bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel mutants of Escherichia coli that accumulate very small DNA replicative intermediates.
Authors: Konrad E B , Lehman I R
Published: May 2006

A new group of mutants has been isolated which, during short pulses, incorporate (3-H)thymidine into DNA fragments that are substantially smaller than Okazaki fragments. These small fragments can be chased into DNA of high-molecular-weight, and thus may be precursors in DNA replication, During longer pulses, label also appears in DNA of higher molecular weight, although at an abnormally slow rate. The mutations map at a previously undescribed locus (dnaS) at 72 min on the E. coli chromosome.
Mouse SmI cortex: qualitative and quantitative classification of golgi-impregnated barrel neurons.
Authors: Woolsey T A , Dierker M L , Wann D F
Published: May 2006

The neurons in layer IV of the mouse somatosensory cortex are arranged in a remarkably consistent pattern of multicellular cytoarchitectonic units called "barrels." Each barrel is known to be related, in a one to one manner, to a contralateral whisker or vibrissa on the animal's face. In this study we have examined Golgi-impregnated neurons that comprise the "barrels." Several criteria, some being quantitative measures of dendritic arbors and somal sizes which were obtained with a computer-microscope system, suggest that all barrel neurons can be placed in two classes, the members of which are present in approximately equal numbers. The cells in the two classes can be further subdivided on the basis of the relationship of their processes to the barrels: 85% of them have processes restricted to a single barrel; 15% of them distribute their processes to two or more barrels. From these observations it is possible to suggest that a majority of neurons comprising the barrels would respond initially to movements of only one whisker while the remainder would respond to movements of two or more whiskers. In addition it has been shown that the quantitation of neuronal structure can provide a numerical basis for the classification of neurons in the central nervous system.
Enzymes as reagents in peptide synthesis: enzymatic removal of amine protecting groups.
Authors: Meyers C , Glass J D
Published: May 2006

A model system is described for the enzymatic deprotection of suitably masked amino groups during stepwise peptide synthesis. Nitrophenyl esters of amino acids, N-protected with trypsin-labile benzyloxycarbonylarginyl groups, were prepared as crystalline, analytically pure picrate salts in a standardized procedure. These intermediates were shown to react with amino compounds to form the expected peptide linkages. A pair of diasteriomeric peptides prepared in this way and featuring benzyloxycarbonylarginyl-L-, AND -D-glutaminyl sequences, respectively, were subjected to tryptic digestion. In both cases, a specific cleavage of the arginyl bond was achieved; however, the peptide containing the L-glutaminyl residue was deprotected much more rapidly than its diasteriomer containing the D-glutaminyl residue. The hydrolysis of the former isomer was not noticeably impeded by the presence of the latter. The results of these studies suggest that C-activated amino-acid derivatives, N-protected with trypsin-labile groups, are readily prepared in convenient form and that the peptide derivatives prepared from these intermediates are readily freed of their amino-protecting groups under mild, aqueous conditions with a potentially useful degree of stereospecificity. Theoretical implications of this first enzyme-catalyzed step in the repetitive cycle of peptide elaboration are discussed along with the procedural advantages implicit in the alternation of strongly and weakly basic groups in the protected and unprotected peptide intermediates, respectively.
Formation of bone marrow in fibroblast-transformation ossicles.
Authors: Reddi A H , Huggins C B
Published: May 2006

The genesis of hemopoietic bone marrow was studied in matrix-induced transformation plaques and ossicles in subcutaneous spaces of thorax and abdomen of rat. With the advent of blood vessels in the plaque on day 9, there began a rapid and radical conglomerate shift, cartilaginous to osseous, which was nearly total in 72 hr. Incorporation of 59-Fe into heme provided a sensitive quantitative assay for hemopoiesis. On day 12 the first colonies of hemopoietic cells were observed. These developed adjacent to cavernous sinuses which had formed to fill the void left by chondrolysis. Total occupation of the ossicle with hemopoietic marrow was found on days 23-28. The thoracic region was favorable for the formation of hemopoietic marrow, whereas lower abdominal sites were disadvantageous.
Antigen-stimulated changes in cyclic nucleotide levels in the mouse.
Authors: Yamamoto I , Webb D R
Published: May 2006

