bluuebunny/crossref_metadata_2025 huggingface dataset:
The Three-Dimensional Structure of a Phosphorylcholine-Binding Mouse Immunoglobulin Fab and the Nature of the Antigen Binding Site
Authors: Segal David M. , Padlan Eduardo A. , Cohen Gerson H. , Rudikoff Stuart , Potter Michael , Davies David R.
Published: May 2006

The structure of the Fab of McPC 603, a mouse myeloma protein with phosphorylcholine binding activity, has been determined to 3.1-Å resoltuion. The four domains are found to be structurally similar with a well-defined double-layer structure. A large cavity exists at one end of the fragment, the walls of which are formed exclusively of hypervariable residues. Phosphorylcholine binds in this cavity and forms specific interactions with several well-defined amino-acid side chains of the protein. The hapten is bound asymmetrically and interacts more with the heavy chain than with the light chain.
Nuclear Coupling of
33
S and the Nature of Free Radicals in Irradiated Crystals of Cystine Dihydrochloride: Part II, Charged Radicals
Authors: Hadley Joseph H. , Gordy Walter
Published: May 2006

The
33
S hyperfine structure has been observed in negatively charged cystine molecule-radicals RCH
2
(SS)
-
CH
2
R. The coupling, found to be axially symmetric about the SS bond, proved the orbital of the unpaired electron to be an antibonding SS σ
*
orbital with the spin density shared equally between 3
p
(σ
*
) orbitals of the two sulfurs. The
33
S hyperfine structure could not be detected for a second radical produced by irradiation of the cystine hydrochloride crystal at 77°K, but interpretation of the proton hyperfine structure and
g
tensor observed by others led to the conclusion that this radical is the positively charged cystine molecule RCH
2
S
+
SCH
2
R with the spin density concentrated in a 3
p
orbital of one S and perpendicular to the SS bond.
Glutamine-Binding Subunit of Glutamate Synthase and Partial Reactions Catalyzed by This Glutamine Amidotransferase
Authors: Trotta Paul P. , Platzer Karen E. B. , Haschemeyer Rudy H. , Meister Alton
Published: May 2006

In the course of studies on glutamine-dependent carbamyl phosphate synthetase from
Aerobacter aerogenes
, we purified another protein which was found to be glutamate synthase (EC 2.6.1.53). The enzyme, obtained in apparently homogeneous form (monomer molecular weight about 227,000;
s
20,ω
= 17.6 S), was found to be a typical glutamine amidotransferase in that it exhibits glutaminase activity and can utilize ammonia in place of glutamine as a nitrogen donor. The enzyme also catalyzes at low rates the oxidative deamination of glutamate in the presence of TPN, and it exhibits TPNH oxidase activity. The enzyme is similar to the glutamate synthase found in
Escherichia coli
in that it is an iron-sulfide flavoprotein. Treatment of the enzyme with sodium dodecyl sulfate or potassium thiocyanate dissociates it into nonidentical subunits exhibiting molecular weights of about 175,000 and 51,500. The glutamine-dependent activity of the enzyme is inhibited by L-2-amino-4-oxo-5-chloropentanoic acid, but this chloroketone analog of glutamine does not affect the ammonia-dependent glutamate synthase activity. Studies with [
14
C]chloroketone show that the reagent binds to the heavy subunit only. Inhibition by the chloroketone and its binding to the heavy subunit are markedly reduced in the presence of L-glutamine. Sedimentation velocity studies carried out in potassium thiocyanate indicate that iron-sulfide and flavin sites are also located on the heavy subunit. While these studies show that glutamate synthase resembles other glutamine amidotransferases in certain of its catalytic properties, the findings indicate that the light subunit of this enzyme, in contrast to that of several other glutamine amidotransferases, does not function to bind glutamine. It is of interest that the enzyme exhibits an unusually high affinity for ammonia as compared to a number of other glutamine amidotransferases. Glutamate synthase is inhibited (competitively with respect to glutamine) by low concentrations of methionine sulfone, methionine sulfoximine, and methionine sulfoxide.
Mitochondrial Genetics in Bakers' Yeast: A Molecular Mechanism for Recombinational Polarity and Suppressiveness
Authors: Perlman Philip S. , Birky C. William
Published: May 2006

Recombinational polarity and suppressiveness are two well-known but puzzling cytoplasmic genetic phenomena in bakers' yeast,
Saccharomyces cerevisiae
. Little progress has been made in characterizing the underlying molecular mechanisms of these phenomena. In this paper we describe a molecular model for recombinational polarity that is compatible with the available genetic evidence. The model stresses the role of small deletions and excision/repair processes in otherwise canonical recombinational events. According to the model, both phenomena require recombination and may share mechanistic elements.
Mutations That Alter the Transmission of Chloroplast Genes in
Chlamydomonas
Authors: Sager Ruth , Ramanis Zenta
Published: May 2006

Two mutations are described that alter the pattern of inheritance of chloroplast genes in
Chlamydomonas
. The mutant gene
mat-1
linked to the mating type allele
mt
-
greatly increases the frequency of exceptional zygotes, i.e., zygotes that transmit chloroplast genes from the
mt
-
(male) parent. In some crosses, 80-90% of the zygotes are biparental, transmitting chloroplast genes from both parents. The
mat-2
mutation, linked to
mt
+
, acts to decrease the frequency of exceptional zygotes below the spontaneous level. The mutant effects are discussed in terms of a DNA modification-restriction system, postulated to regulate the transmission of chloroplast DNA in zygotes.
High Pressure Studies of Solvent Effects on Anthracene Spectra
Authors: Okamoto B. Y. , Drickamer H. G.
Published: May 2006

