bluuebunny/crossref_metadata_2025 huggingface dataset:
13
C NMR chemical shift correlations in application of “tool of increasing electron demand” to stable long-lived carbocations: Comprehensive evaluation
Authors: Olah George A. , Berrier Arthur L. , Prakash G. K. Surya
Published: May 2006

The reliability of
13
C NMR chemical shift correlations in the application of the “tool of increasing electron demand” to stable long-lived carbocationic systems is demonstrated by a comprehensive analysis of 22 stable aryl-substituted carbocationic systems. The observation of slopes of less than unity in such chemical shift correlations for several cationic systems has been attributed to additional charge delocalizing mechanisms present in the system (such as homoallylic, cyclopropyl, and π conjugations). The onset of nonclassical σ-delocalization in 2-aryl-2-norbornyl cations with electron withdrawing-substituents previously observed was further verified by using σ
C+
substituent constants. Difficulties in relating the
C
α
NMR shifts in different carbocationic systems are also discussed.
New reactions and theory in organic photochemistry: The 1,3-vinyl migration and its relevance to exchange integral control
Authors: Zimmerman Howard E. , Penn John H. , Johnson Mark R.
Published: May 2006

The photochemistry of 1,1,4-triphenyl-1,4-pentadiene was investigated. Sensitized irradiation of this compound labeled at carbon 3 with
2
H led to a degenerate rearrangement wherein the diphenylvinyl moiety migrated 1,3, thus affording diene with
2
H substitution at carbon 5. In contrast, direct irradiation of the triphenyl pentadiene led to 1,3,3-triphenylbicyclo[2.1.0]pentane by a [2 + 2] cycloaddition. This multiplicity dependence of the photochemistry is understood on the basis of triplet reactants preferring a linearly conjugated diradical mechanism with a large exchange integral (
K
) and singlet reactants preferring an electrocyclic mechanism with a small exchange integral.
Method for introducing site-specific mutations into adenovirus 2 genome: construction of a small deletion mutant in VA-RNAI gene.
Authors: Kapoor Q S , Chinnadurai G
Published: May 2006

We have developed a method for introducing mutations into the adenovirus type 2 genome at predetermined sites. Specific mutations are introduced into segments of the viral genome cloned in bacteria by using plasmid vectors. The chimeric DNA is used to construct viral mutants by cotransfection with two viral DNA segments derived from both ends of the viral genome, each of which has overlapping sequence homology with the cloned viral DNA segment. To illustrate this procedure, we cloned a large restriction fragment [EcoRI fragment A, map position (mp) 0--58.5] by using plasmid vector pBR322, and a small deletion mutation was introduced at the BamHI cleavage site located within the VA-RNAI gene (mp 29 at residue +75 on VA-RNAI gene). The mutated DNA was then used to construct viral mutants by cotransfection into human cells with the adenovirus type 2 DNA--protein complex digested with Sal I. In vivo recombination occurred via overlapping sequences between the cloned EcoRI fragment A and Sal I-digested DNA--protein complex at two sites, mp 0--25 (i.e., within Sal I fragment B) and mp 45--58.5 (i.e., overlapping sequences between Sal I fragment A and EcoRI fragment A), generating infectious DNA molecules with intact ends. The viral mutant grows as well as the wild type in KB cells and induces the synthesis of smaller VA-RNAI but normal-size VA-RNAII.
Molecuar model of the DNA interaction site for the cyclic AMP receptor protein.
Authors: O'Neill M C , Amass K , de Crombrugghe B
Published: May 2006

A topological model of the DNA binding site for the cyclic AMP receptor protein (CRP) is presented. A consensus sequence drawn from the known CRP binding sites has several symmetrical subregions that are spatially resolved onto different faces of the DNA helix. Consideration of available biochemical and genetic data suggest one particular choice among the possible symmetrical arrangements. In this case, the sequence of its helical form presents nearly the same pattern of exposed base pairs on two faces of the helix. These two faces are separated by a helix angle of 72 degrees; the similar sequences that are exposed in the grooves occur in opposite orientations on the two faces. We propose that this inverted symmetry arrangement provides each of the identical subunits of the CRP with a similar recognition region within the overall site. In gal and ara, the site appears to accommodate a single molecule of the CRP; in lac, the site repeats the symmetrical arrangement and should accommodate two molecules of the CRP.
Generation of fibroblast-like cells from cloned epithelial mammary cells in vitro: a possible new cell type.
Authors: Dulbecco R , Henahan M , Bowman M , Okada S , Battifora H , Unger M
Published: May 2006

We have isolated clonal cell lines from a nitrosomethylurea-induced mammary tumor in Wistar--Furth rats. The epithelial-like cells of these lines give rise to fibroblast-like cells. A study of several markers showed that the epithelial-like cells are similar to epithelial mammary cells. The fibroblastic cells, however, were similar to stromal cells, except for the production of collagen IV. The events occurring in these cultures are identical to those observed in previously isolated mammary cultures [Bennett, D. C., Peachey, L. A., Durbin, H. & Rudland, P. S. (1976) Cell 15, 283--298], suggesting their generality. The fibroblast-like cells generated in culture may be a hitherto unrecognized type of mammary cell.
Evolution of the mutation rate at a heterotic locus.
Authors: Gillespie J H
Published: May 2006