Mice injected intravenously with sheep erythrocytes (sRBC) demonstrate a transient increase in splenic cAMP levels (4-fold), which peak at 2 min after injection and return to basal levels by 20 min. In addition to the change in cAMP, an increase in splenic cGMP levels (1.5-fold) occurs beginning 5-10 min after sRBC injection, and persists for up to 7 days. During this period cAMP levels remain at or below control levels in the spleen. There is no change in 3':5' cyclic nucleotide levels in the liver and a small increase (1.2- to 1.3-fold) in the thymus at the time when splenic cyclic nucleotide levels are elevated. The changes in splenic cyclic nucleotide levels appear to be dependent on the presence of thymus-derived (T) lymphocytes, since little change occurs in cAMP and changes in cGMP are absent in athymic nude mice. In addition, cAMP levels were increased by pretreatment of normal mice with cortisone acetate, which selects for mature T lymphocytes. Agents that block autonomic nervous system functions have no effect on the early sRBC-induced changes in cyclic nucleotide levels.Indomethacin, an inhibitor of prostaglandin synthesis, reduces the change in cAMP level by 50% and blocks the change in cGMP levels completely. Secondary stimulation with sRBC results in a larger increase in cAMP levels than that seen with a primary injection of sRBC, indicating the presence of specific antigen-sensitive memory cells. Changes in splenic cyclic nucleotide levels cannot be detected at early times after the injection of soluble protein antigens such as bovine serum albumin and keyhole limpet hemocyanin. Salmonella H antigen stimulates a 2-fold increase in cAMP levels, the increase occurring more slowly than with sRBC. The in vivo changes incyclic nucleotide levels are correlated with known changes in cyclic nucleotide levels which have been documented in vitro in both T-cells and T-cell-dependent-B-cell (bone-marrow derived) antibody responses.
Hair dyes are mutagenic: identification of a variety of mutagenic ingredients.
Authors: Ames B N , Kammen H O , Yamasaki E
Published: May 2006

We have previously described a sensitive bacterial test for dectecting carcinogens as mutagens. We have previously described a sensitive bacterial test for detecting carcinogens as mutagens. We show here that 89% (150/169) of commercial oxidative-type (hydrogen peroxide) hair dye formulations are mutagenic in this test. Of the 18 components of these hair dyes, nine show various degrees of mutagenicity:2,4-diaminoanisole, 4-nitro-o-phenylenediamine, 2-nitro-p-phenylenediamine, 2,5-diaminoanisole, 2-amino-5-nitrophenol, m-phenylenediamine, o-phenylenediamine, 2-amino-4-nitrophenol, and 2,5-diaminotoluene. Three hair dye components (p-phenylenediamine, 2,5-diaminotuluene, and 2,5-diaminoanisole) become strongly mutagenic after oxidation by H2O2: the mutagenic product of p-phenylenediamine is identified as the known trimer, Bandrowski's base. 2,4-Diaminotoluene, a hair dye component until recently, is also shown to be mutagenic: this compound has been shown to be a carcinogen in rats and is used in large amounts in the polyurethane foam industry. About 20,000,000 people (mostly women) dye their hair in the U.S. and the hazard could be considerable if these chemicals are actually mutagenic and carcinogenic in humans.
Membrane difference in peripheral blood lymphocytes from patients with chronic lymphocytic leukemia and Hodgkin's disease.
Authors: Mintz U , Sachs L
Published: May 2006

Lymphocytes were isolated from the peripheral blood of 21 normal persons and 66 patients with chronic lymphocytic leukemia (CLL), CLL in remission, Hodgkin's disease, Hodgkin's disease in remission, various other tumors, or cardiovascular diseases; The lymphocytes were studied for cap formation and agglutinability by concanavalin A, and for cell attachment to the surface of a petri dish. The frequency of cap formation was lowest in lymphocytes from patients with untreated Hodgkin's disease (2.1 plus or minus 0.8%), next lowest in lymphocytes from patients with CLL who were or were not under treatment (7,0 plus or minus 1;3%), and also low in Hodgkin's disease in remission (10.6 plus or minus 1.2%). The frequencies of cap formation by lymphocytes from patients with various other tumors (19.1 plus or minus 2.5%), with CLL in remission (24.0 plus or minus 0.9%), and with nonmalignant diseases (26.0 plus or minus 2.2%) were more similar to the frequency found in lymphocytes from normal persons (29.4 plus or minus 2.8%). Lymphocytes from all the patients, including those in remission, showed a higher degree of agglutinability by concanavalin A than lymphocytes from normal persons. Cell attachment to a petri dish was highest with CLL, next highest with CLL in remission, and low for normal persons and all the other patients. Lymphocytes from normal persons that consisted predominantly of thymus-derived cells gave similar results to isolated normal bone marrow-derived cells. The results indicate that there were different changes in the surface membrane of lymphocytes from patients with CLL, CLL in remission, Hodgkin's disease, and Hodgkin's disease in remission, and that the patients in clinical remission still showed abnormalities in their lymphocytes.
Coupled in vitro transcription and translation of vesicular stomatitis virus messenger RNA.
Authors: Breindl M , Holland J J
Published: May 2006