Measurements have been made of the effect of pressure on the peak location and peak shape for anthracene in a variety of liquid and plastic environments; both absorption and fluorescence studies were made. The results are discussed from two standpoints: in terms of the dielectric model and of a configuration coordinate model. For the latter model, the change of configuration coordinate (volume decrease of the system upon electronic excitation) is shown to correlate well with the product of the compressibility and polarizability of the solvent. For the dielectric model, it is found that the change of cavity volume with density is complex. However, the relative cavity volume obtained from emission measurements was consistently 10-15% smaller than that obtained from absorption. The cavity volume decreased with increasing polarizability of the solvent, and results obtained from absorption and emission were quite consistent in this regard.
Preparation and Spectroscopic Studies of Cobalt(II) Derivatives of Blue Copper Proteins
Authors: McMillin David R. , Rosenberg Robert C. , Gray Harry B.
Published: May 2006

Preparation of cobalt(II) derivatives of type 1 copper proteins has been extended to include bean plastocyanin and azurin from
Pseudomonas aeruginosa
. Fluorescence quenching data suggest that Co(II) binds to the type 1 site of both apoplastocyanin and apoazurin. Electronic absorption spectral measurements have been made for cobalt(II)-stellacyanin, cobalt(II)-plastocyanin, and cobalt(II)-azurin. In each case two visible bands with moderate intensities and two rather strong ultraviolet absorption peaks are observed. The intensity pattern and the separation of the two ultraviolet bands in the Co(II) derivatives correspond closely to the two intense, low-lying absorption peaks in the analogous, type 1 copper proteins. The evidence suggests that the intense, two-band systems represent ligand-to-metal charge transfer transitions in both Cu(II) and Co(II) derivatives. It is proposed that the transitions in each case originate in the 3pπ and 3pσ orbitals of a cysteine sulfur ligand at the type 1 site. The visible absorption bands in the Co(II) derivatives are assigned to
d-d
transitions. The large
4
P splitting observed indicates that the type 1 Co(II) site is of low symmetry. The
d-d
band pattern suggests that the high-spin Co(II) center is either distorted tetrahedral or five-coordinate. The observed band intensities are in much closer accord with the values for Co(II) complexes known to have distorted tetrahedral structures.
Demonstration of a Genetic Factor Influencing Spontaneous Release of a Xenotropic Virus of Mouse Cells
Authors: Stephenson John R. , Aaronson Stuart A.
Published: May 2006

There is increasing evidence that mouse cells of different strains contain different numbers and biologic classes of naturally-integrated type-C RNA viruses. The present studies have examined the cellular regulation of one class of virus, xenotropic in host range, which is common to mice of NIH Swiss and NZB strains. This virus is spontaneously released at high level by NZB embryo cells but its production by NIH Swiss embryo cells is below detectable levels. Quantitative analysis of the chronic level of virus release by embryo cell lines established in tissue culture from genetic crosses of NIH and NZB strains has demonstrated the existence of a partially dominant gene influencing virus release. Evidence is presented indicating that this gene may act to provide a factor necessary for expression of a specific class of endogenous virus.
A Quantal Analysis of the Synaptic Depression Underlying Habituation of the Gill-Withdrawal Reflex in
Aplysia
Authors: Castellucci Vincent F. , Kandel Eric R.
Published: May 2006

Habituation, one of the simplest behavioral paradigms for studying memory, has recently been examined on the cellular level in the gill-withdrawal reflex in the mollusc
Aplysia
and in the escape response in cray-fish. In both cases short-term habituation involved a decrease in excitatory synaptic transmission at the synapses between the sensory neurons and their central target cells. To analyze the mechanisms of the synaptic depression in
Aplysia
, we applied a quantal analysis to synaptic transmission between the sensory and motor neurons of the gill-withdrawal reflex. Our results indicate that short-term habituation results from a presynaptic mechanism: a decrease in the number of transmitter quanta released per impulse. The sensitivity of the postsynaptic receptor remains unaltered.
Absence of a Specific Ganglioside Galactosyltransferase in Mouse Cells Transformed by Murine Sarcoma Virus
Authors: Fishman Peter H. , Brady Roscoe O. , Bradley Roy M. , Aaronson Stuart A. , Todaro George J.
Published: May 2006

The ganglioside composition of a nonproducer subclone (derived from BALB/c 3T3 mouseembryo cells) transformed by Kirsten murine sarcoma virus was drastically altered compared to the nontransformed parental clone. The transformed clone was unable to synthesize the mono- and disialogangliosides, G
M1
and G
D1a
, due to the complete absence of a specific galactosyltransferase. The lack of this enzyme activity was established by sensitive radiochemical and enzymological techniques
in vivo
and
in vitro
.
Fluorotyrosine Alkaline Phosphatase from
Escherichia coli
: Preparation, Properties, and Fluorine-19 Nuclear Magnetic Resonance Spectrum
Authors: Sykes Brian D. , Weingarten Harold I. , Schlesinger Milton J.
Published: May 2006

Alkaline phosphatase (EC 3.1.3.1) containing
m
-flurotyrosine has been prepared from
E. coli
grown in the presence of
m
-flurotyrosine. The kinetic properties of the
m
-fluorotyrosine enzyme measured with
p
-nitrophenylphosphate at pH 8.0 and dinitrophenylphosphate at pH 5.5 are essentially the same as those of normal alkaline phosphatase. However, the ability of the
m
-fluorotyrosine protein to refold active enzyme after acid denaturation, while unchanged at pH 5.8, was markedly decreased at pH 7.6. This result implies that the tyrosines must be in their protonated form for the protein to refold, reassociate, and take on zinc. The
19
F nuclear magnetic resonance spectrum of
m
-fluorotyrosine alkaline phosphatase contains resolved resonances corresponding to different chemical environments for each
m
-fluorotyrosine in the folded protein. This demonstrates that
19
F nuclear magnetic resonance spectroscopy of enzymes specifically labeled with
19
F, even with enzymes as large as alkaline phosphatase (molecular weight, 86,000), will provide a very valuable probe for conformational changes in proteins.
Immunostimulation with Bacterial Phospholipid Extracts
Authors: Fauve Robert M. , Hevin Brigitte
Published: May 2006

