bluuebunny/crossref_metadata_2025 huggingface dataset:
The Mechanism of Photoaffinity Labeling
Authors: Ruoho Arnold E. , Kiefer Hansruedi , Roeder Phoebe E. , Singer S. J.
Published: May 2006

Photoaffinity labeling is a recently introduced method for covalently binding chemical tags to the active sites of protein molecules, which is potentially capable of very great specificities of labeling. A labeling reagent is used that is converted by photolysis to an extremely reactive intermediate. According to the expected mechanism, the reagent molecules that are specifically and reversibly bound to the active site at the instant of photolysis react irreversibly in the site before they can dissociate from the site. In two such reagent-protein systems studied in this paper, however, it is shown that, while by the usual criteria photoaffinity labeling appears to have occurred, the expected mechanism in fact does not hold. This was discovered in experiments with scavengers present in the mixtures that were photolyzed. The general properties of, and criteria for, photoaffinity labeling reactions are discussed in the light of these findings.
Inhibition of Transcription of the Histidine Operon
In Vitro
by the First Enzyme of the Histidine Pathway
Authors: Blasi Francesco , Bruni Carmelo B. , Avitabile Alessandra , Deeley Roger G. , Goldberger Robert F. , Meyers Marilyn M.
Published: May 2006

An
in vitro
system was developed for transcription of the histidine operon of
Esherichia coli
carried in the genome of a defective ϕ80 transducing phage. The messenger RNA (mRNA) of the histidine operon synthesized in the
in vitro
system was detected by hybridization to single strands of both ϕ80 and ϕ80d
his
DNA, and by competition of this hybridization with unlabeled histidine mRNA that had been synthesized
in vivo
(RNA extracted from cells in which the histidine operon had been derepressed). Under the conditions used, RNA complementary to the histidine operon was about 15% of the total RNA that was synthesized
in vitro
from the ϕ80d
his
DNA template. The RNA complementary to the histidine operon was synthesized on the “sense” strand (the R strand) of ϕ80d
his
in the form of a polycistronic message with a sedimentation coefficient (about 38 S) very close to that observed for the histidine mRNA synthesized
in vivo
. Synthesis of the histidine operon RNA appears to be subject to control
in vitro
. Addition of the first enzyme of the pathway for histidine biosynthesis blocked transcription of the histidine operon specifically, strongly suggesting that this enzyme acts as a regulatory protein for the histidine operon.
Indirect Ultraviolet-Reactivation of Phage λ
Authors: George Jacqueline , Devoret Raymond , Radman Miroslav
Published: May 2006

When an F
-
recipient
Escherichia coli
K12 bacterium receives Hfr or F-
lac
+
DNA from an ultraviolet-irradiated donor, its capacity to promote DNA repair and mutagenesis of ultraviolet-damaged phage λ is substantially increased.

We call this phenomenon indirect ultraviolet-reactivation, since its features are essentially the same as those of ultraviolet-reactivation; this repair process occurs in pyrimidine dimer excision-deficient strains and produces clear plaque mutations of the restored phage. Moreover, this process is similar to indirect ultraviolet-induction of prophage λ, since it is promoted by conjugation. However, contrarily to indirect induction, it is produced by Hfr donors and occurs in recipients restricting the incoming ultraviolet-damaged donor DNA.

The occurrence of indirect ultraviolet-reactivation provides evidence for the existence in
E. coli
of an inducible error-prone mechanism for the repair of DNA.
The Thermodynamic Stability Theory of Non-Equilibrium States
Authors: Glansdorff P. , Nicolis G. , Prigogine I.
Published: May 2006

The paper by J. Keizer and R. F. Fox entitled “Qualms Regarding the Range of Validity of the Glansdorff-Prigogine Criterion for Stability of Non-Equilibrium States” [(1974)
Proc. Nat. Acad. Sci. USA
71, 192-196.] is shown to be based on a misunderstanding of the work of the Brussels group. In order to avoid further confusion, we summarize the formulation of the stability criterion in accordance with our published work. The differences with the presentation by Keizer and Fox are pointed out and it is shown that, when correctly applied, our approach does not lead to any contradiction with other methods available for studying stability.
Giemsa C-Banding and the Evolution of Wheat
Authors: Gill Bikram S. , Kimber Gordon
Published: May 2006

The somatic chromosomes of common wheat,
Triticum aestivum
L. (2
n
= 6x = 42), and those of two of its diploid progenitors and
T. speltoides
, have been individually identified by a Giemsa staining technique. In wheat, telocentric chromosomes were used to aid the recognition of individual chromosomes, and an ideogram has been constructed depicting the C-band positions. There is no similarity in the C-banding of chromosomes within a homoeologous group, with the possible exception of group 5. Comparisons of the C-banding of the diploid species
T. monococcum, T. speltoides
, and
T. tauschii
with that of the A, B, and D genomes, respectively, in hexaploid wheat corroborate that
T. speltoides
could not be the donor of the B genome to wheat and that
T. monococcum
and
T. tauschii
are the probable donors of the A and D genomes, respectively.
Tyrosine Hydroxylase: Activation by Nerve Stimulation
Authors: Morgenroth Victor H. , Boadle-Biber Margaret , Roth Robert H.
Published: May 2006

