bluuebunny/crossref_metadata_2025 huggingface dataset:
Autoregulation: A Role for a Biosynthetic Enzyme in the Control of Gene Expression
Authors: Calhoun David H. , Hatfield G. Wesley
Published: May 2006

It was previously proposed, primarily on the basis of evidence
in vitro
, that L-threonine deaminase, the
ilvA
gene product, is required for repression of its own synthesis and for repression of the other genes in the
ilv-ADE
operon. In this communication, evidence
in vivo
is presented that supports this autoregulatory model. Further evidence is presented that suggests that L-threonine deaminase is also required for induction of the
ilvC
gene product. The autoregulatory model is presented in an expanded form to include recent evidence that L-threonine deaminase (EC 4.2.1.16) is a central element for repression of the
ilvADE
and
ilvB
operons, and for induction of the
ilvC
operon.
Familial Hypercholesterolemia: Identification of a Defect in the Regulation of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Activity Associated with Overproduction of Cholesterol
Authors: Goldstein Joseph L. , Brown Michael S.
Published: May 2006

The homozygous form of the autosomal dominant disorder, familial hypercholesterolemia, is characterized by the presence in children of profound hypercholesterolemia, cutaneous planar xanthomas, and rapidly progressive coronary vascular disease that usually results in death before age 30 years. Cultured skin fibroblasts from three unrelated subjects with this disorder showed 40- to 60-fold higher activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34), the rate-controlling enzyme in cholesterol biosynthesis, when compared with fibroblasts of seven control subjects. Enhanced enzyme activity resulted from a complete absence of normal feedback suppression by low-density lipoproteins, which led to a marked overproduction of cholesterol by the mutant cells. The demonstration of apparently identical kinetic properties of the reductase activity of control and mutant cells, coupled with the evidence that this enzyme is normally regulated not by allosteric effectors but by alterations in enzyme synthesis and degradation, suggests that the primary genetic abnormality does not involve the structural gene for the enzyme itself, but a hitherto unidentified gene whose product is necessary for mediation of feedback control by lipoproteins. The fibroblasts of two obligate heterozygotes, the parents of one of the homozygotes, showed a pattern of enzyme regulation intermediate between that of controls and homozygotes.
The Amplification of Ribosomal RNA Genes Involves a Rolling Circle Intermediate
Authors: Hourcade Dennis , Dressler David , Wolfson John
Published: May 2006

During the development of
Xenopus
oocytes there is a special DNA synthesis that leads to a thousandfold amplification of the genes that code for ribosomal RNA. We have used the electron microscope to study this process. Our primary observation is the presence of ribosomal DNA in rolling-circle intermediates at the time of amplification. We believe that these intermediates are involved in the amplification process, and as such offer the first example of the involvement of a rolling circle in the replication of eukaryotic DNA.
Binding of Human Lymphotoxin to Target-Cell Membranes and Its Relation to Cell-Mediated Cytodestruction
Authors: Hessinger David A. , Daynes Raymond A. , Granger Gale A.
Published: May 2006

One of the lymphocyte effector molecules produced
in vitro
by antigen- and mitogen-stimulated lymphocytes is lymphotoxin, which has been proposed to be the cytodestructive mediator in cell-mediated immune reactions. Our
in vitro
findings suggest that lymphotoxin binds to sites on the plasma membrane of sensitive target cells, and this binding represents the earliest detectable effect in cell destruction induced by lymphotoxin. The kinetics of binding are rapid, and the affinity of lymphotoxin for binding sites is strong. Furthermore, cytodestruction can be localized, for lymphotoxin-coated cells cannot release lymphotoxin to affect adjacent
51
Cr-labeled, noncoated cells in mixed cultures. This evidence suggests how a nonspecific soluble cytotoxin could cause highly specific localized tissue destruction.
Assembly of the Mitochondrial Membrane System. Purification of a Mitochondrial Product of the ATPase
Authors: Sierra Marcelino F. , Tzagoloff Alexander
Published: May 2006

A low-molecular-weight protein synthesized in yeast mitochondria was purified. The protein was identified as a component of the rutamycin-sensitive ATPase. The amino-acid composition of the purified protein shows an extremely large preponderance of nonpolar residues, which may account for its solubility in chloroform-methanol. Indirect evidence suggests that this component is involved in the conferral of rutamycin sensitivity and may also have a function in the assembly of the ATPase complex.
Construction of Biologically Functional Bacterial Plasmids
In Vitro
Authors: Cohen Stanley N. , Chang Annie C. Y. , Boyer Herbert W. , Helling Robert B.
Published: May 2006

The construction of new plasmid DNA species by
in vitro
joining of restriction endonuclease-generated fragments of separate plasmids is described. Newly constructed plasmids that are inserted into
Escherichia coli
by transformation are shown to be biologically functional replicons that possess genetic properties and nucleotide base sequences from both of the parent DNA molecules. Functional plasmids can be obtained by reassociation of endonuclease-generated fragments of larger replicons, as well as by joining of plasmid DNA molecules of entirely different origins.
Application of Fingerprinting Techniques to Iodinated Nucleic Acids
Authors: Robertson Hugh D. , Dickson Elizabeth , Model Peter , Prensky Wolf
Published: May 2006