Injection of bacterial phospholipid extracts (EBP) into mice increased their resistance towards a
Listeria monocytogenes
infection. The blood clearance of virulent
Salmonella typhimurium
was enhanced and the degree of clearance correlated with the dose of extract injected. The multiplication of
Listeria monocytogenes
in spleen and liver of mice was inhibited and this inhibition was also correlated with the amount of extract injected. The absence of apparent toxicity in mice, of splenoand hepatomegaly, and of lymphoid hyperplasia, distinguish this immunostimulant from other known bacterial stimulants of host resistance to infection.
Siroheme: A New Prosthetic Group Participating in Six-Electron Reduction Reactions Catalyzed by Both Sulfite and Nitrite Reductases
Authors: Murphy Matthew J. , Siegel Lewis M. , Tove Shirley R. , Kamin Henry
Published: May 2006

Ferredoxin-nitrite reductase (EC 1.7.7.1) of spinach, an enzyme that catalyzes the six-electron reduction of nitrite to ammonia, contains siroheme, the new type of prosthetic group recently found in several sulfite reductases (both assimilatory and dissimilatory) that can catalyze the reduction of sulfite to sulfide, also a six-electron reduction. The prosthetic group of sulfite reductase had previously been shown to be an iron-tetrahydroporphyrin of the isobacteriochlorin type (adjacent pyrrole rings reduced) with eight carboxylate side chains. This finding suggests that both types of “multi-electron” reduction processes may share common mechanistic features.
DNA Repair in
Escherichia coli
Mutants Deficient in DNA Polymerases I, II, and/or III
Authors: Tait Robert C. , Harris Andrew L. , Smith Douglas W.
Published: May 2006

E. coli
mutants deficient in DNA polymerase I, in DNA polymerases I and II, or in DNA polymerase III, can efficiently and completely execute excision repair and post-replication repair of UV-damaged DNA at 43° when assayed by alkaline sucrose gradients. Repair by cells deficient in polymerase I and in polymerases I and II is inhibited by 1-β-D-arabinofuranosylcytosine at 43°, whereas that by cells deficient in polymerase III is insensitive to the inhibitor. When both DNA polymerases I and III are deficient, both excision repair and post-replication repair are greatly reduced at 43°, and the residual repair capability is inhibited by 1-β-D-arabinofuranosylcytosine. Very little dark repair is observed in cells deficient in DNA polymerases I, II, and III, and the DNA is extensively degraded. These results suggest that either DNA polymerase I or DNA polymerase III is required for complete and efficient repair, and that when both DNA polymerases I and III are deficient, DNA polymerase II mediates a limited, incomplete dark repair of UV-damaged DNA. DNA polymerases I and III thus appear to be important enzymes in both DNA replication and DNA dark repair.
Chromosome Cycles Turned on in Unfertilized Sea Urchin Eggs Exposed to NH
4
OH
Authors: Mazia Daniel
Published: May 2006

In unfertilized sea urchin eggs treated with NH
4
OH-sea water, the chromosomes condense after a first round of DNA synthesis and go through a chromosome cycle. The chromosomes split visibly, but sister chromosomes are not further separated. They regress into an interphase nucleus. These cycles repeat, producing eggs with large numbers of chromosomes. No mitotic apparatus is seen and the eggs do not divide. There is some microscopic evidence of limited chromosome movement, interpreted as centrifugal movement of the condensed chromosomes before they split and a centripetal movement as the split chromosomes decondense to reconstitute the nucleus. The eggs so treated with NH
4
OH are considered to be unfertilized eggs and can be fertilized later. Such later fertilization permits the introduction of paternal nuclei after the maternal nuclei have progressed some way toward the above-described chromosome condensation. The paternal chromosomes condense prematurely at the time when the maternal chromosomes condense. At the same time, premature with respect to the time of fertilization, mitotic apparatus form.
Mechanism of Action of the Mycotoxin Trichodermin, a 12,13-Epoxytrichothecene
Authors: Wei Cha-mer , Hansen Bent S. , Vaughan Maurice H. , McLaughlin Calvin S.
Published: May 2006

Trichodermin is a member of a group of closely related compounds—the 12,13-epoxytrichothecenes—that form a medically and economically important class of mycotoxins produced by fungi that spoil fruit and grain. Our studies show that trichodermin is a very potent inhibitor of protein synthesis in mammalian cells. Since ribosomes remain in polyribosomes in inhibited cells, trichodermin inhibits the elongation and/or termination processes of protein synthesis.
In vitro
, trichodermin is a potent inhibitor of the peptidyl transferase activity required for elongation and/or termination. An
in vitro
comparison of the effects of three peptidyl transferase inhibitors on elongation and termination indicates that anisomycin acts primarily on elongation while trichodermin and sparsomycin act primarily on termination. A new
in vivo
test to distinguish elongation inhibitors from termination inhibitors confirms that trichodermin inhibits primarily the termination process. Thus trichodermin inhibits protein synthesis by blocking the activity of peptidyl transferase required for termination. These studies suggest that the toxicosis caused by one of the 12,13-epoxytrichothecenes is due to its action as a protein synthesis inhibitor involving the peptidyl transferase activity of the eukaryotic ribosomes.
Replication of Colicin E1 Plasmid DNA in Cell Extracts
Authors: Sakakibara Yoshimasa , Tomizawa Jun-Ichi
Published: May 2006

