bluuebunny/crossref_metadata_2025 huggingface dataset:
Involvement of Two Protein Factors and ATP in
In Vitro
DNA Synthesis Catalyzed by DNA Polymerase III of
Escherichia coli
Authors: Hurwitz Jerard , Wickner Sue
Published: May 2006

The
in vitro
conversion of single-stranded DNA from bacteriophage fd to duplex structures depends on
E. coli
RNA polymerase, DNA polymerase III, riboand deoxyribonucleoside triphosphates, Mg
+2
, spermidine or DNA-unwinding protein of
E. coli
, and two additional protein factors, referred to here as Factors I and II. These two factors are also essential for dTMP incorporation catalyzed by DNA polymerase III and dependent on poly(dA)·oligo(dT) primer-template. In the latter reaction, there is an absolute dependency on ATP or dATP.
Solutions to the Cost-of-Selection Dilemma
Authors: Grant Verne , Flake Robert H.
Published: May 2006

There are various biologically realistic ways around the cost-of-selection restriction on rapid multiple-gene substitution. Some of these ways depend upon particular forms of interaction or linkage in the genes undergoing substitution; other ways depend on particular conditions of population size and structure. The special genotypic and populational conditions required for rapid evolutionary change in genetically complex characters are not unusual in higher organisms.
Carbohydrate Composition of the Membrane Glycoprotein of Vesicular Stomatitis Virus Grown in Four Mammalian Cell Lines
Authors: Etchison James R. , Holland John J.
Published: May 2006

The carbohydrate composition of the membrane glycoprotein of vesicular stomatitis virus has been determined for virus grown in four different mammalian cell lines. The glycoprotein contains mannose, galactose,
N
-acetylglucosamine, and neuraminic acid as the major carbohydrate components, whereas
N
-acetyl-galactosamine and fucose are present in lesser amounts. The glycoprotein contains approximately 9-10% carbohydrate regardless of the host cell in which it is synthesized. Small quantitative differences are evident in the composition of the component sugars of the glycoprotein when the virus is grown in different host cells, and the glycoprotein of virus grown in a mouse fibroblast line (L cells) lacks fucose. The major oligosaccharide moieties of the virus glycoprotein from all cells are approximately the same size (3000-3400 daltons). The data presented here, in conjunction with previous data, indicate that the viral glycoprotein contains two major oligosaccharide constituents regardless of the host cell in which it is synthesized.
A Comparative Study of Cytokinesins I and II and Zeatin Riboside: A Reply to Carlos Miller
Authors: Wood Henry N. , Rennekamp Michael E. , Bowen David V. , Field Frank H. , Braun Armin C.
Published: May 2006

Two cell-division-promoting factors, which have partition coefficients of 1.9 and 2.75 determined by 500-tube countercurrent distribution in a butanolwater system, have been repeatedly isolated in this laboratory from crown gall tumor tissues of
Vinca rosea
L. These substances have been given the trivial names cytokinesin I and cytokinesin II, respectively. Chemical and mass spectrometric analyses suggest that both cytokinesins are substituted hypoxanthines and are thus very different compounds from the 6-substituted adenyl cytokinins. Carlos Miller, using a very different and far more drastic isolation procedure, obtained one main cell-division-promoting factor from these same tumor tissues, which he identified as ribosyl-trans-zeatin. On the basis of this finding, and without an attempt to repeat our studies, questions have been raised by Miller concerning the existence of the cytokinesins as biologically active substances. We have, therefore, compared some pertinent physical, chemical, and biological properties of the cytokinesins with those of zeatin riboside, have demonstrated that these three substances can be cleanly separated from one another by a number of different methods and that each behaves as a pure substance in the several systems, and, finally, we have shown that the cytokinesins are not contaminated with ribosyl-trans-zeatin and thus do not owe their biological activity to such a contaminant.
Detection of Mutagenic Activity in Cigarette Smoke Condensates
Authors: Kier Larry D. , Yamasaki Edith , Ames Bruce N.
Published: May 2006

The
Salmonella typhimurium
microsomal test system for mutagenic activity was successfully used to detect the presence of mutagenic compounds in the smoke condensates of several types of cigarettes. The condensates were shown to contain compounds which could cause frameshift mutations when activated by microsomal enzymes. An analysis of fractions of smoke condensate revealed that the detected mutagenic activity was distributed in several of the fractions. Most of the activity of the whole condensate was in basic fractions and in a weakly acidic fraction. Condensates from cigarettes treated with magnesium nitrate differed from other condensates in two respects. They contained frameshift mutagens which did not require microsomal activation and mutagens which could cause base-pair substitution mutations. Although the detection system usually employs rat liver microsomal preparations, a rat lung microsomal preparation was also found to be capable of converting smoke condensates and known chemical carcinogens into mutagenic forms.
The Three Dimensional Structure of the Lysozyme from Bacteriophage T4
Authors: Matthews B. W. , Remington S. J.
Published: May 2006

The three dimensional structure of the lysozyme from bacteriophage T4 has been determined from a 2.5 Å resolution electron density map. About 60% of the molecule is in a helical conformation and there is one region consisting of antiparallel β-structure. The polypeptide backbone folds into two distinct lobes linked in part by a long helix. In the region between the two lobes, there is a cleft which deepens into a hole or cavity, about 6-8 Å in diameter, extending from one side of the molecule to the other. This opening is closed off by side chains which extend to within 3-5 Å of each other. A number of mutant lysozymes in which residues in the vicinity of the opening are modified have markedly reduced catalytic activity, suggesting that this region of the molecule may be catalytically important. The three dimensional structure of T4 phage lysozyme is quite different from that of hen egg-white lysozyme although it is not clear at this time whether or not the mechanisms of catalysis of the respective enzymes are related.
Viral DNA in Transformed Cells. III. The Amounts of Different Regions of the SV40 Genome Present in a Line of Transformed Mouse Cells
Authors: Botchan Michael , Ozanne Brad , Sugden Bill , Sharp Phillip A. , Sambrook Joe
Published: May 2006