Several techniques of RNA and DNA finger-printing and determination of sequence have been applied to nucleic acids labeled with
125
I. Fingerprints of human 5S RNA and bacteriophage f2 RNA resemble those of their noniodinated counterparts both in complexity and in specific pattern. Iodination as used here is thus a general labeling procedure, and appears principally to label cytidine residues. This iodination method shows little sensitivity to potential structure in single-stranded RNA molecules, yields stable oligonucleotide products in a reproducible manner, and does not change the specificity of several ribonucleases and deoxyribonucleases.
Intrasomatic Injection of Radioactive Precursors for Studying Transmitter Synthesis in Identified Neurons of
Aplysia californica
Authors: Eisenstadt Michael , Goldman James E. , Kandel Eric R. , Koike H. , Koester John , Schwartz James H.
Published: May 2006

We introduced radioactive precursors directly into identified neurons of
Aplysia californica
. [
3
H]-Choline and L-[
3
H]tryptophan were injected with pressure into nerve cell bodies to study synthesis of acetylcholine and serotonin. We confirmed the cholinergic nature of R2, L10, and L11, identified neurons of the abdominal ganglion. Cells in the LD cluster (which contains motor neurons to the heart and gill) also converted most of the injected choline into acetylcholine. Neurons in the RB cluster (which contains an excitatory motor neuron to the heart) and the two metacerebral cells of the cerebral ganglion converted injected tryptophan to serotonin. No cell studied could convert both choline to acetylcholine and tryptophan to serotonin. Pressure permits rapid injection of precursors, from small amounts to amounts large enough to saturate intracellular synthetic pathways. In contrast to the results with injection, we found far less synthesis of acetylcholine and serotonin in identified nerve cell bodies when ganglia were incubated in the presence of the radioactive precursors.
Anaerobic Transport in
Escherichia coli
Membrane Vesicles
Authors: Konings Wilhelmus N. , Kaback H. Ronald
Published: May 2006

Anaerobic β-galactoside transport in whole cells and membrane vesicles from
E. coli
ML 308-225 is coupled to the oxidation of α-glycerol-
P
or D-lactate with fumarate as an electron acceptor. Alternatively, anaerobic β-galactoside transport may be coupled to the oxidation of formate utilizing nitrate as electron acceptor. Both anaerobic electron-transfer systems are induced by growth of the organisms under appropriate conditions. Components of both systems are loosely bound to the membrane, necessitating the use of a modified procedure for vesicle preparation in order to demonstrate anaerobic transport
in vitro
. Addition of ATP or an ATP-generating system to vesicles prepared from anaerobically-grown cells or inclusion of ATP or the ATP-generating system during preparation of vesicles does not stimulate transport. The results support the conclusion that active transport under anaerobic conditions is coupled primarily to electron flow.
Conformational Control of the Interaction of Eukaryotic Elongation Factors EF-1 and EF-2 with Ribosomes
Authors: Nombela Cesar , Ochoa Severo
Published: May 2006

As in the case with prokaryotic systems,
Artemia salina
elongation factors EF-1 and EF-2 interact with a common site or with closely overlapping sites on the
Artemia
ribosome. This feature of ribosomal design must restrict interaction with the ribosome to only one of the factors at alternating steps of chain elongation. In support of this view we find that EF-1, but not EF-2, interacts with the post-translocation ribosome, whereas the reverse is true of the pre-translocation ribosome. Conformational changes probably account for the alternating selectivity of the translating ribosome for each elongation factor.
Role of Cyclic 3′:5′-Adenosine Monophosphate in the Early Transport Changes Induced by Serum and Insulin in Quiescent Fibroblasts
Authors: Rozengurt Enrique , Asua Luis Jimenez De
Published: May 2006

Serum or insulin added to quiescent mouse-embryo fibroblasts produced rapid increases in the rate of transport of uridine and phosphate and a decrease of the intracellular concentration of cyclic AMP. Incubation of the cells with prostaglandin E
1
, theophylline, or both prevented the increase in uridine transport produced by serum or insulin. Prostaglandin E
1
was more effective than prostaglandins E
2
and B
1
. Kinetic experiments showed that the addition of prostaglandin E
1
and theophylline causes the uridine transport rate to return to the basal level within 5 min; the rate rose rapidly after their removal. Similar effects were obtained when insulin was used instead of serum. Associated with these transport changes were significant variations in the levels of cyclic AMP. An inverse correlation between the changes in uridine transport and those in cyclic AMP concentration was shown under various experimental conditions. In contrast to the effects observed with uridine transport, phosphate uptake was only slightly affected by changes in the endogenous level of cyclic AMP. We propose that at least two different sorts of membrane changes are rapidly initiated by serum, one under cyclic AMP control and the other not related to this nucleotide.
Infectious DNA from Herpes Simplex Virus: Infectivity of Double-stranded and Single-stranded Molecules
Authors: Sheldrick P. , Laithier M. , Lando D. , Ryhiner M. L.
Published: May 2006

The infectious units in native and alkalidenatured preparations of DNA of herpes simplex virus were characterized with respect to their sensitivity to
Neurospora crassa
endonuclease, their sedimentation properties in high-salt, neutral sucrose gradients, and their sensitivity to hydrodynamic shearing forces. Infectious molecules in native preparations were resistant to
N. crassa
endonuclease, sedimented at 56 S, and were highly sensitive to shearing forces. After alkaline denaturation, infectious molecules became sensitive to the
N. crassa
enzyme, sedimented at 200 S, and were relatively resistant to shear. We conclude that both intact duplex molecules ([unk]100 × 10
6
daltons) and intact single strands ([unk]50 × 10
6
daltons) are capable of initiating productive infection.
Cell-Free Synthesis of Rat Growth Hormone
Authors: Bancroft F. Carter , Wu Guang-Jer , Zubay Geoffrey
Published: May 2006

