bluuebunny/crossref_metadata_2025 huggingface dataset:
Heme Proteins: Effect of an Intermediate on Photochemical Behavior
Authors: Phillipson Paul E. , Ackerson Bruce J. , Wyman Jeffries
Published: May 2006

This paper analyzes, in terms of a triangular kinetic scheme, the possible effects of an intermediate in the photochemical behavior of simple heme proteins. Both steady-state and transient phenomena are analyzed. The magnitude of the quantum yield for a given system is determined by a competition between quenching and ligand detachment, measured by the two rate constants, κ
-1
and κ
2
, respectively; as a first approximation, it can be described by a single parameter, namely the ratio κ
-1
/κ
2
. The individual values of κ
-1
and κ
2
can only be determined at light intensities so high that the measured quantum yield becomes itself a function of light intensity. Under these conditions the relaxation time for transient approach to the steady-state can be complex, corresponding to heavily damped chemical oscillations. It is pointed out that when the model is extended to include more than one intermediate, multiple oscillations are possible. In this more general case the system in the steady-state may also show pseudocooperativity or anticooperativity.
Studies on
In Vitro
DNA Synthesis Purification of the
dna
G Gene Product from
Escherichia coli
Authors: Wickner Sue , Wright Michel , Hurwitz Jerard
Published: May 2006

ϕX174 DNA-dependent dNMP incorporation is temperature-sensitive (ts) in extracts of uninfected
E. coli dna
A, B, C, D, E, and G ts strains. DNA synthesis can be restored in heat-inactivated extracts of various
dna
ts mutants by addition of extracts of wild-type or other
dna
ts mutants. A protein that restores activity to heat-inactivated extracts of
dna
G ts cells has been extensively purified. This protein has also been purified from
dna
G ts cells and is thermolabile when compared to the wild-type protein. The purified
dna
G protein has a molecular weight of about 60,000, is insensitive to
N
-ethylmaleimide, and binds poorly to DNA. It does not stimulate heat-inactivated crude extracts of
dna
B, C, D, or E ts cells and lacks detectable RNA and DNA polymerase activities.
Glutamine Synthetase Induction in Embryonic Neural Retina: Immunochemical Identification of Polysomes Involved in Enzyme Synthesis
Authors: Sarkar P. K. , Moscona A. A.
Published: May 2006

Glutamine synthetase (EC 6.3.1.2) in embryonic neural retina in culture is rapidly induced by hydrocortisone. Retina polysomes involved in translation of this enzyme were precipitated with a high degree of specificity by the gammaglobulin isolated from antiserum against the enzyme (anti-enzyme gammaglobulin). Using immunoprecipitation procedures, we determined that the amount of polysome-bound nascent enzyme was maximal in polysomes comprising 9-14 ribosomes and was about 3-fold higher in the induced than in the noninduced retina. Within this size group of polysomes, those comprising 11-13 ribosomes showed consistently greater binding of anti-enzyme [
125
I]gammaglobulin than of normal [
125
I]-gammaglobulin. This size of polysomes corresponds to that calculated for a monocistronic messenger RNA for the subunit of this enzyme, which has a molecular weight of 42,000. The application of immunochemical techniques to identification of templates for synthesis of an enzyme in embryonic cells that constitutes less than 1% of the total cellular proteins indicates the usefulness of this method for detailed studies on regulation of other quantitatively minor products significant in cell differentiation.
Glycopeptides from Surface Membranes of Neuroblastoma Cells
Authors: Glick Mary Catherine , Kimhi Yosef , Littauer Uriel Z.
Published: May 2006

Sequential removal of surface glycopeptides was achieved by subjection of mouse neuroblastoma cells to a two-step trypsin treatment under different conditions. The glycopetides released by each trypsinization step were digested by Pronase and examined on columns of Sephadex G-50. Different chromatographic patterns were found for the two digests. Thus, several groups of glycopeptides can be distinguished by the trypsinization procedure. One group is readily removed and appears to be at a more accessible location on the cell surface. Among the four neuroblastoma clones examined, the glycopeptide patterns from axon-forming cells differed from those of axon-minus cells.
A General Method of Gene Isolation
Authors: Shih Thomas Y. , Martin Malcolm A.
Published: May 2006

A general method of gene isolation has been developed that involves the chemical linkage of RNA to cellulose by a water-soluble carbodiimide, and the continuous circulation of DNA containing specific sequences complementary to the RNA. The temperature of the cellulose matrix is maintained at 37° (50% formamide, 0.3 M NaCl-0.03 M Na
3
citrate) to allow efficient DNA-RNA interaction in the stationary phase, while unreacted and any reassociated DNA is denatured at 90° and then recirculated into the hybridization chamber. Between 40 and 45% of fragmented
32
P-labeled simian virus (SV)40 DNA was removed from the circulating solution when cellulosebound SV40-specific RNA, assymmetrically transcribed
in vitro
with
Escherichia coli
RNA polymerase, was used. In the presence of 10
4
-fold excess of sheared
E. coli
DNA, nearly half of the [
32
P]SV40 DNA was recovered from the mixture as a DNA-RNA hybrid with negligible contamination by bacterial DNA. The isolation procedure is almost quantitative for the complementary DNA. The efficiency and selectivity of this method permit the isolation of a defined DNA sequence from a large and complex genome.
Control of Pineal Indole Biosynthesis by Changes in Sympathetic Tone Caused by Factors Other Than Environmental Lighting
Authors: Lynch Harry J. , Eng Jamie P. , Wurtman Richard J.
Published: May 2006

