bluuebunny/crossref_metadata_2025 huggingface dataset:
Mepacrine blocks beta-adrenergic agonist-induced desensitization in astrocytoma cells.
Authors: Mallorga P , Tallman J F , Henneberry R C , Hirata F , Strittmatter W T , Axelrod J
Published: May 2006

C6 astrocytoma cells contain beta-adrenergic receptors coupled to adenylate cyclase. A 2-hr exposure to l-isoproterenol results in an 80% decrease in cyclic AMP production in response to a subsequent challenge by l-isoproterenol (desensitization). This loss in responsiveness is paralleled by a 20-30% decrease in the apparent number of beta-adrenergic receptors and by increased release of arachidonic aciid into the medium. The increased release of arachidonic acid is caused by the action of phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) and corresponds to increased turnover of methylated phospholipids. Mepacrine and tetracaine, both inhibitors of this phospholipase A2, are able to block l-isoproterenol-induced desensitization of cyclic AMP production and the decrease in beta-adrenergic receptors. Mellitin and phorbol ester, two activators of phospholipase A2, when preincubated with the cells cause a decreased cyclic AMP response of the cells to l-isoproterenol. These results suggest that the activation of phospholipase A2 in the local domain of the beta-adrenergic receptor may be involved in desensitization.
ATP-dependent conjugation of reticulocyte proteins with the polypeptide required for protein degradation.
Authors: Ciechanover A , Heller H , Elias S , Haas A L , Hershko A
Published: May 2006

The heat-stable polypeptide (APF-1) required for ATP-dependent proteolysis in reticulocytes enters into high molecular weight conjugates upon incubation with the fraction of reticulocytes that is retained by DEAE-cellulose. Conjugate formation requires ATP and Mg2+ and its inhibited by N-ethylmaleimide. UTP and GTP are inactive. These properties are identical to those of ATP-dependent protein breakdown in the same system, suggesting that the conjugates are intermediates in this process. The APF-1 conjugates are stable in sodium dodecyl sulfate/polyacrylamide gel electrophoresis and Sephadex G-75 isolation and are resistant to mild acid, alkali, heat denaturation, and reduction; the conjugates are therefore covalent.
Evidence for four different polymerization sites involved in human fibrin formation.
Authors: Olexa S A , Budzynski A Z
Published: May 2006

The mechanism of association and the organization of human fibrin were studied by using affinity chromatography. Insolubilized fibrinogen, fibrin monomer, and crosslinked fibrin were used to localize the binding sites on fibrinogen and fibrin derivatives. Four different polymerization sites have been distinguished. A binding site ("a"), available without thrombin action, is present on the fibrinogen fragment D domain. The complementary ("A") is inoperative in fibrinogen and requires thrombin for activation; it is located on the fibrinogen NH2-terminal domain. A third polymerization site ("b") appears to be formed by the alignment of the fragment D domains on two fibrin monomer molecules upon polymerization; this site functions without thrombin mediation and the alignment is stabilized by the Factor XIIIa-catalyzed crosslink bonds. The "b" site is complementary to another thrombin-activated site ("B") on the fibrinogen NH2-terminal domain. The two thrombin activable sites, "A" and "B", are distinguishable, although they are located in the same fibrinogen domain.
Classification of cultured mammalian cells by shape analysis and pattern recognition.
Authors: Olson A C , Larson N M , Heckman C A
Published: May 2006

We have developed a method for classifying cultured cells on the basis of shape characteristics. High-resolution optical information on three-dimensional shape was obtained by anodic oxide interferometry. Each interference order formed in a cell was considered as a closed figure; measurement of 37 mathematical descriptors was carried out for each figure. The individual cells were classified according to the values of their descriptors. We used standard principles of pattern recognition, such as hierarchical cluster analysis and nearest neighbor analysis, as a basis for ordering the cells into groups. Alternatively, linear discriminant functions could be used, but they provided only a slight improvement in correct classification of the cells. We anticipate that the method will be appropriate for classification of cultured cell lines and for determination of the magnitude and direction of cell shape changes implicated in various biological processes.
Noradrenergic alpha 1 and alpha 2 receptors: light microscopic autoradiographic localization.
Authors: Young W S , Kuhar M J
Published: May 2006

[3H]WB-4101 and p-[3H]aminoclonidine were used for light microscopic autoradiographic localization of alpha 1 and alpha 2 adrenergic receptors, respectively, in the rat brain. The binding of these ligands to slide-mounted tissue sections had all of the characteristics associated with alpha 1 and alpha 2 receptors. It was saturable with appropriate kinetic constants and was blocked only by other alpha-adrenergic drugs with the appropriate potency. Autoradiographic studies revealed a distribution of alpha-adrenergic receptors throughout the nervous system. Certain areas had elevated levels. These included parts of the olfactory bulb and nucleus, parts of the cerebral cortex and dentate gyrus, the more medial portions of the hypothalamus and thalamus, the locus ceruleus and nucleus tractus solitarii, and parts of the spinal cord. In certain areas, the distribution of alpha 1 and alpha 2 receptors was markedly different. These results provide some rational basis for the observed actions of alpha-adrenergic drugs on the central nervous system. For example, the finding of high densities of alpha 2 receptors in the nucleus tractus solitarii is most likely related to its antihypertensive action. The observed codistribution of alpha 2 receptors with opiate receptors would provide an explanation of the observation that alpha 2 agonists block opiate withdrawal. The results are also discussed in relationship to the anatomy of catecholamine systems in the brain.
Deoxyribonucleotide pools, base pairing, and sequence configuration affecting bromodeoxyuridine- and 2-aminopurine-induced mutagenesis.
Authors: Hopkins R L , Goodman M F
Published: May 2006