The synthesis of the sympathetic neurotransmitter, norepinephrine, is accelerated by electrical stimulation of the guinea pig vas deferens. The molecular mechanism responsible for this enhanced formation of transmitter is unknown but has been attributed to an increase in the activity of tyrosine hydroxylase (EC 1.14.16.2; tyrosine 3-monooxygenase) during nerve stimulation. In the present experiments, we found that crude preparations of tyrosine hydroxylase isolated from guinea pig vasa deferentia that were electrically stimulated or depolarized by potassium show an increase in activity compared with enzyme obtained from untreated paired control tissues. This increase in activity is partially antagonized by addition of the Ca
++
chelator, ethylene glycol bis(β-aminoethyl ether)-
N,N
′-tetraacetic acid (EGTA), to the assay medium, and can be completely blocked if Ca
++
is removed from the potassium-rich medium used to depolarize the intact tissue, before preparation of the enzyme. A similar increase in enzyme activity occurs when Ca
++
ions are added directly to enzyme prepared from untreated vasa deferentia. In this instance, the activation is completely reversed by EGTA. The increase in activity produced by addition of Ca
++
to the isolated enzyme or by electrical stimulation or potassium depolarization of the tissue before isolation of the enzyme appears to be mediated by changes in the kinetic properties of tyrosine hydroxylase. All treatments appear to activate tyrosine hydroxylase by causing an increase in its affinity for substrate and pteridine cofactor and by decreasing its affinity for the end-product inhibitor, norepinephrine. These results provide direct evidence that the enhanced formation of norepinephrine seen during stimulation of sympathetically innervated tissues arises from an activation of tyrosine hydroxylase. The fact that the activation produced by nerve stimulation is mimicked by Ca
++
ions raises the intriguing possibility that the influx or mobilization of Ca
++
that accompanies nerve stimulation and that is intimately involved in release of transmitter may also participate in the activation of tyrosine hydroxylase.
The Linkage Between Oxygenation and Subunit Dissociation in Human Hemoglobin
Authors: Ackers Gary K. , Halvorson Herbert R.
Published: May 2006

The use of subunit dissociation as a means of probing intersubunit contact energy changes which accompany cooperative ligand binding has been studied for the case of human hemoglobin. An analysis is presented delineating the information that can be obtained from the linkage relationships between ligand binding and subunit dissociation of hemoglobin tetramers into dimers. The analysis defines (
a
) the variation of the saturation function,
Ȳ
, with total protein concentration, (
b
) the variation of the subunit dissociation constant

x
K

2
with ligand concentration (
X
) and (
c
) the correlations between changes in dimer-dimer contact energy and the sequential ligand binding steps. Sensitivity of the linkage function has been explored by numerical simulation. It is shown that subunit dissociation may appreciably affect oxygenation curves under usual conditions of measurement and that relying solely on either

x
K

2
or
Ȳ
may lead to incorrect picutres of the energetics, whereas the combination defines the system much more exactly.
Biological Membranes as Bilayer Couples. A Molecular Mechanism of Drug-Erythrocyte Interactions
Authors: Sheetz Michael P. , Singer S. J.
Published: May 2006

We propose that membranes whose proteins and polar lipids are distributed asymmetrically in the two halves of the membrane bilayer can act as bilayer couples, i.e., the two halves can respond differently to a perturbation. This hypothesis is applied to the interactions of amphipathic drugs with human erythrocytes. It is proposed that anionic drugs intercalate mainly into the lipid in the exterior half of the bilayer, expand that layer relative to the cytoplasmic half, and thereby induce the cell to crenate, while permeable cationic drugs do the opposite and cause the cell to form cup-shapes. This differential distribution of the drugs is attributed to interactions with the phosphatidylserine that is concentrated in the cytoplasmic half of the membrane. Impermeable amphipathic drugs intercalate only into the exterior half of the bilayer, and therefore are crenators of the intact cell. Several predictions of this hypothesis have been confirmed experimentally with erythrocytes and erythrocyte ghosts. The bilayer couple hypothesis may contribute to the explanation of many membrane-mediated phenomena in cell biology.
Atmospheric Corrosion
Authors: Eyring Henry , Robertson Blake , Chu Chih Chien , Andersen Terrell
Published: May 2006

A model of electrolytic corrosion is developed. It is shown that electrically conducting channels threading through the oxide layer and connecting anodic and cathodic areas, obey the equation for a reactant being catalyzed by its product. The resulting autocatalytic equation is compared with available experimental data and found to be widely applicable and capable of unifying many experimental observations.
Differential Interaction of Cholesterol with Phosphatidylcholine on the Inner and Outer Surfaces of Lipid Bilayer Vesicles
Authors: Huang Ching-Hsien , Sipe James P. , Chow S. T. , Martin R. Bruce
Published: May 2006