The virion transcriptase (nucleosidetriphosphate: RNA nucleotidyltransferase, EC 2.7.7.6) of vesicular stomatitis virus was fully active when ribonucleoprotein cores from purified virions were added to cell-free protein synthesizing systems of eukaryotic origin. Synthesis of mRNA was linear for at least 3 hr and the newly synthesized viral mRNA was efficiently utilized for the synthesis of viral proteins N (nucleoprotein), NS, and M (matrix); small amounts of a putative G (glycoprotein protein precursor and several unidentified polypeptides were regularly synthesized. The ratio of the various newly synthesized viral proteins was identical after different periods of coupled mRNA and protein synthesis. Identical proteins were obtained when the cell-free protein synthesizing systems were programmed with purified VSV mRNA synthesized in vitro. No detectable L protein was synthesized, even though transcripts complementary to the complete viral genome were detectable in the mRNA preparation by hybridization.
Functional arginyl residues as ATP binding sites of glutamine synthetase and carbamyl phosphate synthetase.
Authors: Powers S G , Riordan J F
Published: May 2006

The reaction of phenylglyoxal with two enzymes in which ATP plays a complex role has been studied. Both ovine brain glutamine synthetase and Escherichia coli carbamyl phosphate synthetase [carbamoyl-phosphate synthase (glutamine); ATP:carbamate phosphotransferase (dephosphorylating, amido-transferring); EC 2.7.2.9]were inactivated by phenylglyoxal. The specificity of this reagent for arginyl residues of the two proteins was confirmed by amino acid analysis. ATP, but not the other substrates, protected these enzymes against inactivation by phenylglyoxal. Carbamyl phosphate synthetase was also protected by IMP and ornithine, positive allosteric effectors that alter the enzymatic activity be increasing the affinity for ATP. UMP, a negative allosteric effector that decreases the affinity for ATP, did not protect against inactivation. Differential labeling experiments with [14C]phenylglyoxal showed that the number of arginyl residues protected by ATP corresponded quite well to the known number of ATP catalytic sites for each protein. These data indicate that arginyl residues at the active sites of glutamine synthetase and carbamyl phosphate synthetase are involved in the binding of ATP. This phenylglyoxal inactivation study also provided information about the mechanistic role of ATP in the two synthetases. The data obtained on glutamine synthetase support the theory that ATP is attached to the enzyme as a portion of the catalytic site, and that its presence is essential for the binding of glutamate and glutamine. The data obtained on carbamyl phosphate synthetase are consistent with the previous proposal that carbonyl phosphate is an intermediate in the ATP-dependent activation of bicarbonate by this enzyme. It is also of interest that, with both glutamine synthetase and carbamyl phosphate synthetase, only a small portion of the total arginyl population of these enzymes reacted with phenylglyoxal. A summary of previous studies on the modification of enzyme arginyl residues is presented.
An octamer of histones in chromatin and free in solution.
Authors: Thomas J O , Kornberg R D
Published: May 2006

Crosslinking with dimethyl suberimidate reveals a chain of histone octamers in chromatin. The octamer can be isolated free in solution at high ionic strength and pH. The identification of dimers formed by crosslinking reveals two or more contacts of each histone with others within the octamer. The molecular weight (110,000) and pattern of dissociation of the octamer are compatible with the composition (F2A1)2(F3)2(F2A2)2(F2B)2.
Evolutionary and structural influences on light chain constant (CL) region of human and mouse immunoglobulins.
Authors: Kabat E A , Padlan E A , Davies D R
Published: May 2006

A comparison of five constant region sequences of human and mouse k and lambda immunoglobulin chains has been undertaken in order to reveal sequence homologies and evolutionary relationships. Simultaneously, a comparison with the three-dimensional structure of one mouse k-chain (McPC 603) has suggested structural reasons why many of the residues are invariant or conserved along k versus lambda lines. There are a number of residues that have remained invariant despite exposed positions for reasons that do not apppear to be connected with the folding of the CL domain.
Methylmalonicacidemia: biochemical heterogeneity in defects of 5'-deoxyadenosylcobalamin synthesis.
Authors: Mahoney M J , Hart A C , Steen V D , Rosenberg L E
Published: May 2006

