bluuebunny/crossref_metadata_2025 huggingface dataset:
Immune Lysis of Liposomes and Erythrocyte Ghosts Loaded with Spin Label
Authors: Humphries Gillian Kitch , McConnell Harden M.
Published: May 2006

It is shown that the paramagnetic resonance of spin labels offers a convenient technique for monitoring the complement-mediated immune lysis of erythrocyte ghosts, and sensitized phospholipid liposomes. The ghosts or liposomes are loaded with a concentrated solution of a water-soluble, membrane-impermeable spin label, so that there is a strong exchange broadening of the paramagnetic resonance signal due to labels enclosed within the liposomes or ghosts. Complement-mediated lysis releases the labels into a dilute solution, where a relatively sharp and intense paramagnetic resonance signal is detected.

An unanticipated result is also reported: this is the augmentation of release of spin label from loaded ghosts sensitized with egg albumin, in the presence of antibody against egg albumin, complement, and egg albumin in solution, over and above the release in the absence of egg albumin in solution. Comparison with complement fixation suggests that the augmentation of lysis is effected by crosslinking of immune complexes with the cell membrane.
Molecular Heterosis for Heat-Sensitive Enzyme Alleles
Authors: Singh R. S. , Hubby J. L. , Lewontin R. C.
Published: May 2006

Heat denaturation studies were carried out and revealed hidden genic variants with the same net charge at the
Octanol dehydrogenase-1
locus in
Drosophila pseudoobscura
. Studies of several genetic crosses between strains with different heat-sensitivity alleles showed that the F
1
retained more
in vitro
enzyme activity after being heat-treated for a specified amount of time at a given temperature than the heat-resistant parent. We call this phenomenon “heterosis for heat-stability of enzyme activity” and discuss its possible molecular mechanism, its relation to maintenance of genetic variation in natural populations, and its bearing on the “classical” and “balance” hypotheses.
Thermodynamics of Micelle Formation: Prediction of Micelle Size and Size Distribution
Authors: Tanford Charles
Published: May 2006

This paper presents a simple theory for the calculation of micelle size and other properties of micelleforming systems. The theory is based on the separate estimation of the components of the free energy arising from hydrophobic attraction and from head group repulsion, each as a function of micelle size. The difficult problem of an
a priori
calculation of the repulsive factor is circumvented by using experimental values of this parameter, derived from pressure-area curves of monolayers at an interface between an aqueous solution and liquid hydrocarbon. Though some parameters of the theory are still somewhat uncertain, self-consistent and physically realistic values can be assigned that lead to almost exact prediction of experimental micelle sizes and critical micelle concentrations for two distinctly different ionic detergents.
Enzyme Activity in Invasive Tumors of Human Breast and Colon
Authors: Bosmann H. Bruce , Hall Thomas C.
Published: May 2006

Elevated levels of glycoprotein:sialyltransferase activity (EC 2.4.99.1; CMP-
N
-acetylneuraminate: D-galactosyl-glycoprotein
N
-acetylneuraminyltransferase) were found in human malignant neoplastic tissues compared to normal, benign, and “preneoplastic” tissues. This increase was not due to the cell density of the tissue. Elevated levels of certain proteases and glycosidases were also found. The increase in transferase activity may be associated with altered membrane synthesis in the neoplastic state; changes in the activity of degradative enzymes may be associated with tumor invasiveness and maintenance of the neoplastic state. Measurements on human tumors are possibly more directly relevant to cancer than those described for transformed fibroblastic cells
in vitro
.
Ultrastructural, Immunologic, and Functional Studies on Sézary Cells: A Neoplastic Variant of Thymus-Derived (T) Lymphocytes
Authors: Zucker-Franklin Dorothea , Melton John W. , Quagliata Franco
Published: May 2006

The vast majority of human lymphoid neoplasms examined to date have been associated with a proliferation of bone marrow-dependent (B) lymphocytes. In an effort to delineate human tumors of T-cell (thymusdependent) lineage, use was made of the peripheral blood leukocytes of sixteen subjects with various forms of mycosis fungoides. The abnormal cells in the circulation of these patients are morphologically identical to those that infiltrate their nodes and skin. On electron microscopy, such neoplastic lymphocytes (Sézary cells) had “cerebriform” nuclei and an abundance of cytoplasmic fibrils not described heretofore. Sézary cells were nonadherent and nonphagocytic and usually responded to stimulation with phytohemagglutinin, refuting earlier suggestions that the cells represent monocytes or histiocytes. In contrast to chronic lymphocytic leukemia lymphocytes, the Sézary cells lacked surface immunoglobulin and receptors for complement. Ultrastructural analysis identified Sézary cells in the center of directly formed rosettes (E-rosettes) characterizing the behavior of T lymphocytes in this test. Though some Sézary cells lacked both T and B cell-surface properties, in general, these observations support the view that the Sézary cell is a neoplastic variant of a thymusderived lymphocyte.
Discontinuous Variability, in the Form of a Geometric Progression, of Albumin Production in Hepatoma and Hybrid Cells
Authors: Peterson Jerry A.
Published: May 2006

