bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for Allosterism in
In Vitro
DNA Synthesis on RNA Templates
Authors: Cavalieri Liebe F. , Modak Mukund J. , Marcus Stuart L.
Published: May 2006

Hemoglobin mRNA and (rA)
n
·(dT)
10
have been used as primer-templates in a kinetic study of DNA synthesis with
Escherichia coli
DNA polymerase I (DNA nucleotidyl transferase, EC 2.7.7.7) and Mason-Pfizer monkey virus reverse transcriptase (RNA-directed DNA polymerase). The rate
versus
enzyme concentration curve is sigmoidal and is consistent with a cooperative phenomenon. The results could be interpreted in terms of the formation of an active complex containing enzyme dimers (or oligomers) on the primer-template. We have also observed sigmoidal kinetics in rate
versus
deoxynucleotide triphosphate concentration. These results are consistent with an allosteric mechanism in which the triphosphates act as both modifiers and DNA precursors. In the critical range, a 6- to 8-fold increase in both enzyme and triphosphate concentrations can lead to a 1500-fold increase in the rate of synthesis on an RNA template. Thus, small changes in enzyme and precursor concentrations could play a regulatory role
in vivo
.
Structure of Nascent ϕX174 Replicative Form: Evidence for Discontinuous DNA Replication
Authors: Eisenberg Shlomo , Denhardt David T.
Published: May 2006

ϕX174 RF (replicative form) II DNA, labeled
in vivo
with [
methyl
-
3
H]thymidine, was isolated from
Escherichia coli pol
A (DNA polymerase I-deficient) and
pol
A
+
cells during RF replication. [
32
P]dCMP was incorporated into the gaps present in the RF II DNA with [α-
32
P]dCTP and T4 DNA polymerase. Sedimentation in alkaline sucrose gradients revealed that much of the incorporated
32
P was present in a heterogeneous collection of fragments shorter than unit length. Inclusion of polynucleotide ligase in the gap-filling reaction increased the average size of the
32
P-labeled fragments. Gel electrophoresis of the products formed by digestion of the
32
P-labeled RF II molecules with the restriction nuclease, endonuclease R, indicated that in the population of RF II molecules gaps could occur anywhere in the genome. Competition-annealing experiments provided evidence that the majority of the label incorporated into gaps was present in the minus strand. RF II molecules isolated from
pol
A
+
cells were enriched for gaps in a unique region of the genome in comparison with RF II molecules isolated from
pol
A cells. The presence of multiple gaps in the minus strand implies that it is synthesized by a discontinuous mechanism during ϕX RF replication.
Synthesis of Simian Virus 40 DNA in Isolated Nuclei
Authors: Qasba Pradman K.
Published: May 2006

Nuclei isolated from African green monkey kidney cells infected with simian virus 40 at different times after infection maintain
in vitro
the same temporal sequence of host and viral DNA synthesis as that seen in intact cells. The viral DNA synthesized by the nuclei of cells previously infected for 32-35 hr was characterized by centrifugation through neutral and alkaline sucrose gradients, and by isopycnic banding in a propidium iodide-cesium chloride gradient. DNA synthesis in this system is maintained for only 4-5 min. Neutral sucrose gradient analysis showed that most of the radioactivity is associated with the replicative intermediate of simian virus 40 DNA and the rest sediments at 5-7 S. Alkaline gradient analysis showed that 50-60% of the radioactivity sediments as 3-7S fragments, and the rest between 7 and 16 S. Pulsechase experiments showed that in this system 3-7S fragments do not mature into long chains. A model is presented to explain the failure of these fragments to join into long chains in this
in vitro
nuclear system.
An Association Between Globin Messenger RNA and 60S RNA Derived from Friend Leukemia Virus
Authors: Ikawa Yoji , Ross Jeffrey , Leder Philip
Published: May 2006

The association between certain cellular RNAs and purified RNA tumor viruses prompted us to examine the possibility that specific host messenger RNAs might also be incorporated into RNA tumor viruses. Using a mouse cell line infected with Friend leukemia virus, T-3-Cl-2, which can be induced to accumulate mouse-globin messenger RNA, we show that mouse-globin messenger RNA sequences are present in viral particles purified from the culture medium of globin-producing cells. These globin messenger RNA sequences are absent from viral particles derived from T-3-Cl-2 cells that are not producing globin messenger RNA. Virus-associated globin messenger RNA sequences sediment in association with the 60S viral RNA complex as well as in free, 9S form. However, under mild denaturing conditions which result in the conversion of viral 60S RNA to 30S and smaller forms, all the globin sequences sediment as 9S RNA. Appropriate control experiments indicate that the virus-associated globin messenger RNA is resistant to degradation by exogenous ribonuclease; that exogenously added globin messenger RNA does not become associated with the 60S viral RNA complex; and that globin messenger RNA can be detected in virions derived from cells both induced for and constitutively synthesizing globin messenger RNA.
Photophosphorylation in
Halobacterium halobium
Authors: Danon Arlette , Stoeckenius Walther
Published: May 2006

Halobacterium halobium
cells grown under semi-anaerobic conditions convert part of their cell membrane into “purple membrane” which contains a rhodopsin-like protein, bacteriorhodopsin. Under anaerobic conditions in the dark the ATP content of such cells decreases sharply. Either light or oxygen restores the ATP content to the original level. The light effect is mediated by the purple membrane. Inhibitors of the respiratory chain abolish the oxygen response but do not affect the light response. Uncouplers, which function as proton translocators, abolish the light response. These results indicate that the purple membrane functions as a lightdriven proton pump and the cells use the resulting chemiosmotic gradient for ATP synthesis.
Synthesis and Properties of
Clostridium acidi-urici
[Leu
2
]-Ferredoxin: A Function of the Peptide Chain and Evidence Against the Direct Role of the Aromatic Residues in Electron Transfer
Authors: Lode Eglis T. , Murray Cheryl L. , Sweeney William V. , Rabinowitz Jesse C.
Published: May 2006