Growth hormone has been synthesized in a cell-free system derived from Krebs II ascites cells, under the direction of RNA prepared from rat pituitary tumor (GC) cells. Growth hormone synthesized in the cell-free system was identified by precipitation with antiserum against growth hormone developed in baboon, followed by electrophoretic analysis of the dissolved precipitate on sodium dodecyl sulfate-polyacrylamide gels. RNA from both the membrane and the post-membrane fractions of the cytoplasm of GC cells stimulated protein synthesis in the cell-free system, but only RNA from the membrane fraction was found to direct the synthesis of growth hormone.
Sequence Homologies Among Bacterial and Mitochondrial Superoxide Dismutases
Authors: Steinman Howard M. , Hill Robert L.
Published: May 2006

Superoxide dismutase from chicken-liver mitochondria (manganese enzyme) and the two dismutases from
Escherichia coli
(manganese and iron enzymes) were analyzed through 29 cycles of automated Edman degradations. The high degree of homology among the amino-terminal sequences of these three dismutases corroborates their known similarity of structural and functional properties, and serves as further evidence for the endosymbiotic origin of mitochondria. In contrast, these three sequences exhibit no significant homology with the amino-terminal sequence of bovine-erythrocyte superoxide dismutase, which is consistent with the classification of eukaryotic copper-zinc dismutases as a family distinct from the manganese enzymes in stability and catalytic properties.
Interrelationship Between Adenylate Cyclase Activity, Adenosine 3′:5′ Cyclic Monophosphate Phosphodiesterase Activity, Adenosine 3′:5′ Cyclic Monophosphate Levels, and Growth of Cells in Culture
Authors: Anderson Wayne B. , Russell Thomas R. , Carchman Richard A. , Pastan Ira
Published: May 2006

To investigate how cell population density influences the intracellular concentration of cyclic AMP we have measured adenylate cyclase and cyclic AMP phosphodiesterase activities and cyclic AMP levels at various stages of cell density in normal rat-kidney (NRK) cells, which exhibit contact-inhibition of growth, and in normal chick-embryo fibroblasts (CEF), which do not show contact inhibition of growth under our conditions. Until NRK cells reach confluency, both activities increase with increasing cell population and cyclic AMP levels are low. As NRK cells reach confluency, cyclic AMP phosphodiesterase activity decreases somewhat whereas adenylate cyclase activity continues to rise. This increase in synthetic ability is accompanied by the increase in cyclic AMP levels which occurs in these cells at confluency. In CEF grown in 5% serum where density-dependent inhibition of growth is not observed, both adenylate cyclase and cyclic AMP phosphodiesterase activities increase proportionately with increasing cell population density. No significant alteration occurs in the ratio between these two enzyme activities and no change is observed in cyclic AMP levels.

The NaF-stimulated activity in NRK cells increases with increasing cell density until the cells reach confluency; thereafter the NaF-stimulated activity remains constant. In contrast, the NaF-stimulated activity observed in CEF does not vary appreciably between light and heavy density.

The observed changes in the enzymes of cyclic AMP metabolism accurately reflect the changes in cyclic AMP concentration as a function of cell population density. The data indicate that these two enzyme activities respond to increasing cell density to elicit a rise in intracellular cyclic AMP levels. The elevated cyclic AMP levels are thought to be involved in the regulation of cellular growth rate and the mediation of contact inhibition of growth.
Regulation of Cyclic Nucleotide Concentrations in Photoreceptors: An ATP-Dependent Stimulation of Cyclic Nucleotide Phosphodiesterase by Light
Authors: Miki Naomasa , Keirns James J. , Marcus Frederick R. , Freeman Jenny , Bitensky Mark W.
Published: May 2006

Regulation of cyclic nucleotide concentrations in rod outer segments (
Rana pipiens
) has been further examined. The present studies show that illumination markedly diminishes the concentration of cyclic nucleotides in suspensions of photoreceptor membranes, but the locus of regulation is cyclic nucleotide phosphodiesterase (EC 3.1.4.c) (light-stimulated) and not adenylate cyclase. There is a marked disproportionality between bleaching of rhodopsin and stimulation of phosphodiesterase. Bleaching only 0.6% of the rhodopsin produces half the stimulation produced by bleaching 100% of the rhodopsin. The process of activation of phosphodiesterase by light is in two steps, a light-dependent step followed by an ATP-dependent step. Illumination (in the absence of ATP) produces a trypsin-resistant, heat-labile, macromolecular stimulator. In the presence of 0.75 mM ATP (GTP or ITP) this stimulator produces a greater than 5-fold increases in the
V
max
of photoreceptor phosphodiesterase without changing the

K
m

. At physiological substrate concentrations (10
-7
M) the rate of hydrolysis of cyclic GMP is 23 times greater than that of cyclic AMP. The light-produced stimulator appears unique to the photoreceptor membranes and does not activate phosphodiesterase in other tissues.
Stimulation of Hepatic β-Hydroxy-β-methylglutaryl Coenzyme A Reductase Activity in Hypophysectomized Rats by L-Triiodothyronine
Authors: Ness Gene C. , Dugan Richard E. , Lakshmanan M. R. , Nepokroeff Carl M. , Porter John W.
Published: May 2006