A diffusion model of the modification of mutation rates at a heterotic locus in a finite population is examined. An asymptotic analysis assuming strong selection and weak linkage shows that selection can operate on mutation rates in this setting. There exists a favored mutation rate which is a function only of the equilibrium allele frequency of the heterotic locus and the population size. It is independent of the strength of selection at the heterotoxic locus. Computer simulations are also provided to show that this form of natural selection can occur.
Terminal proteins and short inverted terminal repeats of the small Bacillus bacteriophage genomes.
Authors: Yoshikawa H , Ito J
Published: May 2006

The genome of Bacillus phage phi 29 contains covalently linked protein at both ends. These DNA terminal proteins are essential for phi 29 DNA replication. We have isolated phi 29 terminal protein from each end separately and compared their two-dimensional peptide maps. Our results showed the two proteins to be identical. The DNAs of four phages examined (phi 15, Nf, M2Y, and GA-1) also contain protein at both ends of the DNA molecules. The chymotryptic peptide maps of these DNA terminal proteins have been compared with the map of the phi 29 terminal protein. Despite the similarities in molecular size, peptide maps of the terminal proteins show clear differences among the unrelated phages. These results are consistent with the idea that the terminal proteins are encoded by viral DNA rather than by the host chromosome. We have also determined the nucleotide sequences of the termini of four phage DNAs and compared them with the sequence of phi 29 DNA. The sequence data indicate that all of these phages DNA contain short inverted terminal repeats: 5'A-A-A-G-T-A for phi 29 and phi 15, 5' A-A-A-G-T-A-A-G for Nf and M2Y, and 5' A-A-A-T-A-G-A for GA-1.
Epidermal growth factor stimulation of ornithine decarboxylase activity in a human hepatoma cell line.
Authors: Moriarity D M , DiSorbo D M , Litwack G , Savage C R
Published: May 2006

Epidermal growth factor (EGF) bound specifically to the human hepatoma cell line PLC/PRF/5. Treatment of these cells with nanomolar concentrations of EGF for 4-6 hr resulted in a 2- to 6-fold increase in ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activity. 12-O-Tetradecanoylphorbol 13-acetate also produced an increase in enzyme activity in these cells and exhibited an additive effect with EGF. It did not inhibit the binding of 125I-labeled EGF to these cells. The stimulation of enzyme activity by EGF was not inhibited by cycloheximide or actinomycin D, although these agents did cause a significant decrease in enzyme levels when added without EGF. Also, colchicine, chloroquine, ammonium chloride, and methylamine, compounds that inhibit EGF degradation in various cells types, did not interfere with the ability of EGF to elevate enzyme levels in the human hepatoma cells.
Immunofluorescent staining of poly(ADP-ribose) in situ in HeLa cell chromosomes in the M phase.
Authors: Kanai Y , Tanuma S , Sugimura T
Published: May 2006

Randomly and synchronously growing HeLa cells were tested for poly(ADP-ribose) by direct and indirect immunofluorescent antibody techniques. Fluorescence of poly(ADP-ribose) was seen only in the nuclei of intact cells when the direct immunofluorescent antibody technique was used but in both the nuclei and cytoplasm when the indirect immunofluorescent antibody technique was used; fluorescence in the cytoplasm was nonspecific. When randomly or synchronously growing HeLa cells were fixed in acetone and treated with DNase I before incubation with fluorescein-labeled antibody, intense fluorescence was observed only in the nuclei when the direct immunofluorescent staining technique was used. Addition of 3-aminobenzamide, a potent inhibitor of poly(ADP-ribose) polymerase, with the DNase I completely abolished the fluorescence in the nuclei of synchronously and randomly growing HeLa cells, except in M-phase nuclei. These results suggest that poly(ADP-ribose) can be synthesized even in the nuclei of acetone-fixed HeLa cells from "endogenous NAD+" during incubation with fluorescent antibody and also that the fluorescence of chromosomes of HeLa cells in the M phase is, in fact, due to the in situ presence of poly(ADP-ribose), not to poly(ADP-ribose) synthesized during incubation with antibody.
Proton transport in photooxidation of water: A new perspective on photosynthesis
Authors: Arnon Daniel I. , Tsujimoto Harry Y. , Tang George M.-S.
Published: May 2006

The currently prevalent concept of the generation of photosynthetic reducing power in oxygen-evolving cells envisions a linear (noncyclic) electron flow from water to ferredoxin (and thence to NADP
+
) that requires the collaboration of photosystems I and II (PSI and PSII) joined by plastoquinone and other electron carriers (the Z scheme). The essence of the Z scheme is that only PSI can reduce ferredoxin—i.e., that, after being energized to an intermediate reducing potential by PSII, electrons from water are transported via plastoquinone to PSI which energizes the electrons to their ultimate reducing potential adequate for the reduction of ferredoxin. Basic to the Z scheme is the function of plastoquinone as the obligatory link in electron transport from PSII to PSI. However, we have found that, when plastoquinone function was inhibited, ferredoxin was photoreduced by water without the collaboration of PSI. We now report evidence for an important function of plastoquinone in the translocation of protons liberated inside the thylakoid membrane by photooxidation of water. When the oxygenic photoreduction (i.e., by water) of ferredoxin was blocked by plastoquinone inhibitors, dibromothymoquinone or dinitrophenol ether of iodonitrothymol, the photoreduction of ferredoxin was restored by each of four chemically diverse uncouplers, similar only in their ability to facilitate proton movement across membranes. Similar results were obtained for the oxygenic reduction of NADP
+
. Our results suggest that the light-induced electron flow from water cannot be maintained unless the simultaneously liberated protons are removed from inside the membrane via plastoquinone. The new evidence is embodied in a concept of an
oxygenic photosystem
for photosynthetic electron and proton transport, which we propose as an alternative to the Z scheme, to account for photoreduction of ferredoxin-NADP
+
by water and the coupled oxygenic (formerly noncyclic) ATP formation without involving PSI. The role of the
anoxygenic photosystem
(formerly called PSI) is ATP formation by cyclic photophosphorylation.
X chromosome reactivation in oocytes of Mus caroli.
Authors: Kratzer P G , Chapman V M
Published: May 2006