Tyrosyl or other aromatic residues generally occur in two conserved positions in the peptide chain of clostridial-type ferredoxins and have been implicated in the electron transfer function of these iron-sulfur proteins. We have prepared and determined some of the properties of a derivative of
Clostridium acidi-urici
ferredoxin, [Leu
2
]-ferredoxin, in which a leucyl residue has been substituted for the tyrosyl residue in position 2 from the amino terminus. [Leu
2
]-ferredoxin is fully active as an electron carrier in two biological assays, the phosphoroclastic enzyme system and the ferredoxin-dependent reduction of cytochrome
c
in the presence of ferredoxin-TPN reductase and TPNH. Quantitative electron paramagnetic resonance experiments indicate that [Leu
2
]-ferredoxin accepts nearly two electrons upon enzymatic reduction by pyruvate-ferredoxin oxidoreductase and an excess of pyruvate. If electron transfer to an iron-sulfur cluster is the rate-limiting step in the assays used, and if the rate of electron transfer through Tyr
30
is not much faster than through Tyr
2
, these results indicate that the primary pathway of electron transfer in clostridial-type ferredoxins is not via Tyr or other aromatic amino-acid residues. The syntheses of other ferredoxin derivatives with amino-acid substitutions or deletions in positions 1 and 2 indicate that a large bulky residue, but not necessarily an aromatic residue, is needed in position 2 for the stability of this ferredoxin. The residue in position 2, therefore, appears to act as a hydrophobic shield for an iron-sulfur cluster.
Tandem Inverted Repeats in Mitochondrial DNA of Petite Mutants of
Saccharomyces cerevisiae
Authors: Locker Joseph , Rabinowitz Murray , Getz Godfrey S.
Published: May 2006

Denatured mitochondrial DNA (mtDNA) from a grande (wild-type) yeast strain and a series of derived genetically characterized cytoplasmic petite mutants was examined in the electron microscope as DNA-protein monolayers prepared under conditions that permitted little bimolecular renaturation. In the grande and some petite strains, the mtDNA remained predominantly single-stranded. However, in several petite strains, a large proportion of molecules contained double-stranded segments indicative of unimolecular renaturation due to the presence of inverted repeat sequences. The length of the double-stranded segments of strain E41 was compared to the periodicity seen on denaturation maps. A repeat spacing twice the length of the inverted repeats was observed in the denaturation map. Inverted repeat length was similar to contour length of circular mtDNA molecules in this strain. On the basis of these observations most of the mtDNA from petite strain E41 appeared to consist of polymers of tandem inverted repeats interspersed with a small single-stranded “spacer” sequence between the repeat segments. In contrast, petite strain F13 mtDNA had few or no inverted repeats and showed a regular periodicity of 0.14 μm in the denaturation map, similar in length to the 0.13-μm circles present in the isolated mtDNA.
The Stoichiometry of the Conversion of Cholesterol and Hydroxycholesterols to Pregnenolone (3β-Hydroxypregn-5-en-20-one) Catalysed by Adrenal Cytochrome
P
-450
Authors: Shikita Mikio , Hall Peter F.
Published: May 2006

The stoichiometry of the side-chain cleavage of cholesterol (cholest-5-en-3β-ol), 20α-hydroxycholesterol (cholest-5-ene-3β,20α-diol), and 20α,22-dihydroxycholesterol (cholest-5-ene-3β,20α,22-triol) has been examined with respect to TPNH, oxygen and H
+
. Side-chain cleavage of cholesterol can be described by the following equation:

Cholesterol + 3TPNH + 3H
+
+ 3O
2
→ Pregnenolone (3β-hydroxypregn-5-ene-20-one) + isocapraldehyde + 3 TPN
+
4H
2
O

Stoichiometry of 20 α-hydroxycholesterol is 2TPNH and 2O
2
per mole of cleavage and with 20α, 22-dihydroxycholesterol the values are 1:1:1. In addition 1 mole of H
+
is consumed per mole of TPNH oxidized in each of these reactions. These observations are in keeping with a mechanism previously proposed in the literature, namely:

Cholesterol → 20α-OH-Cholesterol → 20α, 22-di-OH-Cholesterol → pregnenolone

Discordant observations are reviewed and it is concluded that insufficient data are available to sustain objections to this pathway.
Protein Fusion: A Novel Reaction in Bacteriophage λ Head Assembly
Authors: Hendrix Roger W. , Casjens Sherwood R.
Published: May 2006

Parts of two phage-coded head proteins, pE and pC, become fused during bacteriophage λ head assembly. pE is the main structural component of λ heads and pC is a minor head protein that is not found as such in mature heads. The bond joining the two proteins appears to be covalent and is not a disulfide bond. Only a specific subset of the sequences of each protein is found in the fusion products, and these sequences are found in the products in equimolar amounts. Two nearly identical fusion products; X1 and X2, are detected; X2 is slightly smaller than X1 and appears to be a proteolytic cleavage product of X1. The fusion reaction probably takes place on a nascent head structure.
Acylation of α-Chymotrypsin by Oxygen and Sulfur Esters of Specific Substrates: Kinetic Evidence for a Tetrahedral Intermediate
Authors: Hirohara Hideo , Bender Myron L. , Stark Richard S.
Published: May 2006