The melatonin (5-methoxy-
N
-acetylserotonin) content and
N
-acetyltransferase activity of rat pineal increase rapidly in response to physical immobilization or insulin-induced hypoglycemia. Carbohydrate consumption, which causes insulin release without hypoglycemia, does not elicit these pineal responses. Prior treatment with propranolol, a β-adrenergic blocking agent, inhibits the
N
-acetyltransferase responses to hypoglycemia and immobilization, indicating that these changes result from stimulation of pineal β-receptors by a catecholamine, presumably norepinephrine released from pineal sympathetic nerve terminals. Prior destruction of those terminals with 6-hydroxydopamine does not block, but actually potentiates, the increase in melatonin content and
N
-acetyltransferase activity after induced hypoglycemia or immobilization. This finding probably reflects an action of circulating catecholamines, secreted from the adrenal medullae or surviving sympathetic nerve terminals, on supersensitive pineal cells. These observations indicate that factors other than changes in environmental lighting, which modify sympathetic nervous tone, can also influence pineal function.
Replication of Bacteriophage ϕX-174 in a Mutant of
Escherichia coli
Defective in the
dna
E gene
Authors: Greenlee Lorance L.
Published: May 2006

Strains of
E. coli
bearing a temperature-sensitive mutation at the
dna
E locus were unable to support growth of bacteriophage ϕX-174 at 43° while permitting normal growth at 30°. The
dna
E gene product was implicated in all stages of ϕX-174 DNA replication. Differences were observed between a double mutant (
pol
A
-
,
dna
E
ts
) and a single mutant (
pol
A
+
,
dna
E
ts
) in the ability to synthesize parental replicating form and its subsequent replication. The implications of these observations are discussed in terms of the relationship between DNA polymerases-I and -III.
A DNA-Binding Protein Induced by Bacteriophage T7
Authors: Reuben Roberta C. , Gefter Malcolm L.
Published: May 2006

A DNA-binding protein has been purified from
Escherichia coli
infected with bacteriophage T7 by DNA-cellulose chromatography. The protein is absent in uninfected cells. The purified protein has a molecular weight of 31,000 and binds strongly and preferentially to single-stranded DNA.
In vitro
studies show that this protein can stimulate the rate of polymerization catalyzed by the T7-induced DNA polymerase 10-15 times under conditions where the polymerase is unable to effectively use a single-stranded template. The degree of stimulation is dependent upon the ratio of binding protein to DNA template and is independent of polymerase concentration.

The observed stimulation is specific for the T7 DNA polymerase in that addition of the protein to reactions catalyzed by
E. coli
DNA polymerases I, II, or III or T4 DNA polymerase is without effect.
Loss of the Sigma Activity of RNA Polymerase of
Bacillus subtilis
during Sporulation
Authors: Linn Thomas G. , Greenleaf Arno L. , Shorenstein Rosalind G. , Losick Richard
Published: May 2006

The activity of the sigma subunit of the RNA polymerase of
Bacillus subtilis
decreases markedly during the first 2 hr of sporulation. Moreover, sigma activity remains deficient throughout the sporulation process and in dormant spores. The time course of changes in RNA polymerase during sporulation indicates that alterations in the core of RNA polymerase occur after the loss of sigma activity. Core RNA polymerase purified after the second and before the ninth hour of sporulation fails to respond to vegetative sigma subunit
in vitro
and contains variable amounts of a 110,000-dalton polypeptide in place of the β′ subunit. Core RNA polymerase purified from dormant spores has a subunit structure indistinguishable from vegetative core enzyme.

RNA polymerase purified by antibody precipitation from an extract of a mixture of sporulating and excess vegetative cells separately labeled with two different radioisotopes contains β′ subunit and no 110,000-dalton polypeptide. However, RNA polymerase purified from sporulating bacteria in the absence of excess vegetative cells progressively loses the β′ subunit at each stage of purification even in the presence of the protease inhibitor, phenylmethyl sulfonyl fluoride. These findings suggest that the alteration of the β′ subunit is due to proteolysis
in vitro
.
Purification and Properties of Ribonuclease H of Calf Thymus
Authors: Stavrianopoulos Jannis G. , Chargaff Erwin
Published: May 2006

Ribonuclease H of calf thymus has been purified better than 3000-fold to yield an almost homogeneous preparation. The enzyme, which comprises about 0.03% of the total protein in the initial extract, is a slightly acidic protein (pI = 4.95) of molecular weight of about 64,000, possibly composed of subunits. The enzyme requires a metal ion for activation; the conditions for activation by Mg, Co, and Mn are described. It is inhibited by S-adenosylmethionine. The substrates cleaved were poly(dT)·poly(rA) and the DNA-RNA hybrid made from phage f1 DNA; ribosomal RNA was not attacked.
Characteristics of Polarographic Catalytic Waves Observed with Bovine-Serum Albumin: Kinetic or Diffusion Control
Authors: Kolthoff I. M. , Yamashita K. , Hie Tan Boen , Kanbe A.
Published: May 2006

Conditions are described under which the catalytic Brdička currents observed in ammoniacal buffer solutions containing cobalt(III) hexammine chloride or cobalt(II) and very little bovine-serum albumin (0.1-0.2 μM) are purely kinetically controlled. Under these conditions the kinetic current at pH 9.3-10.3 exhibits a sharp maximum followed by a decrease of the current to a well-defined minimum. The maximum and minimum are eliminated in the presence of 5 mM or more concentrated calcium chloride when a short plateau occurs at the potential of the maximum followed by a well-defined second wave. Both currents are kinetically controlled. When the albumin concentration is 2 μM or greater, the kinetic currents approach diffusion control, the rate of diffusion of cobalt(III) or (II) being close to rate determining. Under these conditions the currents become proportional to the cobalt(III) or (II) concentration in the concentration range between 25 and 200 μM.
Synthesis of Globin Ribonucleic Acid from Duck-Reticulocyte Chromatin
In Vitro
Authors: Axel Richard , Cedar Howard , Felsenfeld Gary
Published: May 2006