A clonal rat hepatoma cell line (Fu5) produces rat serum albumin at a constant rate over at least 3 months of continuous cultivation. Ten hybrid cell clones derived from the fusion of Fu5 cells and mouse fibroblasts, as well as 14 hepatoma subclones of Fu5 cells, all produce albumin but at different rates, ranging from about 0.09 to 36.7 μg/mg of protein per 72 hr. Despite this variability in albumin production, the distribution of clones is not random but discontinuous, with both hepatoma and hybrid clones clustering around discrete values that can be fitted to the geometric progression:
a
,
a
(√2)
1
,
a
(√2)
2
.....
a
(√2)

n

. The values of the majority of clones fall into alternate members of this geometric progression, which differ by a factor of 2. Hepatoma subclones with indistinguishable karyotypes differ in level of albumin production by as much as 4-fold. In contrast to hepatoma clones, albumin production in hybrid clones decreases with increasing cell generations. A survey of 28 enzymes of different hepatomas reveals a large variability in enzyme levels which, for most enzymes, can be arranged into classes that form a geometric progression. The apparent widespread nature of this discontinuous phenotypic variability suggests that it may reflect a basic mechanism of control of gene expression in animal cells.
Total Substitution of Bromodeoxyuridine for Thymidine in the DNA of a Bromodeoxyuridine-Dependent Cell Line
Authors: Bick Michael D. , Davidson Richard L.
Published: May 2006

In an attempt to isolate cells that could survive with total replacement of thymidine by bromodeoxyuridine in nuclear DNA, cells of a bromodeoxyuridine-dependent Syrian hamster line were cultured in medium containing aminopterin and bromodeoxyuridine but no thymidine. A line of cells, called HAB, was isolated. The HAB cells have been maintained in continuous cultivation for over nine months and have undergone more than 125 population doublings. Direct base analysis showed that the level of substitution of bromodeoxyuridine for thymidine in nuclear DNA was at least 99.8%, and possibly 100%. The existence of such cells raises many questions. The expected high frequency of bromodeoxyuridine-induced base transitions, including errors in both replication and transcription, would seem to be incompatible with the apparently stable transmission and expression of the genetic information in these cells.
Stimulation of Extracellular Matrix Synthesis in the Developing Cornea by Glycosaminoglycans
Authors: Meier Stephen , Hay Elizabeth D.
Published: May 2006

Previously, it was demonstrated that the embryonic corneal epithelium produces the chondroitin sulfate and heparan-sulfate-like compounds and the collagen of the primary corneal stroma. Synthesis of all of these extracellular materials is greatly enhanced
in vitro
when isolated epithelium is grown on collagenous substrata instead of Millipore filters. We report here that chondroitin sulfate, heparin, and heparan sulfate added to the culture medium at a concentration of 200 μg/ml enhance the synthesis by the epithelium of chondroitin sulfate and heparan-sulfate-like compounds 2-fold, whether or not collagenous substrata are employed. Collagen synthesis is unaffected by adding glycosaminoglycan to the medium. Chondroitin sulfate proteoglycan (chondromucoprotein) has the same stimulatory effect as chondroitin sulfate, but dermatan sulfate and hyaluronate have no measurable effect on glycosaminoglycan production by epithelial cells. Keratan sulfate however, seems to depress glycosaminoglycan synthesis. Thus, in this system, only sulfated polyanions like those produced by the corneal epithelium have a stimulatory effect on glycosaminoglycan synthesis. The results are discussed in terms of how the tissues of the cornea (epithelium, endothelium, keratocytes) may interact by changing the composition of the stromal extracellular matrix.
Ambient Pyrite in Precambrian Chert: New Evidence and a Theory
Authors: Knoll Andrew H. , Barghoorn Elso S.
Published: May 2006

Ambient pyrites of two distinct types were described from middle Precambrian rocks of the Lake Superior area. A new class of this phenomenon is here described from middle Precambrian chert from western Australia. The newly found ambient pyrites are quite minute and characteristically occur in groups forming a “starburst” pattern. All three types of ambient pyrite may be explained in terms of pressure solution initiated by gas evolution from organic material attached to the pyrite. Thermal degradation of the kerogen produces the gases which, due to the impermeability of the encompassing chert, build up the pressures necessary to initiate solution. Pyrite appendages bear a striking resemblance to micro-organisms and, thus, constitute the smallest pseudofossils known.
Quantitative Affinity Chromatography. Determination of Binding Constants by Elution with Competitive Inhibitors
Authors: Dunn Ben M. , Chaiken Irwin M.
Published: May 2006

The affinity chromatographic separation procedure was tested for its utility in quantitating the affinity of proteins to both insolubilized ligand and corresponding competing soluble ligand. An expression has been derived that (
1
) allows the determination of binding constants for the interaction of a soluble protein species with an affinity chromatography matrix involving active site binding, (
2
) yields binding constants for the interaction of the protein with soluble ligands that can compete with the insoluble matrix for binding to the active site of the protein, and (
3
) utilizes readily obtainable parameters from conventional chromatography. This expression has been applied to the quantitation of the binding of staphylococcal nuclease to thymidine-5′-phosphate-3′-amino-phenylphosphate-Sepharose in competition with thymidine-3′,5′-bisphosphate.
Selective Removal of Histones from Calf-Thymus Nucleohistone with Sodium Dodecylsulfate
Authors: Hayashi Kenshi , Ohba Yoshiki
Published: May 2006