The acylation step of the α-chymotrypsincatalyzed hydrolysis of
N
-acetyl-L (or DL)-tryptophan
p
-nitrophenyl,
p
-nitrothiophenyl, ethyl, and thiolethyl esters has been studied by the stopped-flow technique at 25°. The acylation rate constant,
k
2
, and the enzyme substrate dissociation constant,

K
s

, were directly determined at pH 4, 5, and 8. Steady-state kinetics were studied at pH 7. The
k
2
values are nearly identical for oxygen esters and their sulfur counterparts, whereas the

K
s

value of the ethyl ester is larger by an order of magnitude than those of the other three. The results strongly suggest that oxygen and thiol esters of these specific substrates are hydrolyzed via the same pathway, and furthermore that acylation consists of more than one step, the formation and breakdown of a tetrahedral intermediate, the former being rate-determining. Effects of leaving-group hydrophobicity on
k
2
and

K
s

are also discussed.
X-Ray Diffraction Studies of Nucleohistone: A Polyhelical Model of Chromosome Organization
Authors: Subirana Juan A. , Puigjaner Luis C.
Published: May 2006

The possibility that nucleohistone is constituted by a helical arrangement of DNA molecules is analyzed in this paper. A polyhelical model of nucleohistone in plectanemic double coils of variable dimensions is found to be compatible with the x-ray diffraction results obtained in this and other laboratories. The radius of the coils varies between 35 and 45 Å, whereas the pitch varies between 200 and 120 Å. Another part of nucleohistone is much less coiled and contributes to the “background” scattering of the sample. This model is compatible with a lampbrush organization of the chromosome.
Encapsulation of Lymphocyte DNA by Vesicular Stomatitis Virus
Authors: Kingsbury David T. , Lerner Richard A.
Published: May 2006

Vesicular stomatitis virus, grown on the WIL
2
-3A line of continuously growing human lymphocytes, contains DNA in addition to the viral RNA. By contrast, virus grown on BHK 21-C13 fibroblasts has no detectable DNA. The virus-associated DNA is found in both the B and T particles of the virus and is resistant to deoxyribonuclease. The DNA is intimately associated with the virus and appears to be incorporated into the viral ribonucleoprotein core structure produced by treatment of the virus with Nonidet P40 follow edby CsCl isopycnic banding.

The virus-associated DNA has an isopycnic density of 1.699 g × cm
-
-3
in CsCl, identical to that of human DNA. The average molecular weight of the DNA molecules associated with the virus is 9.0 × 10
5
, as determined by velocity sedimentation in sucrose density gradients and studies of its contour length in the electron microscope. DNA·DNA reassociation kinetics of this DNA demonstrate that the DNA is of host origin and rules out the possibility that it originates from contaminating microorganisms or mitochondria. The analytical complexity of the virus-associated DNA shows that 50% of the virus-associated DNA sequences are homologous to the repeated DNA sequences of human DNA and the remaining 50% are homologous to human unique sequences. On the average, there is one molecule of DNA for each four virion particles.
Gene Duplication and Fixed Heterozygosity for Alcohol Dehydrogenase in the Diploid Plant
Clarkia franciscana
Authors: Gottlieb L. D.
Published: May 2006

All individuals of the diploid plant
Clarkia franciscana
, an annual species native to California, have duplicated genes for the dimeric enzyme alcohol dehydrogenase. Since each gene specifies a polypeptide with a distinct charge, the species has a fixed heterozygous phenotype consisting of three isozyme variants. The enzyme is coded by a single gene in closely related species.
Clarkia franciscana
is highly self-pollinated and monomorphic at all but one of its loci that have been examined. Consequently, the duplication provides enzyme variability in the absence of genetic variability.
On the Possibility That DNA Repair Is Related to Age in Non-Dividing Cells
Authors: Wheeler K. T. , Lett J. T.
Published: May 2006

Possible age-related deterioration in the efficacy of DNA repair was investigated in a complement of non-dividing mammalian cells which is not replenished during the lifetime of the animal. Internal granular-layer neurons were extracted from the cerebella of beagle dogs, aged from 7 weeks to 13 years, following exposure
in situ
to 4700 rads of collimated
60
Co gamma rays. The alkaline sucrose-gradient sedimentation profiles obtained from the DNA of those neurons after various post-irradiation periods
in situ
can be interpreted: (
a
) that there is not an age-associated decrease in the ability of the cells to rejoin the single-strand breaks induced by radiation, but (
b
) that there may be an age-associated decline in the size of the DNA-containing species which can be extracted from unirradiated cells. The latter effect may reflect normal aging of the cerebellum.
Activation of Sea-Urchin Eggs by a Calcium Ionophore
Authors: Steinhardt Richard A. , Epel David
Published: May 2006

Micromolar amounts of the divalent ionophore A23187 can activate echinoderm eggs. The activations by ionophore A23187 were examined in terms of membrane elevation, the program of membrane conductance changes, the respiratory burst, and the increases in protein and DNA synthesis which normally accompany activation by sperm. In all these respects activation by the ionophore was fairly normal although subsequent cleavage and embryonic development was limited.

Ionophore A23187 activations of the cortex of
Lytechinus pictus
and
Strongylocentrotus purpuratus
eggs were compared in various ionic media and were found to be completely independent of the ionic composition of the external solution. Respiration and protein synthesis of
L. pictus
eggs in singly substituted ionic media also indicated that these activations were independent of external sodium, calcium, or magnesium. These results suggest that the ionophore acts by releasing intracellular Ca
++
. Consistent with this interpretation is the finding that eggs preloaded with
45
Ca show a 20-fold increase in
45
Ca-efflux when activated by ionophore A23187 or fertilization. Measurements of the “free” and “bound” calcium and magnesium in homogenates of the unfertilized eggs show that most of the Mg
++
is already available in the soluble form, whereas Ca
++
is sequestered but available for release.