The proteins of chromatin serve to restrict the transcription of DNA. The relevance of these findings to the control of gene expression is contingent upon the demonstration that this restriction is specific and mirrors the patterns of RNA synthesis observed
in vivo
. In this study we demonstrate by RNA-DNA hybridization that the vast majority of the chromatin-directed RNA is synthesized from the unique regions of the reticulocyte genome. Furthermore, by use of the DNA complement of globin mRNA as a probe in annealing reactions,
de novo
synthesis of globin RNA was detected in RNA transcripts from duck reticulocyte chromatin. No globin sequences were detected in similar preparations of RNA
in vitro
either from liver chromatin or from DNA freed of protein. These results show that the proteins of chromatin serve to restrict transcription in a very specific manner and provide convincing evidence for the existence of transcriptional control factors in eukaryotes.
Action of Rifamycin Derivatives on RNA Polymerase of Human Leukemic Lymphocytes
Authors: Tsai Ming-Jer , Saunders Grady F.
Published: May 2006

The mechanism of inhibition of human RNA polymerase by four rifamycin derivatives was investigated. Derivative AF/013 (3-formyl rifamycin SV:
O-n
-octyloxime) with strong hydrophobic side chains prevents the polymerase from binding to DNA and also affects the size of RNA synthesized. Derivative PR/19 (3′-acetyl-1′-benzyl-2′-methylpyrrolo[3,2-c]-4-desoxy-rifamycin SV) only affects RNA synthesis when RNA polymerase has been previously incubated with the drug or when the reaction was performed at high salt concentration [0.14 M (NH
4
)
2
-SO
4
]. Our results suggest that these drugs exert their inhibitory actions by binding to the enzyme instead of DNA.
Acceleration of the Rate of Deamidation of GlyArgAsnArgGly and of Human Transferrin by Addition of
l
-Ascorbic Acid
Authors: Robinson Arthur B. , Irving Karen , McCrea Mary
Published: May 2006

Experiments on the model peptide, GlyArgAsnArgGly, and the protein, human transferrin, have shown that hydrolytic deamidation of these molecules is markedly accelerated by addition of physiologically significant concentrations of
l
-ascorbic acid. Since hydrolytic demidation has been suggested as an important timer of biological events, the effects on hydrolytic deamidation of substances that are normally present in living organisms and are subject to nutritional control are of special relevance.
Conformation of Charged and Uncharged tRNA
Phe
Authors: Wong Yeng P. , Reid Brian R. , Kearns David R.
Published: May 2006

The effect of aminoacylation on the conformation of yeast tRNA
Phe
was investigated by high-resolution (300 MHz) proton nuclear magnetic resonance (NMR) spectroscopy. Resonances in the low-field (-11 to -15 ppm) region of the spectra are due to ring NH protons of Watson-Crick base pairs, and to a very high degree of approximation (within 0.05 ppm) the low-field spectra of tRNA
Phe
and phenylalanyl-tRNA
Phe
are identical. From this observation and analysis of the low-field NMR spectra we conclude that the secondary structures of the two tRNAs are identical with respect to base-pairing schemes and interbase distances in the helical region (0.1-0.2 Å). Several tertiary structural features, including conformation of the dihydro-U loop, conformation of the minor loop, relative orientations of the acceptor and the TΨC stems, dihydro-U and anticodon stems, and probably conformation of the anticodon loop are shown to be the same in tRNA
Phe
and phenylalanyl-tRNA
Phe
. Our results leave little remaining opportunity for changes in tertiary structure that would not have been observed by the NMR method.
Direct Participation of dCMP Hydroxymethylase in Synthesis of Bacteriophage T4 DNA
Authors: Wovcha Merle G. , Tomich Paul K. , Chiu Che-Shen , Greenberg G. Robert
Published: May 2006

In order to retain in an
in situ
system the control mechanisms involved in synthesis of bacteriophage T4 DNA, infected cells were made permeable to nucleotides by plasmolysis with concentrated sucrose. Such preparations use exogenous deoxyribonucleotides to synthesize T4 phage DNA. As has been observed with
in vivo
studies, DNA synthesis was drastically reduced in plasmolyzed preparations from cells infected by
amber
mutants of genes 1, 32, 41, 42, 43, 44, or 45. Added 5-hydroxymethyl dCTP did not bypass either a mutant of gene 42 (dCMP hydroxymethylase) or of gene 1 (phage-induced deoxyribonucleotide kinase). In a phage system lacking deoxycytidine triphosphatase (gene 56) and the gene-46 product, and therefore incorporating dCTP into DNA, dCTP incorporation did not require dCMP hydroxymethylase, in keeping with
in vivo
results. With a triple
amber
mutant of genes 1, 46, and 56 only slight incorporation of dCTP occurred. By contrast, in experiments performed
in vivo
the synthesis of cytosine-containing DNA was unaffected by an
amber
mutation in gene 1.