Despite recent experiments showing that BrdUrd-induced mutagenesis can be independent of the level of bromouracil (BrUra) substitution [Kaufman, E.R. & Davidson, R.L. (1978) Proc. Natl. Acad. Sci. USA 75, 4982-4986; Aebersold, P.M. (1976) Mutat. Res. 36, 357-362], BrUra.G base mispairs are a major determinant of mutagenesis. We propose that the experiments cited above are sensitive predominantly to G . C leads to A . T transitions driven by the immeasurably small but highly mutagenic substitution of BrUra for cytosine and not by the gross substitution of BrUra for thymine in DNA. More generally, we show how accumulated evidence suggests that both BrdUrd and 2-aminopurine have two mutagenic effects intracellularly: perturbation of normal deoxyribonucleoside triphosphate pools and analogue mispairs in DNA. We propose a molecular basis for various observations of normal exogenous deoxyribonucleosides as synergists and counteragents to base analogue mutagenesis. A model is proposed to explain the antipolarity of BrdUrd and 2-aminopurine mutagenesis--i.e., why mutants at hot spots for induction by one base analogue are usually hot spots for reversion by the other. It is concluded that the configuration of the neighboring nucleotides surrounding the base analogue mispair, and not the base analogue's preference for inducing A . T leads to G . C or G . C leads to A . T errors, is responsible for the antipolarity of BrdUrd and 2-aminopurine mutagenesis.
Roles of chromophore and apo-protein in neocarzinostatin action.
Authors: Kappen L S , Napier M A , Goldberg I H
Published: May 2006

The methanol-extractable, nonprotein chromophore of the antitumor, protein antibiotic neocarzinostatin (NCS) has at least the full activity of the parent compound in inhibiting DNA synthesis and growth of HeLa cells and in causing DNA strand breaks in vivo and in vitro. In vitro DNA strand scission by the chromophore is markedly stimulated by 2-mercaptoethanol and is inhibited by guanidine hydrochloride and alpha-tocopherol. By high-pressure liquid chromatography, this activity has been localized to fractions eluting at greater than 90% methanol and having fluorescence emission at 420 nm (excitation at 340 nm). The apo-protein of NCS is inactive by itself but complexes with the chromophore so as to regulate its availability during the in vitro reaction. In DNA strand scission the chromophore acts rapidly at both 0 and 37 degrees C, whereas native and reconstituted NCS are inactive at 0 degrees C and slowly active at 37 degrees C. Complex formation with apo-NCS stabilizes the chromophore. Reconstitution of NCS (pI 3.3) from chromophore and apo-protein (pI 3.2) was shown by both activity studies and isoelectric focusing on polyacrylamide gels. "Pre-NCS," the biosynthetic precursor of NCS, is identical to apo-NCS in amino acid composition, spectral properties, isoelectric focusing on polyacryl-amide gels, and ability to complex with isolated chromophore to form material with all the properties of native NCS.
Control of membrane permeability by external and internal ATP in 3T6 cells grown in serum-free medium.
Authors: Dicker P , Heppel L A , Rozengurt E
Published: May 2006

Cultures of 3T6 cells were plated in serum-free medium and grown in the presence of insulin (1 microgram/ml) and epidermal growth factor (0.5 ng/ml). External ATP (250 microM) applied to such cultures caused a rapid efflux of acid-soluble pools labeled with [3H]uridine, 2-deoxy[3H]glucose, or 86Rb+ and allowed the entry of p-nitrophenylphosphate. This increase in passive membrane permeability depended on ATP concentration, pH, and time of ATP contact with the cells, and it was not produced by GTP, UTP, or Pi. In the presence of compounds that decrease intracellular ATP, low concentrations of external ATP (40 microM) caused a massive synergistic stimulation of efflux. The efflux of acid-soluble pools was stopped (sealing) by bringing the cultures of 3T6 cells to neutral pH in the presence of Ca2+ and Mg2+. Exposure of 3T6 cells grown in serum-free medium to [gamma-32P]ATP under the conditions of permeabilization led to the selective labeling of a membrane protein with a molecular weight of 44,000 as revealed by NaDodSO4 polyacrylamide gel electrophoresis and autoradiography. The results show that the control of membrane permeability by ATP is completely independent of serum-deprived proteins. Furthermore, the protein band (Mr, 44 x 10(3)) that shows selective labeling by [32P]ATP during permeabilization is not an adsorbed serum component.
Rapid duplication and loss of genes coding for the alpha chains of hemoglobin.
Authors: Zimmer E A , Martin S L , Beverley S M , Kan Y W , Wilson A C
Published: May 2006