32
P-Labeled SV40 DNA was treated sequentially with restricting endonucleases
Eco
RI and
Hpa
I, and the resulting four fragments of DNA were separated by gel electrophoresis. The kinetics of renaturation of each of the fragments and of complete SV40 DNA were measured in the presence of DNA extracted from the SVT2 line of SV40-transformed mouse cells. It was found that these cells contain about six copies of a segment of DNA which includes the early region of the SV40 genome, and about one copy of the late viral sequences.

To map the region of the viral genome which is transcribed in SVT2 cells, separated strands of each of the four fragments were prepared and hybridized to total transformed cell RNA. Part of the E strands of the two DNA fragments (A and C) which span the early region of the SV40 genome were found to enter the hybrid.
Carbon-13 Nuclear Magnetic Resonance Spectroscopy. Structure of the Anticoagulant Warfarin and Related Compounds in Solution
Authors: Giannini Donald D. , Chan Kenneth K. , Roberts John D.
Published: May 2006

Carbon-13 nuclear magnetic resonance spectra have been obtained for the coumarin-related compounds warfarin and phenprocoumon. The spectral assignments indicate that warfarin exists as a mixture of cyclic hemiketal diastereomers in dimethyl sulfoxide solution. The sodium salt of warfarin exists as the ringopen form in water solution.
Are Recommended Daily Allowances for Vitamin C Adequate?
Authors: Pauling Linus
Published: May 2006

The Recommended Dietary Allowance of vitamin C (ascorbic acid) for adults has now been set at 45 mg day
-1
by the U.S. Food and Nutrition Board. This intake suffices to prevent scurvy in most people. It is, however, much less than the optimum intake, the intake that leads to the best of health. A larger intake decreases the incidence and severity of the common cold and other diseases. Ascorbic acid has antiviral and antibacterial activity and is required for phagocytic activity of leukocytes. Several arguments indicate that for different human beings the optimum intake lies between 250 mg day
-1
and a much higher value, 5000 mg day
-1
or more. It is proposed that the present Recommended Dietary Allowance of 45 mg day
-1
of vitamin C for adults be renamed the Minimum Dietary Allowance, defined as the amount needed to prevent scurvy, and that, after consideration of the evidence about intake and the best of health, there be formulated another category of values, the Recommended Daily Intake, with the suggested range of 250 mg day
-1
to 4000 mg day
-1
of ascorbic acid for an adult.
Chemical Composition of Nebulosities in the Magellanic Clouds
Authors: Aller L. H. , Czyzak S. J. , Keyes C. D. , Boeshaar G.
Published: May 2006

From photoelectric spectrophotometric data secured at Cerro Tololo Interamerican Observatory we have attempted to derive electron densities and temperatures, ionic concentrations, and chemical abundances of He, C, N, O, Ne, S, and Ar in nebulosities in the Magellanic Clouds. Although 10 distinct nebulosities were observed in the Small Cloud and 20 such objects in the Large Cloud, the most detailed observations were secured only for the brighter objects. Results for 30 Doradus are in harmony with those published previously and recent work by Peimbert and Torres-Peimbert. Nitrogen and heavier elements appear to be less abundant in the Small Cloud than in the Large Cloud, in accordance with the conclusions of Dufour. A comparison with the Orion nebula suggests He, N, Ne, O, and S may all be less abundant in the Megellanic Clouds, although adequate evaluations will require construction of detailed models. For example, if we postulate that the [NII], [OII], and [SII] radiations originate primarily in regions with electron temperatures near 8000°K, while the [OIII], [NeIII], [ArIII], and H radiations are produced primarily in regions with
T
ε
= 10,000° K, the derived chemical abundances in the clouds are enhanced.
Stimulation of Division of Sparse and Confluent 3T3 Cell Populations by a Fibroblast Growth Factor, Dexamethasone, and Insulin
Authors: Gospodarowicz Denis , Moran John S.
Published: May 2006

The stimulation of division of Balb/c 3T3 mouse fibroblasts by fibroblast growth factor alone and in combination with insulin and a glucocorticoid (dexamethasone) has been investigated. Fibroblast growth factor stimulates DNA synthesis in sparse, quiescent cultures maintained in a low serum concentration, but does not support more than two division cycles. In the presence of dexamethasone, the growth factor supports continuous division cycles. The addition of insulin significantly augments the response to fibroblast growth factor alone and slightly augments the response to growth factor plus dexamethasone. Fibroblast growth factor stimulates the division of confluent, quiescent cultures grown in 10% serum. When growth factor plus dexamethasone is added to such cultures, “contact inhibition” is overcome.
Singular Integrals and the Principal Series, III
Authors: Knapp A. W. , Stein E. M.
Published: May 2006

The intertwining operators for nonunitary principal series representations of a real semisimple Lie group are used to construct intertwining operators for all the series of unitary representations appearing in the Plancherel formula. The resulting machinery reduces computations with Harish-Chandra's
c
-functions and the Plancherel measure to computations with those
c
-functions and measures obtained from a minimal parabolic subgroup.
Some Population Genetic Models Combining Artificial and Natural Selection Pressures
Authors: Karlin S. , Carmeli D.
Published: May 2006

