bluuebunny/crossref_metadata_2025 huggingface dataset:
Primary induction of vitellogenin mRNA in the rooster by 17beta-estradiol.
Authors: Burns A T , Deeley R G , Gordon J I , Udell D S , Mullinix K P , Goldberger R F
Published: May 2006

We have studied the kinetics of vitellogenin mRNA accumulation in rooster liver after a primary injection of 17beta-estradiol. The levels of vitellogenin mRNA have been determined both by hybridization of total cellular RNA to vitellogenin cDNA and by translation of vitellogenin mRNA in a wheat germ cell-free system. The results obtained by both methods of analysis are in good agreement and indicate that vitellogenin mRNA is present in the liver of normal roosters at a level of 0-5 molecules per liver cell and increases in amount during the 3 days following injection of estrogen, reaching a level of almost 6000 molecules per cell at the peak of the response. The level of vitellogenin mRNA declined exponentially during the next 14 days with a half-life of 29 hr, reaching a level of less than 10 molecules per cell at 17 days after injection of the hormone. The levels of vitellogenin mRNA after stimulation with estrogen have been correlated with the in vivo rate of synthesis of the vitellogenin polypeptide. The results indicate that the rate of vitellogenin synthesis is closely correlated with the level of vitellogenin mRNA. On the basis of these findings, we conclude that vitellogenin mRNA does not exist in the liver in an untranslated form after withdrawal from estrogen.
Xeroderma pigmentosum neurological abnormalities correlate with colony-forming ability after ultraviolet radiation.
Authors: Andrews A D , Barrett S F , Robbins J H
Published: May 2006

Xeroderma pigmentosum is an autosomal recessive disease in which DNA repair processes are defective. All xeroderma pigmentosum patients develop premature aging of sun-exposed skin, and some develop neurological abnormalities due to premature death of nerve cells. Sensitivity to ultraviolet radiation of 24 xeroderma pigmentosum fibroblast strains was studied in vitro by measuring each strain's ability to divide and form colonies after irradiation. The most sensitive strains were derived from patients who had an early onset of neurological abnormalities; less sensitive strains were from patients with a later onset; and the most resistant strains were from patients without neurological abnormalities. The UV sensitivities of strains from each member of a sibling pair with xeroderma pigmentosum were identical, indicating that UV sensitivity of xeroderma pigmentosum strains is determined by the patient's inherited DNA repair defect. The results suggest that effective DNA repair is required to maintain the functional integrity of the human nervous system by preventing premature death of neurons.
Erythrocytic mechanism of sickle cell resistance to malaria.
Authors: Friedman M J
Published: May 2006

The physiological basis for the resistance to falciparum malaria individuals with sickle cell trait has not been understood. Recent advances in erythrocytic Plasmodium falciparum culture have made possible a direct investigation of the development of the malaria parasite in cells with sickle cell homoglobin. In a high (18%) oxygen atmosphere, there is no apparent sickling of cells, and the growth and multiplication of P. falciparum is identical in normal (AA), hemoglobin S homozygous (SS), and hemoglobin S heterozygous (SA) erythrocytes. Cultures under low (1-5%) oxygen, however, showed clear inhibition of growth. The sickling of SS red cells killed and lysed most or all of the intracellular parasites. Parasites in SA red cells were killed primarily at the large ring stage, probably as a result of a disruption of the parasite metabolism. Incubation in cyanate prior to culture reversed the resistance of SA erythrocytes to plasmodium growth, but had no effect on SS red cell sickling or resistance. Thus, the mechanism of resistance in vivo may be due solely to intraerythrocytic conditions.
Evolutionary adaptation of membranes to temperature.
Authors: Cossins A R , Prosser C L
Published: May 2006

The "fluidity" of brain synaptosomal membrane preparations of arctic and hot-springs fish species, two temperature water fish species acclimated to different seasonal temperatures, and two mammals was estimated using the fluorescence polarization technique. At all measurement temperatures, the fluidity decreased in the order: arctic sculpin, 5 degrees-acclimated goldfish, 25 degrees-acclimated goldfish, desert pupfish, and rat. This correlated with increasing adaptation or body (i.e., cellular) temperatures of 0 degrees, 5 degrees, 25 degrees, 34 degrees, and 37 degrees and suggested a partial compensation of membrane fluidity for environmental temperature that occurs over the evolutionary time period as well as during laboratory (seasonal) acclimation. Evolutionary adaptation of relatively stenothermal species to constant thermal environments resulted in a more complete compensation than laboratory (seasonal) acclimation. Each compensation is accompanied by differences in the saturation of membrane phosphoglycerides. At increased cellular temperatures the proportion of saturated fatty acids increased and the unsaturation index decreased; the correlation between these indices and the measured expression of membrane dynamic structure was highly significant. It is concluded that the homeoviscous compensation of synaptic membrane function is an important component of temperature adaptation.
The law of perceptual stability: Abstract foundations
Authors: Shiman Leon G.
Published: May 2006

Confronted with an object of perception, an individual will spontaneously try to identify unambiguously and consistently all its parts; except in rare instances of “illusory phenomena,” he will immediately succeed. This elementary fact is formalized in a law of visual perception. It is used to define sets of stable states for a sensory mode of a biological system. As characterized, stable states are to perception as quantum states are to atomic structure: they represent natural states of physical systems. They are shown to be observable and to have an exact mathematical representation.