Mature mammalian oocytes have both of their X chromosomes active, while somatic cells from the same individual have one of their X chromosomes in an inactive state. We asked whether the X chromosomes of the germ cells never undergo inactivation in their ontogeny or whether inactivation of an X chromosome does occur but is followed by a subsequent reactivation event. Our approach has used an electrophoretic polymorphism for the X-linked enzyme glucose-6-phosphate dehydrogenase (G6PD) in the mouse species Mus caroli. G6PD is dimeric, and a heterodimer is produced in cells from heterozygous females if and only if both X chromosomes are active. Ovaries from heterozygous fetuses at different gestational ages were dissected and either studied cytologically or pressed between microscopy slides to obtain germ cell-rich and germ cell-poor preparations. No heterodimer band was detected on the 10th day of development in germ cell-rich preparations. On subsequent days, an increasingly intense heterodimer band was detected, which, by the 13th day, was approximately twice as intense as the corresponding homodimer bands. Consideration of (i) the G6PD activity per germ cell and per somatic cell and (ii) the percentage of germ cells in the germ cell-rich preparations indicated that a heterodimer band should have been visible on the 10th day had both X chromosomes been active. Cytological examinations showed that the earliest germ cells enter meiotic prophase on the eleventh day. These results demonstrate that oogonia have a single active X chromosome and that the inactive X chromosome is reactivated at or, more likely, shortly before entry into meiotic prophase.
Genes in mice that affect susceptibility to cortisone-induced cleft palate are closely linked to Ir genes on chromosomes 2 and 17.
Authors: Gasser D L , Mele L , Lees D D , Goldman A S
Published: May 2006

Inbred and congeneic strains of mice have been examined for susceptibility to cortisone-induced cleft palate, and the role of genes linked to H-2 on chromosome 17 has been confirmed. Increasing degrees of susceptibility were associated with the H-2d, H-2b, H-2k, and H-2a haplotypes, respectively, with H-2q and H-2s also being associated with fairly high levels of susceptibility. Evidence was obtained that suggests that one gene maps within the B region of H-2, and that a second H-2 linked gene which acts by complementation maps to the right of E. Another gene affecting this trait is closely linked to the H-3 and Ir-2 loci on the second chromosome.
Acetylcholine-induced cation translocation across cell membranes and inactivation of the acetylcholine receptor: chemical kinetic measurements in the millisecond time region.
Authors: Cash D J , Aoshima H , Hess G P
Published: May 2006

Acetylcholine-induced flux of inorganic ions across membranes and inactivation of the acetylcholine receptor were measured at pH 7.0, 1 degrees C, over a 5000-fold concentration range of acetylcholine. Receptor-containing electroplax membrane vesicles prepared from Electrophorus electricus and a quench-flow technique were used, allowing flux to be measured in the 2-msec to 1-min time region. Five different measurements were made: (i) rate of ion translocation with the active state of the receptor, (ii) rate of the slower ion translocation after equilibration of active and inactive receptor states, (iii) rate of inactivation, (iv) equilibrium between active and inactive forms of the receptor, and (v) reactivation of inactivated receptor. The kinetics of the steps in the receptor-controlled ion flux follow single-exponential rate laws, and simple analytical expressions for their ligand concentration dependence can be used. Thus, the rate and equilibrium constants in a scheme that relates the ligand binding steps to ion translocation could be evaluated. It was found that the dependence of the receptor-controlled ion translocation over the concentration range investigated obeys the integrated rate equation based on the proposed mechanism. The flux rate before inactivation was approximately 10(7) ions sec-1 per receptor, which is comparable with that measured electrophysiologically in muscle cells. The half-time of inactivation is approximately 100 msec when the receptor is saturated with acetylcholine. The specific reaction rate of the ion translocation (J) is 3 X 10(7) M-1 sec-1. The results support a minimum reaction mechanism previously proposed on the basis of experiments in which carbamylcholine was used.
Complete nucleotide sequence of minicircle kinetoplast DNA from Trypanosoma equiperdum.
Authors: Barrois M , Riou G , Galibert F
Published: May 2006

The kinetoplast DNA of Trypanosoma equiperdum is composed of about 3000 supercoiled minicircles of 1000 base pairs and about 50 supercoiled maxicircles of 23,000 base pairs topologically interlocked so as to form a compact network. Minicircles of T. equiperdum, which are homogeneous in base sequence, were purified by equilibrium CsCl centrifugation and used as starting material for DNA sequence analysis. One minicircle is composed of 1012 base pairs and has an adenine.thymine base pair content of 72.8%. The termination codons are uniformly distributed along the molecule and restrict the coding potentiality of the molecule to oligopeptides of about 20 amino acids. The molecule contains three dyad symmetries and a sequence of 12 nucleotides is repeated six times. We also noted the presence of a region of about 130 base pairs that is almost perfectly homologous with that of the minicircles from the closely related species T. brucei.
Heat shock proteins of higher plants
Authors: Key Joe L. , Lin C. Y. , Chen Y. M.
Published: May 2006

