bluuebunny/crossref_metadata_2025 huggingface dataset:
Reciprocal stimulation of negatively selected high-responder and low-responder T cells in virus-infected recipients.
Authors: Bennink J R , Doherty P C
Published: May 2006

After depletion of alloreactive potential, immunologically naive T cells from C57BL/6J (Kb-Db) mice (B6) can be induced to respond to vaccinia virus in the context of both H-2Kk and H-2Db when stimulated in B10.A(4R) (Kk-Db) recipients. However, negatively selected B10.A(2R) (Kk-Db) T cells respond to H-2Db-vaccinia virus but not to H-2Kb-vaccinia virus when primed in an irradiated B6 environment. The B6 mouse strain is a high responder to vaccinia virus associated with H-2Db, whereas the B10.A(2R) and B10.A(4R) recombinants are low responders. Responsiveness in the context of H-2Db is thus recognized when the only homology between T cell and recipient is at the H-2D locus and is suppressed when H-2Kk is also present in both situations. The fact that negatively selected H-2Kb-Db T cells can be induced to recognize H-2Kk-vaccinia virus may reflect the existence of an "altered self" complex which is recognized via a single receptor, perhaps drawn from an alloreactive T-cell repertoire. At least in some instances, patterns of T-cell responsiveness are not totally constrained by the spectrum of H-2 antigens encountered in thymus.
Help and suppression by lymphoid cells as a function of cellular concentration.
Authors: Farrant J , Knight S C
Published: May 2006

The phytohemagglutinin-stimulated uptake of [3H]thymidine in mixtures of human lymphocytes from the same source was shown to depend on the cell concentration in vitro as well as on the period of cultivation. "Helper" and "suppressor" effects were obtained by varying the concentration of cells and the periods of cultivation. The possibility that helper and suppressor subpopulations were responsible was avoided by mixing lymphoid cell line cells with others of the same monoclonal origin. Even under these conditions, both the direction and the extent of activity depended on the same two variables. This weakens the case for postulating the existence of distinct subpopulations of lymphocytes with helper or suppressor properties. This case was based on the use of damaging treatments believed to separate cell populations which were then found to differ in their helper and suppressor properties. We propose instead that the effect of such treatments is mediated through changes in the concentrations of interacting cells. Our data make it clear that the function of lymphoid cells ascertained in one set of conditions need not apply within a different cellular environment.
Human glomerular visceral epithelial cells synthesize a basal lamina collagen in vitro.
Authors: Killen P D , Striker G E
Published: May 2006

Isolated human glomeruli were digested with purified bacterial collagenase yielding epithelial cells. These cells grew to saturation density and did not become multi-layered. They were identified as visceral glomerular epithelial cells by their morphologic appearance by phase and electron microscopy and by the presence of surface receptors for C3b. Neither Factor VIII antigen nor Fc receptors were observed. The glomerular epithelial cells synthesized a collagenous protein that was antigenically similar to human glomerular basal lamina. Proteins precipitated from visceral epithelial cell medium with affinity purified antibody against noncollagenous glomerular basal lamina antigens yielded a single collagenase labile protein that by sodium dodecyl sulfate/polyacrylamide gel electrophoresis migrated with an apparent Mr of 168,000 in the presence of reducing agents. Analysis of hydroxyproline isomers yielded a ratio of 3-hydroxyproline to total hydroxyproline of 0.17. Pepsin digestion yielded a disulfide-bonded multimer which, with reduction, migrated with an apparent Mr of 148,000. These data demonstrate that human glomerular visceral epithelial cells can be isolated and propagated in vitro and that they synthesize a collagen similar to that found in vivo.
Role of pain in placebo analgesia.
Authors: Levine J D , Gordon N C , Bornstein J C , Fields H L
Published: May 2006

The hypothesis that perceived pain intensity can influence placebo analgesia was tested. One hundred and seven subjects rated their pain from from 0 to 10 on a visual analog scale after a standard wisdom tooth extraction. The expected course of such postoperative pain in the absence of therapy or placebo is a steady increase; this was confirmed by blind administration of the placebo. When placebos were given intravenously in view of the patients, some (placebo nonresponders) reported that their pain increased, whereas others (placebo responders) reported that their pain either decreased or remained the same over the next 60 min. A placebo response was more likely to occur if the pain rating 5 min prior to placebo administration (initial pain) was greater than 2.6. Furthermore, placebo responders with initial pain above this 2.6 level reported significantly greater mean analgesia than those with lower initial pain. Indeed, responders with initial pain less than 2.6 reported no change in pain during the 60 min after administration of a placebo. When their initial pain level was greater than 2.6, they reported a steady decline in pain over this period. However, above the 2.6 level there was no obvious relationship between the magnitude of the placebo analgesia and the initial pain.
Isolation and culture of motoneurons from embryonic chicken spinal cords.
Authors: Masuko S , Kuromi H , Shimada Y
Published: May 2006