The separate identification of the -N
+
-(CH
3
)
3
groups located on the outside and inside of phospholipid bilayers observed in proton magnetic resonance spectroscopy upon addition of low concentrations of praseodymium ion was exploited to investigate the effects of incorporated cholesterol. Only about 7% of the phosphate groups on the outside of the bilayer belong to a class of strong binding or shifting sites. Upon addition of up to about 30% cholesterol to egg lecithin bilayers, no changes in chemical shift or ratio of areas of peaks due to outer and inner -N
+
(CH
3
)
3
groups appear. At about 30% incorporated cholesterol, an abrupt decrease occurs in the chemical-shift difference between -N
+
(CH
3
)
3
groups located on the outer and inner bilayer surfaces, and an abrupt increase occurs in the ratio of the areas of the two peaks. For L-α-dipalmitoyl lecithin bilayers, an abrupt change in chemical-shift difference occurring between 10 and 20% cholesterol is not accompanied by a change in the relative number of -N
+
(CH
3
)
3
groups located on the outer and inner surfaces. These results are interpreted as due to the homogeneous distribution of up to 30% cholesterol in egg lecithin bilayers. Above 30%, cholesterol is asymmetrically distributed in favor of the inner layer. In egg lecithin with a variety of polyunsaturated side chains, the side chains with the greater number of double bonds are preferentially displaced by high concentrations of cholesterol, which accounts for the increase in the ratio of outer to inner -N
+
(CH
3
)
3
groups. Such preferential displacement by cholesterol cannot occur with the saturated L-α-dipalmitoyl lecithin. It is suggested that modified phospholipid vesicles of low radii of curvature may provide high concentrations of “active sites” present in membranes.
Comparison of Weigert Stained Sections with Unfixed, Unstained Sections for Study of Myelin Sheaths
Authors: Richter Curt P. , Warner Carolyn L.
Published: May 2006

Myelinated fibers can be demonstrated in thin unstained brain sections of freshly killed uninjected animals. With this method myelinated fibers stand out as clearly as in stained Weigert sections from formalin-fixed brains. Unstained unfixed sections can be viewed under ordinary light within minutes after death of the animal and immediately photographed for permanent records. Such sections have value for neuroanatomical studies, and for rapid localization of various types of experimental lesions.
Were Workers of Eusocial Hymenoptera Initially Altruistic or Oppressed?
Authors: Michener Charles D. , Brothers Denis J.
Published: May 2006

Studies of a primitively eusocial halictid bee,
Lasioglossum zephyrum
, strongly suggest that a major factor in originating a worker caste is selection at the individual level for queens that control associated adult females. Even in this scarcely social form, the queen inhibits other adult females from becoming queens, perhaps by her high level of activity and frequent nudging in the nest. Queens are behaviorally less varied than workers and show specialization, particularly in frequency of nudging (which is concentrated on the worker with largest ovaries) and of backing. Backing draws workers, especially those with slender ovaries, down to lower parts of the burrows where the stimuli for cell construction and provisioning probably operate. Eating of worker-laid eggs by queens was also noted. In spite of the suggestion that queens have evolved to control their workers rather than that workers have evolved to help their queens, both may well have occurred, for these processes are not mutually exclusive; moreover, social attributes mutually beneficial to both castes no doubt have arisen.
Carotenoid Transformations in the Chloroplast Envelope
Authors: Jeffrey S. W. , Douce Roland , Benson A. A.
Published: May 2006

The envelope of the spinach chloroplast is a yellow membrane system with a unique carotenoid composition. Envelopes prepared from dark-treated leaves had a violaxanthin content up to 3.5 times the lutein plus zeaxanthin content, whereas in chloroplast envelopes from illuminated leaves this ratio was only 0.75. Light-catalyzed changes in violaxanthin content also occurred in the thylakoid fraction.

The role of this reversible light-catalyzed de-epoxidation of violaxanthin in the function of the envelope of the chloroplast is discussed.
Unequal Mitotic Sister Chromatid Exchange as the Mechanism of Ribosomal RNA Gene Magnification
Authors: Tartof Kenneth D.
Published: May 2006

It is hypothesized that magnification of the gene coding for ribosomal RNA occurs by unequal mitotic sister chromatid exchange on the basis of five different lines of evidence. These are: (
1
) rDNA magnification occurs in mitotically active germ cells; (
2
) decreases in rDNA redundancy can be genetically produced, a phenomenon termed
reduction
; (
3
) magnification and reduction events are reversible and reciprocal; (
4
) it is possible to generate
bb
+
and
bb
somatic bristle mosaics (
bb
mutants are partially deficient for rRNA genes); and (
5
) magnification of
bb
in a ring X chromosome is reduced. Implications of these results and the unequal sister exchange (USE) hypothesis are discussed.
Genetic Control of Imaginal Disc Development in
Drosophila
Authors: Shearn Allen , Garen Alan
Published: May 2006

Many of the functions required for formation of the imaginal discs of
Drosophila melanogaster
larvae, from which adult structures are derived, are disc-specific and not required for formation of other larval tissues. Mutants blocked in disc-specific functions can produce mature viable larvae, indicating that larval development is not dependent on concomitant disc development. Some of the mutant larvae have no detectable discs (
discless
mutants), and other have small discs that cannot differentiate into adult structures (
small disc
mutants). From the results of genetic complementation and mapping experiments with such mutants, it was estimated that the genome of
D. melanogaster
contains around a thousand complementation groups, or about a fifth of all complementation groups in the genome, that are essential specifically for the development of all the discs. The developmental defects in some of the disc mutants appear to involve autonomous functions of the imaginal cells, and in other mutants functions provided by the larval environment to support disc development. This distinction was made on the basis of two functional tests. The purpose of one of the tests was to detect the presence in young embryos of determined imaginal cells capable of differentiating after transplantation to a wild-type host; the other test measured the capacity of early third-instar larvae to act as hosts for the further development of immature discs transplanted from a wild-type donor. Three
discless
mutants that were tested in this way appeared to be defective in autonomous functions of the imaginal cells, since the embryos contained no imaginal cells that could be detected in the first test, whereas the larvae, although devoid of discs, showed a normal capacity to support disc development in the second test. One of the
small disc
mutants tested was defective in a larval rather than an imaginal cell function, since the embryos had a normal complement of functional imaginal cells, whereas the larvae were incapable of supporting disc development. Thus, both types of disc-specific functions are essential for normal disc development.
D-Lactate Dehydrogenase Binding in
Escherichia coli dld
-
Membrane Vesicles Reconstituted for Active Transport
Authors: Short Steven A. , Kaback H. Ronald , Kohn Leonard D.
Published: May 2006