The pattern of protein synthesis changes rapidly and dramatically when the growth temperature of soybean seedling tissue is increased from 28°C (normal) to about 40°C (heat shock). The synthesis of normal proteins is greatly decreased and a new set of proteins, “heat shock proteins,” is induced. The heat shock proteins of soybean consist of 10 new bands on one-dimensional NaDodSO
4
gels; a more complex pattern is observed on two-dimensional gels. When the tissue is returned to 28°C after 4 hr at 40°C, there is progressive decline in the synthesis of heat shock proteins and reappearance of a normal pattern of synthesis by 3 or 4 hr.
In vitro
translation of poly(A)
+
RNAs isolated from tissues grown at 28 and 40°C shows that the heat shock proteins are translated from a new set of mRNAs induced at 40°C; furthermore, the abundant class mRNAs for many of the normal proteins persist even though they are translated weakly (or not at all)
in vivo
at 40 or 42.5°C. The heat shock response in soybean appears similar to the much-studied heat shock phenomenon in
Drosophila
.
Comparison of poly(A)-mRNA prepared from membranes and free polyribosomes of mouse liver.
Authors: Clissold P M , Mason P J , Bishop J O
Published: May 2006

We have compared poly(A)-mRNA isolated from mouse liver endoplasmic reticulum (ER) membranes (ER mRNA) with that from free polyribosomes (free mRNA) by translation in a cell-free system and by mRNA--cDNA reassociation analysis. The partitioning of certain translation products between the two fractions suggests that the physical contamination of the free mRNA by the ER is 10%, and contamination of the ER by the free is 1%. Reassociation crossreactions suggest that no sequences are totally absent from either fraction. In particular, the rare sequences are shared between the two fractions. Among the more abundant sequences, we detect three groups: (i) a group of about 10 sequences that are relatively abundant in both fractions; (ii) a group that occurs mostly in the free fraction; (iii) a group of about 12 sequences, 6 or 7 of them encoding secretory polypeptides. The members of this group are largely or entirely confined to the ER fraction. Secretory proteins are almost entirely absent from the products of th free mRNA fraction. Quantitation of individual mRNA sequences by hybridization with cDNA clones shows that a range of sequence concentrations exists within the abundant class of ER mRNA.
Altered RNA/protein ratio associated with the induction of differentiation of Friend erythroleukemia cells.
Authors: Harel L , Blat C , Lacour F , Friend C
Published: May 2006

The synthesis and accumulation of RNA in Friend erythroleukemia (FL) cells induced to differentiate by treatment with the aminonucleoside of puromycin (AMS) or inhibited from differentiating by the addition of inosine to the medium were studied. When FL cells were grown in the presence of AMS, RNA synthesis was substantially inhibited. This effect could not be attributed solely to the inhibition of de novo purine synthesis because the biosynthesis of purine nucleotides from labeled inosine was much less depressed. The ratios of ATP to protein and of GTP to protein were slightly modified as compared to the untreated controls. However, the RNA/protein ratio was decreased. Thus, the RNA content of the cells was reduced 30-40%, but the protein content was not significantly affected. When the cells were treated with AMS together with inosine at a concentration that inhibits AMS-induced differentiation, the RNA/protein ratio was increased as compared with that found in cells treated with AMS alone and approached the level of the ratio in untreated control cells. Adenosine had a similar effect in overcoming the inhibition of RNA synthesis by AMS. Because the RNA/protein ratio of FL cells treated with dimethyl sulfoxide or sodium butyrate, two other potent inducers, was decreased by 44%, our results suggest that a correlation exists between the RNA content of the cells and the triggering of differentiation by inducers.
Role of basal lamina in neoplastic disorganization of tissue architecture.
Authors: Ingber D E , Madri J A , Jamieson J D
Published: May 2006

We have studied a transplantable carcinoma of the rat pancreas [Reddy, J. K. & Rao, M. S. (1977( Science 198, 78-80] that is composed of cytologically differentiated acinar cells that have lost their epithelial orientation and do not form acini. Light microscopy shows, however, consistent palisading, reorientation, and polarization of these cells in areas of contact with the vasculature. Electron microscopy reveals a normal basal lamina (BL) along the basal portions of repolarized tumor cells that is physically separate from the endothelial BL. We used indirect immunofluorescence to examine the distribution of BL constituents, laminin (Lm) and type IV collagen (type IV), within the different microenvironments of this tumor. In normal pancreas, Lm and type IV are distributed linearly, outlining acini and blood vessels. In the tumor parenchyma, type IV is not detected, whereas Lm appears in a punctate distribution outlining cells. Reorientation of tumor cells is observed only along linearly deposited Lm and type IV bordering vessels. These data indicate that this nonmetastatic tumor has lost the ability to produce or maintain a complete BL within its disorganized parenchyma, while its cells retain the capacity to produce and reorganize along liner BL when in contact with vascular adventitia. We suggest that failure to maintain a complete BL may be involved in the neoplastic disorganization of normal tissue architecture as well as in the breakdown of boundaries during the development of invasive carcinomata.
Ultraviolet light-induced labeling by noncompetitive blockers of the acetylcholine receptor from Torpedo marmorata.
Authors: Oswald R , Changeux J P
Published: May 2006