A method is described for isolating cholinergic alpha motoneurons from the spinal cord of chicken embryos at stage 17-18 (Hamburger and Hamilton numbering), at the time when it has been shown that motoneurons withdraw from the mitotic cycle but neurons of other types and glia are still mitotic. Fragments of the ventral half of the spinal cord are incubated for 24 hr in the presence of 10 microM 1-beta-D-arabinofuranosylcytosine in order to eliminate dividing cells and are subsequently dissociated into a suspension of single cells. The following evidence has been obtained and suggests that these cells are neuronal and appear to be alpha motoneurons: (i) they are resistant to the lethal effect of arabinofuranosylcytosine, and thus are postmitotic at stage 17-18; (ii) when grown in vitro, they exhibit morphological characteristics similar to those of ventral spinal neurons, which include the ability to be stained with silver, Nissl, methylene blue vital stain at pH 6.5-7.0, and choline acetyltransferase histochemistry; (iii) they have high choline acetyltransferase activity; (iv) they are capable of forming functional synapses with muscle.
Proton magnetic resonance studies of cholinergic ligand binding to the acetylcholine receptor in its membrane environment.
Authors: Miller J , Witzemann V , Quast U , Raftery M A
Published: May 2006

Proton magnetic resonance has been used to monitor binding of choline, a known partial agonist, to acetylcholine receptor-enriched membrane preparations from Torpedo californica electroplax. The interaction between choline and receptor led to a broadening of the resonance of the choline methyl groups and this effect was reversed by alpha-bungarotoxin, a quasi-irreversible antagonist of the acetylcholine receptor. From the concentration dependence of line broadening the equilibrium dissociation constant for choline was obtained (Kd = 190 +/- 65 microM). The temperature dependence of the parameters observed in the choline titrations gave an enthalpy of binding delta H less than 1.5 kcal/mol and allowed estimates for the dissociation rate constant of the receptor-choline complex (kdiss greater than 1.6 x 10(3) S(1) and the respective activation energy, Ea (Kdiss) approximately 5.5 kcal/mol. The association of other ligands with the membrane-bound receptor could also be studied by observing effects of varying concentrations of such ligands on the choline methyl group linewidth at a constant choline concentration.
Thermolabile protein kinase molecules in a temperature-sensitive murine sarcoma virus pseudotype.
Authors: Sen A , Todaro G J , Blair D G , Robey W G
Published: May 2006

Murine sarcoma virus-associated protein kinases that bind to actin have been purified by affinity chromatography on actin coupled to Sepharose. Heat inactivation studies showed the presence of thermolabile enzyme activity in pseudotypes containing a temperature-sensitivity mutant of murine sarcoma virus (MSV) but not in two independent wild-type MSV pseudotypes. Studies with Sephadex G-75 column fractions showed that a low molecular weight form, approximately 15,000, is the major thermolabile kinase in the temperature-sensitive MSV virions. Antibodies raised against the MSV-coded p60 protein, when added to the in vitro reaction mixtures, showed specific phosphorylation of the IgG heavy chain and a simultaneous reduction in the extent of phosvitin phosphorylation catalyzed by the various MSV pseudotype kinases. Thus a transforming retrovirus-coded enzyme activity that interacts directly with a major cytoskeletal protein and whose activity parallels the transforming ability of a conditional MSV mutant has now been identified.
Interrupting the early region of polyoma virus DNA enhances tumorigenicity.
Authors: Israel M A , Simmons D T , Hourihan S L , Rowe W P , Martin M A
Published: May 2006

The tumorigenicity of DNA from polyoma virus after cleavage with a variety of restriction enzymes was evaluated in suckling hamsters. Cleavage with enzymes that interrupt the region of the genome coding for the large tumor (T) antigen of polyoma virus markedly enhanced the tumorigenicity above that observed with DNA I of the virus. Cell lines established in vitro from tumors induced by polyoma virions, polyoma virus DNA I, or polyoma virus DNA that had been cleaved with restriction endonucleases in the early region all contain the polyoma virus middle and small T antigens but not the large T antigen of polyoma virus is not required for maintenance of the transformed state and probably not for initiation of tumorigenesis by viral DNA.
Nicking-closing enzyme assembles nucleosome-like structures in vitro.
Authors: Germond J E , Rouvière-Yaniv J , Yaniv M , Brutlag D
Published: May 2006

The four core histones (H2A, H2B, H3, and H4) and DNA were assembled into nucleosome-like particles at physiological ionic strengths either by an extract of chromatin rich in nicking-closing activity or by the purified nicking-closing enzyme itself. When histone-DNA complexes were assembled in vitro from relaxed circular DNA, nearly physiological numbers of superhelical turns were induced in the DNA molecule. Electron microscopy of the complexes assembled by the chromatin extract revealed a beaded structure and a reduction of the contour length compared to free DNA. Micrococcal nuclease digestion of the histone-DNA complexes yielded 145-base-pair DNA fragments typical of nucleosome core particles and shorter subnucleosomal DNA fragments of discrete length.
Immunological and chemical identification of a neurophysin-containing protein coded by messenger RNA from bovine hypothalamus
Authors: Giudice Linda C. , Chaiken Irwin M.
Published: May 2006