These studies provide evidence that dCMP hydroxymethylase, in addition to its known catalytic function, has a second, more direct, role in phage T4 DNA synthesis, apparently in recognition of hydroxymethyl dCTP. The role of the phage-induced deoxyribonucleotide kinase in T4 DNA synthesis in the plasmolyzed system remains unresolved.
Enzymes of the γ-Glutamyl Cycle in the Ciliary Body and Lens
Authors: Ross Leonard L. , Barber Lee , Tate Suresh S. , Meister Alton
Published: May 2006

The enzymes of the γ-glutamyl cycle have been found in rabbit ciliary body and, except for 5-oxoprolinase, also in the ocular lens. Histochemical studies show that γ-glutamyl transpeptidase is localized mainly in the basal portions of the epithelial cells of the ciliary body; the findings are similar to those observed in the chloroid plexuses. The histochemical staining reaction in the ciliary epithelium is more intense than in the chloroid plexus, intestine, and kidney. γ-Glutamyl transpeptidase staining activity in the epithelium of the intestinal and renal proximal convoluted tubules is confined to the microvillus border. Moderate transpeptidase activity was found in the cytoplasm of nonpigmented epithelial cells of the iris at the posterior pupillary margin. The histochemical and enzyme activity studies are consistent with the thesis that the γ-glutamyl cycle functions in transport of amino acids across the blood-aqueous humor barrier.
The Synthesis and Enzymatic Polymerization of Nucleotides Containing Mercury: Potential Tools for Nucleic Acid Sequencing and Structural Analysis
Authors: Dale R. M. K. , Livingston D. C. , Ward D. C.
Published: May 2006

A simple acetoxymercuration reaction for introducing covalently bound mercury atoms into nucleotides is described. The 5-mercuriacetate derivatives of UTP, CTP, dUTP, and dCTP, as well as the 7-mercuriacetate derivative of 7-deazaATP, have been prepared by this procedure and tested as substrates for nucleic acid polymerases. These nucleotides, in the absence of added mercaptan, are not polymerized and in most instances are potent enzyme inhibitors. However, conversion of these mercuriacetates to mercurithio compounds
in situ
by the addition of one of various mercaptans, yields nucleoside triphosphates that are excellent substrates for all polymerases tested:
Escherichia coli
and T7 RNA polymerases, DNA polymerase I of
E. coli
, DNA polymerase of avian myeloblastosis virus, and calf-thymus terminal deoxynucleotidyl transferase. By varying the mercaptan used to promote syntheses it is possible to access certain structural limitations in the enzyme's nucleoside triphosphate binding site. These mercurinucleotides appear to have a diversity of potential applications: (
1
) as heavy-atom reagents for crystallographic and microscopic studies; (
2
) as affinity probes for enzymes sensitive to sulfhydryl modification; (
3
) as steric probes of substrate-binding sites on enzymes; and (
4
) as reagents for forming covalent protein-polynucleotide complexes.
Aminoglycoside Antibiotic-Inactivating Enzymes in Actinomycetes Similar to Those Present in Clinical Isolates of Antibiotic-Resistant Bacteria
Authors: Benveniste Raoul , Davies Julian
Published: May 2006

Various species of
Streptomyces
possess aminoglycoside-modifying enzymes.
Streptomyces kanamyceticus
contains an enzyme that acetylates the 6′-amino group of kanamycin A and B, gentamicin C
1a
, and neomycin.
Streptomyces spectabilis
produces an enzyme that acetylates the 2′-amino group of the hexose ring of gentamicin C
1a
. These enzymes catalyze reactions identical to those catalyzed by enzymes found in gram-negative bacteria containing R(antibiotic resistance)-factors. The discovery of these enzymes suggests the possibility of an evolutionary relationship between the aminoglycosideinactivating enzymes (produced by resistance determinants) in bacteria containing R-factors and similar enzymes found in the actinomycetes.
Partial Similarities Between Yeast and Liver Alcohol Dehydrogenases
Authors: Jörnvall Hans
Published: May 2006

The primary structure of about half of the protein chain of yeast alcohol dehydrogenase has been determined and compared with the amino-acid sequences of other dehydrogenases. The enzyme is found to be distantly related to horse-liver alcohol dehydrogenase, although these two proteins have different quaternary structures and subunit sizes. Some regions show no significant similarities, but long segments within the N-terminal parts of the molecules are homologous, suggesting a common and important function for these segments. Ancestral connections between some different dehydrogenases can be concluded and the degree of evolutionary changes may be estimated.
In Vitro
Transcription of Simian Virus 40 Sequences in SV3T3 Chromatin
Authors: Astrin Susan M.
Published: May 2006

The template properties of chromatin were studied in a system in which transcription of unique genes could be examined. Chromation and DNA were isolated from SV3T3 cells, a line of simian virus 40 (SV40)-transformed mouse cells, and used as templates for
Escherichia coli
RNA polymerase. The SV40 sequences in the RNA transcribed
in vitro
and in RNA isolated from the transformed cells were analyzed by hybridization to radioactive RNA transcribed from SV40 DNA. The results indicate that the same sequences of the SV40 “-” strand (DNA strand which serves as a template for early RNA) are transcribed
in vitro
from chromatin as are found in transformed cells. In contrast, when the DNA isolated from SV3T3 chromatin by removal of proteins is used as a template, the entire SV40 “-” strand is transcribed. It is concluded that the specific template restriction observed with chromatin is due to the presence of proteins associated with the DNA.
Antiviral Effect of Interferon Covalently Bound to Sepharose
Authors: Ankel H. , Chany C. , Galliot B. , Chevalier M. J. , Robert M.
Published: May 2006

Interferon, covalently bound to Sepharose 4B activated by cyanogen bromide, induces the antiviral state in sensitive cells. The antiviral effect is neutralized by antiserum specific to interferon and is recovered thereafter when the antibody is detached from the interferon by treatment at low pH. Binding interferon to Sepharose increases the stability of the molecule. It is likely that the interferon molecule acts on the cell receptor without being detached from the beads. However, the data do not exclude the possibility of a small loss of interferon, or fragments of it, after contact with the cell.
Studies on
In Vitro
DNA Synthesis Purification of
dna
C Gene Product Containing
dna
D Activity from
Escherichia coli
Authors: Wickner Sue , Berkower Ira , Wright Michel , Hurwitz Jerard
Published: May 2006