Reversible ligands were attached covalently to membrane-bound acetylcholine receptor from Torpedo marmorata by a method which is generally applicable and does not require the synthesis of specially designed molecules. UV irradiation of the receptor in the presence of [3H]trimethisoquin, [3H]phencyclidine, or [3H]perhydrohistrionicotoxin resulted in the labeling of the binding site(s) for these noncompetitive blockers of the permeability response. The labeling of the delta chain was enhanced by carbamoylcholine, and this increase was blocked by snake alpha-toxins. The effect of carbamoylcholine on [3H]trimethisoquin binding was more pronounced than with the other two noncompetitive blockers; in all instances, the labeling was abolished by unlabeled histrionicotoxin. These three compounds therefore interact with the high-affinity site for noncompetitive blockers. Incorporation of radioactivity also occurred into the alpha chain but either was insensitive to cholinergic effectors or decreased in the presence of carbamoylcholine (or snake alpha-toxin), probably as a result of an interaction with the acetylcholine-binding site. In contrast to the other noncompetitive blockers tested, [3H]chlorpromazine heavily labeled the four receptor polypeptides (alpha, beta, gamma, delta), and this labeling also was enhanced by carbamoylcholine and decreased by histrionicotoxin. These data indicate a contribution of the delta chain to the binding site(s) of several well-characterized noncompetitive blockers and suggest that other receptor polypeptides may also contribute to this binding.
Rapid recovery of function after partial denervation of the rat pineal gland suggests a novel mechanism for neural plasticity.
Authors: Zigmond R E , Baldwin C , Bowers C W
Published: May 2006

The activity of serotonin N-acetyltransferase (NATase) in the rat pineal gland exhibits a large (approximately 100-fold) circadian variation, with peak activity occurring in the dark part of the light/dark cycle. Surgical removal of both superior cervical ganglia abolishes this rhythm in enzyme activity. Unilateral ganglionectomy caused a 75% decrease in NATase activity during the dark period immediately following the operation; however, by the subsequent dark period (32 hr after operation) the rhythm in NATase activity had returned to normal. Similar results were found after the internal carotid nerve was cut, and data are presented indicating that this is the postganglionic trunk by which sympathetic neurons reach the pineal gland. Denervation of one superior cervical ganglion (unilateral "decentralization") also produced a 75% decrease in NATase activity during the dark period immediately following the operation; however, after decentralization, enzyme activity did not return to normal in subsequent cycles. It is hypothesized that this recovery is due to loss of norepinephrine uptake sites in the degenerating sympathetic nerve terminals. As a result of decreased norepinephrine uptake, the effectiveness of the norepinephrine released by surviving neurons may be enhanced. This hypothesis is supported by experiments in which pharmacological blockade of norepinephrine uptake in unilaterally decentralized animals increased NATase activity to control levels. We propose that neural systems which use transmitter uptake as the mechanism of transmitter inactivation have a built-in "reserve stimulatory capacity."
Recombinant bacteriophages containing the integrated transforming provirus of Gardner--Arnstein feline sarcoma virus.
Authors: Fedele L A , Even J , Garon C F , Donner L , Sherr C J
Published: May 2006

The integrated DNA provirus of the Gardner-Arnstein (GA) strain of feline sarcoma virus (FeSV) was molecularly cloned in a bacteriophage lambda vector. The cloned DNA fragment is 14.4 kilobase pairs long and contains a 6.7-kilobase provirus flanked by cellular sequences derived from nonproductively transformed mink cells. Transfection of mouse NIH/3T3 cells with the cloned DNA fragment induced foci of transformation at efficiencies of 10(4) focus-forming units/pmol of sarcoma virus DNA. Restriction endonuclease mapping and heteroduplex analyses were used to compare the GA-FeSV provirus with that of Snyder-Theilen (ST)-FeSV, a second strain that contains homologous transformation-specific sequences (v-fes). Both viruses have the general structure 5'-gag-fes-env-c region-3', each having retained portions of the feline leukemia virus (FeLV) gag and env genes. In addition to segments shared by the two sarcoma viruses, GA-FeSV contains 1.7 kilobases of extra sequences not found in ST-FeSV. Of these, at least 400-500 base pairs located near the 5' end of v-fes encode a portion of the GA-FeSV polyprotein; the remaining 1.2 kilobases are derived from the FeLV env gene but do not appear to encode any detectable product related to the FeLV envelope glycoprotein. The close homology of the v-fes sequences shows that GA- and ST-FeSV were formed by recombination of FeLV with similar portions of a cat cellular gene (c-fes).
Transposon Tn3 encodes a site-specific recombination system: identification of essential sequences, genes, and actual site of recombination.
Authors: Kostriken R , Morita C , Heffron F
Published: May 2006

The bacterial transposon Tn3 encodes a site-specific recombination system. The recombination requires the product of tnpR, a gene previously identified as a repressor of the transposase. This recombination is site specific and takes place somewhere within the sequence C-G-A-A-A-T-A-T-T-A-T-A-A-A-T-T-A-T-C but requires at least one additional sequence outside this. The phenotype of mutations in this recombination system suggests that transposition proceeds by a mechanism in which cointegrates are intermediates.
Purification of guinea pig pH 3 migration inhibitory factor.
Authors: Remold H G , McCarthy P L , Mednis A D
Published: May 2006