Diurnally varying activity of hepatic β-hydroxy-β-methylglutaryl coenzyme A reductase (EC 1.1.1.34) was decreased to very low levels in hypophysectomized rats with no discernable diurnal rhythm retained. Administration of triiodothyronine (100 μg/100 g of body weight) produced a supranormal level of reductase activity, about 3-4 times the highest activity found in normal rats. Reductase activity began to rise about 30 hr after hormone administration, maintained a constant high level from 48 to 72 hr, and declined to the control level by 96 hr. The supranormal response was elicited equally well either during the day or at night. When normal animals received triiodothyronine, reductase activity was increased only to a level comparable to the highest level found in normal rats. Administration of hydrocortisone markedly inhibited the triiodothyronine-induced increase in reductase activity. This finding suggests that glucocorticoids might act to suppress and thus account for the smaller increase in reductase activity observed in normal rats given triiodothyronine. When actinomycin D was given before the triiodothyronine-induced rise in reductase activity, the increase was effectively blocked, indicating that the hormonal effect requires new RNA synthesis.
Temperature-Sensitive Variants of an Established Myoblast Line
Authors: Loomis W. F. , Wahrmann J. P. , Luzzati D.
Published: May 2006

Upon reaching confluency, mononucleated myoblasts fuse into multinucleated myotubes and concomitantly accumulate various characteristic muscle proteins, including myosin, actin, and several enzymes. We have approached the problem of determining the relationship between morphological and biochemical differentiation of muscle cells by isolating a series of temperature-sensitive clones from the established myoblast line, L
6
.

Twelve phenotypically variant clones were isolated from mutagenized populations of myoblasts. These fell into five classes, distinguishing conditional growth variants from conditional developmental variants. The phenotype of these strains, at least for the more extensively studied ones, was stable for more than 80 generations.

Synthesis of characteristic proteins such as myosin, glycogen phosphorylase (EC 2.4.1.1), and phosphocreatine kinase (EC 2.7.3.2) has been studied in two conditional developmental mutants. One mutant, E
3
, fuses into myotubes at 37° but not at 40°; the other, H
6
, does not fuse into myotubes at 37° but does so at 40°. At permissive temperatures the enzymes accumulated in mutant cells with the same time course as in the parent cell line. Myosin accumulated in strain E
3
but not in strain H
6
. At nonpermissive temperatures neither fusion into myotubes nor accumulation of any of the proteins occured in the cells of these two variant lines.
Evidence for Transport of 75S RNA from a Discrete Chromosome Region via Nuclear Sap to Cytoplasm in
Chironomus tentans
Authors: Daneholt B. , Hosick H.
Published: May 2006

Salivary glands of the dipteran
Chironomus tentans
were exposed to tritiated pyrimidines for different time periods either
in vitro
or
in vivo
. Nonribosomal, high molecular weight RNA molecules of very different sizes (15-100 S) were labeled on chromosomes I-III, while only one main species, 75S RNA, was recorded in Balbiani ring 2, a giant chromosome puff on chromosome IV. 75S RNA was present as a prominent fraction in nuclear sap, but not in cytoplasm, after 90 min of incubation
in vitro
. During the ensuing 90 min, 75S RNA also appeared in cytoplasm. After 1 week of labeling
in vivo
, radioactive 75S RNA accumulated heavily in cytoplasm. Absorbance measurements showed that 75S RNA constituted as much as 1.5% of the total salivary-gland RNA. The half-life of 75S RNA was estimated to exceed 35 hr.

Available data on the intracellular distribution and metabolic stability of nonribosomal, high molecular weight RNA from Balbiani ring 2 and chromosomes I-III indicate that most of the cytoplasmic 75S RNA is transcribed in the Balbiani ring 2 region of chromosome IV. 75S RNA molecules are, therefore, likely to be transferred from Balbiani ring 2, via nuclear sap, to cytoplasm without being measurably reduced in molecular size.
8-Bromoadenosine 3′:5′-Cyclic Monophosphate as a Promoter of Cell Division in Excised Tobacco Pith Parenchyma Tissue
Authors: Wood Henry N. , Braun Armin C.
Published: May 2006

8-Bromoadenosine 3′:5′-cyclic monophosphate, when used in association with an auxin, can completely replace the cell-division-promoting activity of either a cytokinesin or a 6-substituted adenylyl cytokinin in excised tobacco pith parenchyma tissue. The 8-bromo derivative of adenosine 3′:5′-cyclic monophosphate was found to be far more resistant to degradation by plant adenosine 3′:5′-cyclic monophosphate phosphodiesterases than was adenosine 3′:5′-cyclic monophosphate. These findings appear to provide further support for the suggestion made earlier that the cytokinesins, which are potent inhibitors of both plant and animal adenosine 3′:5′-cyclic monophosphate phosphodiesterases, exert their cell-division-promoting effects as regulators of adenosine 3′:5′-cyclic monophosphate.
Translation of Rabbit Hemoglobin Messenger RNA
In Vitro
with Purified and Partially Purified Components from Brain or Liver of Different Species
Authors: Schreier M. H. , Staehelin T.
Published: May 2006

Two mammalian systems have been developed for efficient
in vitro
translation of exogenous messenger RNA (rabbit globin mRNA). One system is completely derived from guinea pig brain, and the other is from liver of different species. Both systems consist of purified 60S and 40S ribosomal sununits, unseparated initiation factors partially purified by ammonium sulfate precipitation and DEAE-cellulose chromatography, and pH 5 enzyme fractions as sources of elongation and termination factors, aminoacyl-tRNA synthetases, and transfer RNA. Translation depends completely upon exogenous mRNA and initiation factors. Extraction of initiation factors from microsomes or ribosomes has been improved for these tissues by inclusion of Mg
++
ions in the 0.5 M KCl extraction solution. Both systems synthesize complete rabbit α- and β-globin chains, but in variable ratios. The overall efficiencies of the two systems are about 60% (liver) and 40% (brain) of a comparable system with rabbit reticulocyte initiation factors.
Insulin-Like Activity of Concanavalin A and Wheat Germ Agglutinin—Direct Interactions with Insulin Receptors
Authors: Cuatrecasas Pedro , Tell Guy P. E.
Published: May 2006