Rapid cycles of gene duplication and loss appear to have been going on in the region coding for the alpha chain of adult hemoglobin. This is inferred from restriction endonuclease analysis of the alpha gene region in five species of apes, whose common ancestor lived about 10 million years ago. Because all five species resemble humans in having duplicate alpha genes, the duplicate state of this region is probably at least as old as the common ancestor of all these species. However, the alpha polypeptides within these species are about 10 times more alike than is expected for 10 million years of divergent evolution. Thus, the alpha polypeptides within each species have been evolving in concert. Changes in gene number have also taken place in the apes. Whereas the predominant number of alpha genes per chromosome is two for most species, it is three for chimpanzees. Concerted evolution appears also to have occurred, but far more slowly, in the region coding for the adult beta-like chains of hemoglobin. Consideration of the structural differences between the two regions leads to the hypothesis that the lengths of the noncoding regions are important determinants of the rates at which genes are gained and lost by intergenic recombination.
Phalloidin-induced cholestasis: a microfilament-mediated change in junctional complex permeability.
Authors: Elias E , Hruban Z , Wade J B , Boyer J L
Published: May 2006

Phalloidin, administered to male rats for 7 days (500 microgram per kg/day), increased the mean hepatic content of filamentous actin. Both bile flow and bile acid excretion diminished proportionally, whereas the bile-to-plasma ratios of [3H]inulin and [14C]sucrose increased significantly from 0.08 and 0.16 in controls to 0.37 and 0.69, respectively, in phalloidin-treated animals. Simultaneously, junctional permeability was altered as noted by the free penetration of ionic lanthanum into the zonula occludens and bile canaliculus. Freeze-fracture replicas of the junctional complex revealed rearrangements of the junctional elements and regions in which only a single element separated the canaliculus from the lateral intercellular space. These findings suggest that microfilaments influence the permeability of "tight junctions" between hepatocytes and that bile constituents might reflux from the canaliculus to the intercellular space in phalloidin-induced cholestasis.
Studies on mechanism of action of anti-tumor-promoting agents: their specificity in two-stage promotion.
Authors: Slaga T J , Klein-Szanto A J , Fischer S M , Weeks C E , Nelson K , Major S
Published: May 2006

The effects of fluocinolone acetonide (FA), retinoic acid (RA), and tosylphenylalanine chloromethyl ketone (TPCK) on two-stage promotion after 7,12-dimethylbenz[a]-anthracene (DMBA) initiation in female Sencar mice were investigated. The two-stage promotion protocol was achieved by twice weekly applications of 2 microgram of 12-O-tetradecanoylphorbol 13-acetate (TPA) for 2 weeks (stage I) followed by twice weekly applications of mezerein for 18 weeks (stage II). Separately stage I and II do not cause any tumors to develop after DMBA initiation. FA was found to be a potent inhibitor of stages I and II but to a greater degree for stage I than for stage II. RA was ineffective in stage I but was a potent inhibitor of stage II; TPCK specifically inhibited stage I but not stage II. FA and TPCK effectively counteract the appearance of the dark basal keratinocytes, whereas RA has no effect. These results provide additional evidence for the importance of dark basal keratinocytes in stage I of promotion and indicate that most of the other biochemical and morphological responses normally associated with promotion (such as polyamines) are actually associated with stage II of promotion.
Memory neuron: operating characteristics for the memory component of a neuroconnective brain model.
Authors: Wooldridge D E
Published: May 2006

In this paper an attempt is made to deduce the principal operating operating characteristics that a neuron would need in order to qualify as the basic memory component of a sensory memory system. The required characteristics are found to include the possession of many--perhaps more than 100--separately innervated "recording connections," in each of which the constituent synapses can be put in a persisting state of (inhibitory) effectiveness or of ineffectiveness depending on whether the input axon is inactive or is carrying spikes at the time a triggering "recording command" comes to the memory neuron. The synapses of the recording connections must also respond to an "erasing command" by assuming a common prerecording state unaffected by previous history. At other times a synapse-regeneration feature must operate, to counter any decay of effectiveness of connections that have been left by recording in an effective state as well as any acquisition of effectiveness by connections that have been left in an ineffective state.
Similarity and differences between conditions for initiation and failure of detonation
Authors: Eyring Henry , Walker Franklin E. , Ma Shao-mu , Coon Nancy
Published: May 2006

A theory is proposed to study the sensitivity of cylindrical explosives. Using the equations governing the conservation of mass, energy, and momentum, the equation of state, and Newtonian mechanics, we have derived the expression
D
=
D
o
e

-
a
2/
d

, in which the apparent length of the reaction zone,
a
, takes into account burned and unburned explosive and pressure release through the back and sides of the reaction zone.
D
is the detonation velocity and
d
is the diameter of the cylindrical charge. From the observed
D
(1/
d
) curves and critical energy values, we can interpret failure and other phenomena associated with detonation.
Evidence that insulin causes translocation of glucose transport activity to the plasma membrane from an intracellular storage site.
Authors: Suzuki K , Kono T
Published: May 2006

The glucose transport activity of fat cells was assayed in a cell-free system. The activity was solubilized and incorporated into egg-lecithin liposomes. The carrier-mediated glucose transport activity was estimated by subtracting the cytochalasin B-insensitive component from the total glucose uptake activity of the modified liposomes. When a crude microsomal preparation from fat cells was fractionated by sucrose density gradient centrifugation, two transport activities (peaks A and B) were separated. Peak A coincided with the peak of 5'-nucleotidase, a marker of the plasma membrane. Peak B appeared to coincide with the peak of UDPGal:N-acetylglucosamine galactosyltransferase, a marker of the Golgi apparatus. Peak A was considerably smaller than peak B under basal conditions. When cells were exposed to 1 nM insulin for 5 min before homogenization, the height of peak A increased whereas that of peak B decreased. Insulin had no significant effect on the galactosyltransferase activity. The Km values of glucose transport facilitated by the activities in peaks A and B were both approximately 10-15 mM. These results imply that insulin facilitates translocation of the transport activity from an intracellular storage site to the plasma membrane.
Agropine in “null-type” crown gall tumors: Evidence for generality of the opine concept
Authors: Guyon Pierre , Chilton Mary-Dell , Petit Annik , Tempé Jacques
Published: May 2006