Macrophage migration inhibitory factor (MIF) from the guinea pig was recently shown to reside in two discrete and separable proteins referred to as pH 3 MIF and pH 5 MIF. One subfraction of pH 3 MIF has now been purified to apparent homogeneity from supernatants of stimulated lymph node cells. To monitor purification, biosynthetically radiolabeled MIF was prepared. Sensitized lymphocytes were stimulated in the presence of [3H]leucine by concanavalin A to produce radiolabeled mediators. MIF was purified approximately 30,000-fold from the culture fluid by using gel filtration, sucrose density gradient electrophoresis, isoelectric focusing, and hydrophobic affinity chromatography. This procedure yielded a single 3H-labeled polypeptide with an apparent Mr of 35,000 that coincides with MIF activity.
Interaction of influenza virus hemagglutinin with target membrane lipids is a key step in virus-induced hemolysis and fusion at pH 5.2.
Authors: Maeda T , Kawasaki K , Ohnishi S
Published: May 2006

The molecular mechanism of hemolysis and fusion by influenza virus in acidic media was studied. First, the effect of trypsin treatment on the activity of fibroblast-grown influenza virus was studied. The results showed that the split form of viral hemagglutinin, HA1 and HA2, but not the precursor, is responsible for the activity. Second, the interaction of egg-grown influenza virus, which contains the split hemagglutinin, with lipid liposomes was studied by spin labeling and electron microscopy. Phospholipid transfer from the viral envelope to the lipid bilayer membrane occurred within 30 s at pH 4.5-5.4. The transfer is largely independent of the lipid composition and the crystalline vs. liquid/crystalline state of the membrane. Virus-induced lysis of liposomes also took place rapidly in the same pH range. Envelope fusion with liposomes occurred at pH 5.2 but not at pH 7.0. These characteristic interactions were similar to those between influenza virus and erythrocytes reported previously. On the other hand, hemagglutinating virus of Japan did not interact with liposomes at neutral pH. These results suggest that protonation of the NH2-terminal segment of the HA2 form causes interaction of the segment with the lipid core of the target cell membrane, leading to hemolysis and fusion.
Revertant seedlings from crown gall tumors retain a portion of the bacterial Ti plasmid DNA sequences
Authors: Yang Funmei , Simpson Robert B.
Published: May 2006

BT37 is a crown gall teratoma incited on tobacco by
Agrobacterium tumefaciens
containing pTi-T37, a nopaline-type Ti plasmid. Treatment of this cloned tumor tissue with kinetin at 1 mg/liter results in the formation of relatively normal-appearing shoots. These shoots can be induced to root and set viable seed. In contrast to BT37 tissue, the derived tissues are not phytohormone independent and do not produce nopaline. The reverted plants, like normal tobacco plants, are susceptible to infection by
A. tumefaciens
. This loss of tumorous traits is accompanied by the loss of most of the Ti plasmid sequences (T-DNA) found in BT37 DNA. Southern blot analysis indicates that the revertant tissues have lost the central portion of the T-DNA, which contains the “common DNA” sequences, a highly conserved region of the Ti plasmid that has been found to be incorporated into all tumors studied. Thus, these sequences appear necessary for oncogenicity and tumor maintenance and their loss is probably directly related to tumor reversal. The reverted plants as well as the plants obtained from seed, however, do retain sequences homologous to the ends of the T-DNA present in the parental teratoma. The persistence of foreign DNA sequences during the process of meiosis and seed formation has important implications for the possibility of the genetic engineering of plants.
Absence of increase of histidine decarboxylase activity in mast cell-deficient W/W mouse embryos before parturition.
Authors: Watanabe T , Kitamura Y , Maeyama K , Go S , Yamatodani A , Wada H
Published: May 2006

The histidine decarboxylase (L-histidine carboxylase, EC 4.1.1.22) activity of whole W/W mouse embryos, which are devoid of mast cells, remained very low and did not show the rapid increase before birth (17-20 days of gestation) seen in wild-type +/+ embryos. During the same period, the histamine content also remained very low and no mast cells were detected in the W/W embryos, in the contrast to the large increase in both histamine content and number of mast cells in wild-type embryos. These findings imply that the histamine in embryos is largely derived from mast cells. In +/+ mice, histidine decarboxylase activity decreased rapidly soon after birth without concomitant decrease in histamine content or number of mast cells, suggesting that the enzyme activity in mast cells is regulated by some unknown mechanism.
Sequences of the ssb gene and protein.
Authors: Sancar A , Williams K R , Chase J W , Rupp W D
Published: May 2006

We have determined the sequences of the ssb gene and protein of Escherichia coli. The coding region of ssb is 534 base pairs and is preceeded and followed by dyad symmetries of 39 base pairs and 27 base pairs, respectively. The promoter for ssb is close to that for uvrA and these two genes are transcribed in opposite directions: ssb clockwise and uvrA counterclockwise on the standard E. coli genetic map. The DNA helix-destabilizing protein encoded by the ssb gene (single-strand binding protein) contains 177 amino acids and has a calculated molecular weight of 18,873. Although there is no extensive sequence homology among the three helix-destabilizing proteins whose sequences are now known, both the E. coli and bacteriophage T4 DNA helix-destabilizing proteins do contain an acidic, alpha-helical region at their carboxy termini that may be functionally homologous. The remainder of the E. coli helix-destabilizing protein can be divided into two apparent domains on the basis of its amino acid sequence. The amino-terminal region (residues 1-105) contains 79% of the charged residues (27 out of 34 total) in the protein and is predicted to have a high degree of secondary structure (alpha helix and beta pleated sheet). In contrast, the region including residues 106-165 contains only two charged amino acids and is devoid of alpha helix or beta pleated sheet.
Tumor-promoting phorbol esters stimulate myelopoiesis and suppress erythropoiesis in cultures of mouse bone marrow cells.
Authors: Sieber F , Stuart R K , Spivak J L
Published: May 2006

