bluuebunny/crossref_metadata_2025 huggingface dataset:
Measles virus-specific IgD antibodies in patients with subacute sclerosing panencephalitis.
Authors: Luster M I , Armen R C , Hallum J V , Leslie G A
Published: May 2006

Indirect immunofluorescent analysis revealed that sera from five patients with subacute sclerosing panencephalitis possessed IgD antibodies directed against measles virus components in persistently infected HeLa cells. IgD levels in these sera were within the normal range. Control studies indicated that the reaction was specific for measles virus. The detection of IgD measles antibodies in these patients suggested that IgD may be involved in the pathogenesis of this viral disease.
15N nuclear magnetic resonance investigations on amino acids.
Authors: Blomberg F , Maurer W , Rüterjans H
Published: May 2006

15N nuclear magnetic resonance investigations of some amino acids were carried out in order to check the applicability of this method to biological problems. Because the natural abundance of the 15N isotope is not sufficient to get readable spectra in a reasonable time, 95% 15N isotope-enriched samples were used for the measurements. Besides the chemical shift values, the line widths, and the nuclear Overhauser enhancement factors, spin lattice relaxation times of the correspondent 15N resonances were measured as functions of pH had temperature.
A protein binding the methylated 5'-terminal sequence, m7GpppN, of eukaryotic messenger RNA.
Authors: Filipowicz W , Furuichi Y , Sierra J M , Muthukrishnan S , Shatkin A J , Ochoa S
Published: May 2006

Ribosomal salt washes of Artemia salina embryos contain a protein(s) that binds [3H]m7GpppGpC and [3H]m7GpppGmpC, as measured by retention on nitrocellulose membrane filters. These oligonucleotides correspond in structure to the methylated 5'-terminal sequences (caps) present in many eukaryotic mRNAs. The cap binding protein does not bind the unmethylated counterparts of caps, e.g., [32P]GpppGpCp, or a derivative of m7GpppGmpC containing ring-opened m7G. None of the purified initiation factors IF-MP, IF-M2A, IF-M2B, IF-M3, or IF-MI binds the m7G-containing oligonucleotides.
Kinetics of glucagon in man: effects of starvation.
Authors: Fisher M , Sherwin R S , Hendler R , Felig P
Published: May 2006

Serum stimulates the production of prostaglandins by transformed mouse fibroblasts. Hydrocortisone (cortisol) inhibits this stimulation. The half-maximal inhibition occurs at 6x10-9 M. Studies with cells labeled with [3H]arachidonic acid in their lipids show that the stimulation by serum results in the release of arachidonic acid from the cellular lipids, mostly phospholipids. Hydrocortisone inhibits this release but does not inhibit the production of prostaglandins from exogenously supplied arachidonic acid. This inhibition of arachidonic acid release from phospholipids may be the mechanism for the anti-inflammatory action of corticosteroids.
Conformation of uncomplexed [Phe4, Val6] antamanide crystallized from nonpolar solvents.
Authors: Karle I L , Karle J , Wieland T , Burgermeister W , Witkop B
Published: May 2006

[Phe4, Val6] antamanide, a synthetic, biologically active analog of the cyclic decapeptide antitoxin isolated from Amanita phalloides, has been crystallized from a mixture of n-hexane and methyl acetate, and its conformation has been established by the direct method of x-ray diffraction analysis, i.e., without the benefit of any heavy atom. The uncomplexed molecule contains a 2-fold rotation axis and cis peptide linkages between Pro2-Pro3 and Pro7-Pro8. Otherwise, its conformation differs extensively from that of the Na+[Phe4, Val6] antamanide-C2H5OH complex. The 30-membered ring is elongated and relatively planar as compared to the folded ring in the Na+ complex. The six NH groups are directed toward the anterior of the molecule. There is one pair of intra-molecular NH---O=C bonds of the 5 leads to 1 type containing a cis peptide unit. The other four NH groups participate in hydrogen bonds to three H2O sites in the interior of the molecule. The 10 hydrophobic side groups cover the bottom and surround the perimeter of the molecule with the phenyl groups in the four Phe residues folded against the molecule. The conformation found for [Phe4, Val6] antamanide crystallized from nonpolar solvents is different from any conformations proposed for antamanide in solution based on nuclear magnetic resonance data.
Sequential translation of nonstructural proteins in cells infected with a Semliki Forest virus mutant.
Authors: Lachmi B E , Kääriäinen L
Published: May 2006

Four nonstructural proteins with apparent molecular weights of 70,000 (ns-70), 86,000 (ns-86), 78,000 (ns-78), and 60,000 (ns-60) were translated in cells infected with Semliki Forest virus ts-1 mutant and maintained at the restrictive temperature. After synchronization of the initiation of protein synthesis these proteins were synthesized in the above order, suggesting that they are translated as a polyprotein starting from one initiation site. Two short-lived intermediates with apparent molecular weights of 155,000 and 135,000 were regularly detected. The former is presumably the precursor of proteins ns-70 and ns-86 and the latter of ns-78 and ns-60. The sequence of the structural proteins in their polyprotein was confirmed to be capsid-envelope E-2 (and E-3)-envelope E-1, beginning from the NH2-terminal end. We conclude that in Semliki-Forest-virus-infected cells two polyproteins are synthesized, one for the structural (130,000 daltons), the other for the nonstructural proteins (close to 300,000 daltons).
A fatty acyl-CoA oxidizing system in rat liver peroxisomes; enhancement by clofibrate, a hypolipidemic drug.
Authors: Lazarow P B , De Duve C
Published: May 2006