We measured the synthesis of 5'-deoxyadenosylcobalamin (AdoCbl) in fibroblast extracts from patients with inherited methylmalonicacidemia due to deficient activity of the cobalamin-dependent holoenzyme, methylmalonyl-CoA mutase (EC 5.4.99.2). Previous studies with intact fibroblasts from patients whose holoenzyme deficiency was secondary to abnormal cobalamin metabolism had defined two phenotypes, one in which whole cells failed to accumulate AdoCbl and a second in which they failed to accumulate both AdoCbl and the second cobalamin coenzyme, methylcobalamin. With a broken cell assay of AdoCbl synthesis in cell extracts and the cell lines are named cbl A mutants; the other class shows severe deficiency of AdoCbl synthesis and the cell lines are named cbl B mutants. We define cbl C mutants as those in which both AdoCbl and methylcobalamin fail to accumulate in intact cells. The assay for AdoCbl synthesis is thought to measure two enzymatic activities, cob(II)alamin reductase (EC 1.6.99.9) and cob(I)alamin adenosyltransferase (EC 2.5.1.17). Subcellular fractionation studies place this combined activity in mitochondria.
Ontogenesis of a biological clock for serotonin:acetyl coenzyme A N-acetyltransferase in pineal gland of rat.
Authors: Deguchi T
Published: May 2006

Serotonin:acetyl coenzyme A N-acetyltransferase (EC 2.3.1.5) Activity in pineal gland was assayed in rats which were born and raised under diurnal lighting conditions, in continuous darkness, or in constant light. N-Acetyltransferase activity in the pups raised under diurnal lighting showed a rhythmic pattern, with high enzyme activity during dark period. The pups raised in continuous darkness also showed a rhythmic pattern, the phase of which was delayed by 8 hr in 7-week-old pups; the rhythmic phase of N-acetyltransferase began in the evening in 12-day-old pups and was regularly delayed by 1 hr every week. The pups raised in constant illumination also showed a rhythmic pattern; the rhythmic phase was delayed by 3 hr every week. When the mother rats were coupled in darkness and maintained in darkness during pregnancy and after the pups were born, their pups again showed a rhythmic pattern. These observations indicate that the biological clock for N-acetyltransferase is generated independently of environmental lighting. When mothers were coupled under reversed lighting conditions and transferred into darkness or light, the rhythmic pattern in their pups was inverted 180 degrees from that of pups born of diurnal mothers. When the pups were raised in darkness, the rhythmic phase of N-acetyltransferase in the pups was similar to that of their mothers. It is suggested that in the absence of light-darkness cycle, the mother rat sets the rhythm of the pups to synchronize with her own rhythm. When pups were reared by a foster mother with a different rhythmic pattern from that of their original mother, the rhythmic phase in the pups was closer to that of the original mother, suggesting that the original mother plays the predominant role setting the rhythm of the pups.
Donor properties of the three carbonyl groups of chlorophyll a: ab initio calculations and 13C magnetic resonance studies.
Authors: Shipman L L , Janson T R , Ray G J , Katz J J
Published: May 2006

The relative donor properties of the three carbonyl groups of chlorophyll a have been studied theoretically by a series of ab initio molecular fragment, floating spherical Gaussian orbital, self-consistent field calculations on ethyl chlorophyllide a and experimentally through a 13C magnetic resonance study on chlorophyll a. The approximate ground state electronic wavefunction of ethyl chlorophyllide a was perturbed by monopole and dipole point charges whose signs, magnitudes, and positions were chosen to mimic the coulombic interactions associated with carbonyl coordination to Mg. Because the polarizability of the ring V keto carbonyl binding site is substantially greater than that for the ester carbonyl binding sites, the ring V keto binding site binds with smallest binding energy for weak perturbations and with largest binding energy for strong perturbations. A comparison of 13C magnetic resonance chemical shifts in chlorophyll a monomer and dimer provides new experimental evidence that the donor-acceptor interactions that bind the chlorophyll dimer together involve a substantial participation by the ring V keto carbonyl and minimal participation by the two ester carbonyl groups, and thus are in agreement with conclusions derived from the ab initio calculations.
Interaction of ubisemiquinone with a paramagnetic component in heart tissue.
Authors: Ruzicka F J , Beinert H , Schepler K L , Dunham W R , Sands R H
Published: May 2006