Tumor-promoting phorbol esters affect the ability of mouse hematopoietic progenitor cells to form morphologically recognizable colonies in culture. They induce myeloid progenitor cells to form colonies of the monocyte/macrophage type in the absence of exogenous granulocyte/macrophage colony-stimulating factor. Conversely, similar concentrations of tumor-promoting phorbol esters inhibit the formation of colonies (bursts) by early erythroid progenitor cells, even when the culture medium contains saturating amounts of burst-promoting activity and erythropoietin. However, late erythroid progenitor cells, are not affected by phorbol esters. Only a temporary (45 min) exposure of marrow cells to phorbol esters is necessary to produce both stimulation of myeloid colony growth and inhibition of erythroid burst formation. Experiments with a radioactively labeled phorbol ester indicate a high affinity for cellular binding sites. The ability of various phorbol esters to stimulate myeloid colony growth and to inhibit erythroid burst formation correlates well with their ability to promote skin tumors in mice. The different responses of two developmentally closely related hematopoietic progenitor cells to the same phorbol esters indicate the usefulness of these substances in the further analysis of regulatory events affecting hematopoiesis.
Indirect induction of mutagenesis of intact parvovirus H-1 in mammalian cells treated with UV light or with UV-irradiated H-1 or simian virus 40.
Authors: Cornelis J J , Su Z Z , Ward D C , Rommelaere J
Published: May 2006

The frequency of mutants among the descendants of intact parvovirus H-1 was increased when cells of human and rat origin were exposed to UV light prior to infection. An enhanced mutagenesis of intact H-1 could be induced to almost the same extent in unirradiated cells by preinfecting them with H-1 or simian virus 40 that had been irradiated with UV light. The expression of an enhanced mutagenesis of unirradiated H-1 after cell treatment with UV light or UV-irradiated virus was delayed, transient, and dose-dependent, and it was dependent on de novo protein synthesis.
Involvement of small-field horizontal cells in feedback effects on green cones of turtle retina.
Authors: Neyton J , Piccolino M , Gerschenfeld H M
Published: May 2006

Light stimuli depolarize green cones of turtle retina through a circuit involving a feedback connection from luminosity horizontal cells (L-HC) to green cones. In turtle retina two types of L-HC have been distinguished: large-field L-HC and small-field L-HC. The spatial properties of the feedback depolarizations of green cones were compared with those of both large- and small-field L-HC. Green cones were found to be more effectively depolarized by relatively small spots of red light than by large red annuli. Moreover, red light stimulation of the periphery of the receptive field could reduce the depolarizing influence of central red stimuli. These spatial properties greatly differ from those of the large-field L-HC, whereas they strongly resemble those of the small-field L-HC. These results suggest that the small-field L-HC mediate the feedback action on green cones.
ATP hydrolysis-dependent protease activity of the lon (capR) protein of Escherichia coli K-12.
Authors: Charette M F , Henderson G W , Markovitz A
Published: May 2006

Mutations in the lon (capR) gene result in multiple phenotypes, one of which is the failure to degrade abnormal and normal proteins (Deg-). Previous work with partially purified preparations showed that the lon (capR) gene product is a 94,000-dalton polypeptide with an affinity for nucleic acids. The lon (capR) protein has now been highly purified and is demonstrated to have an ATP-dependent protease activity. The enzyme hydrolyzed 3H-labeled alpha-casein into trichloroacetic acid-soluble forms in Tris buffer containing Mg2+ and ATP. The reaction has a pH optimum of 8.5 and ATP was the preferred nucleotide. CTP and UTP could substitute for ATP (75% and 67%, respectively) but GTP, ADP, AMP, cyclic AMP, and PPi could not. Proteolysis by the lon (capR) protein required ATP hydrolysis. Nonhydrolyzable analogs of ATP and CTP did not promote casein cleavage. When low concentrations of ATP were used, proteolysis stopped as the ATP pool was depleted. Casein stimulated lon (capR) ATPase activity, and the products were ADP and inorganic phosphate in equimolar amounts. No protein kinase activity was detected. The DNA-binding activity, present in partially pure preparations, was retained in the purified protein. The gene product purified from a lon nonsense mutant that exhibits the Deg- phenotype (capR9), lacked both the ATP-dependent protease and ATPase activities, though it retained DNA-binding activity. Absence of an ATP-dependent protease activity could account for many of the pleiotropic effects observed in lon mutants.
Intracellular hormone receptors: evidence for insulin and lactogen receptors in a unique vesicle sedimenting in lysosome fractions of rat liver.
Authors: Khan M N , Posner B I , Verma A K , Khan R J , Bergeron J J
Published: May 2006