Cell extracts were prepared from
Escherichia coli
carrying colicin E1 plasmid. The DNA in extracts was almost exclusively closed-circular DNA of the plasmid. Labeled deoxyribonucleotides were incorporated into DNA in extracts. DNA of colicin E1 plasmid was the sole DNA product, and was composed of completely replicated molecules and a class of replicative intermediates. The intermediates carried an average of approximately two pieces of DNA fragments that had a sedimentation coefficient of approximately 6 S and were not covalently attached to the parental DNA strands. The replication was initiated on closed-circular molecules and the complete molecules were synthesized semiconservatively. The DNA synthesis depended on the four ribonucleoside triphosphates and was sensitive to rifampicin. A round of DNA replication, once initiated, was completed in the presence of rifampicin, indicating that RNA synthesis is involved in the initiation of replication of the plasmid DNA. Most of the replicated molecules were isolated in super-coiled structures. These results indicate that this soluble system is capable of carrying out a complete round of replication of colicin E1 plasmid DNA.
Expression of Differentiated Functions in Hepatoma Cell Hybrids: High Frequency of Induction of Mouse Albumin Production in Rat Hepatoma-Mouse Lymphoblast Hybrids
Authors: Malawista Stephen E. , Weiss Mary C.
Published: May 2006

We have studied the production of serum albumin by somatic hybrids between well-differentiated 2
s
and 1
s
rat hepatoma cells (Faza), which produce serum albumin, and sub-diploid mouse leukemic lymphoblasts (Lc), which do not produce albumin. We determined the rat or mouse origin of the albumin by double immunodiffusion, using immuno-adsorbed noncrossreacting antisera. Each of 12 karyologically identified 2
s
hybrid clones (Lc2F) produces both rat and mouse albumin. Moreover, unlike 1
s
hybrids reported previously, eight of nine 1
s
hybrids (LcF) also produce mouse albumin; six of them produce rat albumin as well. One clone from the 1
s
cross produces only rat albumin.
Isolation and Analysis of Somatic Hybrids Derived from Two Human Diploid Cells
Authors: Migeon Barbara R. , Norum Robert A. , Corsaro Cheryl M.
Published: May 2006

Lesch-Nyhan fibroblasts and normal human leukocytes with different glucose-6-phosphate dehydrogenase genotypes were fused by Sendai virus. Clones were isolated on the basis of their resistance to a medium containing hypoxanthine, amethopterin, and thymidine and ability to proliferate in monolayer culture. These mononuclear cells (
1
) incorporated [
3
H]hypoxanthine, (
2
) expressed the glucose-6-phosphate dehydrogenase heteropolymer, and (
3
) were polyploid. Therefore, hybrids can originate from the fusion of two diploid human cells. X chromosome inactivation did not occur in these hybrid cells of male origin. The hybrids expressed both parental genomes and exhibited the senescence and contact feeding characteristic of the human skin fibroblast.
Structure and Development of Neuronal Connections in Isogenic Organisms: Transient Gap Junctions between Growing Optic Axons and Lamina Neuroblasts
Authors: Lopresti V. , Macagno E. R. , Levinthal C.
Published: May 2006

We previously showed that the growth of each bundle of eight optic fibers from one ommatidium into the optic lamina of Daphnia occurs in such a way that one of the eight fibers precedes the others into the lamina. The growth cone of this lead fiber makes surface contact with undifferentiated neuroblasts near the midplane. This is followed by a glial-like wrapping of each neuroblast around the fiber. In this report, gap junctions are shown to form for a short period of time between the growing lead fiber and the neuroblast that is wrapping around it. It is proposed that these junctions may represent a morphological correlate of informational exchange between axon and neuroblast. This signaling would then reflect the fact that the sequence of axon proliferation by the lamina neuroblasts within an optic cartrdige, ultimately composed of five lamina neurons and eight optic fibers, parallels the order in which the neuroblasts undergo the wrapping reaction with the lead fiber.
Chemomechanical Coupling without ATP: The Source of Energy for Motility and Chemotaxis in Bacteria
Authors: Larsen Steven H. , Adler Julius , Gargus J. Jay , Hogg Robert W.
Published: May 2006

The source of energy for bacterial motility is the intermediate in oxidative phosphorylation, not ATP directly. For chemotaxis, however, there is an additional requirement, presumably ATP. These conclusions are based on the following findings. (
i
) Unlike their parents, mutants of
Escherichia coli
and
Salmonella typhimurium
that are blocked in the conversion of ATP to the intermediate of oxidative phosphorylation failed to swim anaerobically, even when they produced ATP. When respiration was restored to the mutants, motility was simultaneously restored. (
ii
) Carbonylcyanide
m
-chlorophenylhydrazone, which uncouples oxidative phosphorylation, completely inhibited motility even though ATP remained present. (
iii
) Arsenate did not inhibit motility in the presence of an oxidizable substrate, though it did reduce ATP levels to less than 0.3% (
iv
) Arsenate completely inhibited chemotaxis under conditions where motility was normal.
A Restriction Point for Control of Normal Animal Cell Proliferation
Authors: Pardee Arthur B.
Published: May 2006

This paper provides evidence that normal animal cells possess a unique regulatory mechanism to shift them between proliferative and quiescent states. Cells cease to increase in number under a diversity of suboptimal nutritional conditions, whereas a uniformity of metabolic changes follows these nutritional shifts. Evidence is given here that cells are put into the same quiescent state by each of these diverse blocks to proliferation and that cells escape at the same point in G
1
of the cell cycle when nutrition is restored. The name restriction point is proposed for the specific time in the cell cycle at which this critical release event occurs.