A class of bounded open subsets of a two-dimensional Euclidean space, whose boundaries are piecewise compact analytic arcs, is used to construct a nontrivial mathematical model for stable states. The finitely many components of this mathematical model of a stable state (
image
) are mapped onto an object of perception (
icon
) by perceptual judgments. These judgments, which include the judgment of stability, have an exact interpretation in this model. They unify and make precise such traditional notions of psychology as “
Gestalt
,” “figureground,” and “(visual) boundary.”

Postulates for a general theory of perception are given. They are used to establish a formal relationship between biological and subjective studies of sensory phenomena and so provide a framework in which subjective studies can be used to analyze (their associated) biological processes. In applying these methods to cases, all icons are divided into two classes (the
static
and
dynamic
cases). The static case is treated.
The one-phase Stefan problem and the porous medium diffusion equation: Continuity of the solution in
n
space dimensions
Authors: Caffarelli Luis A. , Friedman Avner
Published: May 2006

The following problems are considered: (
i
) the one-phase Stefan problem, which describes the melting of ice, and (
ii
) the flow of gas in a porous medium. Both problems are considered in the
n
-dimensional space. The main result asserts that the solution [i.e., the temperature in problem (
i
) and the density in problem (
ii
)] is continuous.
Assembly of new nucleosomal histones and new DNA into chromatin.
Authors: Hancock R
Published: May 2006

The assembly of chromatin from newly synthesized nucleosomal histones (labeled with [3H]arginine) and new DNA (density-labeled with [125I]iododeoxyuridine)was studied in growing cultured mouse cells. The nucleosomal histones were specifically examined by dissociating histone H1 and nonhistone proteins from unsheared chromatin either by incubation in 0.6 M NaCl or by digestion with micrococcal nuclease to release nucleosomes. In both cases, the four nucleosomal histones (H2A, H2B, H3, and H4) are essentially the only proteins that remain bound to DNA and that are labeled by [3H]arginine. After formaldehyde fixation, H1-depleted chromatin containing dense DNA can be completely resolved in CsCl buoyant density gradients from that containing unreplicated DNA; separation of nucleosomes is satisfactory although less complete. New DNA and new histones are already assembled into chromatin possessing characteristic nucleosomal structure after 3 min of synthesis (the shortest time studied), as shown by the kinetics of digestion of new DNA by micrococcal nuclease, by the distribution of new DNA and new histones in nucleosomes. However, after 3-30 min of synthesis most new nucleosomal histones are associated with unreplicated DNA rather than with new DNA. It is concluded that new nucleosomes are assembled on DNA at some distance from DNA replication sites, with concomitant migration of preexisting nucleosomes onto new DNA.
Identification of the
N
gene protein of bacteriophage λ
Authors: Shaw Jocelyn E. , Jones Barbara B. , Pearson Mark L.
Published: May 2006

The
N
gene protein, pN, of bacteriophage λ stimulates early gene transcription by allowing mRNA chain elongation to proceed into genes distal to transcription termination sites normally recognized by the
Escherichia coli
transcription termination protein ρ. pN has previously eluded detection on sodium dodecyl sulfate/polyacrylamide gels because of its small size, its instability, and the difficulty of distinguishing pN itself both from host proteins and from other early λ proteins whose synthesis depends on pN action. These problems have now been overcome and we find that the major form of pN present in crude cell extracts of infected cells has an apparent molecular weight of 13,500. λ
bio
256, a deletion-substitution mutant terminating in
N
, codes for a shorter pN of molecular weight 12,500. A nonsense fragment of 10,500 molecular weight coded by λ
N
am7
has also been identified. These conclusions are based on examination of the electrophoretic profiles of the proteins synthesized after infection of UV-irradiated
E. coli
by various λ
N
-
temperature-sensitive, nonsense, and deletion-substitution mutants. It has also been possible to distinguish pN itself from other early λ polypeptides by infecting
ron
-
cells with either λ
N
mar
phage allowing pN synthesis but not pN action or λ
N
am
phage defective in pN synthesis and pN action.

Our results together with previous data are discussed with respect to the possible existence of multiple molecular weight forms of pN and the location of the coding sequences in the
N
gene region.
Genetic recombination and complementation between bacteriophage T7 and cloned fragments of T7 DNA.
Authors: Campbell J L , Richardson C C , Studier F W
Published: May 2006

Frafments of phage T7 DNA have been cloned in Escherichia coli by using the plasmid pMB9. Such cloned fragments are able to recombine with infecting phages, thus providing a means to integrate the physical and genetic maps of T7 DNA. Approximately 65% of the T7 DNA molecule has been found in clones so far, and analysis of these clones has mapped genes 12-17 with an accuracy of about 1% the total length of T7 DNA. At least some cloned segments can supply T7 functions to infecting phages.
Photosynthetic unit size, carotenoids, and chlorophyll—protein composition of
Prochloron
sp., a prokaryotic green alga
Authors: Withers Nancy W. , Alberte Randall S. , Lewin Ralph A. , Thornber J. Philip , Britton George , Goodwin Trevor W.
Published: May 2006

