bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoperiodic regulation of the hamster testis: dependence on circadian rhythms.
Authors: Eskes G A , Zucker I
Published: May 2006

The testes of hamsters exposed to short days (10 hr of light per day) regress within 13 weeks. Administration of 7.5% deuterium oxide to hamsters lengthens the period of free running circadian activity rhythms by 2.2% and prevents testicular regression during short-day exposure. This consistent with predictions derived from an external coincidence model for photoperiodic time measurement: Deuterium oxide changes phase relationships between the light-dark cycle and the circadian system, the hamster's daily photosensitive phase is stimulated with light during short days, and the testes remain large. Conservation of the period of circadian rhythms within narrow limits has adaptive significance for hamster photoperiodism and for the occurrence and phasing of the annual reproductive cycle.
Structure of a poly (adenosine diphosphoribose) monomer: 2'-(5"-hosphoribosyl)-5'-adenosine monophosphate.
Authors: Ferro A M , Oppenheimer N J
Published: May 2006

A preparation of poly(adenosine diphosphoribose) synthase obtained from pigeon liver nuclei has been used to make poly(adenosine diphosphoribose) with an average chain length of 20. Digestion of the purified poly(adenosine diphosphoribose) with snake venom phosphodiesterase (oligonucleate 5'-nucleotidohydrolase; EC 3.1.4.1) gave the monomer, 2'-(5"-phosphoribosyl)-5-AMP. After purification of the monomer on a Dowex-1 column, further digestion with alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum); EC 3.1.3.1] yielded the dephosphorylated product, 2'-ribosyl adenosine. Nuclear magnetic resonance spectra at 360 MHz of the 2'-ribosyl adenosine were obtained in [2H6]dimethylsulfoxide, which allows direct observation of the hydroxyl protons. These spectra show the absence of the adenosine 2'-hydroxyl proton, thus confirming the 2' position as the site of attachment of the ribose to the adenosine moiety. Comparison of the coupling constants and the chemical shifts of the ribose hydroxyl protons of 2'-ribosyl adenosine with the model compounds alpha- and beta-methylribofuranoside establishes an alpha (1" leads to 2') glycosidic linkage in the monomer. No evidence was found for heterogeneity in either the site of attachment or configuration of the linkage in the 2'-(5"-phosphoribosyl)-5'-AMP.
Genetic recombination between mouse type C RNA viruses: a mechanism for endogenous viral gene amplification in mammalian cells.
Authors: Barbacid M , Robbins K C , Hino S , Aaronson S A
Published: May 2006

A strategy based on the identification of type-specific antigenic determinants in the transitional products of gag (p15, p12, and p30 proteins), pol (reverse transcriptase), and env (gp70 glycoproteins) genes of mammalian type C viruses has been used to study genetic recombination between these RNA viruses. By this approach, recombinants involving exogenous and endogenous mouse type C viruses have been identified and genetically mapped. Analogous techniques have been applied to investigate the genetic relationships between different classes of endogenous virus that exist within the same mouse cells. Proteins of the inducible class of xenotropic virus were shown to exhibit extensive antigenic homology with the gag but not the env gene products of the ecotropic virus class. Instead, the env gene-coded glycoproteins of the inducible and noninducible xenotropic virus classes possessed striking antigenic relatedness. These results, as well as supporting findings from molecular hybridization, favor the concept that the inducible xenotropic virus of mouse cells arose by a recombinational mechanism involving the progenitors of the other two endogenous virus classes.
Affinity filters, a new approach to the isolation of tox mutants of Vibrio cholerae.
Authors: Mekalanos J J , Collier R J , Romig W R
Published: May 2006

We have devised a novel plate assay method for detecting mutants of Vibrio cholerae altered in the production of cholera toxin (tox mutants). Colonies replicated from a master plate are grown on the surface of a cellulose filter disc to which ganglioside-albumin conjugates have been attached. Toxin secreted by the colonies is tightly bound to the ganglioside filters. After removal of the cells by washing, the bound toxin may be detected by treating the filters with radioactively labeled antibodies against either whole toxin or one of its constituent polypeptide chains, followed by autoradiography. Colonies producing significantly greater of lesser amounts of toxin than the parental type are easily recognized and can be shown in liquid culture to have the corresponding hypertoxinogenic or hypotoxinogenic phenotype. This method, termed "the ganglioside filter assay," is applicable to screening large numbers of colonies and should facilitate isolation of various specific classes of mutants in cholera toxin production. In modified form the method will be applicable to various systems in which mutants of secreted proteins are sought.
On the algebraic construction and classification of Harish-Chandra modules
Authors: Enright Thomas J.
Published: May 2006

Let
G
be a connected real semisimple Lie group. In this article a functor is defined which assigns to each irreducible finite dimensional representation of a Cartan subgroup of
G
a Harish-Chandra module for
G
. This functor is described by an explicit construction of modules and a sufficient condition is given for the image module to be irreducible. In the case when
G
is a linear group, this functor is used to exhibit all irreducible Harish-Chandra modules of
G
.
DNA polymerase activities in differentiating mouse neuroblastoma N-18 cells.
Authors: Bhattacharya P , Basu S
Published: May 2006