We propose that both normal fertilization and ionophore activation affect the metabolism of the egg by releasing Ca
++
sequestered in intracellular stores.
Differences in Membrane Fluidity and Structure in Contact-Inhibited and Transformed Cells
Authors: Barnett Ronald E. , Furcht Leo T. , Scott Robert E.
Published: May 2006

Studies on contact-inhibited mouse embryo fibroblast 3T3 cells and 3T3 cells transformed by oncogenic RNA and DNA viruses and by a chemical carcinogen have demonstrated differences in plasma membrane architecture. Spin-label and freeze-fracture ultrastructural studies have shown that contact-inhibited cells have ordered membrane lipids and aggregated intramembranous particles, whereas transformed cells have fluid membrane lipids and randomly distributed intramembranous particles. These findings suggest a model for how changes in the cell membrane may account for some of the characteristic differences observed between contact-inhibited and transformed cells.
Ferritin-Conjugated Antibodies Used for Labeling of Organelles Involved in the Cellular Synthesis and Transport of Procollagen
Authors: Olsen Bjørn R. , Prockop Darwin J.
Published: May 2006

An improved procedure was used to conjugate ferritin to antibodies specific for the NH
2
-terminal extensions on the precursor form of collagen known as procollagen. The ferritin-antibody conjugates were then used to determine the localization of procollagen in fibroblasts isolated from chick-embryo tendons. Procollagen was found in the cisternae of the endoplasmic reticulum, indicating that the protein passes into this compartment early in its biosynthesis. Specific labeling of large Golgi vacuoles was also observed, suggesting that this compartment is also involved in the secretory process. When cells were incubated with colchicine so that the secretion of procollagen was delayed, there was an increase of large, smooth-surfaced vacuoles in the cells and these vacuoles were labeled with the ferritin-antibody conjugate.
Effects of Buoyancy and of Magnetic Forces on Osmotic Pressure
Authors: Wenger C. Bruce
Published: May 2006

The commonly held view that the mechanism of osmotic pressure is a mass action effect at the semi-permeable membrane has recently been challenged by several authors who propose that solute molecules, in bombarding the free surface of the solution, subject the solvent to a negative hydrostatic pressure. Thus, they argue that osmotic pressure is a purely hydrostatic phenomenon. Experimental findings that they cite in support of their concept are here analyzed and shown to be consistent with the mechanism of a mass action effect at the semipermeable membrane.
Sulfite Reductase Activity in Extracts of Various Photosynthetic Bacteria
Authors: Peck H. D. , Tedro S. , Kamen M. D.
Published: May 2006

Extracts of representative bacterial strains from the various families of photosynthetic prokaryotes are demonstrated to possess significant levels of sulfite reductase [EC 1.8.99.1; hydrogen-sulfide: (acceptor)oxidoreductase] activity with reduced methyl viologen as electron donor, but not NADPH
2
. The enzyme is localized primarily in the soluble fraction of the extracts, in contrast to adenylysulfate reductase [EC 1.8.99.2; AMP, sulfite: (acceptor) oxidoreductase], which is bound normally in the membrane fractions of those bacteria in which it is found. Assignment of the sulfite reductase activities to the biosynthetic (“assimilatory”) pathway is suggested by levels of specific activity noted and ready solubility.
Intragenomal Distribution of DNA Repair Synthesis: Repair in Satellite and Mainband DNA in Cultured Mouse Cells
Authors: Lieberman Michael W. , Poirier Miriam C.
Published: May 2006

DNA repair synthesis was examined in mouse satellite and mainband DNA derived from confluent Balb/c 3T3 cells damaged with ultraviolet radiation or
N
-acetoxy-
2
-acetylaminofluorene. Two different approaches were used: (
i
) Contact-inhibited cells were treated with hydroxyurea to reduce replicative synthesis to low levels; and (
ii
) bromodeoxyuridine was used to label newly replicated DNA in cells that had escaped contact inhibition. DNA was separated into mainband and satellite fractions in Ag
+
-Cs
2
SO
4
gradients. After treatment with either ultraviolet radiation or
N
-acetoxy-2-acetylaminofluorene, repair synthesis occurred to the same extent in mainband and satellite DNA. Repair synthesis increased over an ultraviolet radiation dose range of 30-200 erg/mm
2
, and the extent of repair in the two DNA species was similar at each dose level. An analysis of the separated strands of satellite DNA from ultraviolet-irradiated cells indicated that the extent of repair is closely correlated with the availability of pyrimidines for cyclobutyl dimer formation and provided evidence that repair synthesis occurs at the site of damage. Within the precision of our experiments the results suggest that at least one group of highly repetitive, nontranslated DNA sequences is repaired to about the same extent as the rest of the genome.
Transfer Factor: A Subcellular Component that Transmits Information for Specific Immune Responses
Authors: Rosenfeld Steven , Dressler David
Published: May 2006

Two transfer factors have been prepared in an animal model system, the guinea pig. They are both small molecules, derived from the leukocytes of immunologically experienced individuals, and capable of transferring information for specific immune responses to naive individuals.
Chemical Synthesis of a Primer and Its Use in the Sequence Analysis of the Lysozyme Gene of Bacteriophage T4
Authors: Padmanabhan R. , Jay Ernest , Wu Ray
Published: May 2006