The restriction point control is proposed to permit normal cells to retain viability by a shift to a minimal metabolism upon differentiation
in vivo
and
in vitro
when conditions are suboptimal for growth. Malignant cells are proposed to have lost their restriction point control. Hence, under very adverse conditions, as in the presence of antitumor agents, they stop randomly in their division cycle and die.
Preparation and Spectroscopic Studies of Cobalt(II)-Stellacyanin
Authors: McMillin David R. , Holwerda Robert A. , Gray Harry B.
Published: May 2006

The cobalt(II) derivative of the “blue” copper protein stellacyanin has been prepared, and its visible-ultraviolet spectrum is reported. Tryptophan fluorescence quenching and
p
-mercuribenzoate titration results strongly suggest that Co(II) and Cu(II) compete for the same stellacyanin binding site and that a cysteine sulfur atom is coordinated in both cases. This interpretation is supported by the finding of an intense band at 355 nm in Co(II)-stellacyanin attributable to a charge transfer transition of the RS
-
→ Co(II) type. The visible absorption spectrum of Co(II)-stellacyanin exhibits band maxima at 540, 625, and 655 nm. These bands are attributable to
d-d
transitions originating in a high-spin Co(II) center. It is suggested that a correspondence exists between charge transfer bands observed at 355 and 300 nm in the Co(II) derivative to those found at 604 and 450 nm in the native protein. It is concluded that the intense 604-nm peak in Cu(II)-stellacyanin is attributable to a cys-S → Cu(II) charge transfer transition.
Evidence for the Presence of the Toxin-Binding Protein on the Plasma Membrane of Sugarcane Cells
Authors: Strobel Gary A. , Hess W. M.
Published: May 2006

Helminthosporoside is a host-specific toxin produced by
Helminthosporium sacchari
, both in culture and in infected sugarcane tissue. The susceptibility of any given clone of sugarcane to disease is invariably associated with the presence of a toxin-binding protein. This report presents evidence for the presence of the toxin-binding protein on the plasma membrane of the plant cell. This evidence includes, among others: (
1
) The protection of susceptible plant tissues by prior treatment with antiserum to the binding protein, (
2
) the successful pyridoxylation and reduction of the binding protein
in vivo
followed by its isolation, (
3
) the reaction of sugarcane cells and free protoplasts with [
3
H]antiserum prepared against the binding protein, and (
4
) the agglutination of sugarcane protoplast preparations with antiserum to the binding protein.
Structure of the Krasnovskii Photoreduction Product of Chlorophyll
a
Authors: Scheer Hugo , Katz Joseph J.
Published: May 2006

A proton magnetic resonance study at 220 MHz shows the Krasnovskii intermediate in the photoreduction of chlorophyll
a
by hydrogen sulfide to be β,δ-dihydrochlorophyll
a
.
Cyclic Electrochemical Inactivation and Restoration of Competence of Bone Matrix to Transform Fibroblasts
Authors: Reddi A. H. , Huggins Charles B.
Published: May 2006

Brief exposure of rat bone matrix to highly charged electrochemicals had profound but reversible effects on its competence to transform fibroblasts into chondroblasts and osteoblasts. Suppression and subsequent reactivation of this function were influenced critically by the charge of the electrochemical reagent and the pH of the reaction mixture. In dilute acids, Evans Blue, a long electronegative molecule, suppressed transforming competence, whereas hexadimethrine, a polycationic quaternary ammonium base, failed to do so. A cycle of inactivation-restoration of transforming competence was achieved by sequential treatment of bone matrix with Evans Blue followed by hexadimethrine; an electrochemical complex was demonstrated by histochemistry. In dilute alkalies, hexadimethrine inhibited, whereas, Evans Blue did not suppress the transforming function of the bone matrix. Electric charge characteristics on the surface of the bone matrix are of crucial significance for the fibroblast-transforming attribute.
Inhibition of Cell Proliferation in the Livers of Hepatectomized Rats by a Rabbit Hepatic Chalone
Authors: Simard Antoine , Corneille Louise , Deschamps Yves , Verly Walter G.
Published: May 2006

A purified chalone isolated from rabbit liver was tested
in vitro
on regenerating rat liver slices incubated with tritiated thymidine to determine more precisely the phase of the normal cell cycle that was blocked by that substance. Biochemical and radioautographic studies showed that the inhibition of tritiated thymidine incorporation during chromosomal DNA replication resulted chiefly from a block in the G
1
-S transition in the normal cell cycle. Under these conditions the chalone had little inhibitory effect on hepatocytes that were in the S phase of the cell cycle. The inhibitory effects of the liver chalone appeared to be specific for hepatocytes and no significant inhibition of cell division was observed when that compound was tested against intestinal villi or tongue epithelial cells of the rat. When, on the other hand, the purified chalone was injected into rats following partial hepatectomy, not only was an inhibition observed during the G
1
-S transition but an increase in the ratio of metaphases to anaphases was found, suggesting that a block also occurs at metaphase as a result of the action of the purified liver chalone used in this study.