The conversion of ϕX174 single-stranded DNA to duplex DNA by extracts of
E. coli
requires products of the
E. coli
DNA replication genes. By use of this complementation system, the
dna
C gene product has been purified from wild-type
E. coli
as well as from a
dna
C temperature-sensitive mutant. The latter preparations are temperature sensitive when compared to the wild-type gene product. The
dna
C and
dna
D gene products copurify, have similar characteristics, are both temperature sensitive in preparations from
dna
C temperature-sensitive cells, and are both undetectable in preparations from
dna
D temperature-sensitive cells.
Mechanism of Action of Nerve Growth Factor and Cyclic AMP on Neurite Outgrowth in Embryonic Chick Sensory Ganglia: Demonstration of Independent Pathways of Stimulation
Authors: Frazier William A. , Ohlendorf Cathleen Earhart , Boyd Linda Forrest , Aloe Luigi , Johnson Eugene M. , Ferrendelli James A. , Bradshaw Ralph A.
Published: May 2006

The suggested role of adenosine 3′:5′-cyclic monophosphate as the “second messenger” in the neurite outgrowth from chick embryonic sensory ganglia mediated by nerve growth factor was examined. Although
N
6
,
O
2
-dibutyryl adenosine 3′:5′-cyclic monophosphate induces fiber outgrowth at concentrations of 1-5 mM, this response is morphologically distinct from that produced by nerve growth factor, is pH dependent, is mimicked by sodium butyrate, and does not occur in sympathetic ganglia. In addition, nerve growth factor does not alter the amounts of intracellular cyclic AMP during incubations up to 24 hr and does not stimulate adenylate cyclase in broken-cell preparations. Addition of theophylline, an inhibitor of phosphodiesterase, causes increases in intracellular levels of cyclic AMP but does not affect fiber outgrowth. These observations indicate that the nerve growth factor response is not mediated through cyclic AMp and that stimulation of sensory ganglia by exogenous cyclic AMP derivatives is probably of limited physiological significance. These findings are also compatible with the developing hypothesis, based on structural similarities, that nerve growth factor and insulin exert their effects on their respective responsive tissues by related mechanisms.
Host Restriction of Friend Leukemia Virus. Role of the Viral Outer Coat
Authors: Krontiris Theodore G. , Soeiro Ruy , Fields Bernard N.
Published: May 2006

Host restriction of oncogenesis of RNA tumor viruses
in vivo
is associated with several gene loci. One of these genes, the
Fv-1
locus in mice, is expressed
in vitro
and may be studied in mouse-embryo cultures that are restrictive or permissive for replication of Friend leukemia virus. Two strains of Friend leukemia virus, N-or B-tropic, show reciprocal ability to replicate successfully in either NIH Swiss (N-type) or BALB/c (B-type) cells that differ at the
Fv-1
locus. These two strains of virus and two cell lines form a system to measure host restriction
in vitro
. Measurement of adsorption of Friend leukemia virus to permissive or restrictive cells reveals no difference in rate or total amount of virus bound. Furthermore, studies with virions of vesicular stomatitis virus phenotypically mixed within an envelope containing Friend leukemia virus protein show no differences in penetration or replication of vesicular stomatitis virus. These results strongly suggest that host restriction of Friend leukemia virus is due to an intracellular event in the viral replication cycle.
A Purine Polyribonucleotide Synthetase from
Escherichia coli
Authors: Milanino Roberto , Chargaff Erwin
Published: May 2006

The isolation, from
E. coli
B, and partial purification of a purine polyribonucleotide synthetase having several unusual properties is described. The enzyme, which seems to be under strict regulation by several nucleoside triphosphates, requires, after removal of internal primer activity, a primer, such as poly(A), poly(U), or a suitable RNA, but acts without a template. It uses purine ribonucleoside triphosphates as precursors. The uptake of adenylic acid, when ATP is offered alone, is highly stimulated by the presence of GTP, in which case both nucleotides are incorporated into mixed polymers; but GTP as the sole precursor is not utilized. CTP has a strongly inhibitory effect. Other unusual features are the high salt concentration, 0.6 M KCl, at which the enzyme is optimally active and evidence of the existence of a relatively heat-stable protein functioning as an activation factor.
Reexpression of the Rat Hypoxanthine Phosphoribosyltransferase Gene in Rat-Human Hybrids
Authors: Croce Carlo M. , Bakay Bohdan , Nyhan William L. , Koprowski Hilary
Published: May 2006

Fusion of hypoxanthine phosphoribosyltransferase (HPRT)
-
rat hepatoma cells with HPRT
+
human fibroblasts yielded hybrid clones that grew in HAT selective medium and contained all the rat chromosomes and one to nine human chromosomes. Among the retained chromosomes was the human X chromosome. In all clones backselected in medium containing 8-azaguanine, human X chromosome was absent. Electrophoretic analysis revealed that, without exception, hybrid clones growing in HAT medium had an active HPRT enzyme, either human or rat, or both. When these clones were backselected in 8-azaguanine, they did not show HPRT enzyme activity. Hybrids that contained the human X chromosome also had human glucose-6-phosphate dehydrogenase. The observed reexpression of rat HPRT in hybrid cells derived from HPRT
-
rat cells suggests that a genetic factor from the human cell determined the expression of the rat structural gene for HPRT.
Replacement of the Sequence G-T-Ψ-C-G(A)- by G-A-U-C-G- in Initiator Transfer RNA of Rabbit-Liver Cytoplasm
Authors: Simsek Mehmet , Petrissant Guy , Rajbhandary Uttam L.
Published: May 2006

