bluuebunny/crossref_metadata_2025 huggingface dataset:
Oncornavirus Expression in Human × Mouse Hybrid Cells Segregating Mouse Chromosomes
Authors: Minna John D. , Gazdar Adi F. , Iverson G. Michael , Marshall Thomas H. , Stromberg Kurt , Wilson Samuel H.
Published: May 2006

Human × mouse hybrid clones obtained by fusing transformed human (VA2) cells with embryonic mouse brain cells were tested for their ability to spontaneously express type C virus particles. It had been previously shown that these hybrid cells preferentially retained human chromosomes while mouse chromosomes were lost. The culture fluid from one cell line was found to contain type C particle markers in abundance, and typical budding C particles were observed in the cells by electron microscopy. In contrast, no particle markers were detected in the culture fluid from parental cells and several other hybrid cell lines. Subclones of the virus-positive cell line continued to lose mouse chromosomes and were found to vary more than 100-fold in their culture fluid DNA polymerase activity. The hybrid cell viruses, termed HMV1, banded in a sucrose gradient between 1.14 and 1.16 g/ml, possessed viral group-specific antigens, and exhibited B-tropic host range for replication in mouse embryo cells, but did not replicate in human cells when directly applied. The virus did not transform mouse cells but was able to rescue the defective murine sarcoma virus from sarcoma-positive, helper-virus-negative cells. Activity of the DNA polymerase associated with HMV1 was similar to the activity of Rauscher murine leukemia virus (MuLV) DNA polymerase in its preference for poly(rA) over poly(dA) as a template, use of endogenous template, detergent requirement, and inhibition by antiserum directed against MuLV.DNA polymerase. The results suggest that human × mouse hybrid cells segregating mouse chromosomes can spontaneously express endogenous type C viruses and that such hybrid cell lines may be used for the isolation of latent mammalian oncornaviruses and analysis of viral gene regulation.
Replication and Transcription of Eukaryotic DNA in
Esherichia coli
Authors: Morrow John F. , Cohen Stanley N. , Chang Annie C. Y. , Boyer Herbert W. , Goodman Howard M. , Helling Robert B.
Published: May 2006

Fragments of amplified
Xenopus laevis
DNA, coding for 18S and 28S ribosomal RNA and generated by
Eco
RI restriction endonuclease, have been linked
in vitro
to the bacterial plasmid pSC101; and the recombinant molecular species have been introduced into
E. coli
by transformation. These recombinant plasmids, containing both eukaryotic and prokaryotic DNA, replicate stably in
E. coli
. RNA isolated from
E. coli
minicells harboring the plasmids hybridizes to amplified
X. laevis
rDNA.
Guanosine 3′:5′-Cyclic Monophosphate-Dependent Phosphorylation of Endogenous Substrate Proteins in Membranes of Mammalian Smooth Muscle
Authors: Casnellie John E. , Greengard Paul
Published: May 2006

Guanosine 3′:5′-cyclic monophosphate (cyclic GMP) stimulated the endogenous phosphorylation of two proteins in isolated membrane fractions from mammalian organs rich in smooth muscle, including ductus deferens, uterus, and small intestine. The apparent molecular weights of the substrate proteins were 130,000 and 100,000. In the presence of 10 mM MnCl
2
, a half-maximal increase in phosphorylation of these proteins was achieved with 20-30 nM cyclic GMP. Approximately 10-fold higher concentrations of adenosine 3′:5′-cyclic monophosphate (cyclic AMP) were required to produce the same increase in phosphorylation of these two proteins. Cyclic AMP, but not cyclic GMP, regulated the phosphorylation of a third protein present in these same membrane fractions; the apparent molecular weight of this protein was 50,000. Cyclic GMP-dependent phosphorylation of endogenous protein was not observed in the cell sap of any of the three preparations of smooth muscle studied. The finding of endogenous cyclic GMP-dependent protein kinase activity and associated substrate proteins in membrane fractions from several mammalian organs containing smooth muscle raises the possibility that physiological actions of cyclic GMP in smooth muscle may be mediated by the phosphorylation of membrane proteins.
A Neurohypophyseal Hormone Analog with Selective Oxytocin-Like Activities and Resistance to Enzymatic Inactivation: An Approach to the Design of Peptide Drugs
Authors: Walter Roderich , Yamanaka T. , Sakakibara S.
Published: May 2006

Stepwise, synthetic alteration of oxytocin, guided by conformational and enzymological considerations, has led to analogs with specifically modified activity profiles and resistance to enzymatic inactivation. General requirements for the design of peptides with therapeutic value are discussed.
Orientation of Mitosis of Fibroblasts Is Determined in the Interphase
Authors: Ivanova O. Yu. , Margolis L. B. , Vasiliev Ju. M. , Gelfand I. M.
Published: May 2006

Time-lapse films of the cultures of mouse L fibroblasts have been analyzed to find out the angles between the direction of the big axis of interphase nucleus before mitosis and the direction of the mitotic furrow in the same cell. In 41 out of 51 mitoses this angle has been found to be more than 60°. Thus, the orientation of mitotic furrows depends on the internal polarity of the cell before mitosis.
RNA-Dependent DNA Polymerase (Reverse Transcriptase) from Avian Myeloblastosis Virus: A Zinc Metalloenzyme
Authors: Auld D. S. , Kawaguchi H. , Livingston D. M. , Vallee B. L.
Published: May 2006