Concanavalin A and wheat germ agglutinin are as effective as insulin in enhancing the rate of glucose transport and in inhibiting epinephrine-stimulated lipolysis in isolated adipocytes. These lectins, also like insulin, inhibit basal as well as epinephrine-stimulated adenylate cyclase activity of membranes obtained from homogenates of fat cells. Low concentrations of wheat germ agglutinin enhance the specific binding of insulin to receptors of fat cells and liver membranes. Higher concentrations of this plant lectin, as well as of concanavalin A, competitively displace the binding of insulin to receptors in these tissues. These effects are equally apparent in insulin-binding proteins solubilized from membranes, indicating that the plant lectins interact directly with insulin receptors. All of the effects observed with the plant lectins are reversed by simple sugars that bind specifically to these plant proteins. Agarose derivatives of the plant lectins effectively adsorb solubilized insulin-binding proteins, and these can be eluted with buffers containing specific simple sugars. The possible implications of these findings to certain biological properties (mitogenicity) of these lectins and to the mechanism of action of other growth-promoting substances are considered.
Separation of Specific Segments of Transforming DNA after Treatment with Endodeoxyribonuclease
Authors: Goodgal Sol H. , Gromkova Rosa
Published: May 2006

Hemophilus parainfluenzae
endodeoxyribonuclease was used to degrade the DNA of
H. influenzae
and to follow the biological activity of 14 markers associated with this DNA. It was found that some
H. influenzae
markers were completely inactivated by endodeoxyribonuclease treatment, while others appeared to retain all or almost all of their original activity. The bulk of the
H. influenzae
DNA was reduced to double-stranded pieces of the order of 8 × 10
5
to 1 × 10
6
daltons. Velocity sedimentation of the DNA in sucrose gradients disclosed that markers that retained biological activity were present in DNA particles that were of the order of 1 × 10
6
daltons or larger, and indicated a close correlation between the size of the DNA fragment and the amount of biological activity retained. These data suggest that
H. parainfluenzae
endodeoxyribonuclease breaks DNA at specific sites. The
nal
r
marker was shown to have twice as much biological activity after treatment with endodeoxyribonuclease when assayed at saturating DNA concentrations. In the linear portion of the DNA dose-response curve, the biological activity of this marker was reduced 3- to 10-fold compared to untreated DNA (in accord with the reduced size of its DNA). These data demonstrate a specific enrichment of the
nal
r
marker by about 6- to 20-fold, and suggest a technique for the separation and purification of specific segments of DNA.
Specification of Positional Information in Retinal Ganglion Cells of
Xenopus:
Assays for Analysis of the Unspecified State
Authors: Hunt R. K. , Jacobson Marcus
Published: May 2006

The central connections of retinal ganglion cells are retinotopically organized, producing a “map” of the retina on the surface of the optic tectum. Exactly how and when individual ganglion cells develop the position-dependent properties (termed
locus specificities
) subserving formation of the map is unknown, but the positional information that each ganglion cell will use in this process is specified in the early
Xenopus
embryo during a critical period at stages 28-32. We report two methods for isolating eye primordia from the axial cues of the animals during this critical period and for then allowing the eyes to form retinotectal connections in a carrier embryo. The results show that, as early as optic vesicle stages 22-23, the eyes already contain orthogonal reference axes, that positional information can be specified with respect to these axes
in vitro
, and that the
specification
process itself may only entail a transition from a reversible to an irreversible state.
Hydroxyphenylazopyrimidines: Characterization of the Active Forms and Their Inhibitory Action on a DNA Polymerase from
Bacillus subtilis
Authors: Mackenzie John M. , Neville Marilyn M. , Wright George E. , Brown Neal C.
Published: May 2006

The active forms of 6-(
p
-hydroxyphenylazo)-uracil and 6-(
p
-hydroxyphenylazo)-isocytosine were isolated and identified as their respective
hydrazino
derivatives. These arylhydrazino pyrimidines selectively inhibited a chromatographically distinct DNA polymerase from
Bacillus subtilis
. The actions of the reduced drugs on this polymerase were identical to those observed on ATP-dependent DNA synthesis in toluene-treated cells; dGTP competitively antagonized the inhibitory activity of the uracil derivative, and dATP competitively antagonized that of the isocytosine derivative. Analysis of the interactions of the arylhydrazinopyrimidines and nucleic acid bases by nuclear magnetic resonance suggested that hydroxyphenylhydrazino-uracil and hydroxyphenylhydrazino-isocytosine pair in a novel manner with, respectively, cytosine and thymine. A mechanism of inhibitor action, involving binding of the reduced drugs to enzyme and the pyrimidines of DNA template, is proposed.
Sugar Transport in Normal and Rous Sarcoma Virus-Transformed Chick-Embryo Fibroblasts
Authors: Venuta S. , Rubin H.
Published: May 2006