Eukaryotic cytoplasmic initiator tRNAs lack the sequence G-T-Ψ-C-G(A)-, which is in every tRNA of known sequence that is active in protein biosynthesis. In initiator tRNA of yeast cytoplasm, which is the only eukaryotic initiator tRNA of known sequence, this sequence is replaced by G-A-U-C-G-. We now report the sequence of a 30-nucleotide-long, 3′-terminal fragment of cytoplasmic initiator tRNA of rabbit liver obtained by specific cleavage of the tRNA at the site occupied by the modified nucleoside, 7-methyl guanosine. We show (
i
) that in rabbit-liver initiator tRNA also, the sequence G-T-Ψ-C-G(A)- is replaced by G-A-U-C-G- and (
ii
) that the sequences of loop IV of both the yeast and rabbit-liver cytoplasmic initiator tRNAs are identical, A-U-C-G-m
1
-A-A-A-.
Leukemia-Specific DNA Sequences in Leukocytes of the Leukemic Member of Identical Twins
Authors: Baxt W. , Yates J. W. , Wallace H. J. , Holland J. F. , Spiegelman S.
Published: May 2006

The discovery in human leukemic cells of particulate elements encapsulating 70S RNA and RNA-directed DNA polymerase made possible the synthesis of a [
3
H]DNA probe that could detect leukemia-specific sequences in the DNA of normal and leukemic individuals. In an earlier study of a series of unrelated leukemic patients, we established that the nuclear DNA of their leukemic cells contain particle-related sequences that cannot be detected in leukocytes of normal individuals. This result is inconsistent with the virogene concept that demands the inclusion of one complete copy of oncogenic information in the genome of every normal cell.

The present study carries this analysis one step further by showing, with two sets of identical twins, that the leukemic member contains particle-related sequences in the DNA of his leukocytes that cannot be detected in the leukocytes of his healthy identical sibling. This finding implies that the additional leukemia-specific information found in the DNA of the leukemic individuals must have been inserted subsequent to fertilization. This outcome argues against the virogene hypothesis or any other etiologic concept that invokes vertical transmission through the germ line of the particle-related information found uniquely in the DNA of leukemic cells.
Nucleotide Sequence of HS-β Satellite DNA from Kangaroo Rat
Dipodomys ordii
Authors: Fry K. , Poon R. , Whitcome P. , Idriss J. , Salser W. , Mazrimas J. , Hatch F.
Published: May 2006

The sequence of the highly repetitive satellite HS-β DNA fraction from kangaroo rat
Dipodomys ordii
was determined independently by RNA and DNA sequencing techniques. A basic iterated sequence of 10 nucleotides with several mutational variations was found. Base-composition data are consistent with the proposed sequence and revealed a high content of 5-methylcytosine. DNA and RNA sequencing techniques used gave identical results, showing that the fidelity of synthesis of riboguanidine-substituted DNA under our conditions is adequate for nucleotide sequence studies.
Proton Magnetic Resonance and Magnetic Susceptibility Characterization of Ferredoxin I from
Bacillus polymyxa
Authors: Phillips William D. , McDonald C. C. , Stombaugh N. A. , Orme-Johnson W. H.
Published: May 2006

Magnetic susceptibility and proton magnetic resonance spectra are reported for the oxidized and reduced forms of the iron-sulfur protein
Bacillus polymyxa
ferredoxin I. The magnetic susceptibility of the oxidized form indicates antiferromagnetic exchange coupling between component iron atoms that is quantitatively similar to that observed for the clostridial ferredoxins and for the [(C
2
H
5
)
4
N]
2
[Fe
4
S
4
(SCH
2
C
6
H
5
)
4
] analog. Contact-shifted resonances observed in the proton-magnetic-resonance spectra of oxidized and reduced forms of the
B. polymyxa
protein can be correlated with the contact-shifted resonances of corresponding redox forms of the clostridial ferredoxins. Characteristics of the contact-shifted resonances observed in partially reduced
B. polymyxa
ferredoxin I are compatible with a “slow” rate of electron exchange between redox forms, which suggests that the “fast” electron exchange earlier observed in the eight-iron clostridial ferredoxins may derive from an intramolecular component.
Tumor-Host Cell Hybrids in Radiochimeras
Authors: Wiener Francis , Fenyö Eva Maria , Klein George
Published: May 2006

F
1
hybrid mice syngeneic or semiallogeneic with respect to the relevant tumor were lethally irradiated and then reconstituted with hemopoietic cells from strain CBAT6T6 mice. After chimerism had been established, the animals were inoculated with solid or ascites tumors. Tumor-host cell hybrids were selected from enzyme-deficient solid tumors by explanting the tumor cell suspension into hypoxanthine-amethopterin-thymidine containing medium. The selection of hybrid cells from ascites tumors was achieved by exploiting the difference between the ascites tumor cells and hybrid cells in their ability to adhere to the surface of culture vessels. T6T6 chromosomal and H-2 antigenic markers served to distinguish between the hemopoietic cells derived from the donor graft and the cells of the host. All solid tumors tested fused with cells of the irradiated host, whereas ascites tumors fused with repopulating cells of hemopoietic origin.
The Number of D and E Regions in the Fibrinogen Molecule
Authors: Plow Edward F. , Edgington Thomas S.
Published: May 2006

The regional structure of fibrinogen was considered in reference to the terminal plasmin-cleavage fragments, D and E. By two independent approaches, a yield of two D and two E fragments was determined and this established the presence of two D and two E regions in each fibrinogen molecule. Immunochemically, it was shown that the expression of native fibrinogen determinants by the D:E complex was fully reconstituted by an equimolar mixture of D and E fragments, while other recombinant ratios failed to yield optimal reconstitution. Utilizing the cleavage-associated neoantigen of fibrinogen, fg-D
neo
, as a quantitative immunochemical marker, it was determined that complete digestion of fibrinogen by plasmin yielded two D fragments. Since the D:E complex appeared to consist of an equal number of D and E fragments, the presence of two E regions and two D regions in fibrinogen was indicated. In polyacrylamide gel electrophoresis, the linear relationship between the concentration of the D or E fragment and its densitometric area in the gel was utilized to quantitate the yield of D and E fragments in terminal digests. The yield of two D and two E fragments was demonstrated and it was also shown that the yield of fragments was independent of the plasmin concentration and of the length of exposure of the D and E fragments to the enzyme. Thus, it appears that fibrinogen is a highly symmetrical molecule consisting of two E regions as well as two D regions.
Modulation of Cell-Surface Antigens of a Murine Neuroblastoma
Authors: Akeson Richard , Herschman Harvey R.
Published: May 2006