RNA tumor viruses contain a characteristic RNA-dependent DNA polymerase (reverse transcriptase) which has been thought to be related to the induction of leukemia by this virus. A disturbance in a zinc-dependent enzyme system was first postulated to account for the demonstrated differences in zinc metabolism of normal and leukemic leukocytes [Vallee
et al.
in (1949)
Acta Unio. Int. Contra Cancrum
6, 869 and (1950)
Acta Unio. Int. Contra Cancrum
6, 1102]. In order to investigate the relationship between zinc and the initiation of leukemia in chickens by avian myeloblastosis virus, we have examined the metalloenzyme nature of its reverse transcriptase. The present data show that this protein is a zinc metalloenzyme demonstrating the postulated relationship between zinc and a leukemic process. Paucity of purified enzyme generated the design of a novel system of analysis incorporating microwave-induced emission spectrometry combined with gel exclusion chromatography. It provides precision, reproducibility, and remarkable limits of detection on μl samples containing 10
-12
to 10
-14
g-atoms of metal, and is thus orders of magnitude more sensitive than other methods. The chromatographic fraction with highest enzymatic activity contains 1.8 × 10
-11
g-atoms of zinc per 1.6 μg of protein, corresponding to either 1.8 or 2.0 g-atoms of zinc per mole of enzyme for a molecular weight previously determined either as 1.6 or 1.8 × 10
5
. Copper, iron and manganese are absent, i.e., at or below the limits of detection, 10
-13
to 10
-14
g-atoms. Agents known to chelate zinc inhibit the enzyme, while their nonchelating isomers do not. The data underline the participation of zinc in nucleic acid metabolism and bear importantly upon the lesions that accompany leukemia and zinc deficiency.
Increase of Cholesterol Level in the Surface Membrane of Lymphoma Cells and Its Inhibitory Effect on Ascites Tumor Development
Authors: Inbar M. , Shinitzky M.
Published: May 2006

An ascites form of malignant transformed lymphoma cells were treated
in vitro
with liposomes of 1:1 lecithin-cholesterol in order to increase the cholesterol level of the cell-surface membranes and thereby to increase the rigidity of the lipid layer. This treatment was found to inhibit the rate of killing by ascites tumor after intraperitoneal inoculation into adult mice of 10
4
and 10
5
treated cells per animal. With 10
3
treated cells per animal, full survival was observed up to 90 days after inoculation, whereas with the same number of untreated cells all infected mice died within 30 days after inoculation. An analogous treatment of the malignant lymphoma cells with liposomes of pure lecithin did not result in any appreciable inhibitory effect on the ascites tumor development
in vivo
, as initiated by inoculation of 10
5
, 10
4
, or 10
3
cells per animal.
Localized Molecular Orbital Description of Nitrogen Lone Pairs
Authors: Kleier Daniel A. , Hall John H. , Halgren Thomas A. , Lipscomb William N.
Published: May 2006

The Boys localization procedure is applied to several molecules possessing nitrogen lone pairs. The Boys structures show a tendency for the N lone pairs to participate in bonding to nearby electron sinks. For example, the Boys structure for planar formamide has two equivalent τ-bond orbitals between the carbonyl carbon and nitrogen atoms. The change in this description with variation of geometry at nitrogen is treated, and analogous Edmiston-Ruedenberg localizations on formamide are included for comparison.
An Antigen in Hodgkin's Disease Tissue Cultures: Fluorescent Antibody Studies
Authors: Long John C. , Aisenberg Alan C. , Zamecnik Paul C.
Published: May 2006

Rabbits were immunized with an antigen of specific gravity, 1.15-1.21 isolated by density gradient sedimentation of the centrifuged medium of long-term monolayer cultures derived from spleens involved by Hodgkin's disease. The globulin fraction of the antiserum was absorbed to reduce reactivity with normal cellular antigens and tissue culture components, and was tested by the indirect fluorescent antibody technique with cells from 18 different Hodgkin's disease cultures, and 16 normal cultures derived from adult spleen and fetal spleen and thymus. With anti-Hodgkin's disease globulin diluted 1:40 and 1:80, positive surface staining was observed in 48% and 41%, respectively, of viable cells from Hodgkin's disease cultures, and in less than 5% of cells cells from normal cultures. Fluorescent staining of the cytoplasm without nuclear staining was observed in 51% of acetone-fixed cells from the Hodgkin's disease cultures and in 4-8% of cells from normal cultures. Reactivity of the antiserum with Hodgkin's disease target cells could be removed by absorption of the antibody with additional antigen of density 1.15-1.21 obtained from other Hodgkin's disease cultures. Antisera to fractionated medium from a normal spleen culture and to
noncultured
Hodgkin's disease tumor tissue were used as controls: 2-10% of viable and acetone-fixed target cells reacted and no difference was observed between Hodgkin's disease and normal cell cultures.
In vitro
propagation of tumor cells from patients with Hodgkin's disease is needed for detection of the Hodgkin's disease tissue culture antigen; the antigen could not be demonstrated in noncultured Hodgkin's disease tissue.
Nucleotide Sequences of Human Globin Messenger RNA
Authors: Marotta Charles A. , Forget Bernard G. , Weissman Sherman M. , Verma Inder M. , McCaffrey Ronald P. , Baltimore David
Published: May 2006