We have developed a general approach for determining the nucleotide sequence of a gene, with the aid of a deoxyribonucleotide primer of defined sequence. The selection of the primer sequence was based on a short segment of mRNA sequence of T4 phage lysozyme. A tetradecadeoxyribonucleotide primer was chemically synthesized and its sequence verified by sequence analysis. This primer was found to bind to the single-stranded region of the exonuclease III-treated T4 DNA, and specific nucleotides were incorporated to its 3′ end. The result indicated that this primer was bound to the expected location on the T4 DNA. Therefore, long sequences of the T4 lysozyme gene can now be determined from this specific starting point.
Preferential Inhibition of the Growth of Virus-Transformed Cells in Culture by Rifazone-8
2
, a New Rifamycin Derivative
Authors: Bissell Mina J. , Hatie Carroll , Tischler Allan N. , Calvin Melvin
Published: May 2006

Rifazone-8
2
, a new rifamycin derivative, is shown to preferentially inhibit the growth of virus-transformed chick cells in culture. Macromolecular synthesis and glucose uptake of transformed cells are also appreciably decreased in the presence of low concentrations of rifazone-8
2
where the normal cells appear unaffected. While rifazone-8
2
is shown to be a selective inhibitor of RNA-directed DNA polymerase
in vitro
, its action on the growth of transformed cells may involve some other mechanism.
K
(π
n
)-Torsors and the Interpretation of “Triple” Cohomology
Authors: Duskin J.
Published: May 2006

A categorical, semi-simplicial interpretation theory for “triple” cohomology is outlined which uses the groups TORS

U

n

[
X
;π] of connected components of certain categories of
K
(π,
n
)-torsors (higher dimensional generalizations of locally trivial principal fiber bundles) to interpret the cohomology groups, i.e., TORS

U

n

[
X
;π] [unk]

H
n

(
X
;π),
n
≥ 1.
Entropy, Dynamics, and Molecular Chaos
Authors: Henin F. , Prigogine I.
Published: May 2006

With the help of simple probabilistic models of Kac and McKean, we discuss the meaning of the generalized expression for entropy that was recently introduced by our group and compare it with Boltzmann's expression. We emphasize the fact that Boltzmann's formulation in terms of the single particle distribution function,
f
1
, requires very restricted assumptions about the preparation of the system (chaos) and the nature of the collision mechanism (Markov processes).

Our generalized [unk]-theorem, however, refers to the complete system; in general, it does not lead to an [unk]-theorem for the single particle distribution function,
f
1
. It is valid whatever the preparation of the system. In McKean's model, situations exist where it gives the correct behavior while the Boltzmann's expression for entropy becomes meaningless. In addition, in Kac's model, we show that correlations reach equilibrium more rapidly than
f
1
and that there is an
asymptotic
regime where both formulations give the same result.
Promotion of Fluorescence upon Binding of Colchicine to Tubulin
Authors: Bhattacharyya B. , Wolff J.
Published: May 2006

Colchicine, which does not fluoresce in aqueous media and organic solvents, exhibits marked fluorescence on combination with brain tubulin, with a corrected excitation maximum at 362 nm, an emission maximum at 435 nm, and a quantum yield of about 0.03. From fluorescence measurements it was found that rat brain tubulin binds 0.83 moles of colchicine per dimer (molecular weight 110,000) with an association constant of 3.2 μM
-1
at pH 7.0 and 37°. These results are in excellent agreement with those obtained with the binding of [
3
H]-colchicine. The enthalpy of binding is 10 kcal/mole, with an entropy change of 62 entropy units. The fluorescence can be ascribed to the tropolone moiety. However, the A ring of colchicine is also involved in binding. Denaturing agents abolish fluorescence, whereas podophyllotoxin, another antimitotic agent, decreases fluorescence competitively. Fluorescence is a convenient method for determining the binding of colchicine to tubulin that does not require the separation of free colchicine from bound colchicine and yields values for physical and biochemical parameters that are in excellent agreement with those obtained from the binding of [
3
H]colchicine.
Fusion and Compatibility of Camphor and Octane Plasmids in
Pseudomonas
Authors: Chou George I. N. , Katz Dvorah , Gunsalus I. C.
Published: May 2006

The octane (OCT) plasmid in
Pseudomonas putida
derived from the ω-hydroxylase-carrying strain of Coon and coworkers is transferable to the camphor (CAM) plasmid-bearing strain by conjugation or by transduction. While the majority of the Cam
+
Oct
+
exconjugants segregate Cam
+
or Oct
+
cells, exconjugants with stable Cam
+
Oct
+
phenotype (CAM-OCT) can be detected at a low frequency. The transductants are all of the CAM-OCT phenotype. In the stable Cam
+
Oct
+
strains, the OCT plasmid resembles the CAM plasmid with respect to curing by mitomycin C, transfer in conjugation, and reaction to
ts
(temperature-sensitive) mutation specifically affecting CAM plasmid replication. Therefore, it is suggested that certain regions of homology exist between the CAM and OCT plasmids that enable them to recombine to form a single plasmid, and to overcome the incompatibility barrier that prevents their coexisting.
A Deletion Mutation Placing the Galactokinase Gene of
Escherichia coli
under Control of the Biotin Promoter
Authors: Ketner Gary , Campbell Allan
Published: May 2006

A deletion has been isolated which fuses
galK
and presumably
galT
to the promoter and operator of the
bioA
operon. The deletion has endpoints in
bioA
and
galE
, and leaves the operator-proximal end of
bioA
intact and the regulatory sites themselves functional. In bacterial strains which carry the deletion, the expression of
galK
is regulated by biotin, although due to the inefficiency of the
bioA
promoter even the fully derepressed level of galactokinase is low. Electron micrographic examination of the mutation shows that it is a simple deletion, uncomplicated by other chromosomal abnormalities.
Expression of Phage Transcription in P2 Lysogens Infected with Helper-Dependent Coliphage P4
Authors: Lindqvist Björn H.
Published: May 2006