Agrobacterium Ti (tumor-inducing) plasmids, the causative agents of crown gall disease, fall into four genetic groups based on the patterns of octopine and nopaline synthesis (by crown gall tumors) and catabolism (by
Agrobacterium tumefaciens
) for which they are responsible. Two classes of Ti plasmids induce tumors that synthesize neither octopine nor nopaline. The existence of these Ti plasmids challenged the view that opines such as octopine and nopaline play a central role in crown gall biology. We now report the occurrence of an opine in tumors induced by one of these classes of Ti plasmids, the “null-type” plasmids typified by pTi Bo542. The opine was purified by biological enrichment based on its utilization by bacteria containing pTi Bo542 but not by bacteria lacking a Ti plasmid. The mass spectrum and biological properties of this opine are identical to those of agropine, an opine recently discovered in octopine-type tumors. We propose that null-type Ti plasmids now be named for their signal opine, agropine-type Ti plasmids.
Recombination genes on the Escherichia coli sex factor specific for transposable elements.
Authors: Hopkins J D , Clements M B , Liang T Y , Isberg R R , Syvanen M
Published: May 2006

The Escherichia coli sex factor stimulates precise excision of transposons Tn5 and Tn10 from sites either within the bacterial chromosome or within the factor itself. We have isolated two kinds of mutations that affect this activity. The ferA mutations eliminate the stimulation; the ferB mutations enhance it in the presence of FerA+. We conclude that ferA defines a sex factor gene that stimulates precise excision. The ferB mutations also specifically increase the rate of recombination between two IS3 elements on F' lac-pro (F'128) in a reaction that requires the product of recA. The stimulation of this recombination by ferB also requires an active ferA gene, which implies that the ferA gene stimulates this reaction as well as precise excision. A ferA mutation was mapped at 84.2 kilobases on the F factor, and a ferB mutation was mapped at 82.5 kilobases. The fer mutants were obtained by an approach that permits the isolation of mutants affecting precise excision.
DNA-damaging agents stimulate gene expression at specific loci in Escherichia coli.
Authors: Kenyon C J , Walker G C
Published: May 2006

Operon fusions in Escherichia coli were obtained that showed increased beta-galactosidase expression in response to treatment with the DNA-damaging agent mitomycin C. These fusions were generated by using the Mud(ApR, lac) vector [Casadaban, M.J. & Cohen, S.N. (1979) Proc. Natl. Acad. Sci. USA 76, 4530-4533] to insert the lactose structural genes randomly into the bacterial chromosome. Induction of beta-galactosidase in these strains, which carried fusions of lac to these din (damage-inducible) loci, was (i) triggered by UV light as well as by mitomycin C and (ii) abolished by either a recA- or a lexA- mutation. Similar characteristics of induction were observed when the lactose genes were fused to a prophage lambda promoter by using Mud(ApR, lac). These results indicate that E. coli contains a set of genes that, like prophage lambda genes, are expressed in response to DNA-damaging agents and regulated by the recA and lexA gene products. These din genes map at five bacterial loci. One din::Mud(ApR, lac) insertion results in a UV-sensitive phenotype and may be within the uvrA transcriptional unit.
Methotrexate polyglutamate synthesis by cultured human breast cancer cells.
Authors: Schilsky R L , Bailey B D , Chabner B A
Published: May 2006

We studied the conversion of methotrexate to poly-gamma-glutamyl derivatives by cultured human breast cancer cells. After incubation with 2 micro M [3',5',9-3H]methotrexate, MCF-7 cells were washed free of extracellular drug and were boiled to lyse cells and to release drug bound to dihydrofolate reductase (tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3). The supernatant fraction was chromatographed on Sephadex G-15 to separate parent drug from polyglutamate forms. These cells rapidly and quantitatively converted methotrexate to polyglutamates, such that after 24 hr of incubation, 70 +/- (SEM) 3% of intracellular methotrexate existed as polyglutamates. Examination of that portion of intracellular methotrexate specifically bound to dihydrofolate reductase indicated that, with prolonged incubation, methotrexate polyglutamates become the predominant drug form bound to the enzyme. These studies demonstrate that methotrexate polyglutamates are readily formed in human tumor cells and bind to dihydrofolate reductase. Because these forms of the drug may be selectively retained within the cell, they may be important determinants of the duration of action and, ultimately, the cytotoxicity of methotrexate in human solid tumors.
Effect of cetiedil on erythrocyte sickling: new type of antisickling agent that may affect erythrocyte membranes.
Authors: Asakura T , Ohnishi S T , Adachi K , Ozguc M , Hashimoto K , Singer M , Russell M O , Schwartz E
Published: May 2006