Purified rat liver peroxisomes contain a cyanide-insensitive fatty acyl-CoA oxidizing system that uses O2 and NAD as electron acceptors. The system was detected by the ability of added palmitoyl-CoA to elicit O2 consumption, H2O2 production, and O2-dependent NAD reduction. The activity of this system is increased approximately one order of magnitude in rats treated with clofibrate, a hypolipidemic drug known to cause peroxisomal proliferation.
Human and murine phosphorycholine-binding immunoglobulins: conserved subgroup and first hypervariable region of heavy chains.
Authors: Riesen W F , Braun D G , Jaton J C
Published: May 2006

The NH2-terminal 36 residues of the heavy chain and the NH2-terminal 40 residues of the light chain from a human Waldenström's IgM with binding activity for phosphorylcholine (phosphocholine) are compared with the published sequences of five mouse IgA myeloma proteins with the same activity. An extensive structural similarity; i.e., 3 amino acid interchanges within framework residues, and one in the hypervariable region, is noted between the heavy chains of both species. The light chains, however, show a considerable diversity and, in contrast to the heavy chain, no correlation between the primary structure of the first hypervariable region and the binding specificity is apparent. The finding of a very similar heavy chain variable region in two different species that are separated by about 75 million years in evolution favors the concept of stable transmission of variable region genes throughout evolution.
Structural evidence that human liver and placental alkaline phosphatase isoenzymes are coded by different genes.
Authors: Badger K S , Sussman H H
Published: May 2006

Human liver alkaline phosphatase [ortho-phosphoric monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] was purified, and some of its physical and chemical properties were examined and compared to those of human placental alkaline phosphatase. The results indicated a different peptide structure for each, based upon HB2-terminal residue sequence, two-dimensional tryptic peptide maps, and different amino acid compositions. These data are interpreted to indicate that the enzymes are synthesized by different structural genes. Other molecular properties differentiating the two enzymes were a higher apparent molecular weight for the liver enzyme from sodium dodecyl sulfate gel electrophoresis, a higher S20,w value, different carbohydrate content, and a different isoelectric point. The immunochemical specificity of each enzyme was not affected by removal of sialic acid groups. Both enzymes are similar in that they are dimers of equal molecular weight subunits, and are probably homodimers.
Origin and direction of synthesis of bacteriophage fl DNA.
Authors: Horiuchi K , Zinder N D
Published: May 2006

The origin and direction of synthesis in vivo of the viral and complementary strands of f1 DNA were studied by measuring the distribution of radioactivity along the genome after a short pulse of [3H]thymidine. The results indicate that the origins of replication of viral and complementary strands are located close to one another, probably both within a restriction fragment (HaeIII-G) which is about 120 bases long. Replication of both viral and complementary strands proceeds in the 5' leads to 3' overall direction. Thus, the viral strand is elongated in the counterclockwise and the complementary strand in the clockwise direction on the standard genetic map. A model is proposed in which only two mechanisms are invoked to generate all f1 DNA species: (1) the conversion of single-stranded viral DNA into double-stranded molecules and (2) the synthesis of viral single strands from double strands.
Nucleotide sequence of region preceding trp mRNA initiation site and its role in promoter and operator function.
Authors: Bennett G N , Schweingruber M E , Brown K D , Squires C , Yanofsky C
Published: May 2006

The nucleotide sequence of the region preceding the transcription initiation site of the tryptophan operon of Escherichia coli was determined. Essentially all of the trp operator precedes the transcribed portion of the operon. The deduced sequence contains the recognition site of endonuclease Hpa I. This site is protected from Hpa I cleavage by RNA polymerase and by trp repressor. Regions of 2-fold symmetry are present in the DNA sequence.
Enhancement of postreplication repair in Chinese hamster cells.
Authors: D'Ambrosio S M , Setlow R B
Published: May 2006

Alkaline sedimentation profiles of pulse-labeled DNA from Chinese hamster cells showed that DNA from cells treated with N-acetoxy-acetylaminofluorene or ultraviolet radiation was made in segments smaller than those from untreated cells. Cells treated with a small dose (2.5 muM) of N-acetoxy-acetylaminofluorene or (2.5 J-m-2) 254-nm radiation, several hours before a larger dose (7-10 muM) of N-acetoxy-acetylaminofluorene or 5.0 J.m-2 of 254 nm radiation, also synthesized small DNA after the second dose. However, the rate at which this small DNA was joined together into parental size was appreciably greater than in absence of the small dose. This enhancement of postreplication repair (as a result of the initial small dose) was not observed when cells were incubated with cycloheximide between the two treatments. The results suggest that N-acetoxy-acetylaminofluorene and ultraviolet-damaged DNA from Chinese hamster cells are repaired by similar postreplicative mechanisms that require de novo protein synthesis for enhancement.
Deficiency of gamma-ray excision repair in skin fibroblasts from patients with Fanconi's anemia.
Authors: Remsen J F , Cerutti P A
Published: May 2006

The capacity of preparations of skin fibroblasts from normal individuals and patients with Fanconi's anemia to excise gamma-ray products of the 5,6-dihydroxydihydrothymine type from exogenous DNA was investigated. The excision capacity of whole-cell homogenates of fibroblasts from two of four patients with Fanconi's anemia was substantially below normal. This repair deficiency was further pronounced in nuclear preparations from cells of the same two patients.
Increase of AKR-specific sequences in tumor tissues of leukemic AKR mice.
Authors: Berns A , Jaenisch R
Published: May 2006