Six samples of the prokaryotic, unicellular algae
Prochloron
sp., which occur in association with didemnid ascidians, were collected from various localities in the tropical Pacific Ocean, and their pigments and chlorophyll-protein complexes were identified and characterized. No phycobilin pigments were detected in any of the species. Chlorophylls
a
and
b
were present in ratios of
a
/
b
= 4.4-6.9. The major carotenoids were β-carotene (70%) and zeaxanthin (20%). Minor carotenoids of one isolate were identified as echinenone, cryptoxanthin, isocryptoxanthin, mutachrome, and trihydroxy-β-carotene; no ε-ring carotenoids were found in any sample. Except for the absence of glycosidic carotenoids, the overall pigment composition is typical of cyanobacteria. A chlorophyll
a
/
b
-protein complex was present in
Prochloron
; it was electrophoretically and spectrally indistinguishable from the light-harvesting chlorophyll
a
/
b
-protein of higher plants and green algae. It accounted for 26% (compared to ∼50% in green plants) of the total chlorophyll; 17% was associated with a P700-chlorophyll
a
-protein. The photosynthetic unit size of 240 ± 10 chlorophylls per P700 in
Prochloron
was about half that of eukaryotic green plants. A model is proposed for the
in vivo
organization of chlorophyll in
Prochloron
.
Mutant strains of clover rhizobium (
Rhizobium trifolii
) that form nodules on soybean (
Glycine max
)
Authors: O'Gara Fergal , Shanmugam K. T.
Published: May 2006

Mutant strains of
Rhizobium trifolii
that induce nitrogenase activity in the free-living state were isolated. These strains, unlike the wild type, nodulated soybean and mungbean plants, producing effective nodules. One of the strains, strain DT72, also nodulated clover but the nodules were ineffective. Strain DT125 consumed hydrogen gas from the gas phase, which can be coupled to nitrogenase activity under appropriate conditions.
Helical
Bacillus subtilis
macrofibers: Morphogenesis of a bacterial multicellular macroorganism
Authors: Mendelson Neil H.
Published: May 2006

Helical bacterial macroorganisms have been produced by the selection of appropriate
Bacillus subtilis
mutants and the establishment of specific growth conditions. Threadlike fibers ranging in length to approximately 1 cm are produced in fluid culture by the parallel association of many division-suppressed filaments in helical arrangement. A more open ball-like structure of complicated woven architecture may also be produced. Macrostructure morphology is regulated by genetic, physiological, and nutritional factors. The pitch angle of surface filaments in helical macrofibers varies as a function of macrofiber diameter, indicating a flexible response of individual cell surfaces to the forces responsible for helical morphology. Three classes of mutants have been obtained that are concerned with helix directionality: (
i
) mutants that form only left-handed helix macrofibers, (
ii
) mutants that form only right-handed helix macrofibers, and (
iii
) conditional mutants able to form either left- or right-handed helix macrofibers depending upon nutritional environment. Aggregate structures containing both left- and right-handed macrofibers have been obtained by coculturing appropriate mutants. In addition to providing information on the organization of the bacterial cell surface, this new system offers unique and unusual opportunities to study cell-cell interactions, primitive morphogenesis, and the properties of a multicellular bacterial form.
Intraventricular administration of nerve growth factor induces ornithine decarboxylase in peripheral tissues of the rat.
Authors: Nagaiah K , Ikeno T , Lakshmanan J , MacDonnell P , Guroff G
Published: May 2006

Intraventricular administration of nerve growth factor causes an increase in the activity of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) in liver, kidney, and adrenal as well as in brain itself. An increase in the concentration of corticosterone in the blood was also observed. Adrenalectomy, hypophysectomy, or pituitary stalk section inhibits the increase of ornithine decarboxylase activity in the peripheral tissues. Ornithine decarboxylase activity in the brain, however, responds to nerve growth factor in these animals. The data indicate that nerve growth factor causes an acitivation of the hypothalamo-hypophyseal endocrine system.
Reconstitution of an Escherichia coli repair endonuclease activity from the separated uvrA+ and uvrB+/uvrC+ gene products.
Authors: Seeberg E
Published: May 2006

An in vitro complementation assay has been used for partial purification of uvrA+, uvrB+, and uvrC+ gene products from Escherichia coli. The uvrB+ and uvrC+ products cochromatograph on DEAE-cellulose and are completely resolved from the uvrA+ product, which has been further purified by phosphocellulose chromatography of the nonadsorbed protein fraction from the DEAE-cellulose. Neither the uvrB+/uvrC+ nor the uvrA+ product shows appreciable endonuclease activity on UV-irradiated DNA when tested separately. However, these factors complement each other to yield and ATP-dependent endonuclease activity specific for UV-irradiated DNA. Gel filtration experiments with the partially purified proteins indicate that the functional uvrA+ gene product has a molecular weight of 100,000. The uvrB+ gene product has an apparent molecular weight of 70,000, but it is presently unclear if this is the size of the uvrB+ product alone or the size of a complex of the uvrB+ and uvrC+ gene products.
Cold pepsin digestion: a novel method to produce the Fv fragment from human immunoglobulin M.
Authors: Lin L C , Putnam F W
Published: May 2006

A strategy for the proteolytic fragmentation of human IgM has been developed. This method is called "cold pepsin digestion" because of its unique feature of achieving restricted peptic cleavages at 4 degrees and pH 4.0. Cold pepsin digestion has been applied successfully to produce an Fv fragment from 14 human IgM proteins. The Fv fragment consists of the heavy chain variable domain (VH) and the light chain variable domain (VL) held together by strong noncovalent interaction. Thus, each Fv fragment contains one intact antigen-binding site and represents the minimal active fragment derivable from an antibody molecule. A series of other structurally and functionally important fragments were also isolated and characterized. Two basic digestion pathways were recognized; these mainly reflect the relative accessibility of five sets of major interdomain cleavage sites.
Molecular field theory of reversible unfolding of biopolymers
Authors: Cerf Roger
Published: May 2006