The antisickling effect of cetiedil, alpha-cyclohexyl-3-thiopheneacetic acid 2-(hexahydro-1H-azepin-1-yl)-ethyl ester, has been investigated. The concentration of cetiedil required for 50% inhibition of erythrocyte sickling was about 140 micro M. An antisickling effect was achieved regardless of whether cetiedil was added before or after deoxygenation. The minimal gelling concentration of deoxy Hb S was increased by less than 10% in the presence of 218 micro M cetiedil. The oxygen equilibrium curves of Hb S were not significantly affected by cetiedil. Erythrocytes treated with high concentrations of cetiedil were swollen and became spheroidal. The antisickling effects of cetiedil might be due to an effect on erythrocyte membranes.
Genetically dominant resistance in mice to 3-methylcholanthrene-induced lymphoma.
Authors: Mayer A , Lilly F , Duran-Reynals M L
Published: May 2006

Mice of the RF/J strain are highly susceptible to induction of thymic lymphoma by skin painting with 3-methylcholanthrene (MCA), whereas mice of the 129/J and I/LnJ strains are resistant. Resistance was the dominant trait in F1 mice of crosses of RF with each resistant strain. Analysis of the lymphoma incidence in MCA-painted backcross populations indicated segregation of a single dominant gene for resistance in both crosses. None of these strains show inducibility of the aryl hydrocarbon hydroxylase enzyme system, a phenotype attributed to the dominant Ahb gene which is also known to influence susceptibility to MCA-induced lymphoma. The occurrence of the disease in these backcrosses was independent of the hosts' phenotype at either the H-2 or Fv-1 locus, both of which have shown an influence on susceptibility to murine leukemia virus-associated lymphoma in other experimental systems.
Characterization of the transforming gene of Fujinami sarcoma virus.
Authors: Hanafusa T , Wang L H , Anderson S M , Karess R E , Hayward W S , Hanafusa H
Published: May 2006

The src gene present in all avian sarcoma viruses is not present in the genome of Fujinami sarcoma virus, a potent sarcoma-inducing virus in chickens. Fujinami virus is defective and requires helper virus for replication. RNA from a mixture of helper and transforming viruses consists of two components, 35S and 28S. Oligonucleotide fingerprinting of each RNA component revealed that the 35S component was identical to the RNA of the helper virus. Thus, the genome of Fujinami virus must be the 28S RNA, which corresponds approximately to a molecular weight of 1.7 x 10(6) or 5300 nucleotides. Fujinami viral RNA shares several oligonucleotides with helper viral RNA at both 3' and 5' ends but contains a unique sequence of at least 3000 nucleotides in the middle of the genome. Fujinami viral RNA contains no src-specific oligonucleotides of the Rous sarcoma virus genome and did not hybridize with DNA complementary to the src sequences. The 60,000-dalton src protein of Rous sarcoma virus was undetectable in Fujinami virus-transformed cells. Instead, these transformed cells contain a protein of 140,000 daltons precipitable by antisera against virion proteins, which is likely to be the transforming protein of this virus.
Increased levels of multiplication-stimulating activity, an insulin-like growth factor, in fetal rat serum.
Authors: Moses A C , Nissley S P , Short P A , Rechler M M , White R M , Knight A B , Higa O Z
Published: May 2006

Multiplication-stimulating activity (MSA), purified from medium conditioned by the BRL-3A rat liver cell line, previously has been shown to be closely related to the human somatomedins or insulin-like growth factors. A radioimmunoassay was utilized to measure MSA levels in sera from fetal, maternal, and young rats. A serum somatomedin-binding protein was found to interfere in the radioimmunoassay by competing with antibody for binding 125I-labeled MSA. Therefore, prior to radioimmunoassay, sera were filtered on Sephadex G-75 in 1 M acetic acid to dissociate and separate somatomedin activity from the binding protein. Concentrations of MSA by radioimmunoassay were 20- to 100-fold higher in feta rat sera (1.8-4.4 micrograms/ml) than in maternal sera. MSA levels gradually decreased after birth, reaching maternal levels by day 25 of extrauterine life. MSA concentrations in feta rat sera also were found to be correspondingly high by a rat liver membrane radioreceptor assay and a competitive binding protein assay using rat serum somatomedin-binding protein. The findings of higher levels of MSA in fetal than in maternal rat sera and the gradual decline in MSA serum concentrations after birth are in direct contrast to total somatomedin activities measured by biosassay. Thus, MSA may function as a growth factor in the fetal rat whereas other somatomedins may play a role in stimulating growth during extrauterine life.
Collinearity-preserving functions between Desarguesian planes
Authors: Carter David S. , Vogt Andrew
Published: May 2006

Using concepts from valuation theory, we obtain a characterization of all collinearity-preserving functions from one affine or projective Desarguesian plane into another. The case in which the planes are projective and the range contains a quadrangle has been treated previously in the literature. Our results permit one or both planes to be affine and include cases in which the range contains a triangle but no quadrangle. A key theorem is that, with the exception of certain embeddings defined on planes of order 2 and 3, every collinearity-preserving function from one affine Desarguesian plane into another can be extended to a collinearity-preserving function between enveloping projective planes.
Anaerobic growth of halobacteria.
Authors: Hartmann R , Sickinger H D , Oesterhelt D
Published: May 2006

An energy-transducing pathway in halobacteria is described. Arginine mediates substrate level phosphorylation and allows the cells to grow anaerobically. Bacteriorhodopsin plus light can function as an alternative energy source under these conditions, provided the cells contain the pigment when transferred to the anaerobic environment. Therefore the selection of mutants functionally defective in ATP synthase or bacteriorhodopsin becomes possible.
DNA-dependent transcription of adenovirus genes in a soluble whole-cell extract.
Authors: Manley J L , Fire A , Cano A , Sharp P A , Gefter M L
Published: May 2006