Globin messenger RNA, isolated from human peripheral blood reticulocytes, was transcribed into complementary DNA by use of the RNA-dependent DNA polymerase of avian myeloblastosis virus. The complementary DNA was then transcribed into
32
P-labeled complementary RNA by
E. coli
RNA polymerase in the presence of α-
32
P-labeled ribonucleoside triphosphates. The fingerprint pattern obtained from ribonuclease T1 digests of human globin complementary RNA was specific and reproducible. Different patterns were obtained from digests of duck, mouse, and rabbit globin complementary RNA. The fingerprint patterns obtained from digests of purified natural human 10S globin messenger RNA, labeled
in vitro
with
125
I or with [γ-
32
P]ATP and polynucleotide kinase, were similar to that of the complementary RNA but contained some additional oligonucleotides. Sufficient nucleotide sequence information has been obtained from about 50% of the intermediate sized oligonucleotides (8-14 base residues long), to make possible examination of correspondence between these nucleotide sequences and globin amino-acid sequences. Approximately 70% of these oligonucleotide sequences can be matched to unique amino-acid sequences in the α- or β-globin chains. The other 30% do not match known amino-acid sequences and presumably correspond to untranslated portions of the mRNA; some of these sequences, however, can be matched to amino-acid sequence in the abnormally long segment of the α chain of hemoglobin Constant Spring, which is thought to result from a chain-termination mutation.
In Vitro
Analysis of the General Properties and Junctional Receptor Characteristics of Skeletal Muscle Membranes. Isolation, Purification, and Partial Characterization of Sarcolemmal Fragments
Authors: Festoff Barry W. , Engel W. King
Published: May 2006

Muscle membranes were partially purified from rat leg muscles. Externally oriented membrane functions were used to monitor and characterize the resulting membrane fractions. Na
+
K
+
-stimulated Mg
++
-adenosinetriphosphatase, acetylcholinesterase, and cholinergic receptor activities are present and enriched in the density-gradient subfractions of crude sarcolemma when compared with the first pellet. The physical separation of the cholinesterase and receptor activities on the gradient subfractions is demonstrated.

Receptor activity, determined by specific
125
I-labeled alpha-bungarotoxin binding, appears in fractions with densities similar to other plasma membranes (D
4
20
1.1015-1.1520). Acetylcholinesterase, on the other hand, is preferentially distributed in lighter density fractions (D
4
20
1.0507-1.0780) and parallels the gradient distribution of the ATPase. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a high-molecular-weight glycoprotein sediments with the higher density fractions only.

The data suggest a molecular dissection of the layers of the sarcolemma. The receptor is tentatively felt to be an integral component of the junctional plasma membrane. Acetylcholinesterase is felt to be superficially located on the ectolamina of the junctional sarcolemma, and may be woven within the matrix of the intersynaptic basement membrane.
Effects of an Antibody to a Highly Purified Na
+
, K
+
-ATPase from Canine Renal Medulla: Separation of the “Holoenzyme Antibody” into Catalytic and Cardiac Glycoside Receptor-Specific Components
Authors: McCans John L. , Lane Lois K. , Lindenmayer George E. , Butler Vincent P. , Schwartz Arnold
Published: May 2006

An antiserum was prepared against a highly purified Na
+
, K
+
-adenosine triphosphatase (ATP phosphohydrolase, EC 3.6.1.3). Purification and fractionation yielded two globulin components, one of which appears specific for a digitalis glycoside receptor site or binding conformation and the other for a catalytic site or conformation.
Cholera Toxin Mimics Melanocyte Stimulating Hormone in Inducing Differentiation in Melanoma Cells
Authors: O'Keefe Edward , Cuatrecasas Pedro
Published: May 2006

Cholera toxin (choleragen) and melanocyte stimulating hormone alter within hours the morphology of melanoma cells in culture, and they slow the growth of serum-stimulated cells. After 7-10 days, cells exposed to choleragen or hormone show increased size and a fibroblastic growth pattern. Tyrosinase (EC 1.14.18.1; monophenol monooxygenase) activity increases after 3 days in the presence of 10
-8
M hormone or 10
-10
M choleragen. Binding studies with
125
I-labeled choleragen indicate that although a melanoma cell can bind a maximum of 10
6
molecules of cholera toxin, only about 4000 binding sites must be occupied to achieve maximum stimulation of tyrosinase activity. Melanocyte stimulating hormone and choleragen probably have different membrane-binding sites. After exposure to choleragen for 5 min, membrane adenylate cyclase (EC 4.6.1.1) activity increases dramatically upon further incubation of intact cells for several hours at 37° and falls slowly to basal values over a period of more than 10 days. Hormone stimulation of adenylate cyclase is rapidly reversed by washing the cells, but subsequent restimulation of cyclase by the hormone is impaired. These studies indicate that cAMP mediates the effects of melanocyte stimulating hormone on growth and morphology as well as on tyrosinase activity. Cholera toxin may permanently activate the available adenylate cyclase molecules, and the protracted decay of stimulation that follows may reflect the biological turnover of adenylate cyclase molecules in these cells.
The Relationship of Gamone to the Mating Reaction in
Chlamydomonas moewusii
Authors: McLean Robert J. , Laurendi Carmen J. , Brown R. Malcolm
Published: May 2006

Gamete-gamete adhesion in
Chlamydomonas
has long been attributed to large glycoprotein particles (gamone) on the flagellar membrane surface. These macromolecules may be incidentally sloughed off or released into the medium. Gamone isolated from the medium of one mating type will cause isoagglutination of opposite gametes. Our study of
Chlamydomonas moewusii
shows that such particles isolated from the cell medium are really membrane vesicles with mastigonemes (flagellar appendages) attached. The vesicles appear to bleb off the flagellar membrane as a normal process. Purified mastigonemes have no isoagglutinating activity, while purified membrane vesicles (with no mastigonemes attached) retain activity. Therefore, the large particles isolated by others from the cell medium of
Chlamydomonas
and thought to be equivalent to the gametic adhesion substance are in fact membrane vesicles upon which the adhesion sites are located, and these sites are probably much smaller than was previously supposed. Mastigonemes appear to have no role in gamete adhesion.
Replication of Mouse-Tropic and Xenotropic Strains of Murine Leukemia Virus in Human × Mouse Hybrid Cells
Authors: Gazdar Adi F. , Russell Edward K. , Minna John D.
Published: May 2006