A simple and general model of reversible conformational changes in biopolymers that lends itself to accounting for cooperativity without resort to a detailed description of the elementary steps is presented. It is suggested that the model permits the description of transitions in specific instances in which long-range effects are present and no simplifying feature allows for a more detailed theory in a straightforward way. The proposed phenomenological approach is based on the concept of molecular field which led to the first theory of ferromagnetism. Equations are given for the temperature dependence of optical properties and of the specific heat, from which the cooperativity parameter introduced by the theory can be obtained when the reaction enthalpy of the elementary step or the number of concerted elements is known. In the limit of a strong molecular field, heterogeneity in composition of a melting sequence does not affect the sharpness of the corresponding transition. Accounting for long-range effects allows for all-or-none transitions that are sharper than those derived from the two-state model.

The feasibility of applying the molecular field concept is illustrated by comparing the results for poly(A)·2 poly(U) triple helices (which exhibit hysteresis) and those for poly(A)·poly(U) double helices (which separate reversibly).

Tertiary structure is considered, among the sources of cooperativity that possibly may be represented in terms of a molecular field. On the basis of recent results for tRNA
1
val
, it is suggested that the proposed approach may be applicable, in particular, to transfer ribonucleic acids.
Determination of molecular motion in membranes using periodic pattern photobleaching.
Authors: Smith B A , McConnell H M
Published: May 2006

The lateral diffusion of a fluorescent phospholipid probe in oriented multibilayers of dimyristoylphosphatidylcholine has been measured by observing the redistribution of fluorescence after photobleaching of the membranes in a periodic pattern of parallel stripes. The diffusion constant D of the fluorescent lipid was found to vary between 1.5 X 10(-11) cm2/sec at 9.6 degrees and 2.0 X 10(-10) at 22.5 degrees in the monoclinic phase. Preliminary studies of dipalmitoylphosphatidylcholine liposomes in the Lbeta' and Pbeta' phases yielded diffusion constants of the order of 10(-11) cm2/sec. These data are relevant to earlier discussions of the rate of complement activation by hapten-sensitized liposomal membranes [Brûlet, P. and McConnell, H. M. (1976) Proc. Natl. Acad. Sci. USA 73,2977--2981; Parce, J. W., Henry, N. and McConnell, H.M. (1978) Proc. Natl. Acad. Sci. USA 75, 1515--1518)]. We have also used this method to study the motion of fluorescent antibodies bound to murine EL-4 tumor cells. Pattern photobleaching techniques have the advantages that cellular or liposomal translation has no major adverse effect on the measurements, that certain nondiffusive motions can be detected and characterized, and that diffusive or other motions can be recorded photographically.
Steroid hormones mediate reversible phenotypic transition between transformed and untransformed states in mouse fibroblasts.
Authors: Armelin M C , Armelin H A
Published: May 2006

Hydrocortisone at physiological concentrations reversibly inhibits DNA synthesis in ST1 cells (a line of mouse fibroblasts possessing 40 chromosomes and derived from Swiss 3T3 cells). This inhibitory activity is a property of glucocorticoids, but the beta-OH of C-11 of glucocorticoids is not essential for the inhibition. The steroid hormone restores to ST1 cells dependency on serum, density, and anchorage for growth. When injected into nude mice, ST1 cells generated malignant invasive fibrosarcoma. Injections of dexamethasone into tumor-bearing animals blocked tumor growth. The steroid hormone seems to induce a reversible transition between a transformed and a "normal" phenotype. ST1 cells treated or untreated with hydrocotisone are not responsive to fibroblast growth factor, epidermal growth factor, or prostaglandin F2alpha whereas they are responsive to a factor that is a contaminant in bovine serum albumin.
Chromosomal locations of mouse immunoglobulin genes.
Authors: Valbuena O , Marcu K B , Croce C M , Huebner K , Weigert M , Perry R P
Published: May 2006

The chromosomal locations of the structural genes coding for the constant portions of mouse heavy (H) and light chain immunoglobulins were studied by molecular hybridization techniques. Complementary DNA probes containing the constant-region sequences of kappa and lambdaI light chain and alpha, gamma2b, and mu heavy chain mRNAs were annealed to a large excess of DNA from a series of eight mouse-human hybrid cell lines that are deficient for various mouse chromosomes. The lines were scored as positive when a high proportion of a probe annealed and negative when an insignificant proportion annealed. Some lines were clearly negative for H and lambda and clearly positive for kappa. Others were positive or intermediate for lambda, positive for kappa and negative for H. Still others, including a line that was selected for the absence of the mouse X chromosome, were positive for all immunoglobulin species. These results demonstrate that the Clambda, Ckappa, and CH genes are located on different autosomes in the mouse. In contrast, the three heavy-chain families exhibited consistently uniform hybridization results, suggesting that the genes for Calpha, Cgamma, and Cmu are located on the same chromosome. A comparison of karyotypic data with hybridization data has limited the possible locations of the Ig genes to only a few chromosomes.
Modulation of γ-aminobutyric acid transport in nerve endings: Role of extracellular γ-aminobutyric acid and of cationic fluxes
Authors: Levi Giulio , Raiteri Maurizio
Published: May 2006