The origin of most of the electron paramagnetic resonances obtained at low temperature and low microwave power from heart tissue and subcellular fractions derived therefrom is now understood. A signal that emerges on partial reduction with characteristic lines at 3227 G (0.3227 tesla) and 3309 G (0.3309 tesla) (at 9.2 GHz) and disappears again on full reduction has remained unidentified. According to its behavior on oxidation-reduction, the substance giving rise to this signal has the properties of a two-electron acceptor. The signal is strongly dependent on temperature and can only be well resolved at less than 20 degrees K. It is readily elicited in submitochondrial particles by partial reduction, but has not been observed in submitochondrial particles from which ubiquinone has been removed by pentane extraction. When ubiquinone is reincorporated into extracted submitochondrial particles, the signal is again easily produced by partial reduction. Electron paramagnetic resonance spectra of partially reduced submitochondrial particles recorded at 34 GHz show lines centered about g approximately 2 with the same separation (approximately 82 G; approximately 0.0082 tesla) as do 9.2 GHz spectra, whereas no lines are detected with a separation of approximately 82 X 34/9.2 G (0.0082 X 34/9.2 tesla). We suggest, on the basis of these observations, that the unidentified signal arises from an interaction of ubisemiquinone and a second paramagnetic species. Three obvious choices exist concerning this second species: ubisemiquinone, flavin semiquinone, or an iorn-sulfur center. It is not possible without much additional information to decide between these possibilities. Since we have never observed the signal in the absence of the membrane-bound, high-potential type iron-sulfur protein, we have considered involvement of this species in the interaction. However, according to computer simulations of the observed electron paramagnetic resonance spectra, which yield best fits for semiquinone-semiquinone interaction, the possibility that ubi- or flavin semiquinone is the interaction partner appears more likely at this time. The interaction appears to be of the magnetic dipole-dipole type, but it is not certain whether there is also a contribution from spin exchange coupling. If it is assumed that the signal is due to magnetic dipole-dipole interaction, the distance of the partners is less than or equal to 7.7 A.
Interaction of enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system with adenylate cyclase of Escherichia coli.
Authors: Peterkofsky A , Gazdar C
Published: May 2006

Transient repression by glucose of induced enzyme synthesis involves lowering of intracellular cAMP levels. This glucose effect is partially explained by a glucose inhibition of adenylate cyclase [EC 4.6.1.1; ATP pyrophosphate-lyase(cyclizing)]. Since the phosphoenolpyruvate:sugar phosphotransferase system has been implicated in repression phenomena, an investigation was made of adenylate cyclase activity in mutants of that transport system. The results suggest that glucose phosphorylation is not necessary for inhibition of adenylate cyclase since an HPr mutant retained sensitivity to glucose inhibition. The results also suggest that adenylate cyclase activity requires the presence of Enzyme I in a phosphorylated form and that adenylate cyclase activity may be regulated by a phosphorylation-dephosphorylation mechanism.
Visualization of a novel junction in bacteriophage lambda DNA.
Authors: Valenzuela M S , Inman R B
Published: May 2006

At early times after infection of a recA derivative of Escherichia coli with lambdab221c126red270a42 phage, a low but significant proportion of intracellular lambda molecules show a novel junction. These junctions are also present, although in reduced numbers, in a lysate obtained at late times after infection of a recA+ host with lambdacIIcIII phage. Fine structure and denaturation mapping analyses showed that these junctions occur at homologous positions and that they are compatible with the occurrence of a cross-strand exchange between lambda DNA duplexes similar to the type proposed in most molecular models for genetic recombination. However, the results are also consistent with the structures expected if a replicating growing point undergoes branch migration.
Dissociation of two polypeptide chains from yeast RNA polymerase A.
Authors: Huet J , Buhler J M , Sentenac A , Fromageot P
Published: May 2006

Yeast RNA polymerase A (RNA nucleotidyltransferase; nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6) can be converted to a new form of enzyme, called RNA polymerase A*, which is lacking two polypeptide chains of 48,000 and 37,000 daltons. Apart from these two missing polypeptides the subunit structures of RNA polymerases A and A* are indistinguishable. RNA polymerase A* differs from the complete enzyme in its electrophoretic and chromatographic behavior, template requirements, and alpha-amanitin sensitivity. RNA polymerase A* transcribes the alternated copolymer d(A-T)n with the same efficiency as RNA polymerase A but its specific activity is greatly reduced with native calf thymus DNA as template. The transcription of a variety of synthetic templates is also altered by removal of the two polypeptide chains. RNA polymerase A* is inhibited by high concentrations of alpha-amanitin (500 mug/ml), whereas RNA polymerase A is comparatively less sensitive to the toxic peptide. The data are discussed in terms of possible roles of the two dissociable polypeptides.
The major cell surface glycoprotein of chick embryo fibroblasts is an agglutinin.
Authors: Yamada K M , Yamada S S , Pastan I
Published: May 2006