3-
O
-methylglucose (3-OMeG) is a nonmetabolizable glucose analog and is, therefore, suitable for transport studies. 3-OMeG and glucose compete for entry into normal and Rous sarcoma virus (RSV)-transformed chick-embryo fibroblasts. Therefore, 3-OMeG can be used to study the transport of glucose in these cells. Chickembryo fibroblasts infected and transformed by RSV take up 3-OMeG at a faster rate than uninfected cells when both cell types are growing at the same rate. The rate of efflux of 3-OMeG also increases after transformation. When the uptake and the efflux reach a steady state, the intracellular concentration of 3-OMeG is equal to the concentration in the medium. This finding indicates that glucose is transported across the plasma membrane by facilitated diffusion. The
V
max
of the transport system for 3-OMeG increases after transformation, while the affinity or
K
m
of the system remains unchanged. We conclude that viral transformation causes a change in the plasma membrane of the infected cells by increasing either the number of molecules or the mobility of the glucose carrier.
A Protein That Binds Specifically to the M-Line of Skeletal Muscle Is Identified as the Muscle Form of Creatine Kinase
Authors: Turner David C. , Wallimann Theo , Eppenberger Hans M.
Published: May 2006

Published information on the properties of two proteins from chicken muscle, creatine kinase (MM-creatine kinase) and an M-line protein, suggested that they might be identical molecules. Different published procedures were used to purify the two proteins to homogeneity, and the properties of the two preparations were compared. Creatine kinase specific activity increased during purification of M-line protein, reaching a value comparable to that of purified MM-creatine kinase. The two proteins migrated identically in two electrophoretic systems and, after electrophoresis, both could be stained for creatine kinase activity. Double immunodiffusion tests with antibody prepared against MM-creatine kinase established the serological identity of the two protein preparations. Immunofluorescent studies showed that antiserum against MM-creatine kinase was bound in a regular pattern at the centers of the A-band regions of isolated myofibrils. These data show conclusively that the M-line protein and MM-creatine kinase are identical.
Deviations from Hardy-Weinberg Frequencies Caused by Assortative Mating in Hybrid Populations
Authors: Shockley William
Published: May 2006

The conventional formulas for genotype frequencies in a hybrid population
H
produced by interbreeding from ancestral populations
P
1
and
P
2
involve only one hybrid parameter
M
, equal to the fraction of alleles derived from
P
2
. For the one-parameter model to be accurate, all individuals of
H
must have probabilities for alleles determined by one and the same
M
. When
H
contains subpopulations that have different values of
M
, the correct genotype frequencies can be predicted by use of two parameters: (
i
)

M
H

, the average of
M
for all individuals of
H
and (
ii
) eta

H

, defined like the eta devised by C. A. B. Smith for testing the Hardy-Weinberg Law and computed with a formula like G. R. Price's eta, which involves assortative mating covariance—in this case for the
M
values of the parents of
H
. If parents of
H
have equal average
M
values for males and females, and mate at random, eta

H

vanishes. For perfect assortative mating, eta

H

is the variance of
M
for
H
. As for Smith's eta, eta

H

provides a test of fit of prediction to observed that is sensitive to signs of deviations. Using eta

H

with T. E. Reed's data for Gm in Oakland, California Negroes, his one-parameter fit (“
good
” by his chi-square test) is significantly rejected (
P
= 0.04). A simultaneous good fit of Reed's Gm data and his Duffy data results (chi-square, 1 df = 0.88,
P
> 0.30) from the use of previously published values of 0.23 and 0.047 for

M
H

and eta

H

. It is concluded that Reed's conclusion that these values were in error is itself in error, as is also his view that differences between
M
values from different genes and deviations from frequencies expected within genes are not likely to give significant information about variance of
M
.
Repeated DNA Sequences in the Heterochromatic Y Chromosome of Adult
Drosophila melanogaster
Authors: Perreault W. J. , Kaufmann B. P. , Gay H.
Published: May 2006

DNA isolated from
Drosophila melanogaster
adults (XX, XY, XXY, XYY) was used in DNA-DNA hybridization experiments on nitrocellulose filters. Filter-bound DNA of “high-heterochromatin” flies (those with one or more Y chromosomes) is more effective in forming hybrid duplexes than is XX DNA. The quantitative difference in hybridization efficiency is due primarily to molecules with a relatively high thermal stability (duplexes that dissociate in the temperature range 80-90°). Hybridization experiments with DNA samples that have been fractionated into reiterated and unique portions show that the majority of the hybrid duplexes formed involve reiterated DNA. A small, but highly specific, interaction of unique DNA sequences has also been detected in our experiments. These data indicate that a class of repeated DNA sequences is associated with the constitutive heterochromatin, specifically with the Y chromosome of
D. melanogaster
. Evidence is presented that this same class of molecules, or very similar ones, is to be found in other portions of the genome, presumably in X-chromosomal or centromeric heterochromatin.
Light-Induced Absorbance Changes Associated with Phototaxis in
Dictyostelium
Authors: Poff Kenneth L. , Butler Warren L. , Loomis William F.
Published: May 2006

Reversible light-induced absorbance changes were observed in the phototactic organism
Dictyostelium discoideum
. Irradiation of cells with light in the 520- to 600-nm region results in an absorbance increase at 411 nm, which decays in darkness with a half-time of about 7 sec. A similar light-induced absorbance change was observed in a 12,000 ×
g
pellet of a cell-free homogenate and in a soluble fraction obtained after sonication of the 12,000 ×
g
pellet. Dithionite had to be added to the cell-free extracts in order for the light-induced change to decay in darkness. The absorbance change was maximally elicited by light in the region of 560 nm. A similar spectral sensitivity was found for the phototactic migration of the pseudoplasmodia. The agreement between the spectral sensitivities of the two processes suggests that the absorbance change is associated with phototaxis.
Minor Base Composition of “70S-Associated” 4S RNA from Avian Myeloblastosis Virus
Authors: Rosenthal Leonard J. , Zamecnik Paul C.
Published: May 2006