The DNA of helper-dependent coliphage P4 and the DNA of its helper—P2—show no detectable sequence homology as measured by DNA·DNA hybridization. The lack of cross-hybridization permits direct analysis of P4 as well as of P2 transcription in P4-infected P2 lysogens by RNA·DNA hybridization. P4-transactivated P2 transcription can be detected around 20 min after P4 infection of the P2 lysogen and the rate (per infected cell) of that transcription becomes equal to that of the P4 transcription at the end of the latent period of P4. Furthermore, P4 transcription appears to be stimulated by the presence of the helper. Conceivably, P2 codes for a stimulator of P4 transcription. Rifamycin has been used to investigate the role of the host RNA polymerase during P4 transactivation of P2 transcription. The results exclude the participation of a P4-coded RNA polymerase and indicate that the original host RNA polymerase is responsible for the bulk of P4 and P2 transcription during transactivation.
The Specificity of Dimethylbenzylrifampicin as an Inhibitor of Viral Induced Transformation
Authors: Smith Helene S. , Hackett Adeline J.
Published: May 2006

The effect of 2′,6′-dimethyl-
N
(4′)-benzyl-
N
(4′)- [desmethyl]rifampicin on viral transformation induced by two unrelated oncogenic viruses was compared. Transformation of Balb/3T3 cells by the small, DNA-containing papova virus simian virus 40 was completely normal under conditions where transformation by the large, RNA-containing oncornavirus murine sarcoma virus was inhibited more than 150-fold. For these experiments a resistant variant of Balb/3T3 was selected that grows well in high concentrations of the drug, is not dependent on the drug for growth, and is probably not blocked at the level of drug uptake. These data show that dimethyl-benzylrifampicin specifically inhibits oncornavirus-induced transformation rather than nonspecifically inhibiting cellular growth or transformation.
Sequences Present in Both Human Leukemic Cell Nuclear DNA and Rauscher Leukemia Virus
Authors: Baxt William G.
Published: May 2006

DNA synthesized by particulate fractions from human leukemic white blood cells has been subfractionated by hybridization to Rauscher leukemia virus 70S RNA followed by hydroxylapatite chromatography. The Rauscher-leukemia-virus-specific DNA fraction is shown to be complementary only to sequences present in the nuclear DNA of Balb/c mouse spleens infected by this virus and the nuclear DNA from human leukemic white blood cells, and not to sequences present in the nuclear DNA of normal Balb/c mouse spleens or the nuclear DNA of normal human white blood cells.
A Molecular Model of Action Potentials
Authors: Dubois D. M. , Schoffeniels E.
Published: May 2006

A quantitatively consistent model of nerve activity is given in terms of two main biochemical cycles narrowly interlocked: an acetylcholine cycle and a calcium cycle. The activity of both cycles is controlled among other things by the electric field and various allosteric effectors. As shown by digital simulations our model accounts for the basic properties of an action potential as described by the electrophysiologists. Thus the shape, time course, and behavior under voltage clamping conditions of both sodium and potassium permeability variations are adequately reproduced.
Resonance between a Prolate and a Superprolate Structure of the
162
Er Nucleus
Authors: Pauling Linus , Blethen John
Published: May 2006

Observed energy levels of
162
Er from the normal state
J
= 0 to the excited rotational state
J
= 18 correspond to values of the moment of inertia and rotational frequency that indicate that a pronounced change in structure occurs at about
J
= 14. It is shown that the observed values agree well with the values calculated on the assumption that there is resonance between a more stable prolate structure with a core of two spherons and a less stable superprolate structure with a core of three spherons in line.
Subellipticity on Pseudo-Convex Domains with Isolated Degeneracies
Authors: Kohn J. J.
Published: May 2006

Previous work has lead the author to conjecture necessary and sufficient conditions for the subellipticity of the [unk]-Neumann problem on pseudoconvex domains. Here we outline a general method which reduces the problem of subellipticity to inequalities between germs of C
∞
functions. We then describe how this method can be applied to prove the sufficiency of the conditions on domains whose boundaries have an isolated set of points on which the Levi form degenerates and such that in a neighborhood of these points the boundary is real analytic.
Persistent Noncytocidal Vesicular Stomatitis Virus Infections Mediated by Defective T Particles that Suppress Virion Transcriptase
Authors: Holland John J. , Villarreal Louis Perez
Published: May 2006

Infectious B virions of vesicular stomatitis virus were 100% lethal to BHK
21
(baby hamster kidney) cells when infecting alone, and persistent noncytocidal infection could not be achieved with cloned B virions alone. However, a mixture of B virions and homologous, short, defective, interfering particles (T particles) of a temperature-sensitive mutant of the virus regularly established persistently infected, noncytocidal carrier cultures. A long T particle was generated during establishment of the carrier culture; we show that this long T particle can establish and maintain persistent noncytocidal infection even when it infects cells along with virulent wild-type B virions. This long T particle causes the production of wild-type B virions with greatly reduced virion transcriptase (EC 2.7.7.6; RNA nucleotidyltransferase) levels when coinfecting the same cells, so it appears to prevent cytopathology by regulating virus transcription. The implications of these findings for rabies and other slowly progressing noncytocidal infections are discussed.
Amino-Acid Sequence of Dihydrofolate Reductase from a Methotrexate-resistant Mutant of
Streptococcus faecium
and Identification of Methionine Residues at the Inhibitor Binding Site
Authors: Gleisner John M. , Peterson Darrell L. , Blakley Raymond L.
Published: May 2006