Calf-thymus nucleohistone studied by a newly developed `SDS gradient' centrifugation technique showed that histones dissociate sequentially when treated with increasing concentrations of sodium dodecylsulfate. Histones F2a1 and F2a2 were dissociated first at about 0.03% sodium dodecylsulfate, and F1 was removed lastly by the highest concentration of sodium dodecylsulfate (0.06% or more). A DNA-histone F1 complex, which consisted of DNA and all of the histone F1 and completely lacked other histones, was obtained by sedimenting nucleohistone through 0.05% sodium dodecylsulfate. Results of equilibrium gel filtrations in 0.05% sodium dodecylsulfate revealed that the binding of sodium dodecylsulfate to nucleohistone caused new binding sites to be available for the detergent which presumably was accompanied with dissociation of histones from DNA. This result indicates that no redistribution of histone F1 on DNA should occur in the presence of 0.05% sodium dodecylsulfate.
Expression of Purine Overproduction in a Series of 8-Azaguanine-Resistant Diploid Human Lymphoblast Lines
Authors: Lever Julia E. , Nuki George , Seegmiller J. Edwin
Published: May 2006

For study of the basis of an X-linked form of gout in man, several clonal lines deficient in hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) were selected from the human lymphoblast line WI-L2 by spontaneous and mutagen-induced resistance to 10 μM 8-azaguanine. Three groups could be defined: (
1
) clones with less than 1% of normal enzyme activity, unable to incorporate [
3
H]hypoxanthine detectable by radioautography, unable to tuilize exogenous hypoxanthine as a source of purines, and showing a 2- to 4-fold accelerated rate of production of early intermediates in
de novo
purine biosynthesis; (
2
) clones with 56-63% of normal enzyme activity, decreased incorporation per cell of [
3
H]hypoxanthine measured by radioautography, able to utilize exogenous hypoxanthine, and showing 1.2- to 2.8-fold purine overproduction; (
3
) clones with 10-15% of normal enzyme activity, able to utilize hypoxanthine but not incorporating amounts detectable by radioautography, and showing a 2.3- to 2.5-fold increase in purine biosynthesis. Resistant clones generated by ICR 191 mutagenesis resembled Group 1 clones. Heat inactivation studies in crude extracts from certain clones in Group 2 suggest a structural gene mutation, but no qualitative alteration in enzyme could be detected by starch gel electrophoresis. These phenotypes have persisted over at least 300 generations of nonselective growth, with retention of a diploid karyotype.
Selective Toxicity of Diphtheria Toxin for Malignant Cells
Authors: Iglewski Barbara H. , Rittenberg Marvin B.
Published: May 2006

Purified diphtheria toxin is shown to inhibit protein synthesis in Ehrlich-Lettré ascites carcinoma cells
in vitro
. Protein synthesis in Ehrlich-Lettré cells is at least 10,000 times more sensitive to toxin than protein synthesis in normal mouse spleen or thymus cells. This sensitivity correlates with the observation that Ehrlich-Lettré tumors regress in mice injected with diphtheria toxin but not diphtheria toxoid. Using the criterion of inhibition of protein synthesis
in vitro
, we show that other mouse malignancies (lymphoma and myeloma) are also more sensitive to diphtheria toxin than normal spleen or thymus. Metastatic human breast carcinoma cells from two individuals, cells from two melanoma nodules removed at different times from a third patient, and cells from melanoma nodules from three additional individuals are shown to be more sensitive to diphtheria toxin than some normal human cells. The toxin sensitivity of protein synthesis in some of the malignant cells tested was so much greater than that of normal cells, that we have proposed that diphtheria toxin should be studied further since it might prove a useful anti-cancer agent in patients whose tumors are first shown to be highly sensitive to toxin
in vitro
.
Disturbance, Patch Formation, and Community Structure
Authors: Levin Simon A. , Paine R. T.
Published: May 2006

A model is developed to relate community structure to level of environmental disturbance in systems in which the effects of disturbance are localized in space and time. In general these disturbances create a pattern of spatio-temporal heterogeneity by renewing a limiting resource, thereby permitting utilization by species that are not dominant competitors. The proposed model predicts the frequency distribution of these renewed areas, with regard to size and age (colonization stage). The model thus allows one to relate overall system pattern to the local biology within these areas, to compare various areas with different levels of disturbance, and to predict the effects of new disturbance.
Antibodies to Yeast Phenylalanine Transfer Ribonucleic Acid Are Specific for the Odd Nucleoside Y in the Anticodon Loop
Authors: Fuchs Sara , Aharonov Aharon , Sela Michael , Von Der Haar Friedrich , Cramer Friedrich
Published: May 2006

Antibodies with specificity to a single species of tRNA were elicited in a goat by immunization with a glutaraldehyde conjugate of yeast phenylalanine transfer RNA with bovine gamma globulin. The specificity of the antibodies was studied by a radioimmunoassay measuring the direct binding of [
3
H]tRNA
Phe
or the inhibition of the binding. The antibodies formed are predominantly directed towards the characteristic highly modified nucleoside Y, which is located right next to the anticodon. The antibodies bind specifically to tRNA
Phe
, to oligonucleotides derived by enzymatic digestion from the anticodon loop of tRNA
Phe
, and to the Y nucleoside itself. tRNA species which do not contain Y in their sequences, or tRNA
Phe
from which the Y base has been excised, do not bind to the antibodies. Yeast tRNA
Phe
can be separated from other tRNA species with an immunoadsorbent of antibodies to tRNA
Phe
.
Interference Competition and Niche Theory
Authors: Case Ted J. , Gilpin Michael E.
Published: May 2006