Using a chemical isotope derivative method, we have determined the minor base composition of the “70S-associated” 4S RNA isolated from avian myeloblastosis virus. The minor base composition of this “70S-associated” 4S RNA is strikingly similar to that of the corresponding “free” 4S RNA of the virion. This minor base content, plus the capacity to esterify amino acids, establishes that both of these virion 4S RNA fractions contain transfer RNA. The percentage of minor bases in virion “70S-associated” 4S RNA is, however, much lower than in “free” 4S virion RNA and in myeloblast 4S RNA. The implication is that the “70S-associated” 4S RNA fraction as isolated herein also contains RNA that is not transfer RNA. This latter RNA may represent either degradation products of high molecular weight RNA or indigenous 4S RNA of undetermined function.
Fluctuation Spectroscopy: Determination of Chemical Reaction Kinetics from the Frequency Spectrum of Fluctuations
Authors: Feher George , Weissman Mike
Published: May 2006

The kinetic parameters of a chemical reaction were obtained from analysis of the frequency spectrum of the fluctuations (i.e., “noise”) in the concentrations of the reactants. In “fluctuation spectroscopy,” no external perturbation is applied and the system remains in macroscopic chemical equilibrium during the experiment. Results obtained by this method for the dissociation reaction of beryllium sulfate agree well with those obtained by relaxation methods in which the approach to equilibrium is analyzed. Other noise sources not originating from a chemical reaction were observed and analyzed. The most prominent of these arose from the flow of an electrolyte through a capillary. The method of fluctuation spectroscopy should be applicable to problems of physical, chemical, and biological interest.
Functional Correspondence Between 30S Ribosomal Proteins of
Escherichia coli
and
Bacillus stearothermophilus
Authors: Higo K. , Held W. , Kahan L. , Nomura M.
Published: May 2006

30S ribosomal proteins from
Bacillus stearothermophilus
(
B
. proteins) have been fractionated and characterized with respect to their ability to replace various
E. coli
30S proteins (
E.
proteins) in the
E. coli
30S ribosome reconstitution system. The functional counterparts of all the
E
. proteins, except S1, S6, S9, and S13, have been tested. In all cases,
B
. proteins can substitute for
E
. proteins. Several purified
B
. proteins are chemically different from their functionally homologous
E
. proteins. Five
B
. proteins are immunochemically related to
E
. proteins; this set includes two proteins that could not be tested in the reconstitution system (S9 and S13). Thus most, if not all, of the
E
. proteins have functionally equivalent counterparts among
B
. proteins, even though properties of the two ribosomes are different in several respects. These results suggest that the fundamental structural organization of ribosomes may be the same throughout prokaryotic organisms.
A Mutant Transcription Factor That is Activated by 3′:5′-Cyclic Guanosine Monophosphate
Authors: Sanders Richard , McGeoch Duncan
Published: May 2006

We report here the isolation of an extragenic suppressor of a promoter mutation in the lactose operon of
Escherichia coli
. Genetic data have indicated that the suppressor of the
P
-
mutation maps in the structural gene for the transcription factor catabolite activator protein. Biochemical studies suggest that the mutant molecules of catabolite activator protein are altered in such a way that they are activated by 3′:5′-cyclic GMP in addition to their normal effector, 3′:5′-cyclic AMP.
Structure of Fibers of Sickle Cell Hemoglobin
Authors: Edelstein Stuart J. , Telford John N. , Crepeau Richard H.
Published: May 2006

Electron microscope studies have been conducted on individual fibers of human deoxyhemoglobin S (sickle cell hemoglobin). The fibers are obtained by injection of gelled samples into a large excess of glutaraldehyde, which quickly stabilizes the fibers by cross-linking. The fibers are negatively stained with phosphotungstic acid or shadowed with platinum-carbon. The fibers are approximately 200 Å in diameter, and display long and short helical striations with an opposite handedness. The long striations occur at an angle of about 15° from the fiber axis, and complete one turn around the helix at a distance of about 2 × 10
3
Å along the fiber axis. The short striations occur at an angle of about 80° from the fiber axis, with a spacing of about 65 Å, and complete one turn around the helix at a distance along the fiber axis of about 130 Å. The structure of the fiber appears to be a sextuple helix in terms of the long striations, and a double helix in terms of the short striations. The shadowed samples are consistent with a left-handed screw sense for the short striations, thus implying a right-handed sense for the long striations. A structural model incorporating these features is compatible with the atomic structure of hemoglobin, with individual molecules oriented with their dyad axis of symmetry perpendicular to the fiber axis and their α
1
-β
1
pseudo-dyad axis roughly parallel to the fiber axis. This orientation places the two β-6 regions of each molecule (sites of the sickle cell mutation) in contact with the β-6 regions of the molecules above and below along the long striations. Both the long and short striations are accounted for by individual hemoglobin molecules arranged in double helical arrays with 6.4 molecules per turn in each array.
Polymorphism for Interspecific Cross-Compatibility in Phlox
Authors: Levin Donald A.
Published: May 2006