AKR mice produce, from shortly after birth, high titers of their endogenous Gross type murine leukemia virus, and develop a thymus-derived leukemia at 7-9 months of age. We show that this oncogenesis is accompanied by an increase in the number of AKR-specific DNA sequences in the tumor tissues, whereas the "non-target" organs are not affected. Sequence increase was determined by kinetic analysis of DNA reassociation using an AKR-murine leukemia virus (MuLV)-specific cDNA and also by hybridization with excess AKR cDNA. The AKR cDNA was selected to recognize AKR sequences without significant crossreaction with DNA sequences of other endogenous viruses. The results show that during the development of the leukemia, the number of AKR-MuLV-specific genes increases in tumor tissues by a factor of 1 1/2 to 2.
Platinum binds selectively to phosphorothioate groups in mono- and polynucleotides: a general method for heavy metal staining of specific nucleotides.
Authors: Strothkamp K G , Lippard S J
Published: May 2006

Platinum binding to nucleoside phosphorothioates has been examined to determine their suitability as heavy metal labeling sites for the potential electron microscopic sequencing of nucleic acids. The complex platinum terpyridine nitrate forms a 1:1 adduct with either adenosine or uridine monophosphorothioate. Spectroscopic evidence strongly indicates the presence of platinum-sulfur bonds. Both platinum terpyridine nitrate and chloroterpyridineplatinum(II) bind to poly(sA-U), a polymer prepared from adenosine 5'-O-(1-thiotriphosphate) and UTP. Binding to the sulfur atoms of the phosphorothioate groups is quantitative, as shown by double label experiments using [35S]poly(sA-U) and [3H]chloroterpyridine-platinum(II). Similar experiments with [14C]poly(A-U) indicated no platinum binding. No evidence of nicking or loss of sulfur from poly(sA-U) could be detected after platinum binding. The phosphorothioate group is a strong, highly selective binding site for platinum in polynucleotides. Previous studies have demonstrated quantitative enzymatic incorporation of phosphorothioate groups into a polynucleotide adjacent to a specific base [Matzura, H. & Eckstein, F. (1968) Eur. J. Biochem. 3, 448-452]. The use of heavy metal-labeled phosphorothioate groups for the sequencing of nucleic acids by electron microscopy therefore appears feasible.
Preliminary analysis of 1H and 13C spectral and relaxation behavior in methionine-enkephalin.
Authors: Bleich H E , Cutnell J D , Day A R , Freer R J , Glasel J A , McKelvy J F
Published: May 2006

Nuclear magnetic resonance studies on the conformational dynamics of the pentapeptide H-Tyr-Gly-Gly-Phe-Met-OH are reported. This peptide, for which the generic trivial name "methionine-enkephalin" has been suggested, is pharmacologically active as a ligand for the mammalian opiate receptor(s). The studies reported are parallel investigations in two solvents (dimethylsulfoxide and water) of: 1H and 13C high resolution spectral assignments; 1H and 13C spin-lattice relaxation times, temperature dependence of amide proton chemical shifts, and half-times for chemical exchange or amide protons. From these data we conclude that the tyrosine side chain of methionine-enkephalin exhibits restricted motion with respect to the main peptide backbone of the molecule. On the other hand both the phenylalanyl and methionyl side chains are undergoing intramolecular reorientation with relatively high frequency.
Subunit structure and isozymic forms of gamma-glutamyl transpeptidase.
Authors: Tate S S , Meister A
Published: May 2006

gamma-Glutamyl transpeptidase is associated with the membranes of a number of epithelial and lymphoid cells. When the enzyme is isolated from rat kidney by a method involving detergent extraction and affinity chromatography, an aggregate of molecular weight greater than 200,000 (heavy form) is obtained. Treatment of the heavy form with bromelain yields a light form of the enzyme (molecular weight of approximately 68,000), which is separable by isoelectric focusing into 12 enzymatically active isozymes which are very similar with respect to catalytic behavior, content of amino acids, hexoses, and aminohexoses, but which differ significantly in sialic acid content. Treatment with neuraminidase converts the acidic isozymes to more basic forms. Each isozyme dissociates in sodium dodecyl sulfate into two nonidentical glycopeptides (molecular weights of 46,000 and 22,000) which can be cross-linked with dimethylsuberimidate to yield a species with an apparent molecular weight of 70,000, which indicates that the isozymes are dimers. Physical and immunological studies indicate that the heavy form of the enzyme contains the dimeric light form as well as other membrane proteins.
Differential degradation of messenger RNAs in mammalian cells.
Authors: Stiles C D , Lee K L , Kenney F T
Published: May 2006

Through the use of an assay that measures cellular capacity for specific enzyme synthesis, mRNA of alanine aminotransferase (EC 2.6.1.2; L-alanine:2-oxoglutarate aminotransferase) was found to be degraded with a half-life of 12-14 hr in cultured Reuber H-35 cells; mRNA of tyrosine aminotransferase (EC 2.6.1.5; L-tyrosine:2-oxoglutarate aminotransferase) has a half-life of 2 hr in the same cells. Rates of degradation of the mRNAs are the same whether new mRNA accumulation is blocked by removal of the steroid inducer or by inhibition of mRNA synthesis (actinomycin). Cycloheximide inhibits the normally rapid turnover of tyrosine aminotransferase mRNA, but agents such as puromycin and sodium fluoride, which disrupt polysome structure, do not alter the turnover rate of the tyrosine and alanine aminotransferase mRNAs. The tyrosine and alanine aminotransferase mRNAs appear to be translated at equivalent rates. The data suggest that the degradation rate of these two mRNAs is determined by the polynucleotide structure of the mRNA molecules at or near the site for ribosome binding and initiation.
Psoralen-crosslinked secondary structure map of single-stranded virus DNA.
Authors: Shen C K , Hearst J E
Published: May 2006