The biosynthetic origin of the 10,000 molecular weight neurophysins, carriers of the peptide hormones oxytocin and vasopressin, has been studied by cell-free synthesis, Poly(A)-RNA was isolated from bovine hypothalamus and translated in a wheat germ system containing
35
S- or
3
H-labeled amino acids. A number of unique [
35
S]cysteine- but few [
35
S]-methionine-labeled proteins were coded by hypothalamic mRNA. A single, major, isotopically labeled protein (molecular weight 23,000-25,000) was immunoprecipitated from these translation mixtures by addition of purified antibodies against bovine neurophysin II and subsequent addition of Cowan I strain of
Staphylococcus aureus
. Specificity of the immunoprecipitation was demonstrated by competition with unlabeled authentic neurophysins and the absence of competition with structurally unrelated ovalbumin. Furthermore, neither nonimmune serum nor purified antibodies against ribonuclease immunoprecipitated the protein. The [
35
S]cysteine-labeled protein that was specifically immunoprecipitated was oxidized with performic acid and digested with trypsin in the presence of unlabeled, authentic bovine neurophysin II. Peptide mapping revealed that most of the major [
35
S]cysteine-labeled peptides (of the translation product) were identical to major cysteine-containing peptides of authentic neurophysin. The data show that hypothalamic mRNA directs the translation of several unique cysteine-rich proteins in an
in vitro
cell-free system. Furthermore, one of these proteins, which has a higher molecular weight than authentic neurophysin, is recognized by purified antibodies to bovine neurophysin II and has cysteine-containing tryptic peptides in common with those of authentic neurophysin. The data suggest that this protein is the primary translation product, pre-pro-neurophysin.
On the molecular basis for chemomechanical energy transduction in muscle.
Authors: Morales M F , Botts J
Published: May 2006

Herein it is developed that energy transduction in muscle is an activity of myosin S-1 and its ligands, actin (A) and nucleotide (N). S-1 shares with other molecular particles (e.g., hemoglobin) the property that binding events at one of its sites, the N-site, influences binding events at a remote site, the A site (specifically, influences both the actin affinity and actin attachment angle at the A site). However, there is a crucial difference between S-1 and the better-known systems. Because the N site is enzymatic, it has a temporal sequence of occupants; this imposes a temporal sequence of actin attitudes--i.e., a sequence of mechanical events.
Rotational motion and evidence for oligomeric structures of sarcoplasmic reticulum Ca2+-activated ATPase.
Authors: Hoffmann W , Sarzala M G , Chapman D
Published: May 2006

The rotational motion of the sarcoplasmic reticulum Ca2+-activated ATPase (ATP phosphohydrolase, EC 3.6.1.3) has been investigated by measuring the decay of laser flash-induced dichroism with the covalently attached triplet probe eosin isothiocyanate. The Arrhenius plot for rotational mobility indicates two discontinuities at approximately 15 degrees C and approximately 35 degrees C. The experimental data are rationalized in terms of a sudden conformeric change in the ATPase at 15 degrees C and a temperature-dependent equilibrium existing between the conformationally altered ATPase and oligomeric forms of it in the temperature range 15-35 degrees C. The enzymatic activity, as indicated by a discontinuity in the Arrhenius plot for the rate of ATP hydrolysis, appears to be sensitive only to the change at 15 degrees C. There is a strong correlation between the activation energy below 15 degrees C for rotational motion (33.6 +/- 2.2 kcal/mol) and enzymatic activity (34 +/- 4 kcal/mol).
Protein influence on the heme in cytochrome c: evidence from Raman difference spectroscopy.
Authors: Shelnutt J A , Rousseau D L , Dethmers J K , Margoliashi E
Published: May 2006

Raman difference spectra have been obtained for the cytochromes c of a number of species by simultaneous data acquisition from two samples. Frequency differences as small as 0.1 cm-1 can be measured reproducibly by the technique we have developed. In comparisons between cytochromes c isolated from two different species, the frequency differences in the heme vibrational modes range from 0 to 6 cm-1. The vibrational frequencies of the heme are sensitive to the electronic charge density on the porphyrin macrocycle. The frequency differences are interpreted in terms of the influence of the heme-packed aromatic and highly electronegative amino acid side chains on the pi* charge density and distribution on the heme. Such a control of the electronic properties of the heme by the protein may be important for the function of cytochrome c.
Molecular analysis of chromosome-mediated gene transfer.
Authors: Scangos G A , Huttner K M , Silverstein S , Ruddle F H
Published: May 2006

Metaphase chromosomes isolated from a cell line carrying the thymidine kinase (TK) gene of herpes simplex virus type I were used to transform the TK-deficient cell line LMTK- to the TK+ phenotype. Four independent transformants were isolated, all of which expressed virus-specific TK. Each of the four transformant cell lines initially became TK- at a rate of 12% per day. All four transformants possessed multiple copies of the TK gene and in one of the four a rearrangement occurred adjacent to the TK sequences. Stable TK+ derivatives of each line, isolated after prolonged cultivation, retained fewer copies of the TK gene than did their unstable parents. The transferred chromosomal fragment was larger than 17 kilobases in each line.
Interfacial free energy and the hydrophobic effect
Authors: Tanford Charles
Published: May 2006

Interfacial free energies demonstrate clearly that the antipathy between hydrocarbon and water rests on the strong attraction of water for itself. However, the unfavorable free energy associated with this antipathy, per unit area of contact between bulk hydrocarbon and water, is about 3-fold larger than a similar figure derived from solubility data per unit area of contact between a single dissolved hydrocarbon molecule and water. The discrepancy illustrates the difficulty in applying macroscopic concepts such as “interfacial surface” at the molecular level and can be formally resolved, at least qualitatively, by the predicted effect of surface curvature on surface tension.
Photoelectric properties and detection of the aromatic carcinogens benza[a]pyrene and dimethylbenzanthracene.
Authors: Houle W A , Brown H M , Griffith O H
Published: May 2006