A linear model of interspecific competition with separate parameters for exploitation and interference is deduced. Interference is assumed to have a cost and an effect. The interfering species realizes a “profit” if some resources, which the species interfered against would have utilized, are made available as a result of the interference. Interference is favored when its cost is small, its effect is high, and the resource overlap with the species interfered against is high. Interference is likely to be an alternative strategy to high exploitation efficiency. The incorporation of interference into niche theory clarifies the competitive phenomenon of unstable equilibrium points, excess density compensation on islands, competitive avoidance by escape in time and space, the persistence of the “prudent predator,” and the magnitude of the difference between the size of a species' fundamental niche and its realized niche.
Replication of the
Escherichia coli
Chromosome with a Soluble Enzyme System
Authors: Kornberg Thomas , Lockwood Arthur , Worcel A.
Published: May 2006

Semi-conservative DNA synthesis is observed when the isolated, folded
E. coli
chromosome is supplemented with a DNA-free, soluble enzyme fraction, the four deoxynucleoside 5′-triphosphates, ATP, and Mg
++
. The DNA synthesized
in vitro
remains associated with the folded chromosome during sedimentation through neutral sucrose, but is released as small DNA fragments in alkali. Sealing of these replicative intermediates to the chromosome requires the presence of both
E. coli
DNA polymerase I (EC 2.7.7.7) and DNA ligase (EC 6.5.1.2).
Hemoglobin Grady: The First Example of a Variant with Elongated Chains Due to an Insertion of Residues
Authors: Huisman T. H. J. , Wilson J. B. , Gravely M. , Hubbard M.
Published: May 2006

A black 25-year-old woman and her father have a fast-moving α chain variant in an amount of 8% (the father) and 18% (the daughter). Structural data indicate that this chain has been elongated by the addition of three amino-acid residues to give the sequence: -Pro(114)-Ala(115)-Glu(116)-Phe(117)-Thr(118)-
Glu-Phe-Thr-
Pro(119)-Ala(120)-.The underlying genetic alteration responsible for hemoglobin Grady appears, therefore, to be a tandem duplication of nine base pairs which may have arisen by a process of mismatched intragenic crossing over. Functional and physicochemical properties of the variant are not greatly altered, and hematological data are normal.
Diffusivity of Gases in Liquids
Authors: Hildebrand J. H. , Lamoreaux R. H.
Published: May 2006

Diffusion coefficients of H
2
, Ne, N
2
, Ar, CH
4
, Cl
2
, CF
4
, C
2
H
6
, SF
6
, I
2
, and isotopic CCl
4
, all in CCl
4
, determined at atmospheric pressure, are linear functions of temperature, converging to zero at the temperature where CCl
4
ceases to be fluid. The slopes of these lines increase with decreasing molecular cross-section of the diffusants, and with increasing entropy of expansion of the diffusants in CCl
4
. Diffusivities in (C
4
F
9
)
2
N, whose molecules are very large and three-armed, do not converge as temperature is decreased. Molecules of H
2
, Ne, and, to a lesser extent, Ar, are able to diffuse in (C
4
F
9
)
2
N even at temperatures where fluidity is low.
Packaging and Maturation of DNA of Bacteriophage T7
In Vitro
Authors: Kerr Carol , Sadowski Paul D.
Published: May 2006

We have developed an
in vitro
complementation assay to demonstrate packaging and maturation of DNA of phage T7. Cells of
Escherichia coli
B infected with an appropriate T7 amber mutant are concentrated 200-fold and lysed by freezing and thawing. Two extracts from cells infected with different amber mutants are mixed and incubated at 30°. Positive complementation results in a 100-fold increase in phage titer.

Using this assay we have demonstrated the packaging of phage DNA from an extract that contains no phage heads (gene 9
-
, 10
-
), within head structures present in an extract that contains no phage DNA (gene 5
-
). We have also demonstrated an activity in extracts that contain no phage DNA or heads (gene 5
-
, 9
-
, 10
-
), which complements gene 19
-
-infected cells. We have proven that this activity is due to the gene-19 product by showing that the activity is temperature-sensitive if the extract is made from cells infected with a mutant having a temperature-sensitive mutation in gene 19. This assay should be useful in elucidating the mechanism of packaging and maturation of DNA of phage T7.
Conversation of the Molecular Structure of Yeast Phenylalanine Transfer RNA in Two Crystal Forms
Authors: Klug A. , Robertus J. D. , Ladner J. E. , Brown R. S. , Finch J. T.
Published: May 2006

A comparison is made between the electron density maps of the monoclinic and orthorhombic crystal forms of yeast tRNA
Phe
which have been obtained respectively by ourselves and by another group. It is concluded that the molecular structures are essentially the same in both crystals, although the models derived from the maps are not the same. The relation between the two molecular packings is discussed, and it is suggested that the intermolecular contact in the orthorhombic form which is not present in the monoclinic form, may arise through base pairing of the anticodons of neighboring molecules.
Mitogenic activity of blood components. I. Thrombin and prothrombin.
Authors: Chen L B , Buchanan J M
Published: May 2006

When added to a culture medium of resting confluent chick embryo fibroblasts in the absence of serum, thrombin (EC 3.4.21.5) is able to stimulate DNA synthesis 12 hr later and to cause a substantial increase in cell number over a period of 4 days. As compared to thrombin, prothrombin exhibits low mitogenic activity. However, in the presence of purified Factor Xa (EC 3.4.21.6) and Factor V, prothrombin is converted to thrombin by "thromboplastin activity" supplied by the fibroblasts. Prothrombin, either purified or as a constituent of plasma or serum, may thus be considered to be a reservoir of mitogenic activity in tissue culture unless antithrombin is present in the culture medium in amounts sufficient to neutralize the thrombin formed. By use of a specific inhibitor of proteases, and by separation of prothrombin by absorption on BaSO4, we estimate that the potential mitogenic activity of prothrombin is approximately 30-50% of the total activity that can be obtained by treatment of fibrinogen-free plasma with thromboplastin. In addition to its mitogenic activity, thrombin can also stimulate the migration of cells. These experiments with thrombin illustrate that well-characterized proteases of blood can act as potent mitogens and suggest that they may play a role in the process of wound healing.
A theory of group selection.
Authors: Wilson D S
Published: May 2006