The activities of two DNA polymerases (DNA nucleotidyltransferases) were characterized in mouse neuroblastoma clone N-18 on the basis of their apparent molecular weights (determined by sucrose density gradient centrifugation: polymerase-alpha, 7.5-8 S; polymerase-beta, 3-4 S) and relative inhibition by sulfhydryl-blocking agents. N-Ethylmaleimide (10 mM) and iodoacetamide (1.5 mM) inhibited DNA polymerase-alpha activity completely, whereas only 35-40% inhibition was observed for DNA polymerase-beta under similar conditions. DNA polymerase-alpha activity was reduced 50-70% in N-18 cells that had been induced to differentiate by 4 micro M bromodeoxyuridine, and the low molecular weight DNA polymerase-beta activity remain unchanged. With activated calf thymus DNA as template, only DNA polymerase-alpha activity was stimulated in the presence of added ribonucleotides and purified Escherichia coli RNA polymerase.
Model for capping of membrane receptors based on boundary surface effects
Authors: Gershon N. D.
Published: May 2006

Crosslinking of membrane surface receptors may lead to their segregation into patches and then into a single large aggregate at one pole of the cell. This process is called capping. Here, a novel explanation of such a process is presented in which the membrane is viewed as a supersaturated solution of receptors in the lipid bilayer and the adjacent two aqueous layers. Without a crosslinking agent, a patch of receptors that is less than a certain size cannot stay in equilibrium with the solution and thus should dissolve. Patches greater than a certain size are stable and can, in principle, grow by the precipitation of the remaining dissolved receptors from the supersaturated solution. The task of the crosslinking molecules is to form such stable patches. These considerations are based on a qualitative thermodynamic calculation that takes into account the existence of a boundary tension in a patch (in analogy to the surface tension of a droplet). Thermodynamically, these systems should cap spontaneously after the patches have reached a certain size. But, in practice, such a process can be very slow. A suspension of patches may stay practically stable. The ways in which a cell may abolish this metastable equilibrium and thus achieve capping are considered and possible effects of capping inhibitors are discussed.
Molecular alteration in a Neurospora crassa morphological mutant and its phenocopy.
Authors: Springer W D , Srb A M
Published: May 2006

A procedure using ion exchange chromatography has been developed to detect alterations in a polysaccharide produced by Neurospora crassa. The polysaccharide, isolated from medium that has supported the growth of a culture, is highly responsive to the 3-methyl-2-benzothiazolinone hydrazone assay, indicating a high hexosamine content. The substance elaborated by wild-type N. crassa can be fractionated into two components that appear by rechromatography to be closely related. When isolated from mutants of the peak (pk) locus, the corresponding polysaccharide cannot be resolved into two components. Instead, a single component is consistently found. This variant chromatographic pattern cosegregates with morphological effects of the pk allele after crosses with the wild type. The polysaccharide isolated from a wild-type culture that has been induced by sorbose to phenocopy the hyphal characteristics of pk mutants elutes from the ion exchange column in a manner similar to the corresponding polysaccharide from the pk mutants.
Ion flow through a membrane: concentration and current responses to a step potential change.
Authors: Hays T R , Buckwalter C Q , Lin S H , Eyring H
Published: May 2006

Solutions of the simplified time-dependent Nernst-Planck electrodiffusion equations for various membrane models under the influence of a step voltage change are presented. Comparison of the results for a membrane with continuous sites to those for membranes with two, three or five intermediate sites shows little difference either qualitatively or quantitatively in the concentration of the diffusible ion inside the membrane, although some quantitative differences are evident in the calculated currents.
Clark's Theorem on linear programs holds for convex programs
Authors: Duffin R. J.
Published: May 2006

Given a linear minimization program, then there is an associated linear maximization program termed the dual. F. E. Clark proved the following theorem. “If the set of feasible points of one program is bounded, then the set of feasible points of the other program is unbounded.” A convex program is the minimization of a convex function subject to the constraint that a number of other convex functions be nonpositive. As is well known, a dual maximization problem can be defined in terms of the Lagrange function. The dual objection function is the infimum of the Lagrange function. The feasible Lagrange multipliers are those satisfying: (
i
) the multipliers are nonnegative and (
ii
) the dual objective function is not negative infinity. It is found that Clark's Theorem applies unchanged to dual convex programs. Moreover, the programs have equal values.
Site-specific initiation of a DNA fragment.
Authors: Hourcade D , Dressler D
Published: May 2006

The first step in the replication cycle of the single-stranded DNA phages is the conversion of the infecting positive strand circle to a duplex ring. This event involves the de novo initiation of a negative strand, using the infecting positive strand cycle as a template. The synthesis of the negative strand is in many respects analogous to the formation of a fragment during cellular DNA replication. In this paper we describe the initiation of the negative strand of bacteriophage G4. The data establish that, in vivo, the synthesis of the G4 negative strand is initiated at a specific site, which we have mapped on the 5400-base viral chromosome.
Strand-specific break near the origin of bacteriophage P2 DNA replication.
Authors: Chattoraj D K
Published: May 2006

Membrane-associated P2 DNA isolated early after infection under conditions that block replication (amB in phage and rep in Escherichia coli C) was analyzed by electron microscopy. Most DNA was in the form of relaxed circles (40%) and circles with short single-stranded tails (60%). When this DNA was hybridized with separate strands of linear P2 Hy dis DNA (which provides suitable reference points along the heteroduplex molecules), an interruption was located near the previously mapped origin of P2 DNA replication in one specific strand. The same strand was sometimes extended in the direction consistent with the unidirectional mode of P2 DNA replication. Similar conclusions were reached when the intracellular DNA was analyzed after partial denaturation. These results are consistent with the rolling circle mode of DNA replication.
Identification and properties of two methyltransferases in conversion of phosphatidylethanolamine to phosphatidylcholine.
Authors: Hirata F , Viveros O H , Diliberto E J , Axelrod J
Published: May 2006