The aim of the present study was to elucidate the possible functional significance of γ-aminobutyric acid (GABA) homoexchange at nerve endings. Using synaptosomes from adult rat cerebrum, we found that a number of conditions altering cationic fluxes produced a concomitant change in the stoichiometry of GABA homoexchange, In fact, exogenous GABA (10 μM), while not causing net release of intrasynaptosomal GABA in standard conditions, triggered a large net GABA release in the presence of veratridine, Na
+
-K
+
-ATPase inhibitors, or the ionophore A23187, superimposed on that due to the various agents tested alone. This extra release was mediated by the membrane carrier, being largely inhibited by the GABA carrier-blocker L-diaminobutyric acid. The altered stoichiometry of GABA homoexchange observed under these conditions (efflux > influx) appeared to be coupled to the influx of Na
+
(or of Ca
2+
), rather than determined by the establishment of a high intrasynaptosomal [Na
+
]. Under conditions of reversed Na
+
flux (Na
+
efflux), the GABA outward/inward flux ratio was also reversed, and the stoichiometry of GABA homoexchange was in favor of net influx. The possible contribution of K
+
to the effects observed is also discussed. It is concluded that the GABA transport system of nerve endings is susceptible to fine modulation by changes in cationic fluxes similar to those occurring
in vivo
during depolarization and repolarization. These fluxes may have a prominent role in determining the direction of net GABA transport in GABA-ergic nerve terminals of the living brain.
Nanosecond relaxation processes of phospholipid bilayers in the transition zone.
Authors: Gamble R C , Schimmel P R
Published: May 2006

Ultrasonic relaxation spectra of dipalmitoyl lecithin vesicles have been recorded as a function of temperature over the frequency range 14-265 MHz. A relaxation process is observed with a time constant of about 10(-8) sec. At the mid-point of the crystalline-liquid crystalline transition (about 41.3 degrees), the relaxation amplitude is maximal. This suggests that the relaxation process is intimately associated with the order-disorder transition. Further support for this conclusion comes from the finding that the volume change of the reaction, as calculated from the relaxation amplitude at the transition midpoint, agrees with that determined independently by equilibrium dilatometry measurements of the deltaV of the transition. The results show that a major step in the transition occurs on a far shorter time scale than previously recognized. Similar fast processes have also been detected in dimyristoyl and distearoyl lecithin vesicles. From a consideration of various lines of evidence, it appears that the relaxation monitors the elementary step associated with the isomerization of lipid chains, such as kink formation through internal bond rotations, as the bilayer transforms between ordered and disordered phases.
Maize plastid gene expressed during photoregulated development
Authors: Bedbrook John R. , Link Gerhard , Coen Donald M. , Bogorad Lawrence
Published: May 2006

RNAs larger than about 6 S prepared from etioplasts of dark-grown maize seedlings, and from plastids at later stages of light-induced development, were labeled
in vitro
and hybridized to separated fragments of maize chloroplast DNA digested with endonucleases. The major nonribosomal RNA present in developing plastids, but virtually undetectable in etioplasts, hybridizes to chloroplast DNA
Bam
fragment 8 and has been mapped on the maize plastid chromosome. Other aliquots of RNA from plastids were translated in a rabbit reticulocyte-derived system. Developing plastids, and mature chloroplasts, but not etioplasts, contain mRNA for an approximately 34,500 dalton polypeptide. The simultaneous appearance, during light-induced maize plastid development, of RNA which hybridizes to
Bam
8 and is translated into a 34,500 dalton protein indicates that photoregulated expression of a single gene is being observed.
Site-specific initiation of a DNA fragment: nucleotide sequence of the bacteriophage G4 negative-strand initiation site.
Authors: Sims J , Dressler D
Published: May 2006

The synthesis of the bacteriophage G4 negative strand is an example of the de novo initiation of a polynucleotide chain. This initiation is performed by the Escherichia coli replication protein dna G which selects a unique site on 5400-base positive-strand template. In this paper we present the nucleotide sequence of the G4 negative-strand initiation site. This is the template element recognized by the dna G priming protein. In conjunction with the sequence of the nascent negative strand, obtained by Bouché, Rowen, and Kornberg [Bouché, J.-P., Rowen, L. & Kornberg, A. (1978) J. Biol. Chem. 253, 765-769], the present data provide a description of a dna G-dependent origin of replication in which one knows the place at which polymerization starts at the nucleotide level.
Nucleotide sequence at the 5′ extremity of turnip yellow mosaic virus genome RNA
Authors: Briand Jean-Paul , Keith Gérard , Guilley Hubert
Published: May 2006

The sequence of the first 110 nucleotides at the 5′ extremity of turnip yellow mosaic virus genome RNA has been determined. The sequence is blocked at its 5′ terminus with the group pppm
7
G and contains two AUG triplets. The determined sequence bears a strong resemblance to the 5′ noncoding region of rabbit β-globin mRNA. Region 95-103 of the sequence can base-pair with part of the 3′ extremity of either the genome RNA or the coat protein mRNA.
Role of nucleotides in tubulin polymerization: effect of guanosine 5'-methylene diphosphonate.
Authors: Sandoval I V , Jameson J L , Niedel J , MacDonald E , Cuatrecasas P
Published: May 2006