When membrane vesicles prepared from a D-lactate dehydrogenase mutant of
E. coli
ML 308-225 are treated with a homogeneous preparation of D-lactate dehydrogenase, the enzyme binds to the vesicles and they regain the capacity to catalyze D-lactate oxidation and D-lactate-dependent active transport. Although membranebound enzyme increases linearly with addition of increasing quantities of enzyme, reconstituted transport activity and D-lactate oxidation are saturable functions of the amount of enzyme bound. The maximal specific transport activity obtained in the reconstituted system is similar in magnitude to that of wild type vesicles. Titration studies with 2-(
N
-dansyl)-aminoethyl-β-D-thiogalactoside demonstrate that there is at least a 7- to 8-fold excess of
lac
carrier protein relative to D-lactate dehydrogenase. Hydroxybutynoate-inactivated enzyme does not bind to the vesicles, indicating that the coenzyme moiety is critically involved in binding. Conformational changes are also apparently involved since 0.6 M guanidine·HCl is required for optimal binding and reconstitution. The relative unreactivity of reconstituted vesicles towards vinylglycolic acid suggests that D-lactate dehydrogenase is bound to the outer surface of the reconstituted vesicles.
Agglutination of Jelly Coat and Cortical Granule Components and the Block to Polyspermy in the Amphibian
Xenopus laevis
Authors: Wyrick Ron E. , Nishihara Tatsuro , Hedrick Jerry L.
Published: May 2006

A block to polyspermy in amphibians is established at fertilization by the conversion of the vitelline envelope to the fertilization envelope. In
Xenopus laevis
a major ultrastructural change in the envelope at fertilization is the appearance of an electron-dense layer, termed the F layer, between the envelope and the inner-most jelly coat layer, J
1
. The F layer is derived, at least in part, from materials released from the cortical granules. Further definition of the origin and chemical nature of the F layer was sought by using isolated cortical granule (CG) exudate and jelly coat layer J
1
. In double diffusion experiments, the isolated components interacted in an agglutination reaction producing a band of precipitation. The agglutination involved α-galactoside residues and metal ions (Ca
++
). Employing chemically modified jelly, we demonstrated that sulfhydryl-disulfide interchanges were not involved in the agglutination and, with
35
S-labeled jelly, that the agglutinating J
1
component possessed sulfate esters. Both the CG exudate and the J
1
components contained carbohydrate, as evidenced by their lectin reactivity. A number of ionic polymers, both natural and synthetic, were tested as chemical analogs of CG exudate and J
1
; none gave an agglutination band. Dissolved jelly coat material from eggs of two different species of frogs agglutinated with CG exudate, while jelly from sea urchin eggs and hyaluronic acid from mammalian eggs did not. Thus, the agglutination reaction was chemically and phylogenetically specific. An electron-dense layer, similar to the F layer, formed on the outer of the vitelline envelope when jellied unfertilized eggs were immersed in CG exudate; such eggs were not fertilizable. We suggest that in
Xenopus laevis
, and perhaps other organisms as well, an agglutination type of reaction between cortical granule components and egg integuments is a participant in the structural and molecular events establishing a block to polyspermy.
Unique Double-Stranded Fragments of Bacteriophage T5 DNA Resulting from Preferential Shear-Induced Breakage at Nicks
Authors: Hayward Gary S.
Published: May 2006

Nicks within one strand of the bacteriophage T5 DNA molecule act as “ weak points” for a novel kind mechanical breakage that can be utilized for “dissecting” the genome. The products from sheared T5
+
DNA include five unique double-stranded segments of the molecule and various combinations of adjacent segments. These specific fragments are not obtained after repair of the nicks with DNA ligase (EC 6.5.1.1). The duplex fragments and most of their single-stranded components have been separated, identified, and mapped by means of agarose gel electrophoresis. Even the complementary strands of the unique fragments separate in agarose gels; hence, there are now three useful classes of DNA fragments available from T5: the natural
r
-strand fragments, their complements from the normally intact
l
strand, and the corresponding duplex segments. By summing the apparent molecular weights of their single-stranded components, the unique duplex fragments from T5
+
DNA can be assigned molecular weights of approximately 6 × 10
6
(A), 8 × 10
6
(B), 11 × 10
6
(C), 27 × 10
6
(D), and 30 × 10
6
(E) from left to right along the genome. The most abundant overlapping fragments are segments AB (14 × 10
6
) and ABC (26 × 10
6
). Differences in the number and relative positions of nicks within two distinct groups of heatstable deletion mutants [represented by T5st(O) and T5b3] account for the large differences observed in their patterns of breakage products.
Alteration in the Acetylation Level of Ribosomal Protein L12 During Growth Cycle of
Escherichia coli
Authors: Ramagopal S. , Subramanian Alap R.
Published: May 2006