Two methyltransferases involved in the methylation of phosphatidylethanolamine to form phosphatidylcholine were demonstrated in a microsomal fraction of bovine adrenal medulla. The first methyltransferase catalyzes the methylation of phosphatidylethanolamine to form phosphatidyl-N-monomethylethanolamine. This enzyme has an optimum pH of 6.5, a low Km for S-adenosyl-L-methionine (1.4 micron), and an absolute requirement for Mg2+. The second methyltransferase catalyzes the two successive methylations of phodphatidyl-N-monomethylethanolamine to phosphatidyl-N,N-dimethylethanolamine and phosphatidylcholine. In contrast to the first methyltransferase, it has an optimum pH of 10 and a high Km for S-adenosyl-L-methionine (0.1 mM) and does not require Mg2+.
Enrichment of special Novikoff hepatoma and regenerating liver mRNA by hybridization to cDNA-cellulose
Authors: Hirsch Friedrich W. , Nall Katrina N. , Spohn William H. , Busch Harris
Published: May 2006

Total polysomal poly(A)+ RNA of Novikoff hepatoma and of 18-hr regenerating rat liver were compared by analysis of their
in vitro
translational products on two-dimensional isofocusing/sodium dodecyl sulfate gels. This technique resolved the translated proteins sufficiently to permit detection of quantitative and some qualitative differences between the two mRNA populations. Excess cDNA from regenerating liver or Novikoff hepatoma, covalently linked to cellulose, was used to adsorb the complementary mRNA sequences from Novikoff hepatoma or regenerating liver. As shown by two-dimensional gel electrophoresis, the translated products of the bound mRNA fractions contained proteins common to both tissues. Novikoff hepatoma mRNA which did not bind to regenerating liver cDNA was enriched in sequences encoding for proteins 11/5.1, 15/6.8, 40/8.2, and 65/5.1 (shown as molecular weight/pI). These polypeptides were not detectable in the translational products of regenerating liver mRNA. Regenerating liver mRNA that was not bound to Novikoff hepatoma cDNA was enriched in sequences coding for proteins 12.5/4.9, 13.5/7.4, 17/8.2, 24/5.5, and 46/6.4; these proteins were not found in the translational pattern from Novikoff hepatoma. These results show that adsorption of mRNA to solid-phase cDNA provides a valuable technique for differentiating mRNA species in related tissues and for corresponding enrichment of these specific mRNAs.
Mechanism of action of the cro protein of bacteriophage lambda.
Authors: Johnson A , Meyer B J , Ptashne M
Published: May 2006

The mechanism of action of cro protein was probed by measuring its ability to protect DNA against methylation by dimethyl sulfate and its effect on transcription in vitro. The cro protein binds to the same three sites in the right operator (OR) of bacteriophage lambda DNA as does the lambda repressor. Dimethyl sulfate protection experiments reveal major groove contacts for both proteins, and cro protein protects from methylation a subset of those purines protected by lambda repressor. These experiments also show that the relative affinity of these two proteins for the three operator sites is different: whereas lambda repressor binds with an affinity OR1 greater than OR2 greater than OR3, the order for cro protein is OR3 greater than (OR1, OR2). As predicted by these results, cro protein, like the lambda repressor, blocks in vitro transcription of cI and cro from the two divergent promoters that overlap OR. Also as predicted, transcription of cI is turned off at lower cro protein concentrations than is transcription of cro, whereas the opposite order of repression is obtained with lambda repressor. These results describe the molecular mechanism of cro protein action and show that two regulatory proteins can bind to the same three adjacent sites in DNA with markedly different consequences.
Immunogenicity of the envelope glycoprotein of avian sarcoma virus.
Authors: Halpern M S , Friis R R
Published: May 2006

The expression of type E-specific glycoprotein in chick-helper factor-positive [chf(+)] chickens is not restricted to a certain stage of embryogenesis but persists in postembryonic life. This finding prompted an investigation of the immunogenicity of the viral envelope glycoprotein of exogenous avian sarcoma virus in chf(+) and chf(-) chickens. Sensitization of both classes of chickens resulted in the induction of detectable antibody reactivity to determinants of the glycoprotein that were type-specific as well as group-specific. Because group-specific determinants are present on type E-specific glycoprotein, these results link immunity to exogenous viral envelope glycoprotein in chf(+) chickens with autoreactivity. A model is proposed to rationalize the induction of reactivity in this system.
Ion flow through a membrane: effect of chemical reaction on time dependence.
Authors: Hays T R , Lin S H , Eyring H
Published: May 2006

The membrane model previously described [Hays, T.R., Buckwalter, C.Q., Lin S.H. & Eyring, H. (1978) Proc. Natl. Acad. Sci. USA 75, 1612-1615] for ion flow through a membrane is expanded to include the effect of binding of the mobile ion at the occupiable sites in the membrane. Two different effects were investigated: alteration of the association-dissociation rates at constant equilibrium constant and alteration of the equilibrium constant at constant dissociation constant. Increasing the rates of association and dissociation initially causes an increased slowing of the relaxation to the final steady state, though ultimately the curves for the faster rates cross those for the slower states. Increasing the equilibrium constant causes a greater delay in the relaxation curve, with the curves for different equilibrium constants not crossing. Overall, the effect of binding is not very great unless the equilibrium constant for binding is quite large.
Nerve growth factor potentiates actomyosin adenosinetriphosphatase.
Authors: Calissano P , Monaco G , Castellani L , Mercanti D , Levi A
Published: May 2006