The photochemical crosslinking of DNA by 4,5',8-trimethylpsoralen (trioxsalen) has been used to freeze the secondary structures of single-stranded DNA molecules of bacteriophage fd at different ionic strengths. These secondary structures (hairpins or looped hairpins) have been visualized in the electron microscope. Most of the single-stranded circular fd DNA molecules show only one hairpin after irradiation at 15 degrees in 20 mM NaCl in the presence of trioxsalen. As the ionic strength is increased, more hairpins appear on the DNA molecules. To map these secondary structures, double-stranded supercoiled fd DNA (RFI) was cleaved with the restriction enzyme HindII, which makes only one cut on each RFI molecule. After denaturation and crosslinking of the linear single-stranded fd DNA (a mixture of viral and complementary strands), all the hairpins have been mapped on the DNA molecule with respect to this HindII site. The results show that these hairpins occur at specific sites. The most stable hairpin has been assigned to the position where the initiation site for the conversion of single-stranded fd DNA to the double-stranded covalently closed form has been mapped. The remaining hairpins map in or near regions corresponding to in vitro promoter sites on the fd DNA.
Small fragments from the A subunit of cholera toxin capable of activating adenylate cyclase.
Authors: Matuo Y , Wheeler M A , Bitensky M W
Published: May 2006

Exposure of cholera toxin to membrane particles prepared from sarcoma 180 cells gives rise to a variety of fragments which are capable of activating adenylate cyclase [ATP:pyrophosphate-lyase (cyclizing), EC 4.6.1.1]. A major component of these fragments has an apparent molecular weight in the 8,000-10,000 range. The smallest stimulatory fragment has a molecular weight of approximately 1400. The small size of the fragments is confirmed by Sephadex gel filtration, in the presence of either sodium dodecyl sulfate or formic acid. These fragments are produced from holotoxin or its A subunit by protease(s) found in sarcoma membrane particles. Production of fragments appears optimal in 40-60 min at 30 degrees and pH 7, and is prevented by protease inhibitors. The ability of the small fragments to activate adenylate cyclase is reversed by anti-holotoxin, but not anticholeragenoid, antibodies. These fragments require NAD for the activation of adenylate cyclase and are fully active after heating at 90 degrees for 5 min (pH 7).
Membrane potential dependent binding of scorpion toxin to action potential Na+ ionophore.
Authors: Catterall W A , Ray R , Morrow C S
Published: May 2006

Depolarization of neuroblastoma cells causes a 70-fold increase in the apparent dissociation constant KD for scorpion toxin enhancement of activation of the action potential Na+ ionophore by veratridine and a large increase in the rate of reversal of scorpion toxin action. Depolarization also inhibits binding of 125I-labeled scorpion toxin to a small number of saturable binding sites on electrically excitable neuroblastoma cells and increases the rate of dissociation of scorpion toxin from these sites. The results suggest that scorpion toxin binds to a regulatory component of the action potential Na+ ionophore whose conformation changes on depolarization.
Structural (shape-maintaining) role of the cell surface glycoprotein of Halobacterium salinarium.
Authors: Mescher M F , Strominger J L
Published: May 2006

The obligate halophile, Halobacterium salinarium, maintains a rod-shaped morphology under normal growth conditions. Lactoperoxidase(EC 1.11.1.7;donor:hydrogen-peroxide oxidoreductase)-catalyzed iodination and treatment with proteolytic enzymes were used to demonstrate that the recently described envelope glycoprotein (Mescher, M.F. & Strominger, J.L. (1976) J. Biol. Chem. 251, 2005-2014) is the only major cell surface component of this organism. The morphological changes that accompany alteration of the structure of the glycoprotein by growth in the presence of bacitracin or its removal with proteolytic enzymes strongly suggest that it forms a rigid matrix at the cell surface and is responsible for maintenance of the characteristic rod shape.
Control of renal vitamin D hydroxylases in birds by sex hormones.
Authors: Tanaka Y , Castillo L , DeLuca H F
Published: May 2006

Kidney homogenates from adult male Japanese quail or chickens demonstrate hydroxylase activity predominantly for the 24 rather than the 1 position of 25-hydroxyvitamin D3 (25-hydroxycholecalciferol). A single injection of 5 mg of estradiol-17beta into a male bird completely suppresses the 24-hydroxylase and greatly increases the 1-hydroxylase activity. Immature males do not respond well to estrogen alone, but they do respond well to estradiol plus testosterone. Testosterone alone has little or no effect on the hydroxylases of either species. Castrated male chickens show an estradiol response only when testosterone is also given. Optimal 24 hr responses to 5 mg of estradiol per kg in the castrate male were obtained with about 12 mg of testosterone per kg. These optimal amounts of estradiol and testosterone increased the activity of 25-hydroxyvitamin D3-1-hydroxylase approximately 225-fold (this enzyme is also known as 25-hydroxycholecalciferol 1-monooxygenase; 25-hydroxycholecalciferol, NADPH: oxygen oxidoreductase (hydroxylating), EC 1.14.13.13). These results demonstrate a strong regulation by the sex hormones of the renal vitamin D hydroxylases in birds.
Cell recognition in plants: Determinants of the stigma surface and their pollen interactions
Authors: Knox R. Bruce , Clarke Adrienne , Harrison Susan , Smith Patricia , Marchalonis John J.
Published: May 2006