The replication of mouse-tropic and xenotropic strains of murine leukemia virus in human × mouse hybrid cells was investigated. NB-tropic strains of the leukemia virus replicated efficiently in several hybrid lines, including those that contained a complete complement of human chromosomes and many mouse chromosomes. In lines with only a few mouse chromosomes, NB-tropic viruses failed to replicate. N- and B-tropic viruses replicated in human × N-type and human × B-type cells, respectively. The N- and B-tropic viruses replicating in these hybrid cells retained their original tropism. The viral restrictive functions of the mouse
Fv-1
locus were expressed in the hybrid cells, restricting the replication of N- and B-tropic strains in human × B-type and human × N-type mouse cells, respectively. In contrast to mouse-tropic viruses, AT-124 virus, a xenotropic strain, replicated in human but not in mouse cells or in hybrid cells containing a complete complement of human chromosomes and near complete complement of mouse chromosomes However, hybrid lines with only a few mouse chromosomes supported AT-124 replication. Thus, human genes in hybrid cells do not restrict the replication of mouse or xenotropic murine leukemia virus strains, while mouse genes in such cells restrict xenotropic leukemia virus replication and, as determined by the mouse
Fv-1
phenotype, mouse-tropic murine leukemia virus. These results indicate that exogenously applied mouse-tropic and xenotropic oncornaviruses exhibit different patterns of restriction in human-mouse hybrid cells and that such hybrid cells may be used for genetic analysis of oncornavirus replication.
Role of ATP in Excision Repair of Ultraviolet Radiation Damage in
Escherichia coli
Authors: Waldstein E. A. , Sharon R. , Ben-Ishai R.
Published: May 2006

The effect of ATP on the first step of excision repair of ultraviolet damage in DNA has been studied using toluene-treated
E. coli
. During postirradiation incubation, five to six times more single-strand breaks are formed in DNA in the presence of exogenous ATP than in its absence. The ATP-dependent as well as the ATP-independent endonucleolytic activities appear to be catalyzed by the same enzyme since both activities are almost completely absent in
uvrA
and
uvrB
mutants. An ATP-dependent endonucleolytic activity has been detected in nonirradiated toluene-treated
E. coli
. It is concluded that ATP is required
in vivo
for either the incision step of repair or an enzymatic reaction preceding it.
Phosphotransferase-System Enzymes as Chemoreceptors for Certain Sugars in
Escherichia coli
Chemotaxis
Authors: Adler Julius , Epstein Wolfgang
Published: May 2006

For D-glucose and analogs there are two distinct phosphotransferase enzymes II with different specificities. Transport and chemotaxis were studied in
E. coli
mutants having only one or the other of these two enzymes. It was found that the transport specificity of a given enzyme II correlates with taxis specificity, and mutational loss of an enzyme II abolishes taxis toward only those sugars which it alone transports. Although enzyme I and the phosphate-carrier protein are required for full D-glucose taxis, it could not be determined if phosphorylation and transport are also required.
The Decay of Genetic Variability in Geographically Structured Populations
Authors: Nagylaki Thomas
Published: May 2006

The geographical structure of a population distributed continuously and homogeneously along an infinite linear habitat is explored. The analysis is restricted to a single locus in the absence of selection, and every mutant is assumed to be new to the population. An explicit formula is derived for the probability that two homologous genes separated by a given distance at any time
t
are the same allele. The ultimate rate of approach to equilibrium is shown to be
t
-3/2
e

-2
ut

, where
u
is the mutation rate. An approximation is given for the stationary probability of allelism in an infinite two-dimensional population, which, unlike previous expressions, is finite everywhere. For a finite habitat of arbitrary shape and any number of dimensions, it is proved that if the population density is very high, then asymptotically the transient part of the probability of allelism is spatially uniform and decays at the rate
e

-[2
u
+1/(2
N
)]
t

, where
N
is the total population size. Thus, in this respect the population behaves as if it were panmictic. The dependence of the amount of local gene frequency differentiation on population density and habitat size and dimensionality is discussed.
The Surface Morphology and Fine Structure of CHO (Chinese Hamster Ovary) Cells Following Enucleation
Authors: Shay J. W. , Porter K. R. , Prescott D. M.
Published: May 2006

Chinese hamster ovary cells grown in monolayer culture and exposed to cytochalasin B were enucleated by centrifugation. Thereafter, the karyoplasts (the nucleated parts obtained from the bottoms of the centrifuge tubes) and the cytoplasts (the enucleated cytoplasmic parts attached to the coverslips) were allowed to recover and subsequently were examined by scanning and transmission electron microscopy. Microscopy of thin sections revealed that the karyoplasts, limited by an intact plasma membrane, contain an intact nucleus surrounded by a layer of cytoplasm that includes ribosomes, mitochondria, and fragments of the endoplasmic reticulum, but no centrioles or microtubules. The cytoplasts, similarly examined, appear to contain all cytoplasmic organelles and systems, including centrioles and microtubules. The karyoplasts, when replated in fresh medium adhere to the substrate but remain essentially spherical and are incapable of motility. They disintegrate in about 72 hr. The cytoplasts, under identical conditions, recover a shape similar to that of the whole Chinese hamster ovary cell and display some motility. They generally survive not more than 48 hr. It appears that this enucleation procedure consistently separates the nucleus and limited cytoplasm from the centrosphere and microtubule-containing cytoplasts and, furthermore, that the formdetermining and motility mechanisms reside in the cytoplast and function without nuclear participation for the short period of viability.
5′-Guanylylimidodiphosphate, A Potent Activator of Adenylate Cyclase Systems in Eukaryotic Cells
Authors: Londos Constantine , Salomon Yoram , Lin Michael C. , Harwood James P. , Schramm Michael , Wolff J. , Rodbell Martin
Published: May 2006