Incubation of purified rat brain tubulin with guanosine 5'-methylene diphosphonate [GMP(CH2)P] (1 mM), a GDP analog resistant to hydrolysis, results in the polymerization of 20-30% of the total tubulin present. Analogous incubations with GDP (1 mM) do not result in tubulin polymerization. Polymerization with GMP(CH2)P occurs in the presence of alkaline phosphatase (EC 3.1.3.1) under conditions that completely hydrolyze the likely phosphate donors (GTP, GDP, and GMP) as well as the potential product [GMP(CH2)PP] of the transphosphorylase activity present in purified tubulin preparations. Tubulin polymerization in vitro thus can occur in the absence of gamma-phosphate and phosphate bond hydrolysis at the exchangeable nucleotide-binding site of tubulin. Polymerization of tubulin by GMP(CH2)P is neither prevented nor reversed by concentrations of calcium (2 mM) that prevent microtubule assembly and disrupt already formed microtubules induced by GTP. However, tubulin polymerized with GMP(CH2)P is readily depolymerized by cold (4 degrees, 30 min). The possible involvement of GTP alpha-beta bond hydrolysis must be considered seriously as playing a role in the process of microtubule depolymerization.
Hydrogen peroxide production, chemiluminescence, and the respiratory burst of fertilization: Interrelated events in early sea urchin development
Authors: Foerder Charles A. , Klebanoff Seymour J. , Shapiro Bennett M.
Published: May 2006

After fertilization of the sea urchin,
Strongyl-ocentrotus purpuratus
, a crosslinked fertilization membrane is formed; the crosslinks (dityrosine residues) are synthesized in a reaction catalyzed by an ovoperoxidase that is released from the cortical granules during fertilization. The substrate for ovoperoxidase activity, hydrogen peroxide, is generated by the egg coincident with the “respiratory burst” that follows parthenogenetic activation by the divalent ionophore A23187 or fertilization. This burst of oxygen consumption may be almost quantitatively accounted for by hydrogen peroxide evolution, as measured by the peroxidase-catalyzed quenching of scopoletin fluorescence. Neither the burst of oxygen consumption nor hydrogen peroxide production occurs when the inhibitor of cortical granule discharge, procaine, is present at fertilization.

Fertilization or parthenogenetic activation with A23187 also is associated with a burst of light emission. This chemiluminescence is inhibited
in vivo
by inhibitors of the ovoperoxidase, such as 3-amino-1,2,4-triazole, phenylhydrazine, sulfite, or azide. A crude ovoperoxidase preparation catalyzes hydrogen peroxide-dependent chemiluminescence that is similarly inhibited. Thus, the bursts of oxygen uptake, peroxide production, and chemiluminescence appear to be several manifestations of the peroxidative system released at fertilization. This system may additionally be responsible for spermicidal activity and thus may act as a component of the block to polyspermy.
Messenger RNA for G1 protein of French bean seeds: Cell-free translation and product characterization
Authors: Hall T. C. , Ma Y. , Buchbinder B. U. , Pyne J. W. , Sun S. M. , Bliss F. A.
Published: May 2006

The fraction of poly(A)-containing RNA isolated from ripening bean (
Phaseolus vulgaris
) cotyledons that sedimented at 16 S in linear logarithmic sucrose gradients was at least as active a messenger as viral RNA when added to a cell-free protein-synthesizing system from wheat germ. The major products synthesized
in vitro
were polypeptides of about 47,000 and 43,000 daltons, corresponding to two of the three subunits of G1 protein, the most abundant bean seed storage protein. No trace of the largest (53,000 daltons) subunit was found among the polypeptides synthesized
in vitro
. Proof that the 47,000- and 43,000-dalton polypeptides coded by the 16S RNA were indeed subunits of G1 protein was obtained by immunoprecipitation with monovalent antibody to G1 protein and by electrophoretic mapping of peptides on acrylamide gels after digestion of mixtures of authentic protein and radioactive translation products with protease V8, chymotrypsin, and trypsin. The subunits synthesized
in vitro
were slightly smaller than the native subunits, probably because they lacked the sugar residues present on the holoprotein.
Cole-Moore effect in the frog node.
Authors: Ganot G , Palti Y , Staempfli R
Published: May 2006

Potassium currents were recorded from the voltage-clamped frog node (Rana esculenta) during various test pulses that followed hyperpolarizing prepulses of different amplitudes and durations. Both the delay in potassium current onset and the shape of the current trace as a function of time were found to be a function of prepulse parameters. This finding is different from the current trace superposition described by Cole and Moore for a specific test pulse, sodium equilibrium potential in the squid giant axon. The Cole-Moore effect, which was found here only under a specific set of conditions, thus may be a special case rather than the general property of the membrane. The implication of these findings to the various excitable membrane potassium channel models, which are based on the Cole-Moore effect, is discussed.
Association of Thy-1 differentiation alloantigen with synaptic complexes isolated from mouse brain.
Authors: Acton R T , Addis J , Carl G F , McClain L D , Bridgers W F
Published: May 2006