In organisms possessing a dispersal phase the processes of mating, competition, feeding, and predation are often carried out within "trait-groups," defined as populations enclosed in areas smaller than the boundaries of the deme. A simple model shows that this can lead to the selection of "altruistic" traits that favor the fitness of the group over that of the individual. The extent of group selection that occurs depends mainly on the variation in the composition of genotypes between trait-groups. The traditional concepts of group and individual selection are seen as two extremes of a continuum, with systems in nature operating over the interval in between.
Temperature-sensitive mutants of chemically transformed epithelial cells.
Authors: Yamaguchi N , Weinstein I B
Published: May 2006

The first temperature-sensitive mutants of epithelial cells transformed with chemical carcinogens have been isolated. Like the wild-type transformed parental cells, the mutants readily grow in agar suspension at 36 degrees, but in contrast to the wild type, they do not do so at 40 degrees. Detailed studies of one of these mutants, TS-223, indicate that at high temperature it also has reduced cloning efficiency in monolayer culture and a lower saturation density. Scanning electron microscopy revealed that at 40 degrees confluent cultures of TS-223 consist of a monolayer of generally flat polygonal cells, whereas 36 degrees cultures contain many patches of piled-up cells that are spherical and have rougher surface membranes. All of these cellular changes are reversible with upward or downward temperature shifts. The temperature-sensitive lesion appears to reside in a host cell gene which modulates expression of the transformed cell phenotype. These mutants may provide a useful system for elucidating the minimal biochemical changes required for expression of the transformed phenotype in epithelial cells.
Light-stimulated phosphorylation of rhodopsin in the retina: the presence of a protein kinase that is specific for photobleached rhodopsin.
Authors: Weller M , Virmaux N , Mandel P
Published: May 2006

A protein kinase has been extracted from bovine rod outer segments by a mild procedure. The enzyme acts specifically on photobleached, not unbleached, rhodopsin and will not catalyze the phosphorylation of histones, phosvitin, or casein. We propose the name "opsin kinase" for the enzyme, which is not affected by cyclic nucleotides but which is inhibited by theophylline. Preparations of purified rod outer segments, however, appear to contain only low concentration of opsin phosphatase activity.
Point estimates for probability moments
Authors: Rosenblueth Emilio
Published: May 2006

Given a well-behaved real function
Y
of a real random variable
X
and the first two or three moments of
X
, expressions are derived for the moments of
Y
as linear combinations of powers of the point estimates

y(x
+
)

and

y(x
-
)

, where
x
+
and
x
-
are specific values of
X
. Higher-order approximations and approximations for discontinuous
Y
using more point estimates are also given. Second-moment approximations are generalized to the case when
Y
is a function of several variables.
Partial knowledge, entropy, and estimation
Authors: MacQueen James , Marschak Jacob
Published: May 2006

In a growing body of literature, available partial knowledge is used to estimate the prior probability distribution
p
≡(
p
1
,...,

p
n

) by maximizing entropy
H
(
p
)≡-Σ

p
i

log

p
i

, subject to constraints on
p
which express that partial knowledge. The method has been applied to distributions of income, of traffic, of stock-price changes, and of types of brand-article purchases. We shall respond to two justifications given for the method:

(α) It is “conservative,” and therefore good, to
maximize “uncertainty,”
as (uniquely) represented by the entropy parameter.

(β) One should apply the mathematics of statistical thermodynamics, which implies that
the most probable distribution
has highest entropy.

Reason (α) is rejected. Reason (β) is valid when “complete ignorance” is defined in a particular way and both the constraint and the estimator's loss function are of certain kinds.
Major nonhistone proteins of rat liver chromatin: preliminary identification of myosin, actin, tubulin, and tropomyosin.
Authors: Douvas A S , Harrington C A , Bonner J
Published: May 2006

Two major nonhistone polypeptides from rat liver chromatin have been identified as myosin and actin. Preliminary observations indicate that three other chromatin polypeptides of molecular weights 50,000, 34,000, and 32,000 are tubulin and heavy and light tropomyosin, respectively. A sixth component of molecular weight 65,000 which has been purified and electrophoreses as a single band on sodium dodecyl sulfate-polyacrylamide gels may be composed in part of protease-digested myosin. These six polypeptides together account for as much as 38% of the nonhistone protein mass of chromatin in this tissue.
Methylation of a membrane protein involved in bacterial chemotaxis.
Authors: Kort E N , Goy M F , Larsen S H , Adler J
Published: May 2006

A protein methylation reaction involved in chemotaxis of Escherichia coli has been identified. The involvement of this reaction in chemotaxis in indicated by four lines of evidence. (a) The methylation reaction is altered in several classes of generally nonchemotactic mutants and is coreverted with the chemotaxis defects. (b) The methylation level of the protein is affected by chemotactic stimuli. (c) The transferred methyl group is derived from methionine and is labile, in accord with the known fact that chemotaxis requires a continuous supply of methionine. (d) Methylation is abnormal in various mutants having defective or missing flagella.
The turning wheel: a study in steady states.
Authors: Wyman J
Published: May 2006