The evolutionary behavior of a diploid population characterized by a trait determined at one or two major loci subject to the combined effects of artificial and natural selection pressures is investigated. A number of different genotypic phenotypic associations are set forth, including additive allelic effects and additive loci effects with a variety of culling programs. Threshold selection schemes as well as culling favoring intermediate phenotypic values are considered. For these formulations results are reported concerning the dynamic progress of the population, a delineation of the numbers and properties of the stable equilibria outcomes, and a discussion of their qualitative and quantitative dependence on the two kinds of selection forces. The level of culling can be used as a control through which natural selection parameters can be estimated.
Chloramphenicol Restores Sigma Factor Activity to Sporulating
Bacillus subtilis
Authors: Segall Jacqueline , Tjian Robert , Pero Janice , Losick Richard
Published: May 2006

The σ subunit of RNA polymerase from sporulating
Bacillus subtilis
is markedly inhibited in its ability to direct active transcription of phage ϕe DNA
in vitro
. Treatment of sporulating bacteria with chloramphenicol rapidly restores σ activity, suggesting that sporulating cells contain an inhibitor of σ that is physiologically unstable or that becomes unstable after drug treatment. The hypothetical inhibitor is depleted exponentially with an apparent half-life of 11 min at 37°.
Heavy Meromyosin Mg-ATPase: Presteady-State and Steady-State H
+
Release
Authors: Chock Stephen P. , Eisenberg Evan
Published: May 2006

The presteady state and steady state release of protons during hydrolysis of ATP by myosin has been studied by using a proteolytic subfragment of myosin, heavy meromyosin, isolated from rabbit skeletal muscle. Under the conditions of 0.5 M KCl, 9 mM MgCl
2
, pH 8, and 25°, the rate of the H
+
initial burst is proportional to the concentration of ATP added, and shows no plateau even when the concentration of ATP added is increased up to 750 μM. The apparent second order rate constant is approximately 7 × 10
5
M
-1
sec
-1
. When the concentration of ATP added is equal to or less than the concentration of heavy meromyosin catalytic sites, the H
+
initial burst is followed by a slow exponential release of H
+
with a rate constant of 0.017 sec
-1
. This rate constant is equal to the steady state rate constant calculated for each heavy meromyosin catalytic site, suggesting that both sites split ATP independently. The magnitude of the H
+
released per ATP bound is always 0.4 in the initial burst, and 0.6 in the slow exponential phase, which equals to a total of 1 H
+
released per ATP hydrolyzed. On the basis of these observations, it is concluded that the H
+
initial burst may well represent a fast ionization of H
+
due to a conformational change as a result of nucleotide binding.
Regulation of Immune Response by Autogenous Antibody against Receptor
Authors: Kluskens L. , Köhler H.
Published: May 2006

BALB/c mice repeatedly immunized with
Pneumococcus
R36A vaccine produce antibodies to phosphorylcholine having the TEPC-15 myeloma idiotype (murine IgA myeloma protein that binds phosphorylcholine). The plaque-forming cell response to phosphorylcholine shows a decrease with repeated immunizations. In contrast, spleen cells from multiply immunized mice responded better
in vitro
than spleen cells from nonimmunized mice. The serum of animals immunized four or five times agglutinates TEPC-15-coated sheep erythrocytes. Inhibition of hemagglutination shows that the agglutinating activity is directed against the TEPC-15 idiotype. Sera from these mice, when added to cultures of normal spleen cells, specifically suppress the response to phosphorylcholine. The suppressive activity in the serum can be removed by solid absorption with TEPC-15. Evidently, repeated immunization with antigen induces two kinds of antibody responses: one directed against antigen and the other directed against the antibody to the antigen. It is proposed that this “auto” antibody against receptor is involved in the regulation of the immune response.
Mitogenic Properties of a Calcium Ionophore, A23187
Authors: Luckasen John R. , White James G. , Kersey John H.
Published: May 2006

A23187 is a carboxylic antibiotic that selectively transfers calcium, magnesium, and other divalent cations across biologic membranes. This ionophore was found to produce morphologic blast transformation, DNA synthesis, and mitosis in human lymphocytes. Several hours of ionophore-cell contact were necessary to produce optimal mitogenesis. The effects were highly dependent on the presence of extracellular calcium and much less dependent on extracellular magnesium. Lanthanum chloride prevented the development of the observed ionophore effects.

Results are consistent with the hypothesis that under physiologic conditions the interaction of antigens or mitogens with specific receptors at the lymphocyte membrane initiates events that alter calcium fluxes and result in increased cytoplasmic calcium. Increased cytoplasmic calcium is postulated to play a central role in the generation of surface-to-nuclear signals that initiate the process of DNA synthesis and cell division.
Redox Potentials of Certain Vitamins K: Implications for a Role in Sulfite Reduction by Obligately Anaerobic Bacteria
Authors: Wagner G. C. , Kassner R. J. , Kamen M. D.
Published: May 2006

Redox potentials of a menaquinone (MK-6), isolated in earlier researches from two species of the obligately anaerobic genus,
Desulfovibrio
, as well as two other vitamins K
2
—menaquinones (MK-5) and (MK-9)— have been determined polarographically. The measurements have been validated by determination of redox potentials of 1,4-naphthoquinone and vitamin K
1
which agree with published potentiometric values. E
m7
for menaquinone (MK-6) is -0.067 ± 0.010 V. Redox potentials calculated for terminal acceptor couples currently proposed in the mechanisms of sulfate reduction by
Desulfovibrio
are consistent with the involvement of menaquinone (MK-6) in at least one of the steps postulated during electron transfer with ultimate production of sulfide.
Immunohistochemical Localization of Glutamate Decarboxylase in Rat Cerebellum
Authors: Saito Kihachi , Barber Robert , Wu Jang-Yen , Matsuda Tomohiro , Roberts Eugene , Vaughn James E.
Published: May 2006