The amino-acid sequence of dihydrofolate reductase (7,8-dihydrofolate:NADP
+
oxidoreductase, EC 1.5.1.4) from
S. faecium
var
Durans
strain A is reported, and methionine residues 28 and 50 are shown to be protected by the inhibitor aminopterin from carboxymethylation by iodoacetate which occurs in absence of the inhibitor. Comparison of the sequence with that of the
Escherichia coli
reductase reveals two domains of considerable homology, one (the N-terminal region) presumably concerned with dihydrofolate and inhibitor binding and the other with dinucleotide binding. No significant sequence homology was found between larger dehydrogenases and the dihydrofolate reductases, which must, therefore, have evolved from a different ancestral protein.
Hereditary Orotic Aciduria: Evidence for a Structural Gene Mutation
Authors: Worthy Thomas E. , Grobner Wolfgang , Kelley William N.
Published: May 2006

Orotic aciduria is a rare autosomal recessive disease in man due to a deficiency of orotate phosphoribosyltransferase (EC 2.4.2.10; orotidine-5′-phosphate:pyrophosphate phosphoribosyltransferase) and orotidine-5′-phosphate decarboxylase (EC 4.1.1.23; orotidine-5′-phosphate carboxy-lyase). We have compared certain physicochemical properties of orotidine-5′-phosphate decarboxylase from normal and mutant fibroblasts grown under identical conditions. Orotidine-5′-phosphate decarboxylase from homozygous mutant cells was more thermolabile and exhibited a different electrophoretic mobility when compared to the enzyme from normal cells; orotidine-5′-phosphate decarboxylase from one heterozygous cell strain exhibited an intermediate thermolability while the other heterozygote displayed a thermal inactivation curve indistinguishable from normal. The enzyme from both normal and mutant cells exhibited biphasic kinetics with the same apparent Michaelis constants. These data suggest that the molecular defect in the enzyme of this patient with orotic aciduria is due to a mutation in a gene that affects the structure of either orotate phosphoribosyltransferase or orotidine-5′-phosphate decarboxylase and cannot be attributed to a mutation in a regulatory gene, as previously suggested.
A DNA-Protein Complex Involved in Bacteriophage ϕX174 Particle Formation
Authors: Weisbeek Peter J. , Sinsheimer Robert L.
Published: May 2006

A ϕX-specific DNA-protein complex has been isolated from ϕX-infected cells. This complex contains infective circular single-stranded DNA, the proteins of the genes
F, G, H
, and
J
in the same proportions as in the phage particle, and, in addition, the gene
D
-protein. The
D
-protein makes up 12-22% of the protein part of the complex. The sedimentation value of the complex is about 140 S.
In vitro
, the complex can be converted to the normal 114S phage particle (with a concomitant loss of its D-protein) or to an uninfective 70S particle and a small amount of free single-stranded DNA. The fast sedimenting particle is not associated with membranes.
Poly(ADP-Ribose): Release of Template Restriction in HeLa Cells
Authors: Roberts Jerry H. , Stark Patricia , Smulson Mark
Published: May 2006

Evidence is presented to show that ADP-ribosylation of nuclear proteins by poly(ADP-ribose) polymerase enhances template-primer activity of HeLa cell nuclear DNA. We used
Escherichia coli
DNA polymerase I (EC 2.7.7.7; DNA nucleotidyltransferase) as an exogenous probe of nuclear DNA status. Neither NAD nor free poly(ADP-ribose) acts directly on the bacterial enzyme. The stimulation is specific for formation of ADP-ribosylated proteins and is not a generalized polyanion or nucleotide effect on chromatin. The release of template restriction is proportional to the capacity of a given cell line to synthesize poly(ADP-ribose); both the stimulation and poly(ADP-ribose) formation are coordinately proportional to NAD concentration. Binding studies with DNA polymerase indicate exposure or generation of additional 3′-OH primer sites due to ADP-ribosylation in intact nuclei. With intact cells, there appears a correlation among growth, physiological template restriction, and the above effects of ADP-ribosylation.
Murine Sarcoma Virus Gene Expression: Transformants Which Express Viral Envelope Glycoprotein In The Absence Of The Major Internal Protein And Infectious Particles
Authors: Bilello John A. , Strand Mette , August J. T.
Published: May 2006

Expression of the major internal protein and the envelope glycoprotein of murine C-type viruses in focus-derived lines of normal rat kidney cells infected with Kirsten murine sarcoma virus was measured by radioimmunoassay. Of the clones selected, which do not produce virus particles or the major viral structural protein, approximately half express the viral envelope glycoprotein at concentrations found in productively infected cells. Expression of the envelope glycoprotein did not appear to alter significantly the properties of the transformed cells in culture.
Atomic Regime in Which the Magnetic Interaction Dominates the Coulomb Interaction for Highly Excited States of Hydrogen
Authors: Mueller Ronald O. , Hughes Vernon W.
Published: May 2006

The atomic regime in which the interaction of the electron with an external magnetic field dominates the Coulomb interaction with the nucleus, relevant to pulsars, can be realized at laboratory magnetic fields for discrete autoionized states of hydrogen, at energies above the ionization limit. Approximate wave functions, energy levels, and electric dipole transition probabilities are presented for hydrogen, and an atomic beam absorption spectroscopy experiment at 50 kG is proposed to study this new regime.
Dissociation and Interaction of Individual Components of a Degradative Plasmid Aggregate in
Pseudomonas
Authors: Chakrabarty A. M. , Friello Denise A.
Published: May 2006