The injection of a crude supernatant fluid obtained from rabbit liver homogenates into partially hepatectomized rats resulted not only in a more pronounced block at the G
1
-S transition than was observed when the purified chalone was used, but the supernatant liquid also affected significantly DNA synthesis during the S phase of the cell cycle. These inhibitory effects were observed not only in hepatocytes but in intestinal epithelium and tongue epithelial cells of the rat as well. The rabbit liver supernatant fluid thus appears to contain, in addition to the liver chalone, one or more nonspecific inhibitors of DNA synthesis.
Role of DNA-Dependent RNA Polymerase III in the Transcription of the tRNA and 5S RNA Genes
Authors: Weinmann Roberto , Roeder Robert G.
Published: May 2006

Mouse myeloma cells have previously been shown (L. B. Schwartz, V. E. F. Sklar, J. A. Jaehning, R. Weinmann & R. G. Roeder, submitted for publication) to contain two chromatographically distinct forms of RNA polymerase III (designated III
A
and III
B
). The enzymes are unaffected by low α-amanitin concentrations which completely inhibit RNA polymerase II, but they exhibit characteristic inhibition curves (identical for III
A
and III
B
) at higher toxin concentrations. RNA polymerase I was unaffected at all α-amanitin concentrations tested. Myeloma RNA polymerases II, III
A
, and III
B
appear to be inhibited by the same mechanism, since the toxin rapidly blocks chain elongation by each enzyme. The characteristic α-amanitin sensitivity of RNA polymerase III has been employed in studies of the function(s) of the class III RNA polymerases.

Isolated myeloma nuclei and nucleoli contińue to synthesize RNA via the endogenous RNA polymerases when incubated
in vitro
. With nuclei, newly synthesized 4S precursor (pre-4S) and 5S RNA species were detected by electrophoretic analysis either of the total nuclear RNA or of the RNA released into the supernatant during incubation. The synthesis of both pre-4S and 5S RNA species was inhibited by α-amanitin, but only at high concentrations; and the α-amanitin inhibition curves for these RNAs were identical to those obtained for solubilized RNA polymerases III
A
and III
B
. In control experiments it was shown that the endogenous RNA polymerase II activity of isolated nuclei was inhibited by α-amanitin concentrations similar to those required to inhibit purified enzyme II. However, 40-50% of the endogenous activity of nuclei and 100% of the endogenous activity of purified nucleoli was completely resistant to the high α-amanitin concentrations necessary to inhibit the RNA polymerase III activities. These experiments rule out nonspecific inhibitory effects in the endogenous systems.

These results unequivocally demonstrate the role of RNA polymerase III (III
A
and/or III
B
) in the synthesis of (pre) 4S RNAs and a 5S RNA species.
Interspecific Recombination of Mitochondrial DNA Molecules in Hybrid Somatic Cells
Authors: Horak Ivan , Coon Hayden G. , Dawid Igor B.
Published: May 2006

The mitochondrial DNA (mtDNA) in rodent-human hybrid somatic cells was studied in strains that contain nucleotide sequences from both parental mtDNAs. A test for linkage of rodent to human mtDNA was devised on the basis of the density and sequence differences between these DNAs. When a mixture of rodent and human mtDNAs was banded in a CsCl gradient and each fraction hybridized with a mixture of complementary [
3
H]RNA transcribed from human mtDNA and complementary [
32
P]RNA transcribed from rodent mtDNA, each DNA was detected as a distinct and separate band at its expected density by specific hybridization with its complementary RNA. In some of the hybrid cell strains, the mtDNA sequences derived from the two species did not separate in the CsCl gradients. This result is interpreted as evidence for linkage between sequences from the two parental mtDNAs. While the exact nature of the linkage and the structure of the molecules containing both types of sequences are not known, the evidence supports the conclusion that the linkage is realized by a covalent bond. An event leading to the covalent bonding of these different sequences may be described as recombination. Among 18 hybrid cell strains examined, 13 contained large proportions of recombinant molecules. These molecules were found in both mouse-human and rat-human strains, and in strains containing more human or more rodent mtDNA sequences.
Thermal Enhancement of Ultraviolet Mutability in a
tif-1 uvrA
Derivative of
Escherichia coli
B/r: Evidence That Ultraviolet Mutagenesis Depends upon an Inducible Function
Authors: Witkin Evelyn M.
Published: May 2006

Inhibition of DNA replication in
E. coli
results in coordinate expression of a cluster of diverse functions, including prophage induction and filamentous growth, many of which are thermally inducible, without inhibition of DNA synthesis, in strains carrying a mutation in the “
tif
” locus. It has been proposed that one of the inducible functions in this cluster is responsible for the ultraviolet mutability of
E. coli
. As a test of this hypothesis, the effect of postirradiation temperature elevation on ultraviolet mutability was compared in strains differing by a
tif
mutation. In a
tif
+
strain, raising the temperature to 42° after irradiation did not change the frequency of induced mutations to tryptophan-independence. Similar treatment of a
tif-1
strain resulted in as much as a 10-fold increase in the induced mutation yield. Thermal enhancement of ultraviolet mutability in the
tif-1
strain was prevented or promoted by agents known to exert parallel effects on thermal induction of lambda prophage in
tif
lysogens. The results support the hypothesis that ultraviolet mutability in
E. coli
depends upon an inducible function that is normally expressed only when DNA replication is inhibited.
Polyma DNA: A Physical Map
Authors: Griffin Beverly E. , Fried Mike , Cowie Alison
Published: May 2006

The action of restriction enzymes on polyoma DNA was studied with uniformly
32
P-labeled viral DNA obtained from either infected 3T6 or secondary mouse-embryo cells. Three restriction enzymes were used to construct a physical map of the polyoma genome. An enzyme from
Hemophilus parainfluenzae
, Hpa
II
, cleaved polyma DNA into eight unique fragments (Hpa
II
-1 to Hpa
II
-8), ranging in size from 27.3 to 1.8% of the genome. An enzyme from
Hemophilus influenzae
, Hin
III
, gave two fragments (56 and 44%); and a third enzyme from
Escherichia coli
, EcoR
I
, cut at a single unique site. The physical map of the polyma genome was constructed from methods involving: (
1
) further digestion of the fragments produced by enzymes EcoR
I
and Hin
III
with Hpa
II
, and (
2
) analysis of the products of partial digestion with Hpa
II
.