Glutamate decarboxylase (L-glutamate l-carboxylase; EC 4.1.1.15), the enzyme in brain that forms γ-aminobutyric acid, was made visible on sections of rat cerebellum by use of rabbit antiserum to purified mouse-brain glutamate decarboxylase. Cerebellar sections obtained from rats that were perfused with 4% paraformaldehyde were treated with antiserum against the enzyme or with serum from unimmunized rabbits, washed, and then incubated with peroxidase-labeled goat antibody against rabbit immunoglobulin. The glutamate decarboxylase was made visible on sections by means of the product formed by the action of peroxidase on 3,3′-diaminobenzidine and H
2
O
2
. A weak and diffuse reaction was observed in Purkinje cell bodies, suggesting the occurrence of the enzyme within these cells. In addition, an intense, punctate deposition of reaction product was located around the Purkinje cells and around the neurons of the deep cerebellar nuclei, suggesting the impingement of many nerve terminals containing the enzyme upon these neuronal surfaces. No specific reaction product was observed in sections treated with serum from unimmunized rabbits. The distribution of glutamate decarboxylase observed in our preparations is consistent with a large body of indirect biochemical, physiological, and morphological data dealing with the synaptic role of γ-aminobutyric acid neurons in the cerebellum.
Tandem Duplication in Bacteriophage P2: Electron Microscopic Mapping
Authors: Chattoraj Dhruba K. , Inman Ross B.
Published: May 2006

The physical position of
vir37
, a new immunity-insensitive mutant of
Escherichia coli
bacteriophage P2, was mapped by the electron microscopic heteroduplex method. In P2
vir37
, a segment equivalent to 2.8% of P2 DNA is added. The addition was characterized as a tandem duplication of the segment occurring between 77.2 and 80.0% from the left end of P2 DNA (the right half of P2 DNA is arbitrarily defined, from denaturation map studies, as the half richer in A + T). The point of addition of the duplicated segment (the “novel-joint”) was, thus, 80.0% from the left end of P2 DNA. On the basis of previous studies on P2
vir22
, it was tentatively concluded that the physical and genetic maps of P2 are colinear. This conclusion is now further supported by physical and genetic data on P2
vir37
.
Migration and Species Diversity in the Tropics
Authors: Klopfer P. H. , Rubenstein D. I. , Ridgely R. S. , Barnett R. J.
Published: May 2006

If the young of a dominant species are subjected to disproportionately heavy predation, this, together with a limitation on food, can promote a high species diversity. This is seen among tropical birds, which are simultaneously exposed to both conditions to a far greater degree than are Temperate Zone species. Migration to the Temperate Zones during the spring provides a release from these restraints, while also precluding breeding in the Tropics.
On the Very Rapid Enhancement by D
2
O of the Temperature-Tolerance of Adult
Drosophila
Authors: Pittendrigh Colin S. , Cosbey Elizabeth S.
Published: May 2006

Deuterium oxide, D
2
O, increases the temperature-tolerance of
Drosophila pseudoobscura
when it is administered to adult flies as a sucrose solution. The effect is very rapidly exerted; it is detected within 10 min after the flies have a brief (10 min) opportunity to drink. This increased resistance to heat-death surely implies an increased resistance of macromolecules to thermal denaturation. D
2
O is known to exert such an effect on
in vitro
protein solutions. The speed with which the increased stability develops clearly implicates a solvent action of D
2
O, and is most easily understood if the effect is traceable to enhancement of the hydrophobic interactions which contribute to conformational stability. The increased strength of deuterated hydrogen bonds cannot be excluded however. The possible bearing of these results on the hypothesis that D
2
O always increases the period of circadian oscillations by “diminishing the apparent temperature” is briefly considered.
A Mutant of
Escherichia coli
Defective in Leucyl, Phenylalanyl-tRNA-Protein Transferase
Authors: Soffer R. L. , Savage M.
Published: May 2006

A mutant of
E. coli
that lacks leucyl,-phenylalanyl-tRNA-protein transferase (EC 2.3.2.6) has been isolated. Ability to produce the two activities could be introduced into the mutant from an F′ strain whose episome contains genetic material located between 45 and 54 min on the
E. coli
chromosome. When grown into stationary phase and resuspended in minimal medium with glycerol, the mutant exhibited a marked lag before resuming growth. Revertants that did not show this lag were selected and were found to have regained both transfer activities. Extracts of wild-type, mutant, and revertant strains were compared as acceptors for the enzymatic transfer of radioactive phenylalanine. Analysis of the labeled polypeptides by disc gel electrophoresis indicated that certain potential acceptors may be preferentially acylated
in vivo
.