The relative content in ribosomes of L7 and L12, the two forms of a protein in the 50S subunit specifically involved in GTP hydrolysis, is found to undergo a striking shift with the growth phase of
E. coli
. The content of L12 (nonacetylated form) increases during early logarithmic phase, becoming about 85% of the total before midlogarithmic phase. Thereafter, L7 (
N
-acetylated form) content begins to increase, eventually becoming 75-80% in stationary phase. The L7 + L12 content per ribosome, however, remained constant during this shift. Our evidence suggests that the shift did not occur through modification of preexisting ribosomes. The data further indicate that the
E. coli
cell may contain more than one structurally distinct (with regard to L7 or L12 content) 50S subunit population.
Synergistic Interactions of T4 Early Proteins Concerned with Their Binding to DNA
Authors: Huang Wai Mun , Buchanan John M.
Published: May 2006

Under appropriate conditions, 19 distinct early proteins produced by bacteriophage T4 bind DNA with various affinities. They include products of genes that have been implicated in T4 DNA metabolism, such as DNA negative, DNA arrest, and DNA delay genes, and others whose roles have not yet been defined. The identifiable DNA-binding proteins are the products of genes 43, rIIA, 46, 30, 39, 52, βgt, 32, and internal protein III. In some cases, protein-protein interactions are involved in the formation of the DNA-protein complexes.
Actin Antibody: The Specific Visualization of Actin Filaments in Non-Muscle Cells
Authors: Lazarides Elias , Weber Klaus
Published: May 2006

Actin purified from mouse fibroblasts by sodium dodecyl sulfate gel electrophoresis was used as antigen to obtain an antibody in rabbits. The elicited antibody was shown to be specific for actin as judged by immunodiffusion and complement fixation against partially purified mouse fibroblast actin and highly purified chicken muscle actin. The antibody was used in indirect immunofluorescence to demonstrate by fluorescence light microscopy the distribution and pattern of actin-containing filaments in a variety of cell types. Actin filaments were shown to span the cell length or to concentrate in “focal points” in patterns characteristic for each individual cell.
Enhancement of RNA Synthesis in Avian Liver Cell Cultures by a 5β-Steroid Metabolite During Induction of δ-Aminolevulinate Synthase
Authors: Incefy Genevieve S. , Kappas Attallah
Published: May 2006

The porphyrin-heme pathway is controlled in the liver at the level of the mitochondrial enzyme δ-aminolevulinate synthase (EC 2.3.1.37), a protein inducible in cultured avian hepatocytes by a variety of chemicals including certain 5β-metabolites of steroid hormones. The great sensitivity of the induction process to inhibition by agents known to block transcriptional activity of genetic material suggests that some control mechanism may be operating at this level to regulate the formation of the enzyme. We report here enhancement of nuclear RNA synthesis and of Mn
2+
-(NH
4
)
2
SO
4
-stimulated DNA-dependent RNA polymerase (EC 2.7.7.6) activities by the 5β-steroid metabolite, 3α-hydroxy-5β-androstan-17-one (etiocholanolone), in cultured avian hepatocytes during induction of the enzyme. These changes were demonstrated in the G
1
phase of the hepatocyte cell cycle at a time when DNA synthesis is constant. Our findings support the view that one of the early steps in the process of induction of δ-aminolevulinate synthase by steroid metabolites requires new RNA synthesis, very probably messenger RNA, suggesting a 5β-steroid transcriptional control mechanism for induction of this protein.
Purification of a Growth Factor for Ovarian Cells from Bovine Pituitary Glands
Authors: Gospodarowicz Denis , Jones Kenneth L. , Sato Gordon
Published: May 2006

The purification of a growth factor from bovine pituitary glands that controls the division of an ovarian cell line maintained in tissue culture is reported. Extraction of bovine pituitary glands at pH 4.5 followed by ammonium sulfate precipitation, chromatography on carboxymethylcellulose, and gel filtration on Sephadex G-50 gives yields of ovarian growth factor of about 7 mg/kg of glands. Contamination by other pituitary hormones was not detected. The preparation obtained has been characterized with respect to biological activity, molecular weight, and amino-acid composition. The implication of this growth factor in the development of ovarian tumors is discussed.
Temperature Dependence of Isotope Ratios in Tree Rings
Authors: Libby L. M. , Pandolfi L. J.
Published: May 2006

The stable isotope ratios of carbon, oxygen, and hydrogen have been measured for a German oak in wood samples of roughly three years each, for the years 1712-1954 A.D., and correlated with the existing weather records from England, Basel, and Geneva to evaluate the empirical temperature coefficients. Isotope ratios in a second official oak, measured for the years 1530-1800 A.D., show the cold temperatures of the Little Ice Age interspersed with warm intervals.
Programmed Synthesis of Tubulin for the Flagella that Develop During Cell Differentiation in
Naegleria gruberi
Authors: Kowit Joel D. , Fulton Chandler
Published: May 2006