The absolute photoelectron quantum yield spectra for benzo[a]pyrene and dimethylbenzanthracene are presented in the wavelength range 180--230 nm. These polycyclic aromatic carcinogens have photoelectron quantum yields of approximately 2 x 10(-3) electrons per incident photon at 180 nm. The quantum yields fall off quickly and monotonically at wavelengths longer than 210 nm (5.9 eV). Threshold values for benzo[a]pyrene and dimethylbenzanthracene are 5.25 +/- 0.06 cV and 5.27 +/- 0.04 eV, respectively. The photoelectron quantum yields of benzo[a]pyrene and dimethylbenzanthracene are several orders of magnitude greater than typical components of biological membranes (amino acids, phospholipids, and polysaccharides). Preliminary micrographs of benzo[a]pyrene and dimethylbenzanthracene sublimed onto poly(L-lysine) and onto dimyristoyl phosphatidylcholine demonstrate the high contrast of small crystallites of carcinogens against a background of membrane components. These results and calculations involving relative contrast factors suggest that the distribution of these carcinogens in biological membranes can be determined by using photoelectron microscopy.
Structure of genes for human growth hormone and chorionic somatomammotropin.
Authors: Fiddes J C , Seeburg P H , DeNoto F M , Hallewell R A , Baxter J D , Goodman H M
Published: May 2006

A 2.6-kilobase (kb) EcoRI restriction endonuclease fragment containing human growth hormone (hGH; somatotropin) gene sequences and a 2.8-kb EcoRI fragment containing human chorionic somatomammotropin (hCS; choriomammotropin) gene sequences have been identified by hybridization to cloned cDNA. Human DNA was cleaved with EcoRI and fractionated by preparative agarose gel electrophoresis; DNA in the size range 2--3 kb was ligated to lambda gt WES.lambda B DNA and viable recombinant bacteriophage were recovered by in vitro packaging. After infection of Escherichia coli and screening of phage plaques, single isolates of hGH and hCS gene sequences were obtained. Restriction endonuclease mapping showed that the hGH gene contains three intervening sequences interrupting the coding sequence. Partial DNA sequence analysis of the hGH gene, obtained by the chain termination method, confirmed the location of the intervening sequences and the identity of the fragment.
Characterization and regulation of reductase kinase, a protein kinase that modulates the enzymic activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase
Authors: Beg Zafarul H. , Stonik John A. , Brewer H. Bryan
Published: May 2006

The activity of rat liver 3-hydroxy-3-methylglutaryl-coenzyme A reductase [HMG-CoA reductase; mevalonate:NADP
+
oxidoreductase (CoA-acylating), EC 1.1.1.34] can be modulated
in vitro
by a phosphorylation-dephosphorylation reaction sequence. A microsomal reductase kinase catalyzes the phosphorylation of HMG-CoA reductase and histones. Histone phosphorylation was enhanced 2- to 3-fold by cyclic AMP. Reductase kinase exists in interconvertible active and inactive forms. Incubation of reductase kinase with phosphoprotein phosphatase resulted in a time-dependent decrease in the ability of reductase kinase to catalyze the phosphorylation of histones and to inactivate HMG-CoA reductase. Incubation of phosphoprotein phosphatase-inactivated reductase kinase with [γ-
32
P]ATP plus Mg
2+
and a partially purified protein kinase designated reductase kinase kinase resulted in parallel increases in protein-bound
32
P radioactivity and ability to inactivate HMG-CoA reductase. Incubation of
32
P-labeled reductase kinase with phosphoprotein phosphatase resulted in a time-dependent loss of protein-bound
32
P radioactivity and a decrease in the ability to inactivate HMG-CoA reductase. Polyacrylamide gel electrophoresis of purified reductase kinase incubated with reductase kinase kinase and [γ-
32
P]ATP plus Mg
2+
revealed that the
32
P radioactivity and reductase kinase enzymic activity were located in a single electrophoretic position. Dephosphorylation of
32
P-labeled purified reductase kinase with phosphoprotein phosphatase was associated with significant loss of radioactivity and enzymic activity in the protein band ascribed to reductase kinase. These results provide evidence that the activity of reductase kinase, like HMG-CoA reductase, is modulated by a reversible phosphorylation-dephosphorylation reaction sequence.
Accessibility of guanine at position 44 in the invariant sequence 5'CCG44AAC3' of Escherichia coli 5S RNA to reaction with kethoxal.
Authors: Larrinua I , Delihas N
Published: May 2006

The reaction of Escherichia coli ribosomes with beta-ethoxy-alpha-ketobutyraldehyde (kethoxal) in a buffer containing 50--100 mM Tris.HCl at pH 7.4, 50 mM NH4Cl, and 5 mM Mg(OAc)2 readily released the 5S RNA from the ribosomes. When liberated, the 5S RNA is in a conformation such that position 44 is selectively reactive, in addition to the normally reactive quanines at positions 41 and 13. Positions 41 and 13 have been previously shown to react in the 5S RNA in situ. The resulting new RNase T1 resistant oligonucleotides 5'CCG 44K AAUCAG51(3') and 5'ACCCCAUG 41KCCG 44KAACUCAG51(3') have been isolated and identified. These oligonucleotides have not been found in RNase T1 digests of 5S RNA that is not released from the ribosome. The guanine at position 44 is part of the invariant sequence 5'CCG44AAC3' which includes that portion of the molecule thought to interact with the invariant 5'GT psi C3' of tRNAs in the ribosomal A site. This invariant sequence of the 5S RNA may also form part of the binding site for protein L5.
Protein-heme interaction in hemoglobin: evidence from Raman difference spectroscopy.
Authors: Shelnutt J A , Rousseau D L , Friedman J M , Simon S R
Published: May 2006