The nerve growth factor protein (NGF) favors polymerization of brain actin and induces its organization to form paracrystalline structures that activate myosin ATPase (ATP phosphohydrolase, EC 3.6.1.3) to an extent greater than actin alone. Binding studies show that the initial 1:1 stoichiometry of NGF-G-actin complexes decreases to 1:7-10 when polymerization is ended and paracrystalline structures are formed. The ratio becomes even lower when heavy meromyosin is added in the absence of ATP, suggesting that heavy meromyosin displaces NGF bound to actin microfilaments. This conclusion is supported by the finding that when heavy meromyosin is added to NGF-microfilament complexes, under conditions for "decorating" microfilaments, the usual paracrystalline structure of the complexes disappears. The NGF-mediated organization of actin and activation of myosin ATPase is visualized as a self-regulatory and self-propagating mechanism, because progressive displacement of the growth factor induced by heavy meromyosin binding to F actin as ATP consumption proceeds renders an increasingly higher amount of NGF free for new interactions. These findings are discussed in the light of the mechanism of action of NGF in the target cells.
Mechanism of antigen-induced antibody biosynthesis from antibody precursors, the heavy and light immunoglobulin chains
Authors: Haurowitz Felix
Published: May 2006

The immediate precursors of antibody molecules, the heavy (H) and light (L) peptide chains of the immunoglobulins, combine with each other by means of disulfide bonds formed by dehydrogenation of their cysteine residues. In the absence of an antigen this process yields the heterogeneous mixture of normal immunoglobulins. Antigens or their processed derivatives (Ag) interfere with this stochastic process by noncovalent combination with complementarily fitting H chains. The (Ag·H)
n
complexes thus formed, owing to the loss of rotational and translational freedom, combine preferentially with those L chains whose V
L
regions have some affinity for the determinants of the antigen molecule. Subsequent release of Ag from the (Ag·H·L)
n
complexes yields free antigen and antibody molecules. Each of the released Ag molecules can be used repeatedly for the same reaction cycle and thus can induce the biosynthesis of a large number of antibody molecules. Any macromolecule, natural or synthetic, that has at least a few polar groups and that can penetrate to the nascent H and L chains can thus act as an antigen. Whereas the structure of the H and L chains is genetically determined and transmitted through the germ line, the process induced by the antigen is a phenotypic phenomenon. The antigen acts in this process as a stereospecific cofactor or regulator of the thiol-disulfide transhydrogenation of the combining H and L chains of immunoglobulins.
Joint probability distribution of the invariants comprising determinantal inequalities: Heuristic derivation
Authors: Karle Jerome
Published: May 2006

Joint probability distributions are derived that are expressed in terms of the determinants that form the determinantal inequalities associated with the non-negative Fourier series that represent crystal structures. The derivation involves heuristic considerations. It is therefore appropriate to test the distributions extensively by making comparisons with results obtained by other theoretical means and evaluations of the implications of the distributions. Those performed thus far on the low-order determinants (third and fourth orders) have provided satisfactory results. The determinantal probability distributions imply a general maximum determinant rule, contain a wealth of information, and provide numerous paths that may be followed for future development.
Electric double layer dynamics by high-field electroluminescence in aqueous solution (Destriau effect)
Authors: Schelly Z. A. , Lundy-Douglas K. , Eyring H.
Published: May 2006

Transient luminescence induced by high electric fields (>2.5 × 10
4
V/cm) was observed in aqueous solutions of 6,8-dihydroxypyrene-1,3-disulfonic acid. The light emission takes place both at the leading
and the trailing
edges of the perturbing electric square pulse. It occurs only during the variation of the applied field and disappears with a time constant of 0.5 μsec at constant field. In solid state phosphors, where this phenomenon has been reported previously, it is known as the Destriau effect. The mechanisms of excitation and emission can be explained by the electron injection model, in which the time constant of the luminescence decay is associated with the rate of formation of the space charge. This space charge appears as a separation of positive and negative charges into a double layer stabilized by the applied potential.
The "sarcoma-specific" region of Moloney murine sarcoma virus 124.
Authors: Dina D
Published: May 2006

Labeled, purified 30S RNA from Moloney murine sarcoma virus was annealed to an excess of Moloney murine leukemia virus complementary DNA. Upon treatment of the resulting DNA.RNA hybrids with RNase H followed by sucrose gradient sedimentation, and undigested 18S RNA molecule was recovered. This RNA molecule was shown to represent the "sarcoma-specific" region of the virus. The unintegrated linear DNA provirus of murine sarcoma virus 124 was isolated from newly infected cells and a physical map of the sarcoma-specific region was obtained. First, unintegrated full-length linear proviral DNA molecules were cleaved by several restriction endonucleases. The reciprocal position and orientation with respect to the viral RNA of the resulting fragments were established. The location of the sarcoma-specific region was determined by competition-hybridization with 125I-labeled viral genomic RNAs and proviral DNA fragments. A 1500-base-pair fragment was obtained by cleavage with HindIII + Bgl II. This fragment mapped between 750 and 2250 base pairs from the right end of the proviral DNA (corresponding th the 3' terminus of the viral RNA) and contained the whole set of the sarcoma-specific information. This murine sarcoma virus proviral restriction fragment is approximately of the same size and map position as the isolated 18S sarcoma-specific RNA.
Conservation of ribosomal protein binding sites in prokaryotic 16S RNAs.
Authors: Thurlow D L , Zimmermann R A
Published: May 2006