Subject to the limitation of one-step transitions, a system composed of a polyfunctional macromolecule (say a polyfunctional enzyme), present in fixed amount together with its ligands (substrates) in a fixed volume, can be represented by an r-dimensional cube of which each of the 2r corners corresponds to one of the microscopically different forms. In the steady state we may predict circulation of the macromolecule around the edges of the cube. This would provide a molecular mechanism whereby one enzymatic reaction could drive another, the enzyme itself acting as a transducer. Such a system is asymptotically stable and subject to a set of linkage relations derivable by the cofactor principle from the steady state equations.
Infection of preimplantation mouse embryos and of newborn mice with leukemia virus: tissue distribution of viral DNA and RNA and leukemogenesis in the adult animal.
Authors: Jaenisch R , Fan H , Croker B
Published: May 2006

Explanted mouse embryos derived from low leukemia incidence strains were infected with Moloney murine leukemia virus (M-MuLV) at the 4-8 cell stage of development. After cultivation in vitro to the blastocyst stage, the embryos were surgically transferred to the uteri of pseudo-pregnant surrogate mothers. Of 15 animals born, one developed a leukemia at 8 weeks of age. When autopsied, this leukemia was found to be of the lymphatic type, as is typical for the M-MuLV-induced disease. In addition, infectious M-MuLV virus was isolated from the serum. Molecular hybridization tests for the presence of M-MuLV-specific sequences were conducted on DNA and RNA extracted from eight different organs. The DNA-DNA reannealing experiments revealed the presence of two classes of M-MuLV-specific sequences in equal concentrations in all tissues tested. The less abundant class of M-MuLV-specific sequences was not detected in tissues from uninfected animals or in non-target tissues of leukemic animals infected at birth. The results are consistent with the working hypothesis that the virus was integrated in all cells of the animal, possibly including the germ line. Fifty to 100 times more M-MuLV-specific RNA was detected in tumor tissues than was found in non-target organs such as liver, brain, and testes. Since all organs contained the same amount of virus-specific DNA, these results indicate that the M-MuLV-specific DNA can be differentially expressed in different tissues.
Restoration of ultraviolet-induced unscheduled DNA synthesis of xeroderma pigmentosum cells by the concomitant treatment with bacteriophage T4 endonuclease V and HVJ (Sendai virus).
Authors: Tanaka K , Sekiguchi M , Okada Y
Published: May 2006

Ultraviolet (UV)-induced unscheduled DNA synthesis of xeroderma pigmentosum cells, belonging to complementation groups A, B, C, D, and E, was restored to the normal level by concomitant treatment of the cells with T4 endonuclease V and UV-inactivated HVJ (Sendai virus). The present results suggest that (1) T4 endonuclease molecules were inserted effectively into the cells by the interaction of HVJ with the cell membranes, (2) the enzyme was functional on human chromosomal DNA which had been damaged by UV irradiation in the viable cells, (3) all the studied groups of xeroderma pigmentosum ("variant" was not tested) were defective in the first step (incision) of excision repair.
Protection of lethally irradiated mice with allogeneic fetal liver cells: influence of irradiation dose on immunologic reconstitution.
Authors: Tulunay O , Good R A , Yunis E J
Published: May 2006

After lethal irradiation long-lived, immunologically vigorous C3Hf mice were produced by treatment with syngeneic fetal liver cells or syngeneic newborn or adult spleen cells. Treatment of lethally irradiated mice with syngeneic or allogeneic newborn thymus cells or allogeneic newborn or adult spleen cells regularly led to fatal secondary disease or graft-versus-host reactions. Treatment of the lethally irradiated mice with fetal liver cells regularly yielded long-lived, immunologically vigorous chimeras. The introduction of the fetal liver cells into the irradiated mice appeared to be followed by development of immunological tolerance of the donor cells. The findings suggest that T-cells at an early stage of differentiation are more susceptible to tolerance induction than are T-lymphocytes at later stages of differentiation. These investigations turned up a perplexing paradox which suggests that high doses of irradiation may injure the thymic stroma, rendering it less capable of supporting certain T-cell populations in the peripheral lymphoid tissue. Alternatively, the higher and not the lower dose of irradiation may have eliminated a host cell not readily derived from fetal liver precursors which represents an important helper cell in certain cell-mediated immune functions, e.g., graft-versus-host reactions, but which is not important in others, e.g., allograft rejections. The higher dose of lethal irradiation did not permit development or maintenance of a population of spleen cells that could initiate graft-versus-host reactions but did permit the development of a population of donor cells capable of achieving vigorous allograft rejection. These observations contribute to understanding of some of the persisting immunodeficiencies that are observed in man after fatal irradiation and bone marrow transplantation. These results should suggest better approaches to more effective cellular engineering for correction of immunodeficiency diseases and for treatment of immunodeficiency diseases and of leukemias and malignancies of man.
Presence of norepinephrine and related enzymes in isolated brain microvessels.
Authors: Lai F M , Udenfriend S , Spector S
Published: May 2006

Norepinephrine and the enzymes involved in its synthesis and degradation were found to be associated with isolated brain microvessels. The significance of these results are discussed with respect to adrenergic innervation of the cerebral microvessels and thereby neural regulation of the cerebral microcirculation.
The effect of nerve growth factor on cycle AMP levels in superior cerival ganglia of the rat.
Authors: Nikodijevic B , Nikodijevic O , Yu M Y , Pollard H , Guroff G
Published: May 2006