Previous studies have established the presence of polypeptide hormone receptors in Golgi fractions from rodent liver. In this study we attempted to identify peptide hormone receptors in other intracellular elements, particularly lysosomes. Tritosomes were prepared by a standard procedure, and highly purified secondary lysosomes were prepared by fractionating the L fraction of rat liver in a discontinuous metrizamide gradient into subfractions L1 to L4. Binding of 125I-labeled insulin and 125I-labeled somatotropin was studied with membranes prepared from osmotically shocked fractions. The L2 and L3 fractions, virtually devoid of galactosyltransferase (UDP galactose:2-acetamido-2-deoxy-D-glucosylglycopeptide galactosyltransferase, EC 2.4.1.38) but highly enriched in acid phosphatase [orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2], appeared as classical secondary lysosomes by electron microscopy. When compared with Golgi fractions, the level of specific binding per 50 micrograms of protein of 125I-labeled somatotropin in L2 and L3 was 1/3, whereas that of 125I-labeled insulin was comparable. L1, which was reduced in acid phosphatase and increased in galactosyltransferase activities, showed higher hormone binding than did L2 and L3. This was not attributable to Golgi fraction contamination, as evident by specific binding/galactosyltransferase ratios. Binding to tritosome membranes could be largely accounted for by variable contamination with Golgi fractions as judged by specific binding/galactosyltransferase ratios. To clarify the distribution of receptor sites in lysosomal preparations, we fractionated the entire L fraction on a continuous Percoll gradient. Acid phosphatase and galactosyltransferase activities were segregated to the high and low density ranges of the gradient, respectively; however, the fractions enriched in hormone binding were of intermediate density, distinct from Golgi and lysosomal biochemical markers. We conclude that intracellular receptors are found not only in galactosyltransferase-containing very low density lipoprotein-marked Golgi vesicles but also in a unique vesicle of intermediate density between classical Golgi and lysosomal structures.
Electrophoresis of enzyme--monoclonal antibody complexes: studies of human placental alkaline phosphatase polymorphism.
Authors: Gogolin K J , Slaughter C A , Harris H
Published: May 2006

Enzyme--monoclonal antibody complexes formed between six different monoclonal antibodies and the six phenotypes of human placental alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] that represent the homozygous and heterozygous combinations of the three common alleles have been examined by electrophoresis in starch, acrylamide, and agarose gels. Since the complexes formed retain full enzyme activity, they could be detected after gel electrophoresis by an enzyme stain. Distinctive electrophoretic patterns were obtained with each monoclonal antibody. Differential binding of certain of the antibodies with the products of different alleles produces clear discrimination of various homozygous and heterozygous phenotypes. This discrimination parallels the results previously obtained by using a quantitative binding radioimmunoassay. The results show that this general method should prove useful in screening hybridoma fluids for the presence of monoclonal antibodies to specific enzymes; in the detection of allelic variation, even where this is not expressed by electrophoretic differences among the uncomplexed enzymes; and in discriminating between homozygotes and heterozygotes. It could also prove to be a useful tool in the elucidation of the molecular structures of enzyme--monoclonal antibody complexes.
Conversion of soluble immune response suppressor to macrophage-derived suppressor factor by peroxide.
Authors: Aune T M , Pierce C W
Published: May 2006

After incubation with soluble immune response suppressor (SIRS), a product of concanavalin A-activated Ly2+ T cells, macrophages release a factor that suppresses in vitro antibody responses, DNA synthetic responses to T-cell and B-cell mitogens, and division of several tumor cell lines. This factor, macrophage-derived suppressor factor (M phi-SF), is a protein with an apparent Mr of 55,000 that is inactivated by sulfhydryl compounds, certain amines, and iodide but not by other halides. In experiments reported here, conventional SIRS and SIRS produced by a cloned T-cell hybridoma were used to analyze formation of M phi-SF by SIRS-treated macrophages. Formation of M phi-SF was insensitive to inhibitors of protein and prostaglandin synthesis but was sensitive to catalase and cyanide, indicating that M phi-SF was not a newly synthesized product and that peroxide was important to its formation. As M phi-SF and SIRS have similar molecular weights and other properties, it is possible that M phi-SF is SIRS modified by peroxide. To test this possibility, SIRS was treated with H2O2 and M phi-SF activity was determined. H2O2 at 0.1-1 pM was sufficient to convert SIRS to M phi-SF; the reaction required approximately 15-20 min and was sensitive to cyanide. Several conventional peroxidase substrates inactivated M phi-SF produced by the SIRS-H2O2 reaction or by SIRS-treated macrophages. In addition, catalase and several of the compounds that directly inactivate M phi-SF also partially interfere with SIRS-mediated suppression of antibody responses. Collectively, these data suggest that SIRS-treated macrophages produce H2O2, which converts SIRS to M phi-SF, which has properties of an oxidized peroxidase-like protein and acts by oxidizing cellular components essential for cell division.
Lung endocrine-like cells in hamsters treated with diethylnitrosamine: alterations in vivo and in cell culture.
Authors: Linnoila R I , Nettesheim P , DiAugustine R P
Published: May 2006

Diethylnitrosamine is known to cause squamous cell carcinoma and adenocarcinoma of the lung in Syrian golden hamsters. Sections of lungs obtained from hamsters treated with the systemic carcinogen diethylnitrosamine showed a significant increase in the number of argyrophilic cells of neuroepithelial bodies. The hyperplastic response was retained at least 4 weeks after cessation of treatment. To examine whether these affected cells exhibited enhanced survival in vitro, lung cells were dissociated with Pronase and grown in culture. After 7 days, argyrophilia, dense-cored vesicles, and corticotropin-like immunoreactivity were observed in many of the cells derived from hamsters treated for 5 or 8 weeks. These findings suggest that the endocrine-like cells of neuroepithelial bodies are affected by diethylnitrosamine as evidenced by a numerical increase in vivo and by the properties exhibited by cells in vitro. The relationship of this diethylnitrosamine-induced reaction to bronchial carcinoid tumors or small-cell carcinoma of the lung remains to be established.