A major cell surface protein, CSP, of chick embryo fibroblasts has been shown to constitute up to 3% of total cell protein, and to be decreased after viral transformation. Its role in normal cell behavior is not known. We have isolated CSP from chick embryo fibroblasts by extraction with 1 M urea and find that these preparations of CSP agglutinate formalinized sheep erythrocytes at protein concentrations of under 2 mug/ml. In extracts of chick embryo cells, the quantity of such hemagglutinating activity parallels that of CSP determined by electrophoresis, and both are substantially decreased in chick cells transformed by the Bryan hightiter strain of Rous sarcoma virus. Both CSP and hemagglutinating activity are progressively adsorbed onto erythrocytes and can be released by 1 M urea. An antiserum to purified CSP specifically blocks the agglutination. The agglutinating activity is destroyed by boiling or treatment with proteases. The agglutination reaction is inhibited by the chelating agents EDTA and EGTA [ethyleneglycol-bis(beta-aminoethyl ether)N,N'-tetraacetic acid]. Agglutination is also inhibited to a lesser degres by amino sugars and other amines, increased osmolarity, and urea. Other monosaccharides, hyaluronidase, DNase, and RNase have little or not effect on the agglutination reaction. This demonstration that CSP has an agglutinating activity that is sensitive to proteases and that requires divalent cations suggests that this molecule may play a role in cell adhesion.
Binding of autologous erythrocytes to immature T-cells.
Authors: Charreire J , Bach J F
Published: May 2006

A small percentage of normal mouse thymus and spleen lymphocytes form rosettes with autologous erythrocytes. The number of these autologous rosettes increases 15- to 20-fold after adult thymectomy and to a lesser degree with aging. Autologous rosette level is also abnormally high in nude (congenitally athymic) mice. The high level of autologous rosette-forming cells found after adult thymectomy is normalized by injecting ng amounts of purified circulating thymic factor. Autologous rosette-forming cells adhere to nylon, belong to the less dense spleen cells, are in majority steroid-resistant in the thymus. All these properties suggest that autologous rosette-forming cells might belong to immature T-cell (thymic-dependent cell) precursors.
Changes in ribosomal RNA processing paths in resting and phytohemagglutinin-stimulated guinea pig lymphocytes.
Authors: Purtell M J , Anthony D D
Published: May 2006

Processing of rRNA was examined in resting and phytohemagglutinin-stimulated guinea pig lymphocytes. Synthesis of 1.7 (28S) and 0.7 (18S) X 10(6) dalton rRNA was more than 4-fold greater in phytohemagglutinin-stimulated than in resting cells. A 5- to 10-fold increase in flux of molecules through a 2.3 X 10(6) dalton RNA occurred without a concurrent change in the flux through a 2.6 X 10(6) dalton fraction in phytohemagglutinin-stimulated cells. In both resting and phytohemagglutinin-stimulated lymphocytes, the 2.3 X 10(6) dalton intermediate equilibrated with [3H]methyl label and pulse-chased prior to the 2.6 X 10(6) dalton RNA. The data indicate at least two processing paths in guinea pig lymphocytes; one proceeds to rRNA via a 2.3 X 10(6) dalton intermediate, and another proceeds via a 2.6 X 10(6) dalton RNA. The increase in rRNA synthesis in phytohemagglutinin-stimulated cells occurs primarily through that path containing the 2.3 X 10(6) dalton intermediate.
Electron microscopy of defined lengths of chromatin.
Authors: Finch J T , Noll M , Kornberg R D
Published: May 2006

Defined lengths of chromatin were prepared by brief digestion with micrococcal nuclease and fractionation in a sucrose gradient. A length containing a given number of 200 base pair repeating units appeared as the same number of 100 A beads in the electron microscope. The distance between beads within a length was small, usually less than about 20 A.
Glutamine synthetase forms three- and seven-stranded helical cables.
Authors: Frey T G , Eisenberg D , Eiserling F A
Published: May 2006