The Escherichia coli 30S ribosomal subunit proteins S4, S7, S8, S15, S17, and S20 that interact independently with 16S RNA from E. coli formed specific heterologous complexes with 16S RNAs extracted from 11 different prokaryotes covering a broad phylogenetic range. Complex formation was shown to be specific by saturation of binding in the presence of excess protein. Binding stoichiometries and the apparent affinities for a given protein varied depending on which 16S RNA was used, although the pattern of binding was not strictly correlated with phylogenetic relationships. The size-distribution of fragments resulting from limited hydrolysis of free prokaryotic 16S RNAs with T1 and pancreatic ribonucleases indicated that the structural organization of 16S RNA from E. coli is similar to that of 16S RNAs from closely related species, but differs, although to an unknown extent, from that of 16S RNAs from other prokaryotes tested. Digestions of RNA-protein complexes under similar conditions indicated that the proteins remain bound to specific RNA fragments. For those 16S RNAs isolated from species closely related to E. coli, the fragments were comparable to those generated by hydrolysis of the homologous complex.
Bone marrow colony-stimulating factor and tumor resistance-enhancing activity of postendotoxin mouse sera
Authors: Butler R. Christopher , Abdelnoor Alexander M. , Nowotny Alois
Published: May 2006

The passive transfer of postendotoxin mouse serum could enhance nonspecific resistance to the development of TA3-Ha transplantable ascites tumor in mice. The postendotoxin serum was not directly cytotoxic to TA3-Ha tumor cells
in vitro
, nor did it contain significant amounts of residual endotoxin, but it was rich in colony-stimulating factors (CSFs). High-titer CSF serum could be induced by endotoxic lipopolysaccharide (LPS). Nonendotoxic, lipid-free, and polysaccharide-rich hydrolytic breakdown product of LPS (called PS) was less potent but still active in CSF induction. There was a correlation between the level of CSF stimulation and the capacity of the sera to transfer tumor resistance (TUR). Those LPS preparations that had the highest CSF-inducing capacity were the most potent in TUR enhancement. Suppression of CSF production by treatment with theophylline or epinephrine, enhancers of cyclic AMP/cyclic GMP ratios, lowered the enhancement of TUR by endotoxic LPS. The infection of serum donor mice with bacillus Calmette-Guérin (BCG) 18 days prior to LPS treatment gave the highest serum CSF levels and the most potent TUR-inducing serum preparation. Even more notable was the finding that the nontoxic PS preparation could replace toxic LPS in the above BCG-LPS system. The serum harvested from BCG-infected mice 2 hr after PS injection was similarly effective in the passive transfer of TUR.
Local analytic hypoellipticity for □

b

on nondegenerate Cauchy—Riemann manifolds
Authors: Tartakoff David S.
Published: May 2006

The local real analytic regularity of solutions to □

b

, the complex boundary Laplacian, and related operators is proved for (
p,q
) forms on a nondegenerate, abstract, real analytic Cauchy-Riemann (C-R) manifold of dimension 2
n
- 1 satisfying J. J. Kohn's condition
Y
(
q
). The problem is reduced to the study of general, “variable coefficient” operators, satisfying the same
a priori
estimates, on the Heisenberg group.
L
2
methods only are used.
Visualization of the intracellular development of bacteriophage lambda, with special reference to DNA packaging.
Authors: Yamagishi H , Okamoto M
Published: May 2006

To reveal intermediates in lambda DNA packaging, infected cells were osmotically ruptured and the cell lysates were deposited on electron microscope grids by sedimentation through a sucrose/formalin cushion. A fixation procedure that crosslinks head-related structures to DNA allowed us to study successive stages in the process of head filling. Three types of head-related structures can be distinguished: (i) empty heads (petit lambda), less angular in outline than complete lambda heads; (ii) heads partially filled with DNA (partially filled heads), having a roundish outline; and (iii) particles tightly packed with DNA (full heads), having a hexagonal outline. DNA-head complexes were bound either at the terminal end of a DNA thread or at a point intermediate along the thread. The terminal complexes were more abundant. No head-related structures could be found in an induced lambda mutant lysogen blocked in the synthesis of petit lambda (amber in lambda gene E). One type of mutant blocked in DNA packaging (amber in gene A) produces empty heads and free tails, whereas another (amber in gene D) produces partially filled heads in addition. Our data suggest that a DNA-petit lambda complex may be an early intermediate in packaging and that the lambda DNA substrate can be a cohesive-ended concatemer or a concatemer with double-stranded cohesive site sequences.
Identification of epoxide hydrase as the preneoplastic antigen in rat liver hyperplastic nodules.
Authors: Levin W , Lu A Y , Thomas P E , Ryan D , Kizer D E , Griffin M J
Published: May 2006