Analysis by electron microscopy of replicating DNA molecules (less than 50% replicated) cut with the Hin
III
enzyme, in combination with other studies, has indicated that the origin of DNA replication is located at 71 ± 3 map units from the EcoR
I
cleavage site, probably in Hpa
II
-5.
Partial Purification of the Template-Active Fraction of Chromatin: A Preliminary Report
Authors: Gottesfeld J. M. , Garrard W. T. , Bagi G. , Wilson R. F. , Bonner James
Published: May 2006

A fraction of rat-liver chromatin that is transcriptionally active
in vivo
has been purified 6- to 7-fold over whole chromatin. This was accomplished by selectively shearing chromatin with DNase II followed by fractionating the released portion on the basis of its solubility properties in 2 mM MgCl
2
. The resulting soluble material comprises 11% of the total chromatin DNA and is impoverished in histone and enriched in nonhistone protein. Compared with unsheared chromatin, this minor fraction exhibits marked differences in chromosomal protein species. DNA renaturation studies indicate that this fraction is composed of a specific subset of whole genomal DNA sequences. Furthermore, DNA·RNA hybridization experiments suggest that almost 60% of the nonrepetitious DNA sequences of this minor fraction could code for cellular RNA.
Genetic Regulatory Mechanisms and the Ecological Niche of
Escherichia coli
Authors: Savageau Michael A.
Published: May 2006

Whether the regulatory protein of an inducible operon for a catabolic pathway is a positive or a negative element in the control of expression is correlated with the frequent or infrequent presence, respectively, of the system's substrate in the natural environment.
Release of Polarity in
Escherichia coli
by Gene
N
of Phage λ: Termination and Antitermination of Transcription
Authors: Adhya Sankar , Gottesman Max , De Crombrugghe Benoit
Published: May 2006

The induction of λ prophage provokes the constitutive expression of the adjacent
gal
operon in
E. coli
. This “escape synthesis” can result from transcription that initiates at a phage promoter and extends into the
gal
operon. The effect requires the product of the λ gene
N. N
-mediated transcription not only fails to terminate at the prophage-bacterial junction and at the ends of bacterial operons, but ignores termination signals caused by polar insertions or ochre mutations within
gal
. Suppression of polarity by
N
-function is a
cis
-effect; only transcription initiated at the phage promoter is influenced. We propose that the transcription complex is influenced by
N
-product to become termination-resistant at a site in the phage genome (juggernaut model). This site appears to be at or near the phage promoter.
The Second Law of Thermodynamics in Bioenergetics
Authors: Kemeny Gabor
Published: May 2006

Bioenergetic processes are viewed as processes of free energy transduction. The free energies of both local equilibrium and fluctuation states are being considered. It is shown that the exchange of thermal energy with the surrounding medium, acting as a reservoir, does not violate the second law of thermodynamics within broad limits. There is sufficient latitude for proteins to carry out their function of transduction utilizing thermal energy in the process.
The Absence of a Pyrimidine Dimer Repair Mechanism in Mammalian Mitochondria
Authors: Clayton David A. , Doda Jackie N. , Friedberg Errol C.
Published: May 2006

We have investigated whether mammalian cells can repair pyrimidine dimers in their mitochondrial DNA which have been induced by ultraviolet light. The assay system is based upon the ability of the phage T4 UV endonuclease to nick covalently closed circular mitochondrial DNA that contain pyrimidine dimers. Our results show that dimers are not removed from the mitochondrial DNA of mouse L cells or human KB and HeLa cells. There is also no evidence for photoreactivation of mitochondrial DNA. Analyses of ethidium bromide-cesium chloride equilibrium density gradients of mitochondrial DNA isotopically labeled before and after exposure to ultraviolet light show that the total amount of DNA replication is depressed after exposure. In addition, an increase in the frequency of molecules banding at a position expected for intermediate replicating forms and open circular daughter molecules suggests that the rate of replication is slower (or arrested) in molecules with pyrimidine dimers. The absence of a significant amount of mixing of label incorporated before and after ultraviolet-irradiation is evidence against the occurrence of a large amount of genetic exchange between mitochondrial DNA molecules under these conditions.
Theory of Delayed Lateral Inhibition in the Compound Eye of
Limulus
Authors: Coleman Bernard D. , Renninger George H.
Published: May 2006

Although the magnitude of lateral inhibition in the retina of
Limulus polyphemus
depends strongly on the distance between ommatidia, the time of delay τ between the response of one ommatidium and the consequent inhibition of another is independent of the distance between them and is approximately 0.1 sec. Moreover, experimental observations indicate that for intact undamaged retinae in intense spatially uniform illumination, the total inhibitory influence at a given ommatidium can exceed the excitation of that ommatidium. A simple theory combining these two known facts yields the following conclusions: The response of a healthy
Limulus
retina to an intense, temporally constant, and spatially uniform excitation
e
(in the usual Hartline-Ratliff units) should be a sustained synchronous oscillation of period 2τ, with the mean response over one complete cycle equal to approximately 1/2
e
. Under a broad class of circumstances the sustained oscillations should take the form of a succession of “bursts” and “rest periods”, each of duration τ. The oscillations can have, however, a fine structure in which there is repeated information about the duration and sequence of any short pulses of excitation which occurred within a time-interval of length τ before the onset of steady excitation. Because it is repeated every 2τ seconds, this information remains available in the retina for interaction with subsequent changes of excitation.
Acetylation of Reticulocyte Ribosomal Proteins at Time of Protein Biosynthesis
Authors: Liew C. C. , Yip C. C.
Published: May 2006