Nerve growth factor (NGF) produces a several-fold increase in the cyclic AMP concentration in rat superior cervical ganglia in organ culture within 5 min. An increase can be seen with as little as 40 ng/ml of NGF. Oxidized NGF is without effect. The increase in the cAMP concentration produced by NGF is prevented by the addition of antiserum to NGF.
Separation of lymphocyte chromatin into template-active fractions with specificity for eukaryotic RNA polymerase II or prokaryotic RNA polymerase.
Authors: Magee B B , Paoletti J , Magee P T
Published: May 2006

When chromatin prepared from WI-L2 lymphocytes by low salt extraction and shearing is centrifuged on a glycerol gradient, one area of the gradient yields chromatin enriched in template activity for Escherichia coli DNA-dependent RNA polymerase (EC 2.7.7.6; nucleosidetriphosphate:RNA nucleotidyltransferase) as compared to Saccharomyces cerevisiae RNA polymerase II (or B). Another area yields chromatin preferred by the eukaryotic enzyme. Kinetic studies indicate that the differences in activity cannot be explained by differences in affinity of the enzymes for the various templates. The DNA isolated from either fraction has a molecular weight of 8.5 X 106. The "yeast active" fraction seems enriched in proteins. Mixing experiments indicate that the yeast enzyme does not alter the template in such a way as to improve it for the bacterial enzyme.
Determination of the number of superhelical turns in simian virus 40 DNA by gel electrophoresis.
Authors: Keller W
Published: May 2006

Closed-circular, superhelical DNA from simian virus 40 (SV40 DNA I) was treated with an excess of DNA-relaxing enzyme in the presence of increasing amounts of ethidium bromide (EtdBr). After removal of the ethidium, each sample consisted of a group of close-circular DNA molecules differing in their number of superhelical turns (tau) around a mean value of tau in a Gaussian-like distribution. The DNA samples were analyzed by electrophoresis in agarose gels under conditions where the electrophoretic mobility was a function of the number of superhelical turns. Since the distributions around tau of DNA molecules of different samples overlappped, the difference in the mean number of superhelical turns from sample to sample, delta tau, could be determined and used to measure the mean number (tau) for native SV40 DNA I. By this criterion, SV40 DNA I contains a Gaussian-like distribution of molecules differing by integral numbers around a mean value of tau = -24 +/- 2 at 37 degree C [in 0.2 M NaC1, 10 mM Tris-HC1 (pH 7.9), and 0.2 mM EDTA]. The heterogeneity in tau is probably a consequence of thermal fluctuations in the DNA helix at the time when the last phospholiester bond is closed in vivo. When correlated to the buoyant shift of completely relaxed SV40 DNA in a CsC1-propidium diiodide gradient, the number of delta tau = 24 +/- 2 of superhelical versus relaxed DNA implies an unwinding of the DNA helix by 26-28 degree upon intercalation of one molecule of EtdBr.
Signal input for a chemotactic response in the cellular slime mold Dictyostelium discoideum.
Authors: Mato J M , Losada A , Nanjundiah V , Konijn T M
Published: May 2006

Drops with different concentrations of 3':5'-cyclic AMP were deposited at various distances from small populations of Dictyostelium discoideum amoebae, and the distances over which 50% of the amoebae drops reacted positively were determined. The linear regression analysis of a bouble logarithmic plot of distance against concentration gives a straight line with a slope of 1/4.25, which value suggests that the amoebae respond to a spatial gradient of cyclic AMP concentration. The threshold value for the signal is 3.6 X 10(-9) M/mm with a sensitivity of measurement of about 1%. These findings are discussed in relation to our present knowledge of cyclic AMP receptors.
Similarities among hypervariable segments of immunoglobulin chains.
Authors: Wu T T , Kabat E A , Bilofsky H
Published: May 2006

A human lambdaV (Mcg) and a human lambdaII (Vil) myeloma protein have identical sequences in their first hypervariable segments although they differ at 21 positions throughout the variable region. If a different structural gene is responsible for each subgroup, the findings favor insertion of information for the hypervariable or complementarity-determining segments.
Mutation and childhood cancer: a probabilistic model for the incidence of retinoblastoma.
Authors: Knudson A G , Hethcote H W , Brown B W
Published: May 2006

The incidences of some childhood cancers have been shown to fit a two-mutation hypothesis for cancer initiation. According to this hypothesis, the first mutation can be either germinal or somatic while the second is always somatic. A probabilistic model involving the mean number of tumors per genetically susceptible individual is developed as a function of age and is compared with age incidence data for retinoblastoma. The change in the mean number of tumors with time is interpreted in terms of the growth of retinal cells. In patients who are not genetically susceptible, the times of occurrence of the first and second somatic mutations can be inferred from a comparison of familial and non-familial unilateral case incidences. The total incidences of hereditary and nonhereditary forms of retinoblastoma are related to germinal and somatic mutation rates. The even distribution of certain childhood cancers throughout the world suggests that their incidences are determined by spontaneous mutation rates rather than by local environmental mutagenic carcinogens.
A new complement function: solubilization of antigen-antibody aggregates.
Authors: Miller G W , Nussenzweig V
Published: May 2006