A liver microsomal protein, previously referred to as preneoplastic antigen, from hyperplastic nodules of rats fed a diet containing 2-acetylaminofluorene has been identified as the enzyme epoxide hydrase [glycol hydro-lyase (epoxideforming), EC 4.2.1.63]. Purified preneoplastic antigen from hyperplastic nodules and purified rat liver microsomal epoxide hydrase are immunochemically identical on the basis of Ouchterlony double-diffusion analysis. In addition, the purified proteins have identical minimum molecular weights in sodium dodecyl sulfate/polyacrylamide gels, and both proteins catalyze the hydration of arene oxides to dihydrodiols. Chronic feeding of 2-acetylaminofluorene to rats results in a 5- to 7-fold increase in epoxide hydrase activity in rat liver. The induced level of the enzyme is maintained in developing hyperplastic nodules and hepatomas but not in the nontumor tissue after removal of the carcinogen from the diet.
Identification of the major polyadenylylated transcription products and the genes active in their synthesis in a rat insulinoma.
Authors: Duguid J R , Steiner D F
Published: May 2006

Three RNA fractions with molecular weights of 200,000, 280,000, and 360,000, have been identified as the major polyadenylylated transcription products in a transplantable rat pancreatic islet cell tumor that synthesizes insulin. These three RNAs share sequence homology as demonstrated by comparisons of both partial and complete RNase T1 digestion products. The 200,000 and 280,000 molecular weight species hybridize primarily with three EcoRI restriction fragments of the rat genome having molecular weights of 1.4 X 10(6), 1.6 X 10(6), and 6.0 X 10(6). The 360,000 molecular weight species hybridizes preferentially with the 6.0 X 10(6) molecular weight DNA fragment.
Ultrastructure and cytochemistry of Miocene angiosperm leaf tissues
Authors: Niklas Karl J. , Brown R. Malcolm , Santos Richard , Vian Brigitte
Published: May 2006

Angiosperm leaf fossils (16.7-25 × 10
6
years by potassium/argon dating) referable to
Zelkova
were isolated from pyroclastic deposits in the Succor Creek Formation, Oregon. These fossils reveal a three-dimensional structure in mesophyll cell layers and vascular bundles, while transmission electron microscopy of fixed tissues reveals well-preserved chloroplasts with grana stacks and starch, as well as nuclei with condensed chromatin. Transmission electron microscopy indicates that cell walls retain a cellulosic microfibrillar architecture, while ultrastructural and cytochemical confirmation is presented for chloroplast starch and the presence of native cellulose. The preservation of cell walls and cytologic structures in fossil materials of this age indicates an unusually mild fossilization process attending the post-depositional maturation of associated sediments. The preservation observed appears to be associated with rapid physical dehydration coupled with endogenous fixation by organic acids (possibly tannins and/or chlorophyll derivatives).
Late S phase cells (Chinese hamster ovary) induce early S phase DNA labeling patterns in G1 phase nuclei.
Authors: Yanishevsky R M , Prescott D M
Published: May 2006

Cells (Chinese hamster ovary) in G1 phase were fused with cells in late S phase to determine if a cell in late S phase can induce DNA synthesis in the nucleus of a G1 cell and, if so, to determine if the DNA synthesis so induced in a G1 phase nucleus has an autoradiographic pattern characteristic of early or of late S phase synthesis. The results indicate (i) that 89% of the G1 nuclei in late-S/G1 binucleates synthesized DNA, while only 2% of the control unfused G1 cells synthesized DNA, and (ii) that in all late-S/G1 binucleates the G1 nucleus was induced to synthesize early S phase DNA. These results are compatible with the idea that a cytoplasmically transmissible factor initiates DNA synthesis but that an intranuclear mechanism defines the temporal order of replication.
Enhancement of the neonate's nonspecific immunity to Klebsiella infection by muramyl dipeptide, a synthetic immunoadjuvant.
Authors: Parant M , Parant F , Chedid L
Published: May 2006

N-acetylmuramyl-L-alanyl-D-isoglutamine (muramyl dipeptide) and certain derivatives that are structural analogs of part of the bacterial peptidoglycan monomer have been shown to be adjuvant active and to enhance the nonspecific immunity of adult mice infected by Klebsiella pneumoniae. In the present study muramyl dipeptide and two other synthetic analogs were found to be active in newborn mice. This activity could be demonstrated after administration by subcutaneous or even by oral route. In contrast to what was observed after treatment by lipopolysaccharide, 8-day-old mice were definitively protected against bacterial challenge by these glycopeptides. Therefore such molecules could have a great value in view of studying and correcting the neonate's unresponsiveness.
Study of antibodies against human melanoma produced by somatic cell hybrids.
Authors: Koprowski H , Steplewski Z , Herlyn D , Herlyn M
Published: May 2006

We fused spleen lymphocytes obtained from mice immunized against a human melanoma cell line and melanoma-mouse hybrid cells with the P3 X 63 Ag8 mouse myeloma in order to produce hybrids secreting antibodies against a human melanoma. Antibodies secreted by individual hybrids were tested for their reaction with a panel of human melanoma, colorectal carcinoma, and normal cells in an indirect radioimmunoassay, and they displayed different specificities and crossreactivities. Some reacted only with melanomas, whereas others crossreacted with normal human or human colorectal carcinoma cells. By analysis of competitive binding of mixtures of monoclonal antibodies, it was possible to delineate different epitopes on melanomas. Hybrids growing in nude mice and producing antimelanoma antibody suppressed growth of melanoma tumors.
Decomposition of the linking number of a closed ribbon: A problem from molecular biology
Authors: Fuller F. Brock
Published: May 2006