Antisera were produced in rabbits to morphologically differentiated cells from the C1300 murine neuroblastoma (i.e., cells in which process formation was induced by maintenance on serum-free medium for 5 days). These antisera reacted more strongly in the complement fixation reaction with such “differentiated” cells than with “undifferentiated” (nonprocess-bearing) neuroblastoma cells. Adsorption of the antisera with undifferentiated cells removed the reactivity to cells without processes, while the reactivity with serum-free cells which possess processes was retained. Indirect immunofluorescence studies confirmed the results obtained by complement fixation and demonstrated that antibodies to the surface antigens of process-bearing cells could be adsorbed by particulate preparations from brain but not liver, spleen, or kidney. This is the first description of neural-associated cell-surface changes that correlate with the morphological differentiation in culture of neuroblastoma cells.
Metabolic Regulation of Cytoplasmic DNA Synthesis
Authors: Byrnes John J. , Downey Kathleen M. , So Antero G.
Published: May 2006

The regulation of cytoplasmic DNA synthesis by the metabolites ATP and citrate has been demonstrated. Other ribonucleoside and deoxyribonucleoside triphosphates as well as α,β-methylene- and β,γ-methylene-ATP and α,β-methylene-ADP are able to partially substitute for ATP in stimulating the rate of DNA synthesis with the cytoplasmic DNA polymerase (DNA nucleotidyltransferase, EC 2.7.7.7) from bone marrow. The fact that the methylene analogs of ATP and ADP are effective in stimulating DNA synthesis indicates that the mechanism of stimulation does not involve ATP hydrolysis.

The nucleotide activators have been shown by kinetic analysis to affect the
V
max
of the enzyme and not the apparent

K
m

s for the substrates. The curve that results when the rate of DNA synthesis is plotted as a function of ATP concentration is sigmoidal, suggesting that more than one site on the enzyme interacts with ATP and that these sites are acting cooperatively. The concentration of ATP required for maximal velocity is dependent on the Mn
++
concentration. At pH 7.0 maximal activity is obtained when the molar ratio of ATP to Mn
++
is 1.6:1. When either ATP or Mn
++
is present in relative excess, DNA synthesis is inhibited.

The mechanism of ATP activation has been shown to be associated with an alteration in the sedimentation behavior of the DNA polymerase. In the presence of ATP, there is an increase in the fraction of the enzyme that sediments at 8 S with a corresponding decrease in the 11.6S enzyme fraction. Thus, ATP activation corresponds to the dissociation of an 11.6S dimer into 8S monomers.

In addition to ATP and other nucleotides, citrate also stimulates DNA synthesis. At present it is not clear whether the stimulatory effects of ATP and citrate are due to their ability to chelate Mn
++
, which is inhibitory at high concentrations, or whether an ATP-Mn
++
or citrate-Mn
++
complex is the activator.
Characterization of a New Murine Cellular DNA Polymerase
Authors: Livingston D. M. , Serxner L. E. , Howk D. J. , Hudson J. , Todaro G. J.
Published: May 2006

A new DNA polymerase (peak A) has been identified in the high-speed pellet fraction of two subclones of nonvirus producing Balb/3T3 cells. The activity is associated with a molecule of approximately 70,000 molecular weight and chromatographs in two systems like the mouse type-C viral reverse transcriptase and a similar enzyme from the high-speed pellet fraction of a virus producing Balb/3T3 subclone, S
2
Cl
3
. Comparable quantities of peak A are present in both nonvirus infected (A31) and mouse sarcoma virus transformed nonproducer (KA31) subclones. Virus producing cells contain 10-20 times more peak A polymerase activity. A31 and KA31 peak A are comparably inhibited by anti-mouse type C virus reverse transcriptase IgG but to a lesser degree than S
2
Cl
3
peak A or authentic viral reverse transcriptase. They can also be differentiated from the latter two enzymes by template preference studies. KA31 peak A can be distinguished from three other KA31 DNA polymerases (R-DNA polymerase and DNA polymerase N and C), and thus appears to be a new species of cellular DNA polymerase.
Use of Purified Polysomes from Rabbit Reticulocytes in a Specific Test for Initiation Factors
Authors: Lubsen Nicolette H. , Davis Bernard D.
Published: May 2006

Initiation factors, extracted from ribosomal particles by high salt, are usually tested for with the extracted ribosomes. However, it is theoretically possible that such tests may respond not only to factors (i.e., proteins that join and leave a ribosome during its cycle), but also to true ribosomal proteins that may have been extracted. We have eliminated this circularity by tests with purified polysomes, which have not been extracted with high salt; the polysomes are deficient in initiation factors because they have been largely separated from the native subunits. Tests with both systems, applied to extracts of different classes of particles, suggest that high salt does extract both initiation factors and essential ribosomal proteins. Extracts of native subunits contain both, and stimulate both systems; while, in the presence of these extracts, the extracts of polysomes further stimulate only the extracted ribosomes.
Diffusivity of Methane in a Mixture of CCl
4
and c-C
6
F
11
C
2
F
5
of the Critical Composition in the Region above the Temperature of Separation
Authors: Hildebrand J. H. , Lamoreaux R. H.
Published: May 2006