5′-Guanylylimidodiphosphate (Gpp(NH)-p) stimulates adenylate cyclase [ATP-pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity in plasma membranes isolated from frog and salmon erythrocytes, from rat adrenal, hepatic, and fat cells, and from bovine thyroid cells. The nucleotide acts cooperatively with the various hormones (glucagon, secretin, ACTH, thyrotropin, and catecholamines) that stimulate these adenylate cyclase systems with resultant activities that equal or exceed those obtained with hormone plus GTP or with fluoride ion. In the absence of hormones, Gpp(NH)p is a considerably more effective activator than GTP, and, under certain conditions of incubation, stimulates rat fat cell adenylate cyclase to levels of activity (about 20 nmoles of 3′,5′-adenosine monophosphate mg protein per min) far higher than reported hitherto for any adenylate cyclase system examined. The nucleotide activates frog erythrocyte adenylate cyclase when the catecholamine receptor is blocked by the competitive antagonist, propranolol, and activates the enzyme from an adrenal tumor cell line which lacks functional ACTH receptors. In contrast, Gpp(NH)p does not stimulate adenylate cyclase in extracts from
Escherichia coli
B. Gpp(NH)p appears to be a useful probe for investigating the mechanism of hormone and nucleotide action on adenylate cyclase systems in eukaryotic cells.
Nuclear Coupling of
33
S and the Nature of Free Radicals in Irradiated Crystals of Cystine Dihydrochloride
Authors: Hadley Joseph H. , Gordy Walter
Published: May 2006

The
33
S hyperfine structure has been observed and analyzed in the electron spin resonance of γ-irradiated single crystals of cystine dihydrochloride at 77°K and at room temperature. The radicals observed at room temperature and previously assigned as RCH
2
S are proved to be disulfide radicals, RCH
2
SS. However, the RCH
2
S radical is identified by the
33
S measurements in samples irradiated at 77°K, annealed at 200°K, and observed at 77°K. This monosulfide radical appears to undergo reactions to form disulfide radicals at room temperature.
Membrane Fatty Acid Replacements and Their Effect on Growth and Lectin-Induced Agglutinability
Authors: Horwitz Alan F. , Hatten Mary Elizabeth , Burger Max M.
Published: May 2006

The growth of 3T3 and SV101 3T3 cells in a lipid-depleted medium is enhanced by the addition of biotin or some fatty acids. The extent of enhancement depends on the fatty acid(s) supplied. The presence of linoleate is unique, since it induces a morphological alteration in 3T3 cells resulting in a cell similar to an SV101-transformed 3T3 cell. Analyses of the fatty acids from the membrane phosphatides show that the exogenously supplied fatty acids are incorporated and alter the fatty acid composition. This is most clearly evident with heptadecanoate-grown cells, in which this fatty acid and its derivatives comprise over 45% of the fatty acids in the phospholipids.

The fatty acid replacements have a striking effect on the temperature dependence of agglutination by wheat germ agglutinin and concanavalin A, implying that fluidity is involved in agglutination. These temperature dependencies and the effect of fatty acid replacements on them were different for the two lectins, but similar for both transformed and untransformed cells. These observations are interpreted as suggesting that the lipid phase is heterogeneous, and that transformed and untransformed cell membranes have regions of similar fluidity.
Sister Chromatid Exchanges, Indices of Human Chromosome Damage and Repair: Detection by Fluorescence and Induction by Mitomycin C
Authors: Latt Samuel A.
Published: May 2006

Sister chromatid exchanges in chromosomes from human lymphocytes grown two replication cycles in medium containing 5-bromodeoxyuridine can be detected by fluorescence microscopy after staining with the bisbenzimidazole dye 33258 Hoechst. These exchanges are much more frequent than chromosome or chromatid breaks and appear to be partly but not entirely due to 5-bromodeoxyuridine incorporation. Sister chromatid exchanges are extremely sensitive indicators of chromosome damage produced by DNA cross-linking agents such as mitomycin C. Significant increases in the sister chromatid exchange frequency occur with 3 ng/ml of mitomycin C; higher concentrations of mitomycin C induce further sister chromatid exchanges. Comparatively few gross chromosomal aberrations are seen in cells exhibiting as many as one hundred or more sister chromatid exchanges. Most of the damage caused by mitomycin C to chromosomal DNA is apparently repaired without detectable changes in chromosome morphology. Analysis of sister chromatid exchanges may permit more sensitive detection of damage to DNA caused by other agents than has previously been possible by classical cytological techniques.
Genetic Recombination and Commitment to Meiosis in
Saccharomyces
Authors: Esposito Rochelle E. , Esposito Michael S.
Published: May 2006