Raman difference spectroscopy measurements on native and chemically modified human deoxyhemoglobins stabilized in either the R or the T quaternary structure revealed frequency differences in the oxidation state marker lines. The differences indicate that the R structure has an effective increase in the electron density of the antibonding pi* orbitals of the porphyrin rings. This increase is explained by a charge transfer interaction between donor orbitals and the pi* orbitals of the porphyrins. The relative amount of charge transferred, which is inferred from the Raman difference measurements, correlates with some but not all factors that influence the energetics of the quaternary structure equilibrium. In addition, the free energy of cooperativity for a variety of ligated proteins follows the same order as that of the degree of charge depletion of the pi* orbitals upon ligation as determined from the frequency of a Raman mode. The proposed electronic interaction between the protein and heme could result in energies large enough to provide a significant contribution to the energetics of hemoglobin cooperativity.
Experimental hybridization of
Coelomomyces dodgei
and
Coelomomyces punctatus
Authors: Federici Brian A.
Published: May 2006

Two closely related fungi,
Coelomomyces dodgei
and
C. punctatus
(Chytridiomycetes; Blastocladiales), showing considerable potential for mosquito control, have been hybridized. Both species have life cycles involving an obligate alteration of sexual and asexual generations between an intermediate copepod host and a definitive mosquito host, respectively. Hybridization was accomplished by making reciprocal crosses of gametes derived from infected copepods. In both cases,
C. dodgei
[unk] ×
C. punctatus
[unk]
and C. punctatus
[unk] ×
C. dodgei
[unk], zygotes infective for mosquito larvae were formed. Most sporangia produced by the hybrids in infected larvae were not typical of either parental species but resembled
C. dodgei
more than
C. punctatus
. Additionally, the majority of the sporangia formed in several larvae exhibited surface structures similar to
C. lativittatus
, indicating this species may be a naturally occurring hybrid of
C. dodgei
and
C. punctatus
. The experimental methods described provide a system to aid in the study of taxonomic relationships among closely related species of
Coelomomyces
, and furthermore they may contribute to the development of strains efficacious for mosquito control.
Passive modulation of blood-group antigens.
Authors: Shinitzky M , Souroujon M
Published: May 2006

Rh-positive erythrocytes were enriched and depleted of membrane cholesterol, and the mediated change in the degree of exposure of the D antigens was determined by fluorescence-activated cell sorting, using indirect fluorescent antibody labeling. The results are compatible with a model in which the expression of the D antigens can be modulated significantly by the lipid microviscosity (eta). At a high cholesterol-to-phospholipid ratio (C/PL) of 1.55, which corresponds to eta (25 degrees C) = 7.5 poise (1 poise = 0.1 Pa.sec), the relative detectable number of D antigens was about double than that at C/PL = 0.65, eta (25 degrees C) = 4.1 poise. In analogous experiments similar fluidity changes resulted in only about 20% modulation of expression of the A1 antigen, suggesting that in the native state this antigen is already well exposed on the erythrocyte surface. This type of antigenic modulation may also operate in vivo, and may thus bear some fundamental implications on tumor immunology and autoimmune diseases.
DNA synthesis in temperature-sensitive mutants of the cell cycle infected by polyoma virus and adenovirus.
Authors: Rossini M , Weinmann R , Baserga R
Published: May 2006

tsAF8 cells are a temperature-sensitive (ts) mutant of BHK cells that are arrested in G1 at the nonpermissive temperature. When made quiescent by serum restriction, they can be stimulated to enter S phase by 10% serum at 34 degrees C but not at 40.6 degrees C. The same results can be obtained if quiescent cells are infected with polyoma virus or adenovirus 12 instead of serum. However, adenovirus 2 infection stimulates DNA synthesis in tsAF8 cells at both 34 degrees C and 40.6 degrees C. The DNA synthesized after adenovirus 2 infection has been shown to be cellular DNA by CsCl density centrifugation. By density labeling it can be shown that adenovirus 2-induced DNA synthesis is due to semiconservative replication. The difference between adenovirus 2 and polyoma (or serum) is also evident with another ts mutant of BHK cells, ts13 cells. These results open the possibility of identifying the viral or cellular mechanism at the basis of this difference in the induction of host DNA synthesis between adenovirus 2 and polyoma or serum.
Characterization of a protein correlated with the production of knob-like protrusions on membranes of erythrocytes infected with
Plasmodium falciparum
Authors: Kilejian Araxie
Published: May 2006

Membranes of erythrocytes infected with
Plasmodium falciparum
develop protrusions called “knobs.” These protrusions are not apparent on erythrocytes infected with young parasites (rings) but develop with the growth of parasites to the trophozoite and schizont stages. The nature and origin of knobs were characterized by comparing the stage-specific proteins of two culture lines of
P. falciparum
, K+ and K-. K+ parasites produce knobs; K- parasites do not. Erythrocytes infected with both types of parasites were labeled metabolically and samples were analyzed by electrophoresis in sodium dodecyl sulfate/polyacrylamide gels. There were no apparent differences in Coomassie blue-stained or radioactive components of rings of K+ and K- parasites. However, erythrocytes infected with K+ trophozoites or schizonts showed a major labeled protein, with an apparent molecular weight of ≈80,000, that was not present in any developmental stage of K- parasites or in K+ rings. A fraction enriched in membranes from erythrocytes infected with K+ trophozoites showed enrichment of this protein. The results indicate that this protein, synthesized by the parasites, is correlated with the formation of knobs on the host cell membrane. Two additional labeled components were identified. These appeared with the development of schizonts in both K+ and K- parasites and are therefore stage-dependent and not correlated with knobs.
Regulation of the state of phosphorylation of specific neuronal proteins in mouse brain by in vivo administration of anesthetic and convulsant agents.
Authors: Strömbom U , Forn J , Dolphin A C , Greengard P
Published: May 2006