The transfer of the OCT plasmid from
Pseudomonas oleovorans
to
Pseudomonas putida
strain PpGl results in the acquisition of three independent replicons: OCT, factor K, and the MER plasmid. OCT is a nontransmissible plasmid harboring genes that code for the enzymes responsible for the degradation of
n
-octane. Factor K is a transfer plasmid capable of mobilizing OCT as well as chromosomal genes but incapable of enhancing transfer frequencies of other transmissible plasmids such as CAM, SAL, or RP-1. MER is a self-transmissible plasmid which can confer resistance to high concentrations of mercury salts. While OCT and MER are incompatible with CAM, factor K is compatible with it. Transmissible plasmids such as SAL, CAM, MER, or RP-1 cannot mobilize OCT to any significant extent, and exert strong repression on factor K-mediated transfer of chromosomal genes.
Specification of Positional Information in Retinal Ganglion Cells of
Xenopus laevis:
Intra-Ocular Control of the Time of Specification
Authors: Hunt R. K. , Jacobson M.
Published: May 2006

Programming events in the stage 28-31 clawed frog embryo partly determine the organization of the future retinotectal map by specifying the permanent reference axes for cellular positional information in the retina. Thus, when transplanted in 180°-rotated orientation into a stage 27/28 orbit, an
unspecified
(stage 28 or younger) eye can acquire new axes and develop a normally-oriented retinotectal map, whereas a
specified
(stage 31 or older) eye retains its original axes and develops an inverted map. We have used the retinotectal map to determine when (and under what conditions) specification with changes in orientation occurred in eye primordia serially transplanted between embryos of different stages. Specification was not precipitated when stage 22/23 eyes were grafted into stage 28-32 embryos or explanted
in vitro
, nor was specification delayed when stage 28 eyes were grafted into embryos younger than stage 28. Control experiments confirmed the general correlation between the time of specification and the stage of the eye primordium. We infer that intraocular regulatory mechanisms control the time of specification.
Topology of Repeated Sequences: Relationship of Nuclear RNA to the Repeated Sequences of the Main and Satellite DNA in Mouse Plasmocytoma Cells
Authors: Pagoulatos G. N.
Published: May 2006

The topology of repeated sequences in mouse plasmocytoma DNA was studied by high-resolution CsCl density gradient centrifugation and heterogeneous nuclear RNA·DNA hybridization. Satellite region DNA of plasmocytoma cells contains additional components and hybridizes specifically with entire heterogeneous nuclear RNA molecules. A linkage is demonstrated between the A+T-rich satellite sequences and those hybridizing with heterogeneous nuclear RNA. Heavy DNA also hybridizes specifically with heterogeneous nuclear RNA molecules that show sequence similarity to heterogeneous nuclear RNA hybridized to satellite DNA. These results could suggest that part of satellite DNA became heavier after integration of some other DNA species, which could belong to a virus or to immunoglobulin repetitive genes. Dispersed, highly repetitive, short nucleotide sequences could constitute recognition sites for such a process.
Energy Transfer Mechanisms in Mitochondria
Authors: Kemeny Gabor
Published: May 2006

The problem of free energy transfer and transduction in mitochondria is reviewed from the point of view of conservative and dissipative mechanisms. Excited states are inherently dissipative and are not considered viable possibilities. If the free energy is already a local minimum and present in the form of potential energy, conservative transfer is possible within a properly designed medium. The design features are compatible with what is known about mitochondria.
Critical Length of the Transport-Dominated Region for Oscillating Non-Linear Reactive Processes
Authors: Nazarea A. D.
Published: May 2006

Beyond an instability, non-linear processes can give rise to reactive modes exhibiting sustained oscillations in particle numbers. The coupling of such an oscillatory mode to diffusional transport in a system can cause coherent spatio-temporal structures to arise and persist indefinitely, far from thermal equilibrium, provided the system is above some critical size and is maintained open to mass and energy transfer.

In the case of one spatial dimension, the critical size of the system, following Goldbeter [
Proc. Nat. Acad. Sci. USA
70, 3255-3259 (1973)], can be defined as that size up to which there exists exactly one unique time-independent solution (which is completely transport dominated) to the macroscopic equation that characterizes the coupling of the reactive mode to diffusional transport and which is subject to inhomogeneous boundary conditions. A theoretical estimate of the critical size is derived (valid for arbitrary systems involving multicomponent non-linear reactive processes possessing an oscillatory mode) by making use only of the parameter-dependent period of the oscillatory mode and of the elements of the diffusion tensor. This estimate specifically takes cross-diffusion into account. In the special case of simple diagonal diffusion, an illustrative comparison is made with the prediction of a more model-specific estimate of Goldbeter that involves a model for glycolytic oscillations.
Kinetics of the Decomposition of Hydrogen Peroxide Catalyzed by Ferric Ethylenediaminetetraacetate Complex
Authors: Walling Cheves , Partch Richard E. , Weil Tomas
Published: May 2006

Added substrates, acetone and
t
-butyl alcohol, strongly retard the decomposition of H
2
O
2
brought about by ferric ethylenediaminetetraacetate (EDTA) at pH 8-9.5. Their relative effectiveness and the kinetic form of the retardation are consistent with their interruption of a hydroxyl radical chain that is propagated by HO· attack both upon H
2
O
2
and on complexed and uncomplexed EDTA. Similar retardation is observed with decompositions catalyzed by ferric nitrilotriacetate and hemin, and it is proposed that such redox chains may be quite a general path for transition metal ion catalysis of H
2
O
2
decomposition.