When rabbit reticulocytes were incubated
in vitro
with [
3
H]acetate, their ribosomal proteins were rapidly acetylated within 10 min. Polyacrylamide-urea gel electrophoresis showed that several major ribosomal protein fractions were highly acetylated. By the double-isotope labeling technique, the incorporation of [
3
H]acetate and [
14
C]aminoacid mixture into ribosomal proteins and nascent chains was found to be closely associated. Sodium fluoride abolished the acetylation of ribosomal proteins, whereas cycloheximide reduced the acetylation of ribosomal proteins to a much lower level. These findings suggest that acetylation of ribosomal proteins may be involved in the formation of the initiation complex during protein biosynthesis.
Free Ribosomal RNA Genes in the Macronucleus of
Tetrahymena
Authors: Gall Joseph G.
Published: May 2006

In the macronucleus of the ciliated protozoan,
Tetrahymena pyriformis
GL, the genes coding for 17S and 25S rRNA exist as free, extrachromosomal molecules. About 90% of the molecules are linear with a molecular weight of 12.6 × 10
6
. Most of the remainder are circles of the same size, or lariats (circles with tails). A few dimers and oligomers are found. The extrachromosomal rDNA of
Tetrahymena
represents a kind of gene amplification that may be common among primitive eukaryotes.
Pathways of Assembly of Aspartate Transcarbamoylase from Catalytic and Regulatory Subunits
Authors: Bothwell M. , Schachman H. K.
Published: May 2006

A scheme for the assembly of aspartate transcarbamoylase (EC 2.1.3.2; carbamoylphosphate:L-aspartate carbamoyltransferase) from catalytic and regulatory subunits is presented along with a technique for detecting intermediates and measuring the kinetics of assembly at protein concentrations of about 10 nM.
125
I-labeled subunits (10
6
cpm/μg) were used, and the reaction was “topped”at specific times with an appropriate “chase” followed by electrophoretic separation and measurement of the amounts of the various species. Two intermediates were identified. A stable enzyme complex lacking one regulatory subunit is the principal product when catalytic subunits are in excess. A transiently stable complex lacking one catalytic subunit is the principal species when regulatory subunits are in excess. Measurements with mixtures of the purified regulatory-deficient molecules and free regulatory subunits gave a second-order rate constant of 10
5
10
5
M
-1
sec
-1
for the formation of bonding domains between catalytic and regulatory chains. No data for the rate of rupture of these bonds are available, but the kinetics of the assembly of the enzyme
in vitro
can be accounted for if this value is about 10
-2
sec
-1
. Assembly from subunits occurs in seconds at concentrations equivalent to those that would exist
in vitro
even if there were only enzyme molecule per cell.
A Probabilistic Approach to Cooperativity of Ligand Binding by a Polyvalent Molecule
Authors: Wyman Jeffries , Phillipson Paul E.
Published: May 2006

Cooperativity of ligand binding is defined operationally in terms of the Hill parameter
n
, whose values uniquely define the shape of the binding curve. When
n
is everywhere equal to 1 the system behaves as if the sites were all the same and independent. If at any point
n
is unequal to 1 the system is either cooperative (
n
> 1) or anticooperative (
n
< 1) at that point. This means that the binding of ligand at any site is influenced by the presence or absence of ligand at other sites. In the present paper this influence is formulated in terms of probabilities of the various binding events and of conditional probabilities which relate them. The result is a network of linked probabilities which determine the cooperativity or anticooperativity of the system. This probabilistic formulation supplements the more usual one in terms of free energies and places the subject in a broader perspective.
Reversibility of the Pyrophosphoryl Transfer from ATP to GTP by
Escherichia coli
Stringent Factor
Authors: Sy Jose
Published: May 2006

The stringent factor-catalyzed, ribosome-dependent synthesis of guanosine polyphosphates is found to be reversible. The reverse reaction specifically requires 5′-AMP as the pyrophosphoryl acceptor, and guanosine 5′-triphosphate-3′-diphosphate is preferentially utilized as the pyrophosphoryl donor. The primary products of the reaction are GTP and ATP. The reverse reaction is strongly inhibited by the antibiotics thiostrepton and tetracycline, and by ATP and β-γ-methylene-adenosine-triphosphate, but not by ADP, GTP, and GDP. The reverse reaction occurs under conditions for nonribosomal synthesis. The overall reaction for stringent factor-catalyzed guanosine polyphosphate formation may thus be formulated: (p)pp5′G + ppp5′A ⇌ (p)pp5′G3′pp + p5′A.
Assignment of the Human Gene for Hexose-1-phosphate Uridylyltransferase to Chromosome 3
Authors: Tedesco Thomas A. , Diamond Richard , Orkwiszewski Kathryn G. , Boedecker Herbert J. , Croce Carlo M.
Published: May 2006

Mouse-human hybrid clones were tested for the presence of human hexose-1-phosphate uridylyl-transferase (EC 2.7.7.12;UDPglucose:α-D-galactose-1-phosphate uridylyltransferase). Two criteria, starch gel electrophoresis and double-immunodiffusion against a human transferase-specific antibody, were used to identify human enzyme in the hybrid clones. Seventeen of 33 hybrid clones analyzed were found to contain human transferase by both criteria. Karyological analysis of the hybrid clones showed concordant segregation of human transferase with human chromosome 3. Human galactokinase was asyntenic with human transferase. We thus assign this gene to human chromosome 3.