Antigen-antibody aggregates are solubilized when incubated with fresh serum at 37 degrees, yielding immune-complexes of relatively small molecular weight which contain antigen, antibody, and complement (C3)determinants. Solubilization is complement-dependent,requires free Mg++ but not Ca++, and proceeds in sera from C4- or C5-deficient animals. It is accelerated in the presence of Ca++ in normal or C4-deficient guinea pig serum, suggesting involvement of the Cl-bypass activation of the properdin system. Immune precipitates can also be solubilized by monovalent fragments (Fab) of antibodies directed against determinants of the antibody molecules included in the antigen-antibody lattice. Similarly, it is suggested that complement-mediated solubilization might be induced by the combination of a complement fragment with the antibody in the immune-aggregate.
N-formylmethionyl peptides as chemoattractants for leucocytes.
Authors: Schiffmann E , Corcoran B A , Wahl S M
Published: May 2006

Leucocytes such as neutrophils are attracted by N-formylmethionine, but not by methionine. Di- and tripeptides containing formylmethionine are strong attractants for both neutrophils and macrophages, whereas the corresponding nonacylated compounds are not chemotactic. The formylated peptides may be related to an incompletely characterized chemotactic material normally produced by bacteria which attract the same animal cells.
Interaction of a spin-labeled long chain acylcholine with the cholinergic receptor protein in its membrane environment.
Authors: Brisson A D , Scandella C J , Bienvenüe A , Devaux P F , Cohen J B , Changeux J P
Published: May 2006

The choline ester of a spin-labeled fatty acid, 8-doxylpalmitocylcholine, CH3--(CH2)7--CR-(CH2)6-- + COO--(CH2)2--N(CH3)3, where R is the paramagnetic 4',4'-dimethyloxazolidine-N-oxyl (doxyl) ring has been synthesized. 8-Doxylpalmitoylcholine blocks reversibly the depolarization of Electrophorus electroplaque elicited by the bath application of carbamylcholine. It slows down the initial rate of binding of the alpha-[3-H]toxin from Naja nigricollis to receptor-rich membranes fragments from Torpedo, and it displaces [3-H]acetylcholine bound to the cholinergic receptor site present in these fragments. Electron spin resonance spectra of 8-doxylpalmitoylcholine in the presence of the receptor-rich membrane fragments show complete immobilization of the spin label. Various cholinergic agents tested, including N. nigricollis alpha-toxin, reverse this immobilization, probably by displacing the 8-doxylpalmitoylcholine from its complex with the cholinergic receptor protein to the lipid phase of the membrane.
Thymus-derived rat lymphocyte receptor for cell surface antigens is a nonserologically defined product of the major histocompatibility gene complex.
Authors: Wekerle H , Eshhar Z , Lonai P , Feldman M
Published: May 2006

Recognition of cell surface antigens by nonsensitized thymus-derived rat lymphocytes is not affected by antisera against immunoglobulin, yet can be effectively blocked by treatment of the lymphocytes with alloantisera raised against lymphoid cells. However, allo antisera induced by nonlymphoid cells do not inhibit recognition. Adsorption of blocking antisera on immunoglobulin-Sepharose columns does not decrease their blocking activity. Absorption of blocking alloantisera with liver and kidney homogenates removes the cytotoxic alloantibodies, yet does not affect the capacity of the antisera to block recognition. Anti-H1-1 alloantisera block antigen recognition only of lymphocytes of strains that share the H1-1 locus. These results suggest that the constant part of the thymus-derived lymphocyte receptor for cell-surface antigens is a product of the rat major histocompatibility locus, which is not identical with the serologically defined antigens.
Release of discrete subunits after nuclease and trypsin digestion of chromatin.
Authors: Weintraub H
Published: May 2006

Digestion of chromatin with DNase (nucleate 3'-oligonucleotidohydrolase, EC 3.1.4.7) releases 11-12S nucleoprotein particles. After extensive nuclease digestion, the DNA in these particles consists of a collection of eight discrete DNA fragments. When these nuclease-particles are treated with trypsin (EC 3.4.21.4), only 20 to 30 amino-acid residues are cleaved from histone N-terminals, the histone C-terminal segments being resistant. The resulting 5S nucleoprotein particles have now been shown on acrylamide gels to consist of a series of eight discrete DNA-containing bands. Four of these bands contain C-terminal cleavage fragments from four histones (III, IV, IIb2, and IIb1) tightly bound to them; a fifth contains fragments from only histones III and IV. The remaining three bands contain only DNA. Since these protein-free DNA bands were resistant to nuclease prior to trypsin treatment, they were presumably associated with histone N-terminal segments in the native structure. Trypsin, therefore, appears to split nuclease-particles, releasing two subfractions of DNA--one associated with protein, the other not. The data is compatible with a model in which the majority of DNA in the eukaryotic nucleus is folded into hairpin loops of double-stranded helix, each created by the concerted cross-linking action of 6 to 10 histones which interact to form a trypsin-resistant complex composed, for the most part, of all four major histones. These loops may further fold upon themselves to form the "nu" bodies that have been visualized by electron microscopy.
Cell cycle studies of mononucleate and cytochalasin-B--nduced binucleate fibroblasts.
Authors: Fournier R E , Pardee A B
Published: May 2006

The progress of mononucleate and cytochalasin-B-induced binucleate cells through the G1 period of the growth cycle has been studied. DNA synthesis was initiated in synchrony in both of the nuclei of cells rendered binucleate by a brief pulse of cytochalasin B. Furthermore, populations of these cells traversed the G1 period significantly faster than their mononucleate counterparts. That this effect was due to the presence of two nuclei in a common cytoplasm and not to the increased size of binucleate cells was suggested by studies of cells with altered nucleocytoplasmic ratios. No correlation was observed between protein content per cell and the rate of progress through G1. Evidence for the existence of nuclear-nuclear cooperation that results in a shortening of the G1 period is discussed.