The interaction between compatible pollen grains and the female stigma of
Gladiolus gandavensis
has been used as a model system for investigation of cell recognition in plants. The molecular architecture of the receptive stigma surface has been investigated, and determinants binding to both concanavalin A and β-glucosyl artificial carbohydrate antigen, as well as esterase activity, have been characterized, and conditions for their isolation have been established. The stigma surface, before and after modification, was found to bind
125
I-labeled proteins nonspecifically. Pollen tube penetration of the papillar cuticle is prevented when the receptor sites for concanavalin A are occupied. The concanavalin-A-binding determinants of the stigma surface have been fractionated to reveal several glycoproteins in the molecular weight range 43,000-93,000 and a group of glycolipids of molecular weight approximately 22,000. These results are interpreted in terms of two major recognition events regulating pollination.
Demonstration of the inhibitory effect of human alpha-fetoprotein on in vitro transformation of human lymphocytes.
Authors: Yachnin S
Published: May 2006

We have studied the effects of human alpha-fetoprotein (HAFP), isolated from the serum and ascitic fluid of a hepatoma-bearing patient, on the in vitro transformation of human peripheral blood lymphocytes by a variety of mitogenic stimuli. At a concentration of 2.5 mg/ml, HAFP inhibited the lymphocyte response to phytohemagglutinin, concanavalin A, and rabbit anti-human thymocyte serum, but failed to inhibit the response to pokeweed mitogen. HAFP was able to inhibit the one-way mixed lymphocyte culture at concentrations of 250-500 mug/ml, but failed to inhibit at 100 mug/ml. Exposure of lymphocytes to 2.2 mg/ml of HAFP for 18 hr did not result in significant lymphocytotoxicity, and such cells washed free of HAFP were fully capable of participating in the mixed lymphocyte culture. HAFP did not inhibit lymphocyte E-rosette formation. Fetal HAFP was more effective in inhibiting human lymphocyte responses than hepatoma HAFP. These experiments support the suggestion that HAFP plays an important immunoregulatory role during fetal development, possibly through the suppression of thymus-derived lymphocyte responses to antigenic stimuli; they also suggest that there are important differences in the biological properties of hepatoma and fetal HAFP.
Circadian organization of the estrous cycle of the golden hamster.
Authors: Fitzgerald K , Zucker I
Published: May 2006

In constant dim illumination the hamster estrous cycle free-runs with a period that is a quadruple multiple of the concurrently recorded rhythm of wheel-running activity; both activity and estrous cycles are generated by biological clocks. Maintenance of stable phase angle differences between heat onset and running onset before and after treatment with deuterium oxide suggests that a common circadian system generates periodicities in estrus and activity. An organization of the estrous cycle is proposed in which the stimulus for the ovulatory surge of luteinizing hormone is generated by a circadian system that includes the suprachiasmatic nuclei of the hypothalamus. Various possible interactions of estradiol and photoperiod with the neurogenic stimulus for the luteinizing hormone surge are described and implications of different types of circadian organization of the estrous cycle for theories of sexual differentiation are considered.
Metalloprotein electron transfer reactions: analysis of reactivity of horse heart cytochrome c with inorganic complexes.
Authors: Wherland S , Gray H B
Published: May 2006

The reactions of horse heart cytochrome c with Fe(ethylenediaminetetraacetate)2-, Co(1,10-phenanthroline)3(3+), Ru(NH3)6(2+), and Fe(CN)6(3-) have been analyzed within the formalism of the Marcus theory of outer-sphere electron transfer, including compensation for electrostatic interactions. Calculated protein self-exchange rate constants based on crossreactions are found to vary over three orders of magnitude, decreasing according to Fe(CN)6(3-) greater than Ru(NH3)6(2+) greater than Fe(EDTA)2-. The reactivity order suggests that the mechanism of electron transfer involves attack by the small molecule reagents near the most nearly exposed region of the heme; this attack is affected by electrostatic interactions with the positively charged protein, by hydrophobic interactions that permit reagent penetration of the protein surface, and by the availability of pi symmetry ligand (or extended metal) orbitals that can overlap with the pi redox orbitals of the heme group.
Circular DNA of a yeast episome with two inverted repeats: structural analysis by a restriction enzyme and electron microscopy.
Authors: Guerineau M , Grandchamp C , Slonimski P P
Published: May 2006

Small circular DNA molecules from genetically characterized clones of Saccharomyces cerevisiae have been studied by restriction endonuclease analysis and electron microscopy. The circular monomers (6000 bases) are shown to contain two inverted repeats of the same sequence (600 bases) situated opposite each other along the perimeter. Four endonuclease EcoRI fragments are obtained in 1:1:1:1 stoichiometry, and their sum gives a length of about 12,000 bases. The two large fragments and the two small ones differ from each other by 200 bases. We propose a model for the structure of the monomer molecule. Two classes of monomers can be generated by intramolecular recombinations within inverted repeats; they differ by the relative orientation of nonrepeated segments. The structure of dimers as predicted by the model is verified by self-renaturation of single-stranded circles. Inverted repeats in circular molecules may be related to the insertion release faculty of II episome in the chromosomes.
Competition between cellular and viral mRNAs in vitro is regulated by a messenger discriminatory initiation factor.
Authors: Golini F , Thach S S , Birge C H , Safer B , Merrick W C , Thach R E
Published: May 2006