When cobaltous ion is bound to glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2], the two-layered hexagonal molecules polymerize face-to-face, to form long strands. The strands then wind round each other to form three- and seven-stranded cables. The structures of these cables are not immediately evident from electron micrographs because of the confusing superposition of front and back portions of the cables. But optical diffraction and filtering by the procedure of Klug and DeRosier leads to interpretable images of the cables. Because a micrograph of the seven-stranded cable contains 24 views of the glutamine synthetase molecule, it is possible to reconstruct the three-dimensional electron density of a cable and its constituent molecules at a resolution of 30--50 A. This reconstruction confirms that the symmetry of a glutamine synthetase molecule is D6. It suggests that the single subunit is an oblate ellipsoid with its minor axis (about 48 A) roughly parallel to the 6-fold axis of the molecule and its major axis (about 63 A) perpendicular to the 6-fold axis of the molecule. The subunits of the two hexagonal layers of a molecule are eclipsed. Neighboring molecules along a strand also have their hexagonal faces together, but they are rotated about the strand axis by about 7 degrees with respect to one another, rather than being eclipsed. Six outer strands are coiled about a straight central strand, and each forms identical contacts with the central strand. Moreover, these contacts between central and outer strands are apparently similar to the contacts between neighboring outer strands.
Primary acceptor in bacterial photosynthesis: obligatory role of ubiquinone in photoactive reaction centers of Rhodopseudomonas spheroides.
Authors: Okamura M Y , Isaacson R A , Feher G
Published: May 2006

Reaction centers were found to bind two ubiquinones, both of which could be removed by o-phenanthroline and the detergent lauryldimethylamine oxide. One ubiquinone was more easily removed than the other. The low-temperature light-induced optical and electron paramagnetic resonance (EPR) changes were eliminated and restored upon removal and readdition of ubiquinone and were quantitatively correlated with the amount of tightly bound ubiquinone. We, therefore, conclude that this ubiquinone plays an obligatory role in the primary photochemistry. The easily removed ubiquinone is thought to be the secondary electron acceptor. The low-temperature charge recombination kinetics, as well as the optical and EPR spectra, were the same for untreated reaction centers and for those reconstituted with ubiquinone. This indicates that extraction and reconstitution were accomplished without altering the conformation of the active site. Reaction centers reconstituted with other quinones also showed restored photochemical activity, although they exhibited changes in their low-temperature recombination kinetics and light-induced (g = 1.8) EPR signal is interpreted in terms of a magnetically coupled ubiquinone--Fe2+ acceptor complex. A possible role of iron is to facilitate electron transfer between the primary and secondary ubiquinones.
Normal genetically mosaic mice produced from malignant teratocarcinoma cells.
Authors: Mintz B , Illmensee K
Published: May 2006

Malignant mouse teratocarcinoma (or embryonal carcinoma) cells with a normal modal chromosome number were taken from the "cores" of embryoid bodies grown only in vivo as an ascites tumor for 8 years, and were injected into blastocysts bearing many genetic markers, in order to test the developmental capacities, genetic constitution, and reversibility of malignancy of the core cells. Ninety-three live normal pre- and postnatal animals were obtained. Of 14 thus far analyzed, three were cellular genetic mosaics with substantial contributions of tumor-derived cells in many developmentally unrelated tissues, including some never seen in the solid tumors that form in transplant hosts. The tissues functioned normally and synthesized their specific products (e.g., immunoglobulins, adult hemoglobin, liver proteins) coded for by strain-type alleles at known loci. In addition, a tumor-contributed color gene, steel, not previously known to be present in the carcinoma cells, was detected from the coat phenotype. Cells derived from the carcinoma, which is of X/Y sex chromosome constitution, also contributed to the germ line and formed reproductively functional sperms, some of which transmitted the steel gene to the progeny. Thus, after almost 200 transplant generations as a highly malignant tumor, embryoid body core cells appear to be developmentally totipotent and able to express, in an orderly sequence in differentiation of somatic and germ-line tissues, many genes hitherto silent in the tumor of origin. This experimental system of "cycling" teratocarcinoma core cells through mice, in conjunction with experimental mutagenesis of those cells, may therefore provide a new and useful tool for biochemical, developmental, and genetic analyses of mammalian differentiation. The results also furnish an unequivocal example in animals of a non-mutational basis for transformation to malignancy and of reversal to normalcy. The origin of this tumor from a disorganized embryo suggests that malignancies of some other, more specialized, stem cells might arise comparably through tissue disorganization, leading to developmental aberrations of gene expression rather than changes in gene structure.
Plasma membrane alteration associated with malignant transformation in culture.
Authors: Gilula N B , Eger R R , Rifkin D B
Published: May 2006