Extensive polymorphism for the cross-compatibility of
Phlox pilosa
with
P. glaberrima
occurs within Illinois populations. The polymorphism is genetically determined. Thus, there is an opportunity for selection to enhance existing cross-compatibility barriers in areas of species contact. There is no evidence that selection has favored the reinforcement of such barriers.
Use of DNA Polymerase I Primed by a Synthetic Oligonucleotide to Determine a Nucleotide Sequence in Phage f1 DNA
Authors: Sanger F. , Donelson J. E. , Coulson A. R. , Kössel H. , Fischer D.
Published: May 2006

A sequence of 50 residues in f1 DNA has been determined by the extension of a chemically synthesized octadeoxyribonucleotide by
Escherichia coli
DNA polymerase I, with radioactive nucleoside triphosphates and f1 DNA template. The polymerized product was synthesized either in the presence of manganese and a mixture of ribo- and deoxyribotriphosphates or in a magnesium-containing reaction with one or more of the four triphosphates absent. The sequence determination depended largely on fractionation of the polymerized products by two-dimensional “homochromatography.” This approach and the techniques for the subsequent sequence analysis should be of general use for determining other sequences of DNA. Several features of this sequence suggest that it is located in an intercistronic region of f1 DNA.
On the Relation Between λ Lines and Phase Separations
Authors: Rice O. K.
Published: May 2006

It has often been assumed that the slope of the isotherm involving a pair of secondary variable vanishes along a λ line [for example, along a λ line in the pressure-volume plane ([unk]
P
/[unk]
V
)

T

vanishes], and therefore that the specific heat for constant extensive variable (e.g.,

C
V

) has the greatest possible value on the λ line and so obeys the Buckingham-Fairbank relation. It is shown here by a heuristic theoretical argument that in
3
He-
4
He solutions ([unk]μ
4
/[unk]
x
3
)

T

and ([unk]μ
3
/[unk]
x
3
)

T

probably do not vanish and
C

x
3

does not have its maximum possible value, although it may become infinite when
x
3
→ 0. (μ
4
and μ
3
are chemical potentials of
4
He and
3
He and
x
3
is the molefraction of
3
He). Only at the tricritical point does ([unk]μ
4
/[unk]
x
3
)

T

finally vanish and
C

x
3

have a value, which cannot be exceeded without the system's becoming unstable. In the case of the transition in solid NH
4
Cl the experimental facts seem to indicate that at the higher temperatures, where the transition is of higher order, ([unk]
P
/[unk]
V
)

T

does not become zero along the transition line. A statistical thermodynamic description of tricritical points is given, and shown to accord qualitatively with the experimental results for the
3
He-
4
He solutions. There is evidence that any singular behavior at the tricritical point in
3
He-
4
He is already present along the λ line. Finally, an analysis is made of the possible behavior of binary liquid solutions, and it is shown that a tendency of

C
V

to exceed its maximum value can result in a flat top on the coexistence curve.
Do Cells Cycle?
Authors: Smith J. A. , Martin L.
Published: May 2006

We propose that a cell's life is divided into two fundamentally different parts. Some time after mitosis all cells enter a state (A) in which their activity is not directed towards replication. A cell may remain in the A-state for any lenght of time, throughout which its probability of leaving A-state remains constant. On leaving A-state, cells enter B-phase in which their activities are deterministic, and directed towards replication. Initiation of cell replication processes is thus random, in the sense that radioactive decay is random. Cell population growth rates are determined by the probability with which cells leave the A-state, the duration of the B-phase, and the rate of cell death. Knowledge of these parameters permits precise calculation of the distribution of intermitotic times within populations, the behavior of synchronized cell cultures, and the shape of labeled mitosis curves.
Purification of Oncornaviruses by Agglutination with Concanavalin A
Authors: Stewart Margaret L. , Summers Donald F. , Soeiro Ruy , Fields Bernard N. , Maizel Jacob V.
Published: May 2006

Concanavalin A (Con A) has been used to rapidly and selectively agglutinate murine and avian oncornavirions from culture medium or plasma. The agglutinated virus was concentrated rapidly and gently by low-speed centrifugation and solubilization with α-methyl mannoside. Infectious virus was purified 2.3 times with respect to nucleic-acid content, and more than 60% of its infectivity was recovered. Infectious particles of densities 1.18 and 1.16 g/cm
3
were found in mouse cells infected with Friend virus. Con A reacted only with particles of density 1.16 g/cm
3
, indicating heterogeneity with respect to carbohydrate content or structure as well as buoyant density. Electron microscopy of virus agglutinated with Con A showed a zone of Con A-glycoprotein complexes averaging 12-15 nm in thickness.
Genetic Control of Development in
Volvox:
Isolation and Characterization of Morphogenetic Mutants
Authors: Sessoms Ann H. , Huskey Robert J.
Published: May 2006

Morphogenetic mutants of the colonial green alga,
Volvox carteri
f.
nagariensis
, were induced by chemical mutagenesis. The 68 independent mutants are classified into 12 readily identifiable phenotypes affecting various stages of asexual development. Nine of the mutants are temperature sensitive with normal development at 25° and mutant development occurring at 35°. Some mutant genes appear to be involved in the regulation of differentiation or the stability of the differentiated state. Other mutations occur in genes apparently responsible for structural components of dividing cells or adult colonies. Two mutants affect different aspects of the posterior-anterior polarization of the mature colony. One mutation affects a gene which acts very early in colonial development, but affects the appearance of the mature colony. The mutants isolated demonstrate the feasibility of using
Volvox
to study the genetic control of early steps in embryogenesis.