Amebae of
Naegleria gruberi
differentiate into flagellates when transferred from growth medium to nonnutrient buffer. Experiments were performed to determine whether the tubulin that forms the flagellar microtubules pre-exists in amebae or is synthesized during differentiation. Amebae prelabeled uniformly with [
35
S]methionine were allowed to differentiate in the presence and in the absence of exogenous unlabeled methionine. In the presence of unlabeled methionine the flagellar tubulin contained only 30% as much [
35
S]methionine as in its absence. Thus at least 70% of the tubulin was synthesized
de novo
. Isotope dilution and pulse experiments showed that flagellar tubulin synthesis began one-third of the way through differentiation, before any morphological change had occurred. Flagellar tubulin antigen, as measured using a specific antiserum, also began to increase one-third of the way through differentiation and increased 35- to 55-fold during the course of differentiation. These experiments demonstrate that most if not all of the flagellar tubulin is synthesized
de novo
during differentiation.
Isolation and Some Properties of the Genes Coding for Histone Proteins
Authors: Birnstiel M. , Telford J. , Weinberg E. , Stafford D.
Published: May 2006

The DNA coding for histone proteins, together with the intervening spacer DNA, has been isolated from the sea urchin,
Psammechinus miliaris
, by repeated centrifugation on CsCl-asctinomycin gradients. The biophysical data show that a major portion of the spacer is 37% G+C and very divergent in sequence, while the DNA segments coding for histone proteins are high in G+C and have diverged to a lesser extent within the species.
Methylation of Newly Synthesized Viral Messenger RNA by an Enzyme in Vaccinia Virus
Authors: Wei Cha Mer , Moss Bernard
Published: May 2006

Purified vaccinia virions contain an enzyme that incorporates methyl groups from
S
-adenosylmethionine into viral RNA synthesized by the core-associated DNA-dependent RNA polymerase. This incorporation, by partially disrupted virions, was dependent on the presence of all four ribonucleoside triphosphates and Mg
++
and was inhibited by actinomycin D. At saturation, 2.3 methyl groups were incorporated per 1000 nucleotides. The methyl-labeled RNA product was sensitive to alkali and ribonucleases and hybridized to filters containing immobilized poly(U) or vaccinia DNA. The methyl groups were not located on the 3′-terminal polyadenylate sequence, nor were they randomly distributed along the RNA chain. The lability of a large portion of the methyl groups to perchloric acid digestion was consistent with an O-methyl linkage, and the chromatographic properties of the alkali-digested material suggested that either the 5′-terminus or up to three consecutive internal nucleotides were methylated. Methylation probably occurs at the macromolecular level, since added vaccinia RNA was a suitable substrate. The failure of heterologous rRNA and tRNA species as well as homopolyribonucleotides to act as substrate suggested that a specific sequence might be required.
Classical Statistical Mechanics of Constraints: A Theorem and Application to Polymers
Authors: Fixman Marshall
Published: May 2006

A classical system of mass points subject to holonomic constraints has a kinetic energy dependent on the coordinates as well as the moments of the remaining degrees of freedom. Coordinate averages formed in the reduced space of unconstrained coordinates and their conjugate momenta then involve a metric determinant that may be difficult to evaluate. A theorem is derived that permits a relatively easy evaluation when the constraints are distances between particles, and an application is made to a Kramers type freely jointed chain.
Effects of Poly(2′-
O
-Methyladenylic Acid) on Susceptibility and Autogenous Immunity to RNA Tumor Virus Oncogenesis
In Vivo
Authors: Tennant Raymond W. , Hanna M. G. , Farrelly James G.
Published: May 2006

Poly(2′-
O
-methyladenylic acid) [poly(Am)] inhibited tumor development and death induced by the Moloney sarcoma virus-leukemia virus complex in newborn mice. The compound was effective at 10 μg per mouse when given at least 1 hr before inoculation of virus, but the greatest inhibition was seen in mice treated at least 4 hr before infection. Poly(2′-
O
-methyluridylic acid) and poly(vinyladenine) also inhibited sarcoma development and death but were less effective than poly(Am). Poly(Am) also enhanced the antibody response of newborn mice to endogenous leukemia virus envelope antigens, which we refer to as autogenous immunity. The results of these preliminary studies suggest that poly(Am) altered the oncogenic potential of the Moloney sarcoma-leukemia virus complex
in vivo
, and the effect appears to be mediated through an enhancement of the immune response of the treated animals.
Methylated Messenger RNA Synthesis
In Vitro
by Purified Reovirus
Authors: Shatkin Aaron J.
Published: May 2006

Purified human reovirus contains RNA methylase activity in addition to an RNA polymerase. Virions incubated under appropriate conditions in the presence of
S
-adenosyl-L-methionine synthesize mRNA that is specifically methylated in the 5′-terminal guanosine. Alkaline digestion of the methylated RNA released a 5′-terminal dinucleotide, ppG′pCp, indicating that the guanosine contains 2′-
O
-methylribose. The possible roles of methylation in viral and cellular mRNA function is discussed.
The Three-Dimensional Structure of the Fab′ Fragment of a Human Myeloma Immunoglobulin at 2.0-Å Resolution
Authors: Poljak R. J. , Amzel L. M. , Chen B. L. , Phizackerley R. P. , Saul F.
Published: May 2006

The structural analysis of the Fab′ fragment of human myeloma immunoglobulin IgGl(λ) New has been extended to a nominal resolution of 2.0 Å. Each of the structural subunits corresponding to the variable and to the constant homology regions of the light and heavy chains contains two irregular β-sheets which are roughly parallel to each other and surround a tightly packed interior of hydrophobic side chains. About 50-60% of the amino-acid residues are included in β-pleated sheets. Sequence alignments between the homology regions of Fab′ New obtained by comparison of their three-dimensional structures are given. Some of the sequence variations observed in light and heavy chains and the role of the regions of hypervariable sequence in defining the size and shape of the active site of different immunoglobulin molecules are discussed on the basis of the three-dimensional model of Fab′ New.
Constancy in Human Sperm DNA Content
Authors: Sarkar Siddhartha , Jones O. W. , Shioura Norio
Published: May 2006