These data provide genetic confirmation that the same enzyme protein catalyzes the transfer of leucine and phenylalanine and suggest that leucyl,phenylalanyl-tRNA-protein transferase is involved in a growth regulatory mechanism.
Introduction of Specific Cleavages into RNAs of RNA Bacteriophages for Determination of Base Sequences
Authors: Fuke Motohiro
Published: May 2006

Large fragments of R17, MS2, and Qβ RNAs were obtained reproducibly by limited digestion by ribonuclease T1. After digestion of R17 and MS2 RNAs, two pairs of large fragments were obtained that probably resulted from specific cleavages of the whole molecules. The cleavages of MS2 RNA were produced at points 36 and 47% from the 5′ end.
Extent of Transcription of Mouse Sarcoma-Leukemia Virus by RNA-Directed DNA Polymerase
Authors: Tavitian A. , Hamelin R. , Tchen P. , Olofsson B. , Boiron M.
Published: May 2006

The DNA product obtained from the endogenous RNA-directed DNA polymerase (deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) reaction of the Moloney sarcoma:leukemia viruses produced by the 78 A-1 cell line was analyzed and characterized. The extent of transcription of viral 70S RNA was measured by RNA·DNA hybridization (
32
P-viral RNA-
3
H product DNA). No double-stranded DNA was obtained. The product consisted of 95-99% single-stranded DNA with an average length of 200 nucleotides. In contrast to the results reported with avian and other RNA oncogenic viruses, it was found that the entire 70S viral RNA genome was transcribed into DNA pieces and that a small excess of the product DNA was sufficient to anneal the 70S RNA and render it totally resistant to single-stranded-specific enzyme digestion.
The Roles of the Lambda
c
III Gene and the
Escherichia coli
Catabolite Gene Activation System in the Establishment of Lysogeny by Bacteriophage Lambda
Authors: Belfort Marlene , Wulff Daniel
Published: May 2006

Maximum lysogenization of
E. coli
by bacteriophage lambda requires both the λ
c
III gene function and the host catabolite gene activation system mediated by adenosine 3′:5′-cyclic monophosphate. Whereas considerable lysogenization occurs in the presence of either system alone, lysogenization is absolutely prevented in the absence of both systems. Neither system is, however, required for efficient lysogenization when the host bears an
hfl
-
mutation. It is argued that the normal function of these two systems is to negate the antagonistic effect of the Hfl
+
protein upon lysogenization. It is further argued that both the λ
c
III gene function and the Hfl
+
protein do not directly affect the host catabolite gene activation system.
The Electrostatic Basis of Mg
++
Inhibition of Transmitter Release
Authors: Muller Robert U. , Finkelstein Alan
Published: May 2006

The inhibition by Mg
++
of stimulus-evoked transmitter release is attributed to a decrease in surface potential, Ψ
0
, on the outer surface of the presynaptic terminal and hence a lower surface calcium concentration, [Ca
++
]
0
. Data on the frog neuromuscular junction are quantitatively fit by assuming that there is a negative charge density, σ, on the outer surface of the presynaptic terminal of 6.5 × 10
13
charges per cm
2
and that simple diffuse double layer theory is applicable.
No
specific binding of Mg
++
or Ca
++
is required. Without any additional assumptions, the inhibitory effect of univalent cations is also quantitatively predicted.
Genetic Differentiation Within and Between Species of the
Drosophila willistoni
Group
Authors: Ayala Francisco J. , Tracey Martin L.
Published: May 2006

We describe allelic variation at 28 loci in six Caribbean populations of four sympatric species of
Drosophila
. Within any one species the allelic frequencies are very similar from population to population, although there is evidence of local as well as regional genetic differentiation. The genetic distance is greater between populations from different islands than between populations of the same island. When the allelic frequencies are compared between different species, a remarkable pattern appears. In any pair of species nearly half of the loci have essentially identical allelic frequencies, while nearly the other half of the loci have different alleles and in different frequencies. The loci with nearly identical allelic frequencies are different when different pairs of species are compared. The patterns of allelic variation within and between species are inconsistent with the hypothesis that the variation is adaptively neutral. Migration or mutation cannot explain the patterns of genetic variation, either. Balancing natural selection is the main process maintaining protein polymorphisms in natural populations.
Calorimetric Studies of the Role of Magnesium Ions in Yeast Enolase Catalysis
Authors: Faller Larry D. , Johnson Alan M.
Published: May 2006

The binding of magnesium ions and of the competitive inhibitor 3-phospho-D-glyceric acid to yeast enolase (2-phospho-D-glycerate hydrolyase, EC 4.2.1.11) has been studied calorimetrically. Thermal titration of the apoprotein with magnesium ions provides evidence that two magnesium ions bind immeasurably tightly to the dimeric enzyme, either anticooperatively to interacting sites or to two independent, nonidentical sites. Measurements of the saturation heat in buffers with different enthalpies of protonation are consistent with the release of two protons when the metal-binding sites are filled at pH 7.5. The enthalpy of binding of the two magnesium ions, corrected for the release of two protons, is +11.7 kcal (+49.0 kJ) per mole of dimeric protein.

Thermal titration of the magnesium-saturated enzyme with 3-phosphoglyceric acid corroborates the conclusion of Spring and Wold [
Biochemistry
(1971) 10, 4655-4660] that the enolase dimer possesses two equivalent and independent substrate-binding sites. The dissociation constant for the enzyme-inhibitor complex calculated from the thermal data is 2 mM. The thermal studies of 3-phosphoglyceric acid binding also confirm that metal ions are required for substrate binding and that substrate binds at the two specific metal-binding sites on the apoprotein. Experiments in buffers with different enthalpies of ionization provide evidence for proton uptake when 3-phosphoglyceric acid is bound.
Electron Transfer to Clostridial Rubredoxin: Kinetics of the Reduction by Hexaammineruthenium(II), Vanadous and Chromous Ions
Authors: Jacks Charles A. , Bennett Larry E. , Raymond Wayne N. , Lovenberg Walter
Published: May 2006