Conventional fractionation procedures were used in an effort to define the subcellular distribution of the Thy-1 alloantigen in whole mouse brain. After discontinuous sucrose density gradient centrifugation of isotonic postnuclear particulate fractions, the bulk of Thy-1 was recovered in regions of the gradients containing synaptosomes. The synaptosome fraction that banded at 1.2 M sucrose yielded a specific activity for Thy-1 significantly greater than the synaptosomes separating at 1.4 M sucrose. Osmotic lysis of both synaptosome fractions resulted in further enrichment in Thy-1 activity, with no concomitant decrease in yields. The synaptosomal membranes obtained in this way were subsequently treated with Triton X-100 and subjected to further density gradient centrifugation. Although the detergent treatment resulted in some loss of antigenic activity, the gradient fractions that contained Thy-1 also were found by electron microscopy to be richest in synaptic junctional complexes. These findings suggest that Thy-1 is associated with synaptosomes and synaptic junctional complexes and therefore may be involved in the formation and/or maintenance of synaptic connections.
Relationship between somatic mutation and neoplastic transformation
Authors: Barrett J. Carl , Ts'O Paul O. P.
Published: May 2006

Somatic mutation and neoplastic transformation of diploid Syrian hamster embryo cells were examined concomitantly. Mutations induced by benzo[
a
]pyrene and
N
-methyl-
N
′-nitro-
N
-nitrosoguanidine were quantitated at the hypoxanthine phosphoribosyltransferase and Na
+
/K
+
ATPase loci and compared to phenotypic transformations measured by changes in cellular morphology and colony formation in agar. Both cellular transformations had characteristics distinct from the somatic mutations observed at the two loci. Morphological transformation was observed after a time comparable to that of somatic mutation but at a frequency that was 25- to 540-fold higher. Transformants capable of colony formation in agar were detected at a frequency of 10
-5
-10
-6
, but not until 32-75 population doublings after carcinogen treatment. Although this frequency of transformation is comparable to that of somatic mutation, the detection time required is much longer than the optimal expression time of conventionally studied somatic mutations. Neoplastic transformation of hamster embryo cells has been described as a multistep, progressive process. Various phenotypic transformations of cells after carcinogen treatment may represent different stages in this progressive transformation. The results are discussed in this context and the role of mutagenesis in the transition between various stages is considered. Neoplastic transformation may be initiated by a mutational change, but it cannot be described completely by a single gene mutational event involving a dominant, codominant, or X-linked recessive locus. Neoplastic transformation induced by chemical carcinogens is more complex than a single gene mutational process. Thus, this comparative study does not give experimental support to predictions of the carcinogenic potential of chemicals based on a simple extrapolation of the results obtained from conventional somatic mutation assays.
Acetylated histone H4 is preferentially associated with template-active chromatin.
Authors: Davie J R , Candido E P
Published: May 2006

Chromatin from trout testis at an early stage of development was digested with DNase II (deoxyribonucleate 3'-oligonucleotidohydrolase; EC 3.1.4.6), and the solubilized products were fractionated into Mg2+-soluble and -insoluble components. An examination of the histones from these fractions by one- and two-dimensional polyacrylamide gels showed that the highly acetylated species of histone H4 (di-, tri-, and tetra-acetylated) were associated mainly with the Mg2+-soluble material. Digestion of this chromatin fraction with pancreatic ribonuclease converted more than half of it to an insoluble state, and the acetylated H4 remained associated with the precipitated fraction. No changes in the other histones were noted, but two other basic proteins were also found to be associated with the Mg2+-soluble fraction. Since this fraction is enriched in transcribing gene sequences, it is concluded that the histone H4 of active genes is present in a highly acetylated state.
Evidence for the progressive nature of neoplastic transformation in vitro.
Authors: Barrett J C , Ts'o P O
Published: May 2006

The temporal acquisition of in vitro phenotypes associated with neoplasia were examined after exposure of Syrian hamster embryo cells to a chemical carcinogen. Quantitative assays measuring morphological changes, enhanced fibrinolytic activity, and anchorage independent growth were used to detect the development of transformed cells within a population of normal hamster embryo cells. Morphological transformation and enhanced fibrinolytic activity were early changes observed after treatment with benzo[alpha]-pyrene, whereas the ability to grow in semisolid agar was delayed 32-75 population doublings after carcinogen exposure. This delay was not due to selection of a small number of cells that were present early after treatment but at a level below detection, because a large percentage of the cells isolated at early passage (10(3)-fold above the level of detection) developed the potential for anchorage independent growth at later passages. This development of the anchorage independent growth phenotype was induced by the carcinogen treatment, because spontaneous transformation was rare. These observation suggest that multiple cellular changes are required for the acquisition of the capacity for anchorage independent growth and that neoplastic transformation in vitro is a progressive process through qualitatively different stages. Thus, an analogy can be drawn to the progressive nature of in vivo carcinogenesis. These results strongly justify the study of oncogenesis in cell culture as a model for neoplastic transformation in vivo.
Synthesis of globin mRNA in relation to the cell cycle during induced murine erythroleukemia differentiation.
Authors: Gambari R , Terada M , Bank A , Rifkind R A , Marks P A
Published: May 2006