Diploid cells of the yeast
Saccharomyces cerevisiae
become committed to recombination at meiotic levels without becoming committed to the meiotic disjunction of chromosomes. These two events of the meiotic process can be separated by removing cells from a meiosis-inducing medium and returning them to a medium that promotes vegetative cell division. Cells removed at an appropriate time remain diploid, revert to mitosis, and display recombination with meiotic-like frequencies. Those removed after this time are committed to the completion of meiosis. Diploids of three conditional sporulation-deficient mutants (
spo
1-1,
spo
2-1, and
spo
3-1) have been examined for recombination at restrictive temperatures. All exhibit commitment to recombination without commitment to meiotic disjunction as in the wild type. Cells of
spo
1-1/
spo
1-1 do not replicate the spindle pole body for meiosis I; thus, recombination ability can be acquired by cells that do not proceed beyond this cytological stage.
Highly Purified Colicin E3 Contains Immunity Protein
Authors: Jakes Karen S. , Zinder Norton D.
Published: May 2006

Colicin E3, even when highly purified, still contains about one molar equivalent of a second protein, “E3 immunity protein.” The two proteins are bound together in a complex that can be dissociated only under strongly denaturing conditions, such as electrophoresis in sodium dodecyl sulfate-polyacrylamide gles or by gel filtration in 6 M guanidine·hydrochloride.

Colicin and immunity protein were separated by preparative electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. The immunity protein prepared in this way was shown to be functionally and immunologically identical to immunity protein purified from colicinogenic cells by other methods. Colicin E3 that had been freed of immunity protein was much more active than complexed colicin in inhibiting protein synthesis
in vitro
.
Use of Eukaryotic Native Small Ribosomal Subunits for the Translation of Globin Messenger RNA
Authors: Freienstein Christoph , Blobel Günter
Published: May 2006

A highly active
in vitro
system for the translation of globin mRNA, resulting in more than 10 rounds of translation, is described. The reconstituted system consists of native small ribosomal subunits of rabbit reticulocytes (as a source of initiation factors as well as small ribosomal subunits), large subunits derived from rat liver polysomes by the puromycin-KCl procedure, and a pH 5 fraction obtained from a Krebs ascites cell high speed supernatant. In this system no differences were found between globin messenger ribonucleoprotein and globin mRNA.
Surface Antigens of Mammalian Sarcoma Virus-Transformed Nonproducer Cells
Authors: Aoki T. , Stephenson J. R. , Aaronson S. A. , Hsu K. C.
Published: May 2006

In vitro
, clonal BALB/3T3 mouse cells were transformed into nonproductive sarcoma cells by Kirsten murine sarcoma virus. The resulting cells are called K-BALB. Similarly, the Kirsten sarcoma virus and woolly monkey sarcoma virus transformed normal rat embryonic kidney (NRK) cells to nonproductive sarcoma cells K-NRK and W-NRK, respectively. The presence of sarcoma cell surface antigen (SCSA) on these three different cell lines has been examined by immunoelectron microscopy using the rabbit anti-K-BALB, anti-K-NRK, and anti-W-NRK sera preabsorbed with normal embryonic rat cells, NRK cells, and BALB/3T3 cells. Four different specific sarcoma cell surface antigens have been demonstrated: SCSAa, an antigen specific to the surface of W-NRK cells; SCSAb, a surface antigen common to K-NRK and W-NRK cells; SCSAc, a surface antigen common to K-BALB and W-NRK cells; and SCSAd, a surface antigen broadly reactive with the rabbit antisera to W-NRK, K-NRK, and K-BALB.
Inhibition of Murine Leukemia Virus Production in Chronically Infected AKR Cells: A Novel Effect of Interferon
Authors: Friedman Robert M. , Ramseur Janet M.
Published: May 2006

Treatment of AKR cells that had spontaneously become procedures of a murine leukemia virus with a partially purified mouse interferon (> 5 × 10
7
international mouse reference units per mg of protein) inhibited endogenous virus production. This inhibitory effect decreased over a 72-hr period in a manner similar to interferon-induced antiviral activity directed against vesicular stomatitis virus in AKR cells. Despite the inhibitory effect of interferon on infectious murine leukemia virus and viral reverse transcriptase (RNA-dependent DNA polymerase) titers in the culture fluids, intracellular levels of viral groups-specific antigens were significantly increased. These results suggest that interferon treatment in AKR cells inhibited the assembly or release of the virus.
Establishment of a Clone of Mouse Hypothalamic Neurosecretory Cells Synthesizing Neurophysin and Vasopressin
Authors: Vitry F. De , Camier M. , Czernichow P. , Benda Ph. , Cohen P. , Tixier-Vidal A.
Published: May 2006

Hypothalamic cells taken from 14-day-old mouse embryos were cultured for 6 days and transformed with simian virus 40. After cloning, a homogeneous cell population was obtained. Its morphological, Ultrastructural, biochemical, and immunochemical properties were studied. These cells possess ultrastructural features of primitive neurosecretory cells. They synthesize
35
S-labeled protein components that have the molecular weight and isoelectric focusing behavior of, and display the same immunoreactivity as, neurophysin. In addition, a
35
S-labeled peptidic fraction with a molecular weight close to 1000 is synthesized and is radioimmunologically indistinguishable from vasopressin. Immunochemical staining shows that both neurophysin and vasopressin are localized in the cytoplasm. These observations strongly suggest that a clone of mouse hypothalamic neurosecretory cells has been obtained with the synthesizing capacities of secretory neurons of the magnocellular hypothalamic nuclei.
Induction of erythroid differentiation by dimethylsulfoxide in cells infected with Friend virus: relationship to the cell cycle.
Authors: Levy J , Terada M , Rifkind R A , Marks P A
Published: May 2006