A closed duplex DNA molecule relaxed and containing nucleosomes has a different linking number from the same molecule relaxed and without nucleosomes. What does this say about the structure of the nucleosome? A mathematical study of this question is made, representing the DNA molecule by a ribbon. It is shown that the linking number of a closed ribbon can be decomposed into the linking number of a reference ribbon plus a sum of locally determined “linking differences.”
Role of a transmembrane pH gradient in epinephrine transport by chromaffin granule membrane vesicles.
Authors: Schuldiner S , Fishkes H , Kanner B I
Published: May 2006

ATP-driven transport and accumulation of epinephrine in chromaffin granule membrane vesicles isolated from bovine adrenal medulla is inhibited by the proton ionophores carbonylcyanide p-trifluoromethoxyphenylhydrazone and nigericin, but not by valinomycin. Moreover, an artificially imposed pH gradient (interior acid) is able to drive this reserpine-sensitive transport system in the absence of ATP. Dicyclohexylcarbodiimide, an inactivator of the chromaffin granule membrane-bound ATPase, completely inhibits ATP-dependent epinephrine accumulation, but has much less effect when an imposed pH gradient is the driving force for epinephrine transport. The findings provide a strong indication that a pH gradient (interior acid) is the immediate driving force for epinephrine uptake in these storage granules and suggest that ATP-driven epinephrine transport is the result of two processes: (i) generation of a proton electrochemical gradient (interior acid and positive) by the membrane-bound, proton-translocating ATPase; and (ii) pH gradient-driven accumulation of the catecholamine.
"Tension" on heme by the proximal base and ligand reactivity: conclusions drawn from model compounds for the reaction of hemoglobin.
Authors: Sharma V S , Geibel J F , Ranney H M
Published: May 2006

The kinetic data on model compounds of hemoglobin indicate that in oxyderivatives ligand dissociation rates are sensitive to the "tension" exerted by the proximal base on the metal-to-ligand bond; the corresponding rates for carboxy derivatives are not sensitive to the tension. It is suggested that the metal-to-ligand bond becomes weaker with increased "pull" (or tension) on Fe from the proximal base due to the steric and/or electronic interaction between the ligand, the porphyrin ring, and the proximal base. In model compounds the linear heme Fe-to-CO bound vis-a-vis the bent heme Fe-to-O2 bond probably makes such interactions less significant in carboxy derivatives. It is proposed that the kinetic alpha,beta-chain nonequivalence in Hb4(O2)4 is due to the difference in the tension in the two chains on Fe by the proximal base. The absence of alpha,beta-chain differences large enough to show up in CO dissociation rates from Hb4(CO)4 is explained on the basis of lack of sensitivity of the Fe-CO bound to tension from the proximal base. The implications of the results for the observed cooperative effects in ligand combination (for CO) and dissociation (for O2 and NO) rates of hemoglobin have also been discussed.
Abelson antigen: a viral tumor antigen that is also a differentiation antigen of BALB/c mice.
Authors: Risser R , Stockert E , Old L J
Published: May 2006

We report here the serologic detection of a cell surface antigen common to cells transformed by the Abelson murine leukemia virus (A-MuLV) and to normal hematopoietic cells from certain strains of mice. Serum from C57BL/6 mice hyperimmunized with syngeneic A-MuLV lymphoma cells was cytotoxic for the immunizing cells; this reaction was used as the serologic test system for recognition of A-MuLV antigens. Absorption analysis using 40 tumors and 21 cell lines revealed that two serologic specificities were detected by this test system: (i) FMR antigen(s) related to the Moloney MuLV helper (the virus from which A-MuLV was originally derived), and (ii) an antigen expressed on all cells transformed by A-MuLV. The A-MuLV-specific antigen was also present on uninfected cells from BALB/c bone marrow, spleen, and fetal liver but not from adult liver, thymus, lymph nodes, or peripheral blood. Abelson antigen was not expressed on bone marrow or spleen cells of 12 other mouse strains. In light of the original isolation of A-MuLV from a BALB/c mouse infected with Moloney virus, it is possible that Abelson antigen is a serologic marker for a gene of BALB/c mice, normally encoding a cell surface molecule, that was incorporated into the Moloney virus genome during the generation of A-MuLV.
Visualization of specific antibody and C1q binding to hapten-sensitized lipid vesicles.
Authors: Henry N , Parce J W , McConnell H M
Published: May 2006

Specific IgG antibodies directed against the spin-label nitroxide group present as a lipid hapten in single-compartment lipid vesicles have been visualized by using freeze-etch electron microscopy. Individual "particles" with diameters of the order of 20 nm are identified as single IgG molecules bound to lipid hapten. No significant aggregation of these IgG molecules was observed over a period of 1 hr in a dipalmitoyl phosphatidylcholine vesicle at 22 degrees. Binding of the human complement component C1q results in the formation of large (approximately 50-100 nm) asymmetric particles having a partially resolved substructure that may arise from individual IgG molecules bound to the membranes as well as to C1q. The binding of C1q appears to result in a clustering of membrane-bound IgG molecules. Samples containing a serum factor (perhaps anti-IgG antibodies) exhibit some IgG clustering distinct from that produced by Clq.
Ca2+-related regulatory function of fibrinogen.
Authors: Credo R B , Curtis C G , Lorand L
Published: May 2006