The effect of drug treatment in vivo on the state of phosphorylation of two specific neuronal proteins, proteins Ia and Ib, has been studied in mouse brain. For this purpose, animals were killed by immersion into liquid nitrogen, and proteins Ia and Ib were extracted by a procedure designed to prevent alterations in their state of phosphorylation. Several anesthetic agents (pentobarbital, chloral hydrate, and urethane) each caused a decrease in the state of phosphorylation of these proteins. Conversely, the convulsant agents pentylenetetrazol and picrotoxin each caused an increase in the state of phosphorylation of these proteins. Neither the anesthetic nor the convulsant agents affected the total amount of these proteins. The results are compatible with a role for proteins Ia and Ib in neuronal function.
Role of environmental variability in the evolution of life history strategies
Authors: Hastings Alan , Caswell Hal
Published: May 2006

We reexamine the role of environmental variability in the evolution of life history strategies. We show that normally distributed deviations in the quality of the environment should lead to normally distributed deviations in the logarithm of year-to-year survival probabilities, which leads to interesting consequences for the evolution of annual and perennial strategies and reproductive effort. We also examine the effects of using differing criteria to determine the outcome of selection. Some predictions of previous theory are reversed, allowing distinctions between
r
and
K
theory and a theory based on variability. However, these distinctions require information about both the environment and the selection process not required by current theory.
Contacts between Escherichia coli RNA polymerase and an early promoter of phage T7.
Authors: Siebenlist U , Gilbert W
Published: May 2006

Specific contacts between the Escherichia coli RNA polymerase (nucleosidetriphosphate:RNA nucleotidyl-transferase, EC2.7.7.6) and the phosphates and purine bases of the A3 promoter of phage T7 cluster into three regions located approximately 10, 16, and 35 base pairs before RNA initiation site. Two of these contain nucleotide sequences that are fairly conserved among many promoters, known as the "Pribnow box" and "-35 region" homologies; the third, just upstream from the Pribnow box, is not conserved. The polymerase binds preferentially to the coding strand and for the most part touches only one face of the DNA helix.
Monoclonal antibodies to estrophilin: probes for the study of estrogen receptors.
Authors: Greene G L , Fitch F W , Jensen E V
Published: May 2006

Splenic lymphocytes from a Lewis rat, immunized with purified estradiol-receptor complex of calf uterine nuclei, were fused with cells of three different mouse myeloma lines (P3-X63-Ag8, P3-NSI/I-Ag4-1, and Sp2/0-Ag14) to yield hybridoma cultures, 9% of which produced antibodies to the receptor protein (estrophilin). When cloned by limiting dilution, approximately 70% of the viable cultures secreted antiestrophilin antibody. When expanded in suspension culture, three clones derived from Sp2/0-Ag14 were found to secrete rat IgG (gamma 2a class), whereas seven other clones (from all three myeloma lines) secreted IgM. Monoclonal IgG shows comparable affinity for nuclear and extranuclear receptors, whereas IgM reacts preferentially with the nuclear form. Both classes of antibody react with unoccupied as well as with occupied receptor and do not interfere with its ability to bind to estradiol. By growing IgG-secreting clones in the presence of [35S]methionine, radiolabeled monoclonal antiestrophilin has been prepared. Unlike antiestrophilin antibody previously generated in the rabbit or the goat, which crossreacts with estrogen receptors from every animal species tested, antibodies produced by the Lewis rat and by hybridomas derived from its spleen cells react specifically with estrophilin from calf tissues. These monoclonal antibodies provide reagents for the application of immunochemical techniques to study estrogen receptors in calf target tissues.
Origin of replication of the DNA of a herpesvirus (pseudorabies).
Authors: Ben-Porat T , Veach R A
Published: May 2006

During the first round of the replication of pseudorabies virus DNA, replicating DNA is mainly in the form of circles. The main origin of replication is located inthe region of the molecule bearing the inverted repeat. Replication proceeds unidirectionally from the origin.
Unusual features in the nucleotide sequence of a cDNA clone derived from the common region of avian sarcoma virus messenger RNA.
Authors: Yamamoto T , Jay G , Pastan I
Published: May 2006

We have constructed a recombinant plasmid containing a 700-base pair (bp) cDNA copy of the common region present at the 3' end of Schmidt-Ruppin avian sarcoma virus (ASV) 21S mRNA. The cDNA was inserted into plasmid pBR322 at the Pst I site by the G-C tailing method. A restriction map of the cloned insert from a recombinant plasmid pSRI indicates that it corresponds to the 3' end of the ASV genome. R-loop analysis with ASV genomic RNA indicates that the insert is colinear with the ASV genome over most of its length. The sequence of 331 bp at the 3' end of the DNA insert was determined and shows that the insert contains extra sequences not found at the 3' end of ASV genomic RNA. Following the terminally redundant sequence of 20 bp that has been found at the extreme 3' end of genomic RNA is a sequence of 79 bp that is almost identical to that located immediately next to the 20-bp repeat at the 5' end of ASV genomic RNA. This is followed by 18 bp of unique sequence, possibly of host origin. The structure of the clone suggests that ASV mRNA may differ from genomic RNA at its 3' end and that 21S mRNA is transcribed from integrated ASV DNA and contains at its 3' end sequences derived both from the 5' end of the ASV genome and from host DNA adjacent to the site of integration. The presence of termination codons in all three reading frames suggests that the common region probably does not contain coding sequences. However, the presence of sequences that resemble probable promoter sites supports the possibility that this region may be involved in the regulation of transcription.
A two-subunit cytochrome c oxidase (cytochrome aa3) from Paracoccus dentrificans.
Authors: Ludwig B , Schatz G
Published: May 2006