Cells infected with Friend virus can be induced to erythroid differentiation by culture with 2% dimethylsulfoxide. This study was designed to determine if dimethylsulfoxide causes the expression of erythroid differentiation by an effect on a particular phase of the cell division cycle. The infected cells were synchronized by exposure to 2 mM thymidine. It is shown that dimethylsulfoxide must be present during DNA synthesis (S-phase) and, possibly, shortly thereafter, to induce differentiation assayed by measuring hemoglobin synthesis. In order to achieve an effective intracellular incorporation of dimethylsulfoxide, cells must be exposed to the agent for at least 24-30 hr before the critical S phase. It is suggested that induction of erythroid differentiation in cells infected with Friend virus involves an effect of dimethylsulfoxide, or a metabolic product, that alters the program of transcription, during or immediately after DNA synthesis.
Neutron Diffraction Studies on the Location of Water in Lecithin Bilayer Model Membranes
Authors: Zaccai G. , Blasie J. K. , Schoenborn B. P.
Published: May 2006

Lamellar neutron diffraction from oriented multilayers of hydrated dipalmitoyl lecithin was phased by isomorphous H
2
O-D
2
O exchange and swelling techniques. Bound water sites were located in the polar head group region of the bilayer profile. A 6-Å resolution structure based on the neutron scattering density profile is proposed for the bilayer. It is consistent with the electron density profile from x-ray diffraction.
Very short-lived and stable mRNAs from resting human lymphocytes.
Authors: Berger S L , Cooper H L
Published: May 2006

The kinetics of degradation of newly synthesized cytoplasmic poly(A)-bearing RNA have been examined in resting human lymphocytes. Two classes were identified, a very labile component with a half-life of less than 17 min and a stable component which remains apparently undiminished during 24 hr of observation. Both classes have molecular weights between 2.5 and 3.5 x 10(5) but the stable material has a narrower size distribution and a slightly lower average molecular weight than the short-lived component. The fate of stable RNA synthesized in the resting cell was also examined after growth stimulation with phytohemagglutinin after 2 and 6 hr of treatment. No transfer of stable material into the labile pool could be discerned; the amount of stable material remained constant. The existence of two species of mRNAs with different lifetimes in animal cells provides a potential means for regulation of protein synthesis by controlling the supply of specific messages. Furthermore, such a short-lived mRNA species may explain the observed disparity between the amount of poly(A)-bearing heterogeneous RNA produced in the nucleus and the amount of mature message found in the cytoplasm.
Relationship between in vivo degradative rates and isoelectric points of proteins.
Authors: Dice J F , Goldberg A L
Published: May 2006

Previous studies have shown that in mammalian cells proteins of large molecular weight are degraded more rapidly than small ones. Evidence is presented here that half-lives of proteins are also related to their isoelectric points. A double-isotope method was used to compare degradative rates of soluble proteins separated by isoelectric focusing. In rat liver, skeletal muscle, kidney, and brain, more rapid rates of catabolism were found for acidic protein fractions than for neutral or basic ones. Acidic proteins also tended to be degraded faster in several mouse tissues. A literature survey confirmed this trend. For 22 proteins from rat liver, a highly significant correlation was found between rates of degradation and isoelectric points (r = 0.824; P less than 0.01). This relationship between isoelectric point and half-life appears to be distinct from that between protein size and half-life.
Synthesis of acetylcholine receptor during differentiation of cultured embryonic muscle cells.
Authors: Merlie J P , Sobel A , Changeux J P , Gros F
Published: May 2006

Acetylcholine receptor, a component of the specialized muscle membrane, appears during the differentiation of embryonic myogenic cells in tissue culture. Demonstration of incorporation of the radioactive precursor L-[35S]methionine into purified receptor polypeptides is presented as evidence for its synthesis de novo. The identity of the purified radioactive species is established by cosedimentation of the [35S]receptor with [3H]alpha-toxin binding activity on sucrose gradients and by crossreaction with antiserum to purified acetylcholine receptor of Electrophorus electricus.
Meiosis in Phycomyces.
Authors: Eslava A P , Alvarez M I , Delbrück M
Published: May 2006

A four-factor cross between two strains of Phycomyces involving two auxotrophic, one color, and the mating type marker is described. Samples of 40 germspores from 84 individual fertile germsporangia were characterized. The results show: (i) The germspores of a germsporangium are derived from one meiosis in approximately 78% of the cases. (ii) The four markers are on separate chromosomes. They are nonselective. (iii) Analysis of a large sample of germspores from 106 pooled germsporangia confirms that the four markers are unlinked. (iv) From the ditype/tetratype ratios it is inferred that each marker is located about 15 map units from its centromere.
Influence of an aggregated multienzyme system on transient time: kinetic evidence for compartmentation by an aromatic-amino-acid synthesizing complex of Neurospora crassa.
Authors: Welch G R , Gaertner F H
Published: May 2006

The aromatic complex of Neurospora crassa is an aggregated multienzyme system which catalyzes five consecutive reactions in the central pathway leading to the biosynthesis of the aromatic amino acids. In an attempt to understand the physiological importance of this complex in particular, as well as the importance of cellular organization of enzyme systems in general, we have isolated the complex and have begun to characterize its catalytic properties. Optimum conditions for the assay of the overall 5-step reaction catalyzed by the partially purified complex have been determined. An analog computer was programmed to represent an unaggregated system of five enzymes with rate constants identical to those found for the constituent enzymes of the complex. By direct comparison, it was shown that the lags (transient times) obtained for the overall reaction were 10-15 times longer for the hypothetical unaggregated system than for the complex. We conclude from these data that the aggregated multienzyme system compartmentalizes intermediate substrates during the course of the overall reaction. We suggest that, in addition to "channeling" intermediates of competing pathways, reduction of the transient time may be an important consequence of the containment of intermediates within a physically associated enzyme sequence. The fact that the aromatic complex exhibits a second catalytic property unique to aggregated enzyme systems, "coordinate activation" [Welch, G.R. & Gaertner, F.H. (1975) Arch. Biochem. Biophys., in press] indicates that the physical association of these enzymes may have more than one physiological function.
Regulation of synthesis of hepatic fatty acid synthetase: polysomal translation in a cell-free system.
Authors: Strauss A W , Alberts A W , Hennessy S , Vagelos P R
Published: May 2006