We have developed a cell-free system for studying the synthesis of mRNA in mammalian cells. The system consists of a dialyzed and concentrated whole-cell extract derived from HeLa cells, small molecules and cofactors needed for transcription, and exogenously added DNA. Accurate transcription by RNA polymerase II is entirely dependent upon addition of promoter-containing eukaryotic DNA. At optimal DNA and extract concentrations, transcription initiation from the adenovirus serotype 2 late promoter is readily detectable, and specific transcripts over 4000 nucleotides in length are observed. The RNA synthesized in vitro contains the same 5' capped RNase T1 undecanucleotide as does the in vivo transcript. RNA synthesis also initiates accurately at both an early and an intermediate adenovirus promoter site.
Evidence for formation of a rabbit liver aldolase--rabbit liver fructose-1,6-bisphosphatase complex.
Authors: MacGregor J S , Singh V N , Davoust S , Melloni E , Pontremoli S , Horecker B L
Published: May 2006

The ability of rabbit liver aldolase (D-fructose-1,6-bisphosphate D-glyceraldehyde-3-phosphatate-lyase, EC 4.1.2.13) and rabbit liver fructose-1,6-bisphosphatase (Fru-P2ase; D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) to partition into the gel phase of Ultrogel AcA 34 is decreased in a mixture of the two enzymes. Titration experiments indicate that a 1:1 complex is formed. The value for the distribution coefficient of the complex corresponds to a molecular mass of 300,000 daltons, the value expected for a dimer containing one mole of each enzyme protein. Complex formation was not observed when either liver enzyme was replaced by the corresponding isozyme from rabbit muscle. The susceptibility of liver Fru-P2ase to limited proteolysis by subtilisin was reduced in the presence of liver aldolase, but not when the latter was replaced by muscle aldolase, suggesting that the conformation of Fru-P2ase is altered in the complex. Limited proteolysis of liver aldolase abolishes its ability both to form the heterodimer and to protect Fru-P2ase from modification by subtilisin.
Isolation and sequence of the gene for actin in Saccharomyces cerevisiae.
Authors: Ng R , Abelson J
Published: May 2006

The yeast Saccharomyces cerevisiae is known to contain the highly conserved and unbiquitous protein actin. We have used cloned actin sequences from Dictyostelium discoideum to identify and clone the actin gene in yeast. Hybridization to genomic fragments of yeast DNA suggest that there is a single actin gene in yeast. We have determined the nucleotide sequence of that gene and its flanking regions. The sequence of the gene reveals an intervening sequence of 309 base pairs in the coding sequences at the 5' end of the gene. The existence and location of the intervening sequence was verified by using the dideoxy chain termination technique to determine the sequence at the 5' terminus of the actin mRNA. The similarity of the splice junction sequences in this gene to those found in higher eukaryotes suggests that yeast must possess a similar splicing enzyme.
Activation of electrogenic Na+/K+ exchange by extracellular K+ in canine cardiac Purkinje fibers.
Authors: Gadsby D C
Published: May 2006

Transient increments in sodium pump current were elicited in small voltage-clamped Purkinje fibers suspended in a fast flow system by briefly exposing them to K+-free fluid, to temporarily inhibit the pump, and then suddenly returning them to K+-containing fluid. The exponential time course of decay of the current increment provides a measure of the pump rate constant for Na+ extrusion. The dependence of that rate constant, and of the peak amplitude of the increment in pump current, on the extracellular K+ concentration was determined. The results indicate: that in cardiac Purkinje cells, as in many other cells, the pump is half-maximally activated by about 1 mM K+; that the coupling ratio for Na+/K+ exchange is independent of either intracellular Na+ concentration or external K+ concentration; and that a simple model in which intracellular Na+ concentration is determined by a passive "leak," and an active extrusion of Na+, seems sufficient to account for moderate changes in cellular Na+ concentration.
Transepithelial migration of human neutrophils: an in vitro model system.
Authors: Cramer E B , Milks L C , Ojakian G K
Published: May 2006

An in vitro model system for studying transepithelial migration of human neutrophils has been developed. Canine kidney epithelial cells grown on micropore filters form a confluent, polarized monolayer with an average transepithelial electrical resistance of 181 ohms.cm2. Neutrophils in a chemotactic chamber are stimulated to undergo random migration, chemokinesis, or chemotaxis through the epithelium. When stimulated by a gradient of the synthetic chemoattractant fMet-Leu-Phe, significantly more neutrophils traverse the low-resistance epithelium than do under conditions of random migration or chemokinesis. Transmission and scanning electron microscopy of this process reveal that neutrophils traverse the epithelium through the intercellular space. After leukocyte emigration, lateral epithelial cell membranes reapproximate. Neutrophils undergoing chemotaxis can also traverse the polarized epithelium from the basal epithelial surface, which suggests that the chemotactic gradient and not the apical-basal polarity of the epithelial cells determines the direction of transepithelial migration. The data further suggest that (i) the in vitro model of leukocyte transepithelial migration morphologically simulates the in vivo process, (ii) neutrophils more readily penetrate the epithelium when attracted by a chemotactic factor, and (iii) neutrophils can traverse a low-resistance epithelium in the absence of serum and connective tissue factors.
Interferon inhibits the conversion of 3T3-L1 mouse fibroblasts into adipocytes.
Authors: Keay S , Grossberg S E
Published: May 2006

