic Vision in the Cat
Authors: Ringo J. , Wolbarsht M. L. , Wagner H. G. , Crocker R. , Amthor F.
Published: October 2006

Many cat retinal ganglion cells (types X, Y, and W) have inputs from three separate cone systems. Those with peak sensitivities at 450 and 555 nanometers have been previously shown. A γ
max
cone with a peak sensitivity of 500 nanometers can be differentiated from other cones by spectral sensitivity and from rods by receptive field differences, functioning above rod saturation levels, and by cone-rod breaks in the dark-adaptation curves. The similarity of the three-cone cat retina to the extramacular retina of the rhesus monkey suggests that the cat may have photopic trichromatic vision.
First Suckling Response of the Newborn Albino Rat: The Roles of Olfaction and Amniotic Fluid
Authors: Teicher Martin H. , Blass Elliott M.
Published: October 2006

Washing the nipples of anesthetized parturient rats virtually eliminated nipple attachment by their young. Normal attachment was induced only by painting the washed nipples with a distillate of the nipple wash, parturient-mother saliva, or her amniotic fluids. Reinstatement was not achieved by coating the washed nipples with the saliva of virgin females eating the same diet, the parturient mother's urine, isotonic saline, amyl acetate, or vanilla extract. These experiments also provide behavioral evidence for olfactory function in the newborn albino rat.
Odor-Aversion Learning in Neonatal Rats
Authors: Rudy Jerry W. , Cheatle Martin D.
Published: October 2006

Two-day-old rats were exposed to a novel odor and injected with an illness-inducing drug, lithium chloride. When tested at 8 days of age, these pups avoided pine shavings scented with the odor, whereas control pups did not. These results imply that rat pups are capable of associative learning at a much earlier age than was thought possible.
Hunger in Humans Induced by 2-Deoxy-D-Glucose: Glucoprivic Control of Taste Preference and Food Intake
Authors: Thompson Dean A. , Campbell Robert G.
Published: October 2006

Intracellular glucopenia induced by 2-deoxy-D-glucose (2DG) administration in man produces increased hunger ratings and magnitude estimates of pleasantness for sucrose solutions. Augmented food intake substantiates these changes in affective behavior and relieves experimentally induced hunger. Intracellular glucopenia activates counterregulatory mechanisms to raise plasma glucose concentrations. Inducing hunger experimentally with 2DG provides a useful method for studying appetitive behavior in humans. The neurohumoral control of pituitary hormone release and other hypothalamic functions may be examined after 2DG infusion.
The Preservation by Freezing and Drying in Vacuo of the Milk-Influence for the Development of Breast Cancer in Mice
Authors: Bittner John J.
Published: October 2006

The development of spontaneous breast cancer in mice following the feeding of lyophilized tissue prepared from breast tumors suggests that the active influence usually transferred in the milk by nursing may be a virus.