Polysomes were isolated from livers of rats fed various diets and were translated in a protein-synthesizing system derived from cultured Chang liver cells. One of the labeled products was identified as complete subunit(s) of fatty acid synthetase by indirect immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the solubilized immunoprecipitate. The relative amounts of fatty acid synthetase synthesized by polysomes from livers of rats fed a normal diet, starved rats, and rats starved and refed a fat-free diet for 16 hr were 1, 0.1, and 10, respectively. Induction of synthesis of fatty acid synthetase after fat-free refeeding of starved rats began by 2 hr (3-fold increase over starved animals), was increasing rapidly by 5 hr (19-fold over starved animals), and reached a high level by 16 hr (95-fold over starved and 10-fold over normally fed).
Initiation of in vitro mRNA synthesis from the wild-type lac promoter.
Authors: Majors J
Published: May 2006

An in vitro transcription system, dependent on catabolite gene activator protein (CAP), utilizing a 200 base-pair restriction fragment, has been used to show that the initiation site of the wild-type Escherichia coli lac mRNA, and that of two mutants, 8d and ps, are identical to that previously reported for the CAP-independent promoter mutant UV5. Order of addition experiments are used to show that the binding of lac repressor to the operator is competitive with that of the RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) to the promoter, thus demonstrating functional overlap of the operator and promoter sites.
Cytochemical study of secretory process in transplantable insulinoma of syrian golden hamster.
Authors: Novikoff A B , Yam A , Novikoff P M
Published: May 2006

Electron microscopy, including phosphatase cytochemistry, indicates that the secretory granules of an insulinoma producing proinsulin and insulin are packaged by the endoplasmic reticulum (ER) and especially by a specialized region of ER which we call GERL because of the spatial relationship of this region to the Golgi apparatus and its apparent role in producing lysosomes. The granules are not derived from the Golgi apparatus. Preliminary evidence suggests this may be true also of pancreatic beta-cells.
Analysis of changes in collagen biosynthesis that occur when chick chondrocytes are grown in 5-bromo-2'-deoxyuridine.
Authors: Mayne R , Vail M S , Miller E J
Published: May 2006

Chick embryo chondrocytes, in primary culture, initially synthesize only Type ii collagen (chain composition, [alpha1(II)13), as judged by two criteria: (i) carbosymethyl-cellulose chromatography of the denatured collagen, and (ii) carbosymethyl-cellulose chromatography of the cyanogen bromide peptides derived from the isolated chains. After a period of growth in 5-bromo-2'-deoxyuridine, however, synthesis of two different types of collagen could be detected after differential salt precipitation of the newly synthesized native collagens from neutral salt solutions at 2.2 M NaCl and subsequently at 0.01 M Na2hPO4. By criteria indicated above, the collagen precipitating at 2.2 M NaCl was identified as Type I collagen (chain composition, [alpha(I)]2alpha2), whereas the collagen subsequently precipitated at 0.01 M Na2HPO4 was found to be comprised entirely of alpha1(I) chains, indicating a chain composition, [alpha](I)]3. We propose to designate the latter type of molecule as the Type I trimer.
Multiple active sites on human interferons.
Authors: Paucker K , Dalton B J , Ogburn C A , Törmä E
Published: May 2006

Human interferons stimulated in peripheral leukocytes and foreskin fibroblasts are active in cultures of human and rabbit cells. The dominant factors in leukocyte and fibroblast interferons responsible for antiviral activity in rabbit cells were shown to be antigenically distinct from each other as well as from rabbit interferon. In addition, leukocyte interferon contained also a minor component with antigenic determinants characteristic of fibroblast specificity, which could be isolated by affinity chromatography on Sepharose-bound antibodies directed against firboblast interferon. Neutralization tests with selected anti-interferon sera suggested that the antiviral activities of leukocyte and fibroblast interferons in human and rabbit cells were associated with single molecules. A model is proposed where molecules of human interferon contain multiple reactive sites each of which is capable of interaction with cells of a different species. The number and distribution of these determinant sites may vary with the source of the human interferon and account for the differential in antiviral protection expressed in homologous and phylogenetically unrelated host cells.
Viability of Escherichia coli treated with colicin K.
Authors: Kopecky A L , Copeland D P , Lusk J E
Published: May 2006

Conditions permitting survival (colony formation) of E. coli after treatment with colicin K have been found. Survival required K+ and Mg2+ at concentrations high enough to replace the intracellular ions lost from colicintreated cells. Either glucose minimal medium or broth could support survival. Survival was still observed after colicin-promoted efflux of Rb+ and decline in ATP levels had occurred, and after the period during which treatment with trypsin could rescue the cells on media containing low concentrations of K+. In an adenosinetriphosphate (ATP phohsphohydrolase, EC 3.6.1.3) deficient (uncA) mutant, survival after colicin treatment was observed at lower Mg2+ concentrations than those required by the wild type, and Rb+ could replace K+. Cells treated with colicin E1 (but not with colicin I2, E3, or Ib) also survived under conditions permitting survival of colicin K.