Encephalomyocarditis viral RNA has previously been shown to outcompete host cellular mRNA has for translation in vitro in crude and fractionated protein synthesizing systems. In the present communication it is shown that the competition is regulated by an initiation factor or complex of factors, and not the 40S initiation complex per se. The factor primarily involved is the murine equivalent of a component present in a partially purified preparation of rabbit initiation factor M3. Both the murine and rabbit factors are clearly messenger discriminatory.
Regulation of protein synthesis in reticulocyte lysates: phosphorylation of methionyl-tRNAf binding factor by protein kinase activity of translational inhibitor isolated from hemedeficient lysates.
Authors: Levin D , Ranu R S , Ernst V , London I M
Published: May 2006

A previous study demonstrated that the translational inhibitor from lysates of heme-deficient rabbit reticulocytes is associated with a protein kinase activity. Chromatography of this inhibitor preparation on phosphocellulose yields two distinct protein kinase activities, PC1 and PC2. PC1, which consitutes about 90% of the activity in the unresolved preparation, does not inhibit protein synthesis in lysates, but actively phosporylates calf thymus histone II in a 3':5'-cyclic AMP-denpendent reaction. PC2 contains the translational inhibitor, phosphorylates histone poorly, and is not cyclic AMP-dependent. While [gamma-32P]ATP as the phosphate donor, the two kinase fractions were analyzed with the putative substrates, salt-washed 40S ribosomal subunits, and the initiation factor that mediates the binding of Met-tRNAf to the 40S subunit. PC1 is inactive with the initiation factor, but phosphorylates 40S subunits at a single major site that migrates as a 31,000-dalton band in sodium dodecyl sulfate-acrylamide gels; phosphorylation requires cyclic AMP. Similar phosphorylation of the reticulocyte 40S site (31,000 daltons) can be demonstrated with other cyclic AMP-dependent kinases from reticulocytes, rat liver, and bovine heart muscle. PC2 phosphorylates the small subunit (38,000 daltons) but not the large subunit(s) of the initiation factor; the reaction does not require cyclic AMP. PC2 does not phosphorylate 40S subunits. In the presence of 40S subunits, the initiation factor appears to be rapidly bound in a manner that effectively blocks phosphorylation of the initiation factor by PC2; under the same conditions phosphorylation of the 40S subunit by PC1 is not affected. The initiation factor has been shown to reverse the inhibitions of protein chain initiation induced in lysates by heme deficiency, double-stranded RNA, oxidized glutathione, or the purified translational inhibitor. The observation that the Met-tRNAf binding factor is phosphorylated by PC2 supports the hypothesis that this initiation factor is a target for the action of the translational inhibitor activated in heme deficiency.
Amino acids and control of nucleolar size, the activity of RNA polymerase I, and DNA synthesis in liver.
Authors: Bailey R P , Vrooman M J , Sawai Y , Tsukada K , Short J , Lieberman I
Published: May 2006

The volume of nucleolar material per nucleus and the activity of RNA polymerase I (RNA nucleotidyltransferase I) become doubled in the liver cells of rats that are fed for several days a diet that lacks essential amino acids. Omission of methionine from a fully supplemented diet is equivalent to leaving out all the amino acids, and the responses to a deficiency of tryptophan are about 40% as great. Deprivation of one of the remaining essential amino acids gives either small responses or none at all. Supplementation of the methionine-free diet with cystine blocks the nucleolar enlargement and the enhancement of the polymerase activity that would otherwise take place, but the dispensable amino acid does not affect the responses to a deprivation of one of the other essential amino acids. After deprivation of all the essential amino acids or only methionine, hepatocytes make DNA when the rat is fed a meal with protein. A preparatory diet lacking in tryptophan is much less effective; a deficiency in any of the other indispensable compounds tested fails to prepare the liver for DNA synthesis. The results give hope that elucidation of the means by which methionine deprivation affects the nucleolus will also provide information on the regulation of nuclear DNA replication in liver. One attractive possibility is that the amino acid deficiency acts by producing some imbalance in protein metabolism.
Purification of a putative precursor of globin messenger RNA from mouse nucleated erythroid cells.
Authors: Kwan S P , Wood T G , Lingrel J B
Published: May 2006

Nucleated erythroid cells were incubated for 10 min in the presence of [5-3H]uridine, and the total RNA was isolated by three different extraction procedures. RNA containing globin messenger RNA sequences was purified from other cellular RNAs by selective hybridization to globin complementary DNA cellulose. Depending upon the extraction procedure employed, 0.4-0.6% of the radioactively-labeled total cellular RNA applied to the column annealed to globin complementary DNA cellulose. The annealed RNA was treated with formaldehyde and analyzed by formaldehyde/polyacrylamide gel electrophoresis. Mature globin mRNA and an RNA migrating at approximately 15 S were observed. No globin mRNA containing sequences larger than 20 S were present. The 15S RNA was partially resolved from mature globin mRNA by neutral sucrose density gradient centrifugation. The RNA isolated from the heavy region of this gradient migrated as 15 S in the formaldehyde/polyacrylamide gels and retained its ability to quantitatively anneal to globin complementary DNA cellulose. On the basis of these observations, we conclude that nucleated erythroid cells obtained from the spleens of anemic mice have a 15S RNA which contains globin mRNA sequences. The 15S RNA is not an aggregate and is a good candidate for a globin mRNA precursor.
Ligand kinetics of hemoglobin S containing erythrocytes.
Authors: Harrington J P , Elbaum D , Bookchin R M , Wittenberg J B , Nagel R L
Published: May 2006