The rate constants (25°, M
-1
sec
-1
), activation enthalpies (kcal/mol), and activation entropies (e.u.) for the second-order reduction of oxidized clostridial rubredoxin by Ru(NH
3
)
6
2+
, V(H
2
O)
6
2+
, and Cr(H
2
O)
6
2+
at I = 0.10 have been determined or estimated to be 9.5 × 10
4
, ∼1.4, ∼-31 (pH 6.3-7.0); 1.6 × 10
4
, 0.1, -40 (pH 3.5-4.5); and 1.2 × 10
3
, ∼0, ∼-44 (pH 3.5-4.0), respectively. Ionic strength dependencies for the vanadium reaction are suggestive of a direct interaction of the reductants with the Fe(SR)
4
-1
site of oxidized rubredoxin. The results are consistent with outer-sphere mechanisms for all three reductants and an especially high inherent outer-sphere reactivity of rubredoxin. This high reactivity level is attributed to the low activation enthalpy demands of the iron-sulfur site of rubredoxin. Thus, the possibility is raised that the rate of reaction of rubredoxin with its physiological counterparts may be determined largely by the activation entropy demands imposed by the physiological reactant. Evidence is presented in support of an absolute entropy decrease of about 7.5 e.u. on going from oxidized to reduced rubredoxin, which is presumably attributable to the charge increase from Fe(SR)
4
1-
to Fe(SR)
4
2-
at the redox site.
Morphology, Motility, and Surface Behavior of Lymphocytes Bound to Nylon Fibers
Authors: Rutishauser U. , Yahara I. , Edelman G. M.
Published: May 2006

Mouse B lymphocytes that were specifically bound to dinitrophenylated bovine serum albumin on nylon fibers exhibited continuous morphological changes, whereas bound T lymphocytes remained more or less spherical. Cinematomicrographic studies showed that the shape changes were associated with local and global movements, although the attached cells did not translocate along the fiber. Cap formation induced by anti-immunoglobulin was always found to be opposite to the point of attachment. The movements and the shape changes were prevented by cytochalasin B and colchicine. Treatment with these agents did not prevent cap formation but led to randomization of the position of the caps with respect to the fiber. Exposure to concanavalin A or attachment of cells to concanavalin A fibers prevented both movement and patch and cap formation, suggesting that cellular structures regulating the mobility of various receptors are altered by binding to concanavalin A fibers. These observations also indicate that interactions of local areas of the lymphocyte surface with certain ligands and substrates can strongly affect the movement and morphology of the entire cell.
On the Lack of ATP-Induced Midpoint Potential Shift for Cytochrome
b
-566 in Plant Mitochondria
Authors: Lambowitz Alan M. , Bonner Walter D. , Wikström Mårten K. F.
Published: May 2006

Recently proposed mechanisms of site II energy transduction that assign a key role to cytochrome
b
-566 are based on the finding that the apparent midpoint potential of
b
-566 in animal mitochondria increases by more than 250 mV upon addition of ATP [Chance
et al.
(1970)
Proc. Nat. Acad. Sci. USA
66, 1175-1182]. However, since it has never been shown that the redox mediators used in the midpoint potential measurements equilibrate directly with
b
-566, the observed midpoint potential shift could merely reflect reversed electron transport. In mung bean mitochondria, the apparent midpoint potential of
b
-566 is known to be unaffected by addition of ATP [Dutton and Storey (1971)
Plant Physiol.
47, 282-288]. In the present work, mung bean
b
-566 is shown to undergo an ATP-induced reduction similar to that observed for
b
-566 in animal mitochondria. However, in mung bean mitochondria the reduction is found to be rapidly relaxed by addition of redox mediator (phenazine methosulfate, PMS) and concomitantly PMS causes a marked, antimycinsensitive stimulation of ATPase activity. These results suggest that the ATP-induced reduction in mung bean mitochondria is due to reversed electron transport and that PMS can effectively short-circuit reversed electron transport in this system, bringing it close to equilibrium. Moreover, since mung bean and animal
b
-566 are identical in all other respects tested, the results support the idea that the apparent midpoint potential shift in animal mitochondria is also merely due to reversed electron transport, and that the mediators are now not effective enough to bring the system to equilibrium.
Purification and Partial Characterization of a Glycoprotein Sexual Inducer from
Volvox carteri
Authors: Kochert Gary , Yates Ida
Published: May 2006

A method is described for the isolation and purification of the sexual inducer produced by male colonies of the colonial green alga
Volvox carteri
. The procedure yields a highly purified preparation of the inducer. The biologically active principal is demonstrated to be a glycoprotein with a molecular weight of 32,000.
Simian Virus 40 DNA Sequences in DNA of Healthy Adult Mice Derived from Preimplantation Blastocysts Injected with Viral DNA
Authors: Jaenisch Rudolf , Mintz Beatrice
Published: May 2006

Explanted mouse blastocysts were microinjected in the blastocoel cavity with simian virus 40 (SV40) viral DNA. After surgical transfer to the uteri of pseudopregnant surrogate mothers, approximately 40% of the blastocysts developed to term and became healthy adults without apparent tumors at 1 year of age. Molecular hybridization tests for the presence of SV40-specific DNA sequences were conducted on DNA extracted from various organs of these animals. Between 0.5 and 13 SV40 genome equivalents per diploid mouse DNA value were found in some organs of approximately 40% of the adult survivors; this represents a substantial augmentation of the amount administered per embryo. The results are consistent with the working hypothesis that the SV40 DNA may have been integrated into the host genome; alternatively, the viral DNA may have replicated as an extrachromosomal entity or by lytic infection in a few permissive cells. Persistence of the viral DNA from preimplantation stages to adult life may thus provide a new tool for experimental investigation of vertical transmission and expression of tumor viruses.
Pregelation Aggregation of Sickle Cell Hemoglobin
Authors: Wilson W. W. , Luzzana M. R. , Penniston John T. , Johnson Charles S.
Published: May 2006