Cytochrome c oxidase (ferrocytochrome c: oxygen oxidoreductase, EC 1.9.3.1) was purified from the cytoplasmic membrane of the bacterium Paracoccus denitrificans. The enzyme contains two heme groups (a and a3) and two copper atoms per minimal unit, oxidizes mammalian cytochrome c at a high rate, and, when incorporated into liposomes, generates an electrochemical proton gradient during cytochrome c oxidation. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis reveals only two subunits of apparent molecular weights 45,000 and 28,000; they appear to correspond to the two largest mitochondrially made subunits of the seven-subunit cytochrome c oxidase isolated from yeast mitochondria. Because of its structural simplicity. Paracoccus cytochrome c oxidase offers new possibilities for exploring the mechanism of cytochrome c oxidase function.
Insulin receptor synthesis and turnover in differentiating 3T3-L1 preadipocytes.
Authors: Reed B C , Lane M D
Published: May 2006

A density-shift method is described for analyzing insulin receptor synthesis and turnover in cultured cells labeled with "heavy" amino acids (2H, 13C, and 15N). Solubilized newly synthesized heavy and old "light" receptors are separated by isopycnic banding on CsCl gradients and then quantitated. Insulin receptor synthesis and turnover were studied by this technique in 3T3-L1 preadipocytes which undergo an increase in insulin binding capacity during differentiation. The results indicate that the increase in insulin binding capacity is a consequence of new receptor synthesis, that the insulin receptor has a relatively short half-life (6.7 hr), and that an increased rate of receptor synthesis contributes to the increase of insulin receptor level during differentiation.
Organization of the recA gene of Escherichia coli.
Authors: Horii T , Ogawa T , Ogawa H
Published: May 2006

The restriction map of a BamHI DNA fragment that contains the recA gene of Escherichia coli has been established and a large portion of the fragment's nucleotide sequence has been determined. The coding region of the recA gene contains 1059 nucleotide residues and encodes a single protein of 353 amino acid residues. The amino acid sequence of the first five residues of the NH2 terminus of the recA protein agrees with the sequence predicted from the DNA sequence except for the absence of formylmethionine in the purified protein. Immediately after the coding sequence, there is a G+C-rich sequence with dyad symmetry followed by an A+T-rich sequence. These could signal termination of transcription. The site of initiation for synthesis in vitro of the recA messenger RNA has been determined by analysis of the 5' nucleotide sequence of [gamma-32P]ATP-labeled transcripts. The promoter region shos a high degree of symmetry and contains sequences commonly found in recognition and binding sites for RNA polymerase.
Orthorhombic two-dimensional crystal form of purple membrane.
Authors: Michel H , Oesterhelt D , Henderson R
Published: May 2006

A new two-dimensional crystal form of purple membrane has been obtained in vitro. It is produced by the joint use of a cationic detergent, dodecyltrimethylammonium chloride, and the nonionic detergent, Triton X-100. It primarily forms large, rolled-up sheets that look like needles in the light microscope. Liposomes and tubes are also observed. The absorption maximum of the new form of purple membrane is blue-shifted by 6 nm and its density is slightly lower than the natural form of purple membrane. The new form of purple membrane is orthorhombic with space group p22121 and cell dimensions 57.6 x 73.5 A. Four molecules of bacteriorhodopsin occupy the unit cell with an area per molecule close to that found in the native p3 structure. The projected structure to 6.5-A resolution was determined by electron microscopy and diffraction. It shows an identical molecular structure to that of the p3 form and determines the position of the polypeptide boundary.
Chromosomal mutations of Escherichia coli that alter expression of conjugative plasmid functions.
Authors: McEwen J , Silverman P
Published: May 2006

We have identified two chromosomal genes of Escherichia coli K12 that are required for the expression of conjugative plasmid functions in the presence of normal plasmid DNA. Hfr cells with mutations in both of these genes are resistant to donor-specific bacteriophage and defective as conjugal donors. These characteristics can be attributed to the inability of mutant Hfr cells to elaborate F-pili, surface organelles required both for conjugal donor ability and for sensitivity to donor-specific bacteriophages. Mutant cells are also defective in surface exclusion, the property of donor cells to act as poor conjugal recipients. This defect can be attributed in part to a reduction in the amount of the F-plasmid traT gene product in the outer membrane of mutant cells; this protein is one of two plasmid gene products required for the full expression of surface exclusion. We have designated the chromosomal genes identified by these mutations as cpxA and cpxB; the mnemonic cpx signifying conjugative plasmid expression.
Average time until fixation of a mutant allele in a finite population under continued mutation pressure: Studies by analytical, numerical, and pseudo-sampling methods
Authors: Kimura Motoo
Published: May 2006

We consider a single locus, and denote by
A
the wild-type allele and by
A′
the mutant allele that is produced irreversibly in each generation from
A
at the rate
v
. Let 1 +
s
, 1 +
h
, and 1 be, respectively, the relative fitnesses of mutant homozygote
A′A′
, mutant heterozygote
A′A
, and wild-type homozygote
AA
. Then, it is shown, on the basis of the diffusion equation method, that the average time until fixation of the mutant allele (
A′
) in a randomly mating population of effective size

N
e

, given that the initial frequency is
p
, is [Formula: see text] in which
B
(
x
) = (
S
/2)
x
2
+
Hx
(1 -
x
),
S
= 4

N
e
s, H

= 4

N
e
h

, and
V
= 4

N
e
v.