Oxygen uptake of fully deoxygenated sickle (SS) erythrocytes is slower than that of normal (AA) erythrocytes, as demonstrated by the half-times of the overall oxygenation reactions: at 25 degrees in an isotonic phosphate buffer the normal red cells have a t1/2 = 82 +/- 4.7 msec, as compared to sickle red cells where t1/2 = 135 +/- 17.6 msec. The effects of temperature, extracellular osmolality, and the presence of an antisickling agent (n-butylurea) on the rate of red cell oxygenation strongly suggest that the differences in oxygenation rates encountered with sickle red cells is directly related to the intracellular polymerization of deoxyhemoglobin S.
Bacterial flagella rotating in bundles: a study in helical geometry.
Authors: Macnab R M
Published: May 2006

Bacterial flagella are semi-rigid helices that undergo true rotation. In peritrichously flagellated bacteria (e.g., Escherichia and Salmonella) there are many flagella on each cell; during translational cell movement these operate as a coordinated bundle that actively disperses upon reversal of the rotation sense. The dynamic behavior of a set of helices originating on separate rotational axes is explored by a working model, geometrical analysis, and hydrodynamic calculations. A critical relationship exists between the interaxial separation and phase difference of parallel helices with overlapping domains; in the subcritical case the filaments are not intertwisted, whereas in the supercritical case they are intertwisted in the same sense (left-handed) as the helices, with one twist per helical turn. During counter-clockwise rotation (the sense operative in forward swimming) any preexisting twists of this kind are automatically cancelled and the helices brought progressively into phase. Hydrodynamic calculations suggest that some wrapping then occurs in a right-handed sense, opposite to that of the helices; this necessitates a distortion from true helical geometry which is minimized by maintaining a coaxial in-phase relationship. A highly coordinated helical bundle results that is capable of operating smoothly for an indefinite period, in agreement with the observed behavior of swimming bacteria. During reverse rotation, the supercritical case develops to cause jamming of the bundle, as has been observed with bacteria in high-viscosity medium. The explosive dispersal of the bundle during reversal in low-viscosity medium is a consequence of a complicating phenomenon, namely, a drastic change in flagellar quaternary structure. The overall conclusion is that bundle formation and function are perfectly compatible with a rotational mechanism for the individual flagella.
3':5'-cyclic AMP: independent induction of amino acid transport by epinephrine in primary cultures of adult rat liver cells.
Authors: Pariza M W , Butcher F R , Becker J E , Potter V R
Published: May 2006

Liver cells were obtained from adult rats by a collagenase perfusion technique and cultured as monolayers in serum-free media. Epinephrine and isoproterenol both induced large increases in intracellular adenosine 3':5'-monophosphate (cAMP) within 1-2 min whereas epinephrine (but not isoproterenol) induced 2- to 3-fold increases in the rate of alpha-aminoisobutyric acid transport within 2-4 hr after a 1 hr lag. Propranolol abolished the increase in cAMP elicited by epinephrine and isoproterenol, but did not block the induction of alpha-aminoisobutyric acid transport by epinephrine. In contrast, dihydroergotamine abolished and phentolamine diminished the induction of alpha-aminoisobutyric acid transport by epinephrine but did not decrease the stimulation of cAMP levels by epinephrine. Epinephrine dose response curves for cAMP and alpha-aminoisobutyric acid transport were similar. Once exposed to epinephrine, cells became refractory to further stimulation of cAMP levels by epinephrine.
Partial inhibition of postreplication repair and enhanced frequency of chemical transformation in rat cells infected with leukemia virus.
Authors: Waters R , Mishra N , Bouck N , DiMayorca G , Regan J D
Published: May 2006

Postreplication repair of DNA and chemical transformation with the carcinogen 4-nitroquinoline-1-oxide were studied in rat cell lines either uninfected or infected with Rauscher leukemia virus. The results indicate that equivalent amounts of carcinogen are bound to the DNA initially and removed during excision repair. However, the lines differ in that the infected line alone exhibits both sensitivity to nitroquinoline-oxide-induced transformation and a partial inhibition of the postreplication repair process after notroquinoline oxide or UV treatment.
Role of cell surface carbohydrates and proteins in cell behavior: studies on the biochemical reversion of an N-acetylglucosamine-deficient fibroblast mutant.
Authors: Pouysségur J , Willingham M , Pastan I
Published: May 2006

AD6, a mutant derived from 3T3 Balb/c cells, is characterized by low adhesion to substratum, round shape, increase in surface microvilli, increase in agglutinability by concanavalin A, and loss of directional motility. These properties are often observed in transformed cells. However, the mutant has normal growth properties and anchorage-dependence of growth, and it does not form tumors. In AD6, the biosynthesis of complex carbohydrates and glycoproteins is impaired because of a block in the acetylation of GlcN-6-P. This defect is responsible for all the surface alterations because feeding of GlcNAc to AD6 cells corrects the defects in the synthesis of complex carbohydrates and the exposure of glycoproteins at the outer surface of the plasma membrane. Parallel to this biochemical reversion, there is full restoration of the altered biological properties. In contrast, GlcNAc has no effect on the morphologic features of two lines of transformed cells. Our results suggest that the carbohydrate portion of cell surface proteins has an important role in adhesion and related aspects of cell behavior. The fact that a defined alteration of the cell surface induces many properties often encountered in transformed cells, without affecting control of cell division, strongly suggests that these alterations in properties are not sufficient to account for the loss of growth regulation.
Transient inhibition of initiation of S-phase associated with dimethyl sulfoxide induction of murine erythroleukemia cells to erythroid differentiation.
Authors: Terada M , Fried J , Nudel U , Rifkind R A , Marks P A
Published: May 2006