Quasi-elastic light scattering was used to detect the initial stage of aggregation of hemoglobin S solutions. Aggregation of a hemolysate upon deoxygenation was found to occur at concentrations above 11 g/dl, but purified hemoglobin S solutions showed evidence of aggregation only for concentrations greater than 14 g/dl. A transition from a nonaggregated to an aggregated state was observed when the oxygen pressure in solution was reduced below a critical value. The total intensity of the scattered light during the early stages of aggregation was found to increase linearly with time. This result is consistent with a linear association process in which any size aggregate can combine with any other size aggregate.
Regulation of a Plant 5′(3′)-Ribonucleotide Phosphohydrolase by Cyclic Nucleotides and Pyrimidine, Purine, and Cytokinin Ribosides
Authors: Polya G. M.
Published: May 2006

A highly specific 5′(3′)-ribonucleotide phosphohydrolase has been purified extensively from wheat seedling leaves. While catalyzing the hydrolysis of a wide variety of phosphomonoesters, the enzyme has

K
m

values for adenosine 5′-monophosphate and adenosine 3′-monophosphate in the micromolar range and appears highly specific for 5′- and 3′-ribonucleoside monophosphates as substrates at pH 5.0. The cyclic nucleotides adenosine 3′:5′-cyclic monophosphate, guanosine 3′:5′-cyclic monophosphate, and 8-bromoadenosine 3′:5′-cyclic monophosphate, as well as 8-bromoadenosine 5′-monophosphate, are powerful competitive inhibitors of the enzyme; the apparent
K
i
values for these nucleotides are 3.4 μM, 1.6 μM, 26 μM, and 9.1 μM, respectively. The enzyme is inhibited noncompetitively by a variety of pyrimidine and purine (including cytokinin) ribosides and 2′-deoxyribosides. Since the cyclic nucleotide competitive inhibitors are also active growth promoters of higher plants, and, furthermore, since elevation of cyclic AMP levels appears to be a consequence of some phytohormone treatments that promote plant growth, it is suggested that negative control of this 5′(3′)-ribonucleotide phosphohydrolase may be a significant component of growth regulation through the maximizing of the levels of nucleotide precursors for RNA and DNA synthesis.
The 3′-Terminal Sequence of
Escherichia coli
16S Ribosomal RNA: Complementarity to Nonsense Triplets and Ribosome Binding Sites
Authors: Shine J. , Dalgarno L.
Published: May 2006

With a stepwise degradation and terminal labeling procedure the 3′-terminal sequence of
E. coli
16S ribosomal RNA is shown to be Pyd-A-C-C-U-C-C-U-U-A
OH
. It is suggested that this region of the RNA is able to interact with mRNA and that the 3′-terminal U-U-A
OH
is involved in the termination of protein synthesis through base-pairing with terminator codons. The sequence A-C-C-U-C-C could recognize a conserved sequence found in the ribosome binding sites of various coliphage mRNAs; it may thus be involved in the formation of the mRNA·30S subunit complex.
Synthesis of Complementary Strands of Heterologous RNAs with Qβ Replicase
Authors: Palmenberg Ann , Kaesberg Paul
Published: May 2006

Qβ replicase, in the presence of Mn
++
, can use various RNAs as templates for synthesis of full-length RNA products and can also use Qβ plus-strand RNA as template in the absence of host factors.
Electron Transfer Reactions in Biological Systems: The Reduction of Ferricytochrome
c
by Chromous Ions
Authors: Grimes Carol J. , Piszkiewicz Dennis , Fleischer Everly B.
Published: May 2006

Chromous ion reacts with ferricytochrome
c
to yield a one-to-one Cr(III)-ferrocytochrome
c
complex. This material, when hydrolyzed by trypsin and subjected to chromatographic procedures, yielded two fragments containing chromium. The amino-acid compositions and chemical characteristics of each of these fragments indicated that the chromium had crosslinked two segments of polypeptide chain; these were residues 40-53-Cr(III)-residues 61-72 and residues 40-53-Cr(III)-residues 61-73. Examination of a model of the ferricytochrome
c
molecule indicated that only two residues of the crosslinked peptides were sufficiently close to allow crosslinking to take place. These residues were tyrosine 67 and asparagine 52. Enzymatic hydrolysis of one of those fragments by aminopeptidase M supported this identification. The position of the chromic ion implies what is the path of electron transfer from the chromous ion to the ferric ion in this chemical reduction of cytochrome
c
, and suggests a possible path of electron transfer in biological oxidation-reduction reactions.
The Three Dimensional Structure of a Combining Region-Ligand Complex of Immunoglobulin NEW at 3.5-Å Resolution
Authors: Amzel L. M. , Poljak R. J. , Saul F. , Varga J. M. , Richards Frank F.
Published: May 2006

IgG
New
binds ligands such as orceine, menadione, and uridine with a low affinity (
K
0
about 1 × 10
3
liter/mol) and a γ-hydroxy derivative of vitamin
K
1
with a higher affinity (
K
0
= 1.7 × 10
5
liter/mol). Binding studies indicate that both the 2-methylnaphthoquinone rings and the phytyl tail of the vitamin K
1
hapten contribute to the total binding energy.