Of particular interest are the cases in which the mutant allele is deleterious (
s
= -
s′, s′
> 0). Three cases are considered; the mutant is: (
i
) completely dominant
s
=
h
= -
s′
, (
ii
) completely recessive
s
= -
s′, h
= 0, and (
iii
) semidominant
s
= -
s′, h
= -
s′
/2, in which
s′
is the selection coefficient against the mutant homozygote. It is shown that the average time until fixation is shorter when the deleterious mutant allele is dominant than when it is recessive if 4

N
e
v

is larger than 1. On the other hand, the situation is reversed if 4

N
e
v

is smaller than 1. It is also shown that for a mutant allele for which

N
e
s′

> 10, it takes such a long time until fixation that we can practically ignore the occurrence of random fixation of a deleterious allele under continued mutation pressure. To supplement the analytical treatment, extensive simulation experiments were performed by using a device called the pseudo-sampling variable, which can enormously accelerate the process of simulation by a computer. This method simulates the diffusion process itself rather than the binominal sampling process (in population genetics the diffusion model is usually regarded as an approximation of the discrete binomial sampling process).
Selection limits and strategies
Authors: Cockerham C. Clark , Burrows Peter M.
Published: May 2006

Strategies are analyzed for maximizing the ultimate limit to truncation selection for a quantitative trait in finite populations. By using a formulation of Kimura and Crow [Kimura, M. & Crow, J. F. (1978)
Proc. Natl. Acad. Sci. USA
75, 6168-6171], it is shown that the limit is maximized by truncating at the mode with the highest ordinate of the phenotypic distribution. This implies 50% selection for the normal or any unimodal symmetric distribution and, for skewed distributions, selection of more than one-half if desired phenotypes are in the long tail of the distribution, less than one-half if in the short tail. For dioecious populations, the optimal procedure requires, in addition, equal numbers recorded and selected of each sex. For monoecious populations the limit can be improved by using the best individuals mated to the next-best individuals. Limitations of the results are discussed.
Linkage analyses of murine immunoglobulin heavy chain and serum prealbumin genes establish their location on chromosome 12 proximal to the T (5;12) 31H breakpoint in band 12F1.
Authors: Meo T , Johnson J , Beechey C V , Andrews S J , Peters J , Searle A G
Published: May 2006

Analysis of backcross mice carrying the Harwell translocation T(5;12)31H has led to the definitive localization of the immunoglobulin heavy chain gene cluster. Both Igh-1 and Pre-1 loci were found to segregate in tight linkage with the chromosomal markers 5(12) and 12(5), which define the balanced translocation T(5;12)31H. Additional data establish the location of these genes at the telomeric end of chromosome 12. That both loci are proximal to the chromosomal breakpoint in band 12F1 is shown by the phenotypes of segregants aneuploid for the presence or absence of the small marker 5(12). The order of loci inferred from a single recovered recombinant is: centromere-Igh-1-Pre-1-T(5;12)31H.
Spatial frequency specific interaction of dot patterns and gratings.
Authors: De Valois K K , Switkes E
Published: May 2006

Adaptation to patterns of paired random dots produces loss of contrast sensitivity to sinusoidal luminance gratings oriented perpendicularly to the dot-pair direction. This adaptation loss is spatial frequency- and orientation-specific and varies with dot-pair separation in a manner predictable from the Fourier spectra of the stimuli and observed characteristics of the visual system. These results support the idea that the visual system acts as a periodicity analyzer with known restrictions and cannot be accounted for by a feature-detector model. When the bars of the test gratings are aligned in the dot-pair direction, there is no adaptational loss at any frequency despite the fact that the adaptation pattern contains significant spectral power at all frequencies in this orientation. This lack of adaptation may be due to inhibitory interactions among channels or to nonlinear effects within local receptive fields.
Correlation between relaxation and automaticity in embryonic heart cell aggregates
Authors: Clusin William T.
Published: May 2006

Diastolic depolarization in cardiac muscle is due to a decline in potassium permeability that has been ascribed to removal of intracellular free calcium. A continued decline in tension during the pacemaker potential might therefore occur. In this study, contractile responses of chicken embryonic heart cell aggregates are recorded with a photodiode. Photodiode output is well correlated with the position of the aggregate's edge. Movements of different edges are synchronous, and their amplitude and duration vary appropriately during experimental maneuvers that alter the magnitude and duration of contractile force. Edge movement during relaxation has two phases, a rapid phase lasting about 100 msec and a slow phase that may last over 10 sec. The slow phase is not due to viscoelasticity because its time course does not depend on the magnitude or duration of the initial deformation. The rate of relaxation is correlated with the rate of depolarization during the pacemaker potential. Reduction in automaticity during cooling, spontaneous variation, and overdrive pacing are associated with impairment of the slow component of relaxation. Electrophysiological evidence suggests that the diastolic potassium permeability of the aggregates is controlled by intracellular calcium. A possible explanation for the correlation between the slope of the pacemaker potential and the slow component of relaxation is that both phenomena reflect a common physiological process—i.e., the removal of free calcium from the cytoplasm.