The diffusivity of CH
4
in a mixture of CCl
4
and c-C
6
F
11
C
2
F
5
of the critical composition in the region of temperature close to that of unmixing, decreases as in a homogeneous liquid from 36° to about 32°. It then passes through a minimum of 10
5
D ≈ 4.15 cm
2
/sec at about 27.5°, then rises to 10
5
D = 4.61 at 25.00°, then steeply to 6.36 cm
2
/sec in the further drop of only 0.3° to 24.71°.
The Effects of Streptomycin or Dihydrostreptomycin Binding to 16S RNA or to 30S Ribosomal Subunits
Authors: Garvin Robert T. , Biswas Debajit K. , Gorini Luigi
Published: May 2006

Evidence is presented suggesting that streptomycin binds to 16S RNA or to 30S ribosomal subunits at the same topographical site located on the RNA chain. The equally bactericidal dihydrostreptomycin binds to the same site as streptomycin but with lower affinity. The effect of drug binding to 16S RNA (measured by reconstitution inhibition) is readily reversible, while that of drug binding to 30S subunits (measured by misreading) persists after removal of the drug. Binding of the drug is not a necessary and sufficient reason for killing.
Synthesis of Viral DNA in the Cytoplasm of Duck Embryo Fibroblasts and in Enucleated Cells after Infection by Avian Sarcoma Virus
Authors: Varmus Harold E. , Guntaka Ramareddy V. , Fan Warner J. W. , Heasley Suzanne , Bishop J. Michael
Published: May 2006

Two lines of evidence indicate that synthesis of viral DNA occurs in the cytoplasm of duck embryo fibroblasts infected with avian sarcoma virus: (
i
) viral DNA is detected first in the cytoplasmic fraction of infected cells and subsequently in the nuclear fraction; and (
ii
) viral DNA is synthesized at a normal rate in cells infected after enucleation with cytochalasin B. The presence of viral DNA in the cytoplasmic fraction is not a consequence of leakage of newly synthesized viral DNA from the nucleus, since it remains in nuclear fractions late after infection when integration of viral DNA into the host genome is inhibited by ethidium bromide.
Induction of Type-C RNA Virus by Cycloheximide: Increased Expression of Virus-Specific RNA
Authors: Aaronson Stuart A. , Anderson Garth R. , Dunn Claire Y. , Robbins Keith C.
Published: May 2006

Mouse cells contain the genetic information for multiple endogenous type-C RNA viruses. The mechanisms by which the cell controls expression of these naturally integrated viruses are not yet known. Recently, chemicals that inhibit protein synthesis have been shown to induce a specific type-C virus at high frequency from BALB/c mouse embryo cells. In the present studies, virus activation in response to a representative translational inhibitor, cycloheximide, is demonstrated to be transient, with virus release primarily occurring within the first 12-24 hr following drug exposure. Analysis of virus-specific RNA in cells by molecular hybridization revealed an absolute increase in viral RNA concentration in cycloheximide-treated cells. This was blocked by simultaneous exposure of the cells to actinomycin D. Further, inhibition of RNA synthesis during but not subsequent to cycloheximide exposure prevented virus activation. These findings show that virus induction by cycloheximide requires
de novo
RNA synthesis during but not after drug exposure and suggest that the required RNA species may be that of the virus itself. The present results are consistent with the hypothesis that translational inhibitors prevent synthesis of a labile protein whose normal action is to inhibit viral RNA transcription or to cause degradation of viral RNA.
Control of Growth of a Tumor Cell by Linoleic Acid
Authors: Holley Robert W. , Baldwin Julia H. , Kiernan Josephine A.
Published: May 2006

The growth of mouse myeloma XS 63·5 cells in cell culture is dependent on serum. Among the several growth factors present in serum, the lipid fraction is highly active. The growth factor(s) provided by the serum lipid fraction can be replaced by unsaturated fatty acids. If XS 63·5 cells are cultured in medium that is low in serum lipids, the cells become quiescent, with most of the cells in the G
1
(or G
0
) phase of the cell cycle. Addition of linoleic acid to such quiescent cells leads to reinitiation of DNA synthesis and growth.
Role for Heme in Mammalian Protein Synthesis: Activation of an Initiation Factor
Authors: Raffel Corey , Stein Stefanie , Kaempfer Raymond
Published: May 2006

Two nonerythropoietic tissues, brian and liver, contain an initiation factor that can overcome the block in initiation of protein synthesis seen in reticulocyte lysates when exogenous hemin is not present. Upon incubation of the brain factor with hemin and removal of free hemin by gel filtration, the factor activity is strongly stimulated. This stimulation shows a concentration dependence on hemin close to that seen for stimulation of protein synthesis in whole reticulocyte lysates. The data indicate that hemin mediates the formation of an active initiation factor complex from inactive, lower molecular weight components.
Antiinflammatory Effects of Murine Malignant Cells
Authors: Fauve Robert M. , Hevin Brigitte , Jacob Hedwig , Gaillard Jean A. , Jacob Fran[unk]cois
Published: May 2006

Development of teratocarcinoma does not impair immunization of mice against
Listeria monocytogenes
. Endotoxin injection a short time before tumor cell inoculation allows the growth of teratocarcinoma in non syngenic mice despite immune stimulation. In contrast with this absence of impaired systematic immunity, teratocarcinoma cells were found to repulse macrophages
in vitro
. This effect on macrophages was also found with three other malignant cells and with trophoblast cells.
In vivo
, teratocarcinoma cells were found to impair local inflammation. These cells and other malignant cells are able to produce a compound(s) of molecular weight between 10
3
and 10
4
, which prevents inflammatory reaction. These results suggest that mouse teratocarcinomas and other tumors by-pass the host immunological system of surveillance by at least two mechanisms: a direct toxic effect on macrophages and the release of an inhibitor of inflammation. The possible relations between these properties of malignant cells and physiological functions of trophoblast are discussed.