Confluent Swiss mouse 3T3-L1 fibroblasts slowly differentiate functionally and morphologically into adipocytes, a conversion hastened by insulin. The cells are sensitive (although less than L929 cells) to the antiviral action of mouse fibroblast interferons but not to interferons from heterologous species (human and chicken). Cultures stimulated with insulin in the presence of partially purified or electrophoretically pure mouse interferons have a much lower percentage of cells accumulating lipid than do insulin-treated control cultures. Interferon-treated cell cultures also contain much less triglyceride, cholesterol, and cholesterol esters than do replicate control cultures stimulated by insulin to differentiate. Increased de novo lipid biosynthesis that occurs during differentiation is inhibited, as determined by incorporation of [14C]acetate into lipids extractable by the Folch method. This incorporation is a sensitive bioassay of the antidifferentiation effect of interferon; less than 1 antiviral unit is inhibitory. Variously inactivated or mock interferon preparations as well as interferons from several heterologous species fail to inhibit 3T3-L1 adipocyte conversion. Interferon is inhibitory even when applied as long as 3 days after insulin stimulation. The effect of interferon does not appear to depend upon its competition with insulin for cell surface receptors. Because interferon can alter the program of events involved in conversion of 3T3-L1 fibroblasts into adipose cells, it may be able to affect the regulation of eukaryotic cell differentiation.
Role of a 16S glycoprotein complex in cellular adhesion.
Authors: Schubert D , LaCorbiere M
Published: May 2006

Myogenic cells release into their culture medium a glycoprotein complex that mediates cellular adhesion. In the absence of calcium this complex has a sedimentation value of 16S; it aggregates in the presence of calcium. The 16S material both agglutinates and increases the rate of cell-substratum adhesion of a myoblast variant and inhibits the adhesion of a nerve-like cell line to culture dishes. It is also a hemagglutinin. The 16S particle is composed of glycosaminoglycans and several proteins, including fibronectin and collagen.
Differences in intracellular location of pp60src in rat and chicken cells transformed by Rous sarcoma virus.
Authors: Krueger J G , Wang E , Garber E A , Goldberg A R
Published: May 2006

We have investigated the intracellular location of pp60src in Rous sarcoma virus-transformed rat cells (RR1022) by indirect immunofluorescence microscopy and cell fractionation. Immunofluorescence data suggest that pp60src is predominantly associated with the nuclear envelope and the juxtanuclear reticular membrane structures. The bulk of pp60src and of the associated phosphotransferase activity fractionated with nuclei and not with plasma membranes in disrupted cells. This localization contrasts strikingly with the association of pp60src with the plasma membrane of Rous sarcoma virus-transformed chicken fibroblasts. We propose that pp60src is a membrane protein that associates with cellular membranes through hydrophobic regions and that this membrane association is a general feature of the interaction of pp60src with avian and mammalian cells. Although there are major differences in the intracellular localizations of pp60src, it may interact with cellular membranes through one or more NH2-terminal hydrophobic regions.
Transcription of tRNA genes in vivo: single-stranded compared to double-stranded templates.
Authors: Cortese R , Harland R , Melton D
Published: May 2006

The expression of cloned tRNA genes has been studied by injecting single-stranded and double-stranded DNA templates into Xenopus oocyte nuclei. In both forms the genes are faithfully transcribed after injection. Some single-stranded DNA is converted into double-stranded DNA in the oocyte nucleus. This conversion is necessary for the expression of the injected tRNA gene: no tRNA transcription is observed when DNA synthesis is inhibited. We conclude that single-stranded DNA does not serve as a template for faithful transcription of this gene in injected oocytes.
Cellular and molecular basis of the increased splenic hemopoiesis in mice treated with bacterial cell wall components.
Authors: Staber F G , Metcalf D
Published: May 2006

An analysis was made of the mechanisms responsible for the increased splenic hemopoiesis occurring in mice after the injection of the bacterial cell wall components lipid A and outer membrane lipoprotein. No evidence was obtained for the presence of functional lipid A receptors on hemopoietic precursor cells. Serum from lipid A-injected mice, on injection into normal mice, induced in the spleen an increased content of all hemopoietic progenitor cells. The magnitude of the response was dependent on the dose of lipid A used and the volume of serum transferred to the recipients. C3H/HeJ mice unresponsive to lipid A exhibited similar spleen changes when injected with active post-lipid A sera. Progenitor cells of all hemopoietic lineages, including multipotential hemopoietic stem cells, were involved in the response. The results suggest that a humoral factor mediates the lipid A-induced increase of splenic hemopoiesis.
Genomic changes associated with antigenic variation of visna virus durig persistent infection.
Authors: Clements J E , Pedersen F S , Narayan O , Haseltine W A
Published: May 2006

Visna virus undergoes antigenic change during persistent infection of sheep. Antigenic variants of visna virus were compared by using the genomic RNA and analyzing the large RNase T1-resistant oligonucleotides. Mutants isolated from a persistently infected sheep contained a small number of changes in their oligonucleotide patterns when compared with parental virus. To determine whether the changes in the nucleotide structure were clustered in one region of the genome, we determined the order of the oligonucleotides of the parental and mutant RNAs along the genome with respect to the 3' polyadenylylated end. All but one difference between the parental strain and the antigenic mutant used for mapping were located within 2 kilobases from the 3' terminus. Nucleotide sequence analyses showed that several of the oligonucleotides that differed in the parental and mutant RNAs could be accounted for by single base changes.
Coordinate regulation of two estrogen-dependent genes in avian liver.
Authors: Wiskocil R , Bensky P , Dower W , Goldberger R F , Gordon J I , Deeley R G
Published: May 2006