The frequency distribution of DNA content of human sperm was measured in an automated flow microfluorometer. The flow method measures the DNA content by quantifying the amount of fluorescence emitted by the fluorescent Feulgen stained DNA of single sperm cells suspended in microdroplets. The variability in the mean value for the haploid amount of DNA in sperm from 15 randomly chosen donors was less than 1%. Statistical tests on the observed frequency distribution data indicated that each sperm population probably consists of two homogenous components present in almost equal proportions but differing in mean DNA content. The difference in their modal values for DNA is within the range of known values of DNA difference between the two sex chromosomes.

Sperm of donors segregating balanced translocations, when compared to the random samples as a class, showed greater variability in the mean DNA content.
A Ca
++
-Dependent and -Selective Ionophore as Part of the Ca
++
+ Mg
++
-Dependent Adenosinetriphosphatase of Sarcoplasmic Reticulum
Authors: Shamoo Adil E. , MacLennan David H.
Published: May 2006

Solubilized Ca
++
+ Mg
++
-dependent adenosinetriphosphatase (EC 3.6.1.3; ATP diphosphohydrolase) from sarcoplasmic reticulum increased bimolecular lipid membrane (oxidized cholesterol) conductance several hundred-fold. The relative conductance change and the relative permeability elicited by this material has the following sequence: Ba
++
> Ca
++
> Sr
++
> Mg
++
> Mn
++
> Zn
++
, Na
+
, K
+
, Cs
+
, Li
+
, and Rb
+
. Zn
++
and Na
+
strongly inhibit the increase in Ca
++
conductance obtained with solubilized Ca
++
+ Mg
++
-dependent adenosinetriphosphatase. The Ca
++
-ionophore is an integral part of the Ca
++
+ Mg
++
-dependent adenosinetriphosphatase enzyme and may function as a Ca
++
-carrier in the overall Ca
++
-pump of sarcoplasmic reticulum.
Activation of Protein Kinase by Physiological Concentrations of Cyclic AMP
Authors: Beavo J. A. , Bechtel P. J. , Krebs E. G.
Published: May 2006

When determined under the usual conditions of an excess of ligand over protein, the concentration of cyclic AMP necessary to activate pure preparations of cyclic AMP-dependent protein kinase (EC 2.7.1.37; ATP:-protein protein phosphotransferase) half-maximally is in the range of 0.2-0.3 μM when casein or glycogen synthetase is used as the substrate, i.e., essentially the same as the concentration of the nucleotide that is found in resting skeletal muscle. The apparent dissociation constant for cyclic AMP bound to the protein kinase is also about 0.2-0.3 μM when measured under similar conditions. The concentration of the protein kinase in muscle is relatively high (0.23 μM), however, and under these conditions the apparent activation constant of the enzyme for cyclic AMP is raised so that an increase in cyclic AMP levels in the tissue would cause a concomitant increase in protein kinase activity over a wide range of nucleotide concentration. As a result, it is unnecessary to invoke compartmentalization of cyclic AMP to explain how it can control protein kinase activity
in vivo
. Another factor that may increase the effectiveness of changes in cyclic AMP concentration is the heat-stable protein inhibitor of protein kinase that may function to inhibit the activity of nearly all the protein kinase catalytic subunit dissociated by basal concentrations of cyclic AMP. Finally, the near equity between the concentration of cyclic AMP binding sites and the ligand itself provides a potential mechanism whereby agents can affect the total cyclic AMP content without directly affecting adenylate cyclase, cyclic AMP phosphodiesterase, or cyclic AMP transport.
Distinct molecular structures of nuclear class I, II, and III DNA-dependent RNA polymerases.
Authors: Sklar V E , Schwartz L B , Roeder R G
Published: May 2006

Class III RNA polymerases purified from the murine plasmacytoma MOPC 315 and from Xenopus laevis ovaries were compared. The subunit structures of the chromatographically distinct murine enzymes IIIA and IIIB were indistinguishable and were remarkably similar to that of the amphibian enzyme III. The plasmacytoma class III RNA polymerases were also compared with purified plasmacytoma RNA polymerases I and II. Sedimentation studies indicated that RNA polymerase III si significantly larger than RNA polymerase II, which is slightly larger than RNA polymerase I. Structural analyses showed that the molecular weights of the large subunits present in the class III enzymes (138,000 and 155,000) differ from those of the class II enzymes (140,000 and either 170,000, 205,000, or 240,000) and from those of the class I enzymes (117,000 and 195,000). Some low-molecular-weight subunits are also unique to each enzyme class. These results clearly distinguish the class I, II, and III enzymes on a structural basis. In addition, polypeptides of molecular weight 29,000 and 19,000 were found in all enzyme classes, a polypeptide of molecular weight 52,000 was found only in class I and III enzymes, and a polypeptide of molecular weight 41,000 was found only in class II and III enzymes. These findings are discussed in terms of the function and regulation of the RNA polymerases.
A general model for genetic recombination.
Authors: Meselson M S , Radding C M
Published: May 2006