The murine erythroleukemia cell (MELC) line in suspension culture can be induced to differentiate to erythroid cells by various compounds, including dimethyl sulfoxide (Me2SO). Analysis of the cell cycle, during differentiation induced by Me2SO, using thymidine incorporation, thymidine labeling index, and relative DNA content per cell as measured by flow microfluorometry, demonstrates a transient inhibition of entry of cells into S-phase of the cell cycle which is detected as early as 5 hr and is maximal about 20 hr after beginning of nonsynchronous cultures. Furthermore, in the presence of Me2SO there is restricted binding of the intercalating dye propidium iodide to chromatin from MELC in G1 phase of the cell cycle, as early as 10 hr of culture. This restricted binding of propidium iodide to chromatin is observed in MELC cultured with other inducing agents, such as butyric acid and dimethyl-acetamide, but is not detected with an Me2SO-resistant cell line cultured with Me2SO.
Assignment of the integration site for simian virus 40 to chromosome 17 in GM54VA, a human cell line transformed by simian virus 40.
Authors: Croce C M
Published: May 2006

GM54VA human cells transformed by simian virus 40 (SV40) were fused with peritoneal macrophages obtained from three different mouse strains. All 27 hybrid clones studied were positive for SV40 tumor antigen in 100% of their cells and contained human chromosome 17. Human chromosome 17 was the only human chromosome present in five of the hybrid clones. Fusion of GM54VA cells and either thymidine kinase (EC 2.7.1.75)-deficient mouse or Chinese hamster fibroblasts resulted in the growth in hypoxanthine-aminopterin-thymidine medium of hybrid clones positive and negative for SV40 tumor antigen. Counterselection of the hybrid clones positive for tumor antigen in medium containing 5-bromodeoxyuridine resulted in the growth of hybrid cells that were negative for tumor antigen. These experiments indicate that negative for tumor antigen. These experiments indicate that SV40 is integrated in only one of the two parental human chromosomes 17. Because the genome of SV40 has been assigned to human chromosome 7 in two other SV40-transformed human cell lines, at least two different integration sites for SV40 would seem to be present in human cells: one located in human chromosome 7 and the other located in human chromosome 17.
Microcell-mediated transfer of murine chromosomes into mouse, Chinese hamster, and human somatic cells.
Authors: Fournier R E , Ruddle F H
Published: May 2006

In this report, we describe the production and characterization of proliferating hybrid cell populations generated by fusion of murine microcells with intact mouse, Chinese hamster, and human recipient cells. The microcell hybrids so produced contained one to five intact murine chromosomes derived from the microcell donor. these transferred chromosomes were maintained as functioning genetic elements in the hybrid cells. Our results firmly establish subnuclear particle-mediated chromosome transfer as a valid somatic cell genetic tool.
Chlorophyll lasers: Stimulated light emission by chlorophylls and Mg-free chlorophyll derivatives
Authors: Hindman J. C. , Kugel R. , Svirmickas A. , Katz J. J.
Published: May 2006

Stimulated emission and lasing have been demonstrated for chlorophyll
a
, chlorophyll
b
, and bacteriochlorophyll
a
as well as for the Mg-free chlorophyll derivatives pheophytin
a
and methyl pheophorbide
a
. Population inversion was obtained by optically pumping with an N
2
laser. For the three chlorophylls, lasing was observed for only the (0,0) vibronic region of the S
1
→ S
0
fluorescence band. In contrast, lasing was observed for both the (0,0) and (0,1) vibronic regions of the S
1
→ S
0
fluorescence band of pheophytin
a
and methyl pheophorbide
a
. Differences between the lasing behavior of the chlorophylls and the Mg-free derivatives probably reflect differences in aggregation behavior. Laser pulses of duration shorter than the fluorescence lifetimes were generated. This result suggests that stimulated emission must be considered in the interpretation of fluorescence lifetime data for
in vitro
and
in vivo
chlorophyll-containing systems.
Picosecond dynamics of iron proteins
Authors: Huppert D. , Straub K. D. , Rentzepis P. M.
Published: May 2006

The excitation of hemoproteins containing either Fe
2+
or Fe
3+
with a picosecond light pulse resulted in the bleaching and recovery of the iron absorbance bands within 6 psec. A new absorbance band also was observed whose formation and decay rate of less than 6 psec suggests that it is probably due to S
1
→S

n

absorbance. The Soret band relaxation time is deduced to be ∼0.5 psec whereas the free base hemoprotein does not show any of the above fast-decay characteristics. Therefore, there is a strong influence of the metal on the energy dissipation process.
On the mechanism of genetic recombination: the maturation of recombination intermediates.
Authors: Potter H , Dressler D
Published: May 2006

DNA molecules of the plasmid ColEl are normally recovered from wild-type cells as a set of monomer- and multimer-size rings. The data of this paper show that the multimer-size species are a product of genetic recombination. Multimer rings do not arise after transfection of purified monomers into bacterial host cells lacking a functional recA recombination system. Analogously, purified dimers, trimers, and tetramers, transfected into recA- cells, can replicate, but are constrained to remain in those conformations. Only upon transfection into rec+ cells can they regenerate the full spectrum of monomer- and multimer-size species. In this paper we trace the flow of genetic information from the monomer to the multimer state and back again under the guidance of the recA recombination system. The formation of multimer-size DNA rings is discussed as a natural consequence of the maturation of a Holliday recombination intermediate formed between two monomer plasmid genomes.