Fibrinogen displays a regulation of considerable physiological significance by lowering the Ca2+ requirement for the conversion of the fibrin-stabilizing factor (Factor XIII) zymogen to the range of concentrations of this ion found in plasma. Fibrinogen modulates both Ca2+-dependent steps in the complex process of zymogen activation, involving the heterologous dissociation of subunits of the thrombin-modified zymogen (Factor XIII') species : formula: (see text) and the unmasking of iodoacetamide titratable sites during generation of transamidating activity : formula: (see text). It is interesting that a thrombin-independent pathway of zymogen activation : formula: (see text), which we found to operate at Ca2+ concentrations above 50 mM, is not affected by the presence of fibrinogen. Regulation by fibrinogen thus appears to be specific for controlling only the physiological pathway of zymogen conversion.
Supplemental ascorbate in the supportive treatment of cancer: Reevaluation of prolongation of survival times in terminal human cancer
Authors: Cameron Ewan , Pauling Linus
Published: May 2006

A study has been made of the survival times of 100 terminal cancer patients who were given supplemental ascorbate, usually 10 g/day, as part of their routine management and 1000 matched controls, similar patients who had received the same treatment except for the ascorbate. The two sets of patients were in part the same as those used in our earlier study [Cameron, E. & Pauling, L. (1976)
Proc. Natl. Acad. Sci. USA
73, 3685-3689]. Tests confirm that the ascorbate-treated patients and the matched controls are representative subpopulations of the same population of “untreatable” patients. Survival times were measured not only from the date of “untreatability” but also from the precisely known date of first hospital attendance for the cancer that eventually reached the terminal stage. The ascorbate-treated patients were found to have a mean survival time about 300 days greater than that of the controls. Survival times greater than 1 yr after the date of untreatability were observed for 22% of the ascorbate-treated patients and for 0.4% of the controls. The mean survival time of these 22 ascorbate-treated patients is 2.4 yr after reaching the apparently terminal stage; 8 of the ascorbate-treated patients are still alive, with a mean survival time after untreatability of 3.5 yr.
Uncoupling of electrotonic synapses by calcium.
Authors: Baux G , Simonneau M , Tauc L , Segundo J P
Published: May 2006

The degree of axo-axonal synaptic coupling between nerve cells in the buccal ganglion of Navanax was investigated in relation to intracellular ionic calcium. Increasing intracellular Ca2+ by injection of Ca2+, injection of Na+, or application of ionophore X537A produced uncoupling after at least 90 min, if metabolic inhibitor was present in the medium. Subsequent removal of the metabolic inhibitor reestablished the coupling in less than 30 min. Injected Sr2+ also mimicked the uncoupling action of Ca2+. The presence of a metabolic inhibitor alone had no effect on the coupling. These results lead to the following conclusions: (i) Uncoupling is due to an increased free Ca2+ concentration at the junctions. (ii) The liberation of endogenous sequestered Ca2+ is not sufficient to produce uncoupling except if an excess Ca2+ had been previously sequestered. The electrical synapses in the buccal ganglion of Navanax thus appear to be affected by Ca2+ in a similar way as gap junctions studied in non-neural tissues.
Location of the regulatory site for establishment of repression by bacteriophage lambda.
Authors: Jones M O , Fischer R , Herskowitz I , Echols H
Published: May 2006

During the lysogenic response to infection by bacteriophage lambda, the phage-specified cII and cIII proteins provide for the coordinate establishment of repression and integration of the viral DNA. One critical regulatory function of cII/cIII is an activation of synthesis of the cI protein, the repressor that maintains lysogeny. The mechanism and site for regulation of the cI gene by cII/cIII have been a subject of controversy. The two principal hypotheses for cII/cIII action are: initiation of new RNA chains in the y region of lambda DNA just to the left of the cII gene; or antitermination of a short leader RNA (4S or oop RNA) initiated to the right of the cII gene. In an effort to distinguish between these hypotheses, we have studied the cII-mediated turn-on of cI protein synthesis in three classes of prophage deletion strains: deletions of the 4S RNA promoter but not the y region, deletions that remove both regions, and deletions that leave both intact. We find that an intact y region is required for normal regulation of the cI gene by cII, but the 4S RNA promoter is not. From experiments with other mutants, we conclude that rightward transcription from the early lytic promoter is also not necessary for positive regulation. Our results suggest that positive regulation by cII/cIII involves initiation of new RNA chains through activation of promoter sites.
Another approach to in vivo estimation of genetic damage in humans.
Authors: Pero R W , Mitelman F
Published: May 2006

Direct measurements of the genetic hazards to man have been determined previously by the appearance of elevated in vivo levels of chromosome aberrations. Here we report that interindividual variations in N-acetoxy-2-acetyl-aminofluorene-induced unscheduled DNA synthesis values parallel the actual in vivo levels of chromosome damage and, therefore, may be a rapid useful supplement in genetic risk assessment for humans.
Complementary carrier peptide synthesis: general strategy and implications for prebiotic origin of peptide synthesis.
Authors: Walder J A , Walder R Y , Heller M J , Freier S M , Letsinger R L , Klotz I M
Published: May 2006

A method for peptide synthesis is proposed based on a template-directed scheme that parallels that of the native ribosomal mechanism. In this procedure, peptide bond formation is facilitated by the juxtaposition of aminoacyl and peptidyl oligonucleotide carriers bound adjacent to one another on an oligonucleotide template. The general strategy of the synthesis and relevant model studies are described. The scheme provides an intrinsic mechanism by which oligonucleotides can direct the synthesis of polypeptides in the absence of protein or ribosomal machinery and, as such, suggests a model for the origin of prebiotic protein synthesis.