The relationship between the synthesis of globin mRNA and the phase of cell cycle was examined in synchronized murine erythroleukemia cells. Cells were synchronized with respect to the cell division cycle either by culture with 2 mM thymidine or 2 mM thymidine followed by 0.5 mM hydroxyurea, which caused cells to accumulate in late G1 or early S (referred to as G1/S boundary). Cells were induced to erythroid differentiation by culture with 280 mM dimethyl sulfoxide or 4 mM hexamethylene bisacetamide. These inducers do not alter the progression of cells from the G1/S boundary through S, G2, and M, but do cause prolongation of the subsequent G1 phase. Accumulation of newly synthesized globin mRNA is first detected when cells are in this G1 phase.
Human (HLA-A and HLA-B) and murine (H-2K and H-2D) histocompatibility antigens are cell surface receptors for Semliki Forest virus.
Authors: Helenius A , Morein B , Fries E , Simons K , Robinson P , Schirrmacher V , Terhorst C , Strominger J L
Published: May 2006

The proteins coded for by the HLA-A and HLA-B loci in man and the H-2K and H-2D loci in mice were identified as cell surface receptors for Semliki Forest virus. This conclusion is based on the following observations: (i) Water-soluble octamers of viral coat proteins inhibit the complement-dependent cytotoxicity of antibodies directed against H-2K and H-2D antigens in mouse cells. (ii) Isolated detergent-soluble HLA-A and HLA-B antigens reconstituted in lipid vesicles inhibit the binding of viral proteins to human cells (as do the water-soluble antigens to a lesser extent). (iii) Reconstituted HLA-A and HLA-B vesicles interact in solution with Semliki Forest virus (or with vesicles containing viral spike proteins), as demonstrated by coprecipitation with antisera. (iv) Complexes between viral spoke proteins and HLA-A and HLA-B antigens or H-2K and H-2D antigens can be isolated from the cell surface by utilizing affinity chromatography or immunoprecipitation.
Demonstration of specific C5a receptor on intact human polymorphonuclear leukocytes.
Authors: Chenoweth D E , Hugli T E
Published: May 2006

Human C5a, a complement-derived anaphylatoxin, is a potent mediator of human leukocyte chemotaxis. Using a homogeneous preparation of C5a that was 125I-labeled, we have demonstrated the presence of a specific cellular receptor for this glycoprotein on intact human polymorphonuclear leukocytes. Cellular uptake of the radiolabeled ligand occurred rapidly and the rate of dissociation was extremely slow. Cellular binding was saturable with respect to 125I-labeled C5a, and half-saturation occurred at a concentration of 3-7 X 10(-9) M. The number of C5a binding sites per cell was estimated as 1-3 X 10(5). The ligand (C5a) displays specific structural features that are required for binding because analogs of C5a such as C5ades Arg or a yeast carboxypeptidase-digested C5a derivative C5a-(I-69) inhibited the binding but C3a anaphylatoxin, which resembles C5a chemically, did not. Both C5a-mediated leukocyte chemotaxis and C5a-induced lysosomal enzyme release from cytochalasin B-treated cells closely paralleled uptake of the ligand, clearly indicating that it is a receptor-C5a interaction that leads to stimulation of these cellular responses.
Induction of pulmonary indoleamine 2,3-dioxygenase by intraperitoneal injection of bacterial lipopolysaccharide.
Authors: Yoshida R , Hayaishi O
Published: May 2006

Indoleamine 2,3-dioxygenase [indoleamine: oxygen 2,3-oxidoreductase (decyclizing)] activity in the supernatant fraction (30,000 X g, 30 min) of the mice lung homogenate increased approximately 30- to 50-fold after an intraperitoneal administration of bacterial lipopolysaccharide. In all other tissues tested, no significant increase in enzyme activity was observed. The effect appeared to be specific for the lipopolysaccharide fraction because glycogen and zymosan were almost ineffective under the same experimental conditions. In the lung, the enzyme activity increased almost linearly during the first 24 hr after a single injection of the lipopolysaccharide fraction (20 microgram per mouse). The enzyme activity started to decrease after 48 hr and reached a normal value after about 6 days. The increase in enzyme activity was completely abolished by cycloheximide or actinomycin D. Other enzymes in the lung such as beta-glucuronidase, acid phosphatase, and monoamine oxidase did not change significantly with this treatment.
Inversion of a behavioral response in bacterial chemotaxis: Explanation at the molecular level
Authors: Khan Shahid , Macnab Robert M. , DeFranco Anthony L. , Koshland D. E.
Published: May 2006

Certain
cheU
mutants of
Salmonella
show inverted chemotactic behavior, being repelled by attractants and attracted by repellents. Such a dramatic change in behavioral pattern would seem at first glance to require drastic and complex alterations in the sensory processing system. In fact, the behavior can be explained by a simple shift in the level of a response regulator and the subtle effects of this shift on flagellar function. Flagella can exist in either a left-handed or a right-handed structure depending on applied torsion. Wild-type cells swim smoothly by counterclockwise rotation of a left-handed helical bundle and tumble when the motors briefly reverse to clockwise rotation (normal random motility). The
cheU
mutation causes a shift in response regulator level relative to the critical threshold value, resulting in extended clockwise operation so that the flagella are fully converted to the right-handed helical form. These cells therefore swim smoothly by clockwise rotation of a right-handed bundle and tumble when the motor briefly reverses to counterclockwise rotation (inverse random motility). Thus, tumbling is associated with brief reversals and not with a particular sense of rotation. A wild-type cell, with its steady-state response regulator level placing it initially in normal random motility, will swim smoothly on addition of attractant, whereas a
cheU
mutant with inverse random motility will tumble given the same stimulus. The phenomenon illustrates the profound behavioral consequences that can result from a single mutation in a key gene.