The binding of these ligands in the crystalline state has been investigated by difference Fourier maps of Fab′
New
-ligand complexes at 6-Å resolution. A 3.5-Å resolution difference Fourier map obtained for the γ-hydroxy derivative of the vitamin K
1
-Fab′ complex shows that this hapten is bound in a shallow groove or crevice between the light and the heavy chains, in close proximity to the polypeptide segments containing the hypervariable regions. At least 12 amino-acid residues from both the light and the heavy chains appear to be in close contact with the ligand. No major conformational changes were detected in the Fab′ fragment after ligand binding.
Circadian Function in the Photoperiodic Induction of Gonadotropin Secretion in the White-crowned Sparrow,
Zonotrichia leucophrys gambelii
Authors: Follett B. K. , Mattocks P. W. , Farner Donald S.
Published: May 2006

Photosensitive White-crowned Sparrows (
Zonotrichia leucophrys gambelii
) previously maintained on short day lengths (8-hr light; 16-hr darkness) were transferred to complete darkness. At various intervals thereafter (2-100 hr) they were exposed to a single 8-hr light period. To determine if the light period had been inductive, plasma luteinizing-hormone concentration was measured by radioimmunoassay in blood samples taken before and after the light period. Inductive light periods recurred at approximately daily intervals. The data provide further evidence for the involvement of a circadian rhythm in time measurement in the photoperiodic responses of birds.
The Presence of Unique DNA Sequences after Viral Induction of Leukemia in Mice
Authors: Sweet R. W. , Goodman N. C. , Cho J.-R. , Ruprecht R. M. , Redfield R. R. , Spiegelman S.
Published: May 2006

From previous studies, lymphocyte DNA from human leukemias and DNA from involved tissues of patients with Hodgkin's disease or Burkitt's lymphoma contain sequences that are absent from their normal counterparts. These sequences are related to those found in particulate elements associated with these neoplasias and possessing biochemical properties characteristic of RNA tumor viruses. Similar observations have been made of unique sequences related to those of the feline virus RD-114 and found in spontaneous mastocytomas in cats. Here we extend these results to the classical murine model of virus-induced leukemias.

Splenic DNA from BALB/c mice with leukemia induced by Rauscher leukemia virus (RLV) possess some RLV-related sequences that do not exist in normal BALB/c DNA. Furthermore, these leukemia-specific sequences were absent in all other mouse strains examined, including AKR, a strain with a high incidence of spontaneous leukemia.

The DNA of all noninfected mouse strains possesses considerable homology with the RLV genome. Temperature denaturation studies indicate, however, that although the RLV-related sequences found in all normal mice are similar to each other, they are not exactly homologous with RLV sequences.

We conclude that RLV-induced leukemia in BALB/c results in the insertion of RLV sequences into cellular DNA that itself possesses only partial homology with the RLV genome.
An Endonuclease from
Escherichia coli
That Acts Preferentially on UV-Irradiated DNA and Is Absent from the
uvrA
and
uvrB
Mutants
Authors: Braun Andrew , Grossman Lawrence
Published: May 2006

At least two endonucleolytic activities that preferentially incise ultraviolet (UV)-irradiated DNA exist in extracts of
E. coli
. These two activities can be separated by phosphocellulose chromatographic fractionation. The subject of this paper is one of these activities, which elutes from phosphocellulose with 0.25 M potassium phosphate, pH 7.5. This endonucleolytic activity specific for UV-irradiated DNA is absent from partially purified extracts of
uvrA
and
uvrB
mutants, which are defective in excision of pyrimidine dimers, but is present in normal amounts in the
uvrC
excision-defective mutant. The enzyme binds very tightly and specifically to UV-irradiated DNA. Binding can be prevented by prior treatment of the irradiated DNA with photoreactivating enzyme. This binding activity is absent in
uvrA
and
uvrB
mutants, but present in
uvrC
and
uvrD
mutants.
Synthesis of von Willebrand Factor by Cultured Human Endothelial Cells
Authors: Jaffe Eric A. , Hoyer Leon W. , Nachman Ralph L.
Published: May 2006

Cultured human endothelial cells synthesize and secrete a protein(s) which has Factor VIII antigen but which lacks Factor VIII clot-promoting activity (
J. Clin. Invest.
52, 2757-2764, 1973). Von Willebrand factor activity has been identified in medium from cultured human endothelial cells. This activity was demonstrated by the ability to correct the defect in platelet adhesiveness of blood obtained from patients with von Willebrand's disease. This activity also supported ristocetin-induced aggregation of washed normal human platelets. The von Willebrand factor activity from cultured endothelial cells has physicochemical and immunologic properties like those of the von Willebrand factor activity and the Factor VIII antigen present in human plasma and the Factor VIII antigen synthesized by human endothelial cells
in vitro
. Rabbit antibody to chromatographic fractions containing endothelial cell von Willebrand factor inhibits the platelet retention of normal blood in glass bead columns.
A Functional Examination of Hapten-Binding Derivatives from a Murine Myeloma Protein with Immunoglobulin Features
Authors: Merz David Charles , Litman Gary W. , Good Robert A.
Published: May 2006

Various enzymatic derivatives of the murine myeloma protein IgA
MOPC-315
were subjected to hapten-binding quantitation and circular dichroic analysis in an attempt to ascertain the structural localization and functional definition of the immunoglobulin active site. The extrinsic Cotton effects observed with near saturation of the active site of the derivatives using ε-Dnp-L-lysine were qualitatively and quantitatively identical when normalized with respect to their macromolecular content of Dnp-binding sites; ellipticity maxima of 378 and 438 nm and an ellipticity minimum of 325 nm were recorded. Fluorescence quenching data confirmed the molecular nature of the derivation products of IgA
MOPC-315
but also introduced disparity with respect to binding kinetics, i.e.,
K
values of 2.31 × 10
6
, 6.62 × 10
6
, and 2.06 × 10
7
M
-1
were determined for IgA
MOPC-315
, Fab′
MOPC-315
, and Fv
MOPC-315
, respectively. We speculate that the results can be explained by possible modulating effects on haptenbinding contributed by novel conformations introduced through proteolysis.