Livers of egg-laying species contain abundant mRNAs encoded by both estrogen-responsive and constitutively expressed genes. We have recently constructed cDNA clones from three members of the abundant mRNA class of hen liver. One of these mRNA species was identified as serum albumin mRNA, and another as vitellogenin mRNA. In this study we have identified the third member of the group as apo VLDLII mRNA. Hybridization analyses using cloned cDNA probes indicate that expression of the apo VLDLII gene in rooster liver, like that of the vitellogenin gene, is completely dependent upon the administration of estrogen. The apo VLDLII and vitellogenin genes appear to be the only genes capable of high rates of expression in the liver that exhibit such an exceptional response to the hormone. Administration of estrogen resulted in the appearance of both mRNA species within 30 min, followed by a rapid accumulation to several thousand copies per cell. Removal of the hormone caused a marked destabilization of both vitellogenin mRNA and apo VLDLII mRNA. In contrast, the absolute levels of serum albumin mRNA were unaffected by the hormone. Comparative studies on the structure and organization of these three genes may reveal elements involved in determining their rates of expression in the presence and absence of estrogen.
Ouabain-binding-site photoaffinity probes that label both subunits of Na+,K+-ATPase.
Authors: Hall C , Ruoho A
Published: May 2006

4"'-Diazomalonyldigitoxin and its isomer, 3"'-diazomalonyldigitoxin, have been synthesized at high specific radioactivity and used as photolabels for the Na,K-ATPase (ATP phosphohydrolase, EC 3.6.1.3) purified from Electrophorus electricus. Photoaffinity labeling experiments using both type I and type II complexes of enzyme with both photolabels showed ouabain-protectable labeling of the alpha as well as the beta subunit. These data suggest that, in the purified eel enzyme, the alpha and beta subunits are in intimate contact, at least in the region of the third digitoxose of the "sugar-specific" binding site.
Anchorage of a band 3 population at the erythrocyte cytoplasmic membrane surface: protein rotational diffusion measurements.
Authors: Nigg E A , Cherry R J
Published: May 2006

Direct physical evidence for the linkage of a band 3 population to the cytoskeleton in the erythrocyte ghost membrane is presented. The rotational diffusion of band 3 proteins was mesured by observing flash-induced transient dichroism of a covalently bound eosin probe. After proteolytic release of a 40,000-dalton cytoplasmic segment of band 3 by trypsin, a considerable enhancement in the decay of the absorption anisotropy was observed. Analysis of the data indicates that proteolytic cleavage of band 3 produces a mobile band 3 population which has restricted mobility in the unperturbed membrane due to protein-protein interactions involving the cytoplasmic band 3 moiety. Band 2.1 (ankyrin) or 4.1 or both are likely to be involved in this interaction because a similar effect on band 3 mobility is observed after low-salt/high-salt extraction of these components. Quantitatively, it is estimated that up to 40% of band 3 may be linked to the cytoskeleton. Because the ankyrin-band 3 dimer stoichiometry in the membrane is approximately 1:5, only about 20% of band 3 dimers can be directly linked to ankyrin. The remainder could be explained by the existence of higher oligomers of band 3 linked to single ankyrin polypeptides or by linkages involving other components such as band 4.1 or 4.2.
In utero analysis of sister chromatid exchange: alterations in suscptibility to mutagenic damage as a function of fetal cell type and gestational age.
Authors: Kram D , Bynum G D , Senula G C , Bickings C K , Schneider E L
Published: May 2006

Frequencies of baseline and cyclophosphamide-induced sister chromatid exchanges (SCE) were measured in mouse maternal and fetal cells between days 11 and 19 of gestation. Baseline levels of SCE did not vary as a function of gestational age in either the mother or fetus. Cyclophosphamide-induced SCE frequencies remained constant in maternal cells but declined dramatically in the fetus throughout the latter half of development. Because cyclophosphamide is a metabolically activated mutagen, a direct-acting drug, mitomycin C, was given on days 11 and 15 to determine if the decline in induced SCE levels seen with gestational results from alterations in activating enzymes. A similar decline in mitomycin C-induced SCE levels was noted in fetal tissues as a function of gestational age. Dose-response curves to cyclophosphamide performed on day 13 of gestation showed increases in SCE as a function of cyclophosphamide concentration in both the mother and the fetus. When mutagen-induced SCE levels were compared in different fetal organs, the direct-acting drugs (mitomycin C and daunomycin) were found to induce similar levels in all tissues. Cyclophosphamide, which is metabolically activated, induced higher SCE levels in fetal liver than in lung or gut. Whereas cyclophosphamide induced similar SCE levels in fetal and maternal cells on day 13 of gestation, daunomycin produced fetal SCE levels that were approximately 50% of maternal levels. Simultaneous measurement of the distribution of [14C]cyclophosphamide and [3H]daunomycin in maternal and fetal cells revealed that the lower SCE induction by daunomycin was probably due to decreased ability to cross the placental barrier.