A general model is proposed for genetic recombination. Its essential new feature is the hypothesis that recombination is initiated by a single-strand (or asymmetric) transfer, which may, after isomerization, become a two-strand (or symmetric) exchange. The likelihood of this transition from asymmetric to symmetric strand exchange determines certain characteristic features of recombination in any particular organism.
Determination of the iron-sulfur distances in rubredoxin by x-ray absorption spectroscopy.
Authors: Shulman R G , Eisenberger P , Blumberg W E , Stombaugh N A
Published: May 2006

The high intensity x-ray flux from the synchrotron radiation at the Stanford Synchroton Radiation Project has been used to study the extended x-ray absorption fine structure (EXAFS) of the iron-sulfur protein Peptococcus aerogenes rubredoxin. Absorption measurements were made from 7080 eV, which is below the K-edge of iron, to about 650 eV above the edge and structure was obtained over the entire region. By means of a model iron-sulfur compound for evaluating the phase shifts, the variation of the absorption above the edge of lyophilized, oxidized rubredoxin was converted to iron-sulfur distances. The data were fitted with a least squares program to a model in which three distances R3 were kept equal and the fourth R1 was allowed to differ. The mean square error was constant over a region of this parameter space, becoming twice as large at R3 = 2.217, R1 = 2.389 and R3 = 2.268, R1 = 2.108 A. These values, which are the extreme differences allowed by the present data, are definitely closer to being equal than those found by the determination of the x-ray diffraction crystal structure of the similar protein from Clostridium pasteurianum. However, the average distance from our experiment is in excellent agreement with the average distance from the crystal structure determination. Preliminary EXAFS measurements were also made on the oxidized rubredoxin in solution at pH 7.0. The spectra were unchanged, indicating that the average iron-sulfur distance change is less than 0.02 A. Upon reduction the average iron-sulfur bond length increased by about 0.05 A. Since the EXAFS measurements can give accurate determinations of distances in proteins both in crystals and solution, the technique should be widely applicable.
Identification of a soluble protein that stimulates peptide bond synthesis.
Authors: Glick B R , Ganoza M C
Published: May 2006

A soluble protein factor was isolated, free of elongation factor (EF)-T and EF-G, based on its ability to stimulate the synthesis of peptide bonds using ribosomal bound 70S-AUG-N-formyl-[35S]methionyl-tRNA complex and added puromycin as substrates. Over 90% of this activity was found in the ribosome-free cytoplasm of Escherichia coli extracts. Otherfeatures such as molecular weight, purification properties, and catalytic activities distinguish this factor from ribosomal proteins and known activators of translation. The factor requires all components needed for peptide bond synthesis and is inhibited by antibiotics known to specifically block the peptidyl transferase activity of ribosomes. The factor increases the binding affinity of the ribosome for the aminoacyl-tRNA analog puromycin about 10-fold. We suggest that this extraribosomal factor modulates the intrinsic activity of ribosomes to catalyze peptide-bond synthesis, and regard it as a new factor required for peptide chain elongation, which we call EF-P.
Structural properties of pyruvate carboxylases from chicken liver and other sources.
Authors: Barden R E , Taylor B L , Isoashi F , Frey W H , Zander G , Lee J C , Utter M F
Published: May 2006

Varieties of pyruvate carboxylase [pyruvate: CO2 ligase (ADP-forming), EC 6.4.1.1] obtained from the livers of several species of vertebrates, including humans, all show the same basic structure. They are composed of large polypeptide chains of molecular weights ranging from 1.2 to 1.3 X 10(5) for the different varieties of the enzyme. The native form of the enzyme appears to be a tetramer with a molecular weight of about 5 X 10(5). In the case of pyruvate carboxylase from chicken liver each polypeptide chain contains a biotin moiety, thus supporting the thesis that the tetramer contains four identical polypeptide chains. Pyruvate carboxylase from yeast appears to be basically similar to those from the vertebrate species and has a tetrameric structure. Each protomer contains a single polypeptide chain with a molecular weitht of 1.25 X 10(5). In contrast, pyruvate carboxylase from two bacterial species, Pseudomonas citronellolis and Axotobacter vinelandii, appears to be a dimer with a molecular weight (2.5 X 10(5)) about half that of the animal and yeast species. As a further difference, each of the protomers of the bacterial enzymes contain two polypeptides of 6.5 and 5.4 X 10(5) molecular weight in case of the Pseudomonas enzyme. The larger of the two polypeptides contains the biotin moiety. The functional units of the bacterial enzyme thus appear to contain two polypeptides while that of the liver and yeast enzymes is made up of a single chain. Neither of these arrangements corresponds with those of other biotin enzymes whose structure has been extensively studied (acetyl-CoA carboxylases from liver or Excherichia coli, and transcarboxylase from Propionibacterium).
General model for nutritional responses of higher organisms.
Authors: Morgan P H , Mercer L P , Flodin N W
Published: May 2006

A general saturation equation is derived which is shown to describe a wide variety of nutrient-response relationships in higher organisms. Iterative multiple linear regression analysis is used to obtain least squares estimates of the constants defining theoretical nutrient-response curves. Curves thus generated accurately predict experimentally observed responses. From this treatment, response parameters are developed which are analogous to Vmax and Km of enzyme kinetics. It is proposed that this model be applied in evaluating nutritional requirements and in assessing the relative biological efficiency of nutrient sources.