The intramembrane organization of the plasma membranes of nonmalignant cells in culture has been compared by freeze-fracturing with that of virally-transformed malignant cells. No dramatic differences are present in the distribution of intramembrane particles in the plasma membranes of these cells when the cells are examined without fixation or with mild fixation (glutaraldehyde treatment) prior to freezing. However, a redistribution of intramembrane particles into aggregates occurs in the membranes of nontransformed cells after treatment with glycerol. The aggregation of particles is extensive in normal chick embryo fibroblasts, and less extensive in mouse 3T3 cells. The glycerol-induced particle redistribution is not inhibited at 4 degrees, but it is inhibited by pretreatment with 2.5% glutaraldehyde. A significant number of the cells remain viable after the glycerol treatment, and the process is reversible. Particle aggregation does not appear to be related to either growth rate or cell density. Transformed Rous sarcoma virus/chick embryo fibroblasts and simian virus 40/3T3 cells have few particle aggregates after glycerol treatment. The plasma membranes of chick embryo fibroblasts transformed with a mutant of Rous sarcoma virus (TS-68) that is temperature sensitive for transformation, have few particle aggregates when grown at the permissive temperature (37 degrees). Extremely prominent particle aggregates are present in the plasma membranes of cells grown at the nonpermissive temperature (41 degrees). These observations indicate that there is an alteration in the plasma membrane associated with viral transformation which is related to a glycerol-sensitive mechanism that controls the distribution of intramembrane particles.
Rapid changes in rat pineal beta-adrenergic receptor: alterations in l-(3H)alprenolol binding and adenylate cyclase.
Authors: Kebabian J W , Zatz M , Romero J A , Axelrod J
Published: May 2006

The properties of the beta-adrenergic receptor which regulates adenylate cyclase [ATP pyrophosphate-lyase (cyclizing)8 EC 4.6.1.1] in the pineal gland are similar to the properties of the sites which specifically bind l-[3H]alprenolol, a potent beta-adrenergic antagonist. Stimulation of the beta-adrenergic receptor results in a 30-fold increase in the activity of N-acetyltransferase (= arylamine acetyltransferase; acetyl CoA:arylamine N-acetyltransferase, EC 2.3.1.5), an enzyme involved in the synthesis of thepineal hormone melatonin. In the normal diurnal light-dark cycle there is greater physiological stimulation of the beta-adrenergic receptor in the pineal during the night than during the day. Pineals from rats kept in constant light for 24 hr possess more hormone-sensitive adenylate cyclase and specifically bind more l-[3H]alprenolol than do pineals from rats kept in the dark overnight. When rats, exposed to light for 24 hr, are treated with the beat-adrenergic agonist isoproterenol, there is a rapid loss of both hormone-sensitive adenylate cyclase activity and specific l-[3H]alprenolol binding sites. There is no change in the affinity of adenylate cyclase for isoproterenol or for its substrate, ATP. Similarly, although there are fewer binding sites, there is no change in the affinity of the remaining sites for either agonist or antagonist. Inhibition of protein synthesis with cycloheximide does not affect the loss of either adenylate cyclase activity or specific binding sites. The data suggest that stimulation of the beta-adrenergic receptor causes a rapid decrease in the number of available receptors and in hormone-sensitive adenylate cyclase activity; conversely, lack of stimulation causes an increase in these parameters. It is suggested that these changes contribute to the phenomena of super- and subsensitivity in the pineal gland by regulating the capacity of the pineal to synthesize cyclic AMP in response to beta-adrenergic stimulation.
An effect of castration and testosterone replacement on a circadian pacemaker in mice (Mus musculus).
Authors: Daan S , Damassa D , Pittendrigh C S , Smith E R
Published: May 2006

Castration of mice in freerunning conditions (total darkness, DD) causes a reduction of running wheel activity in the beginning of the active period (alpha) and stimulates activity at the end of alpha. Simultaneously, the period (tau) of the freerunning rhythm is increased. Both effects are abolished by implantation of a Silastic capsule from which a physiological dose of testosterone is released at a constant rate. The results are tentatively explained by differential endocrine influences on two oscillating components in the pacemaker of the circadian activity rhythm.
Spike-forming model of neural membrane: computer simulation of additional perfused axon experiments.
Authors: Wooldridge D E
Published: May 2006

In this paper a physical model of the neural membrane that I developed is tested for its ability to account for the details of the action potential spikes observed in squid giant axons, when perfused with sodium- and potassium-free fluids and surrounded by a calcium chloride solution. The near-zero resting potential of these perfused axons is accounted for by the model. The sizes, shapes, and conductances of the spikes observed with a number of different perfusates are also accounted for, when suitable values are assigned to the so-far unmeasured membrane constants that control the model properties. The three papers comprising the series are summarized at the end of this paper.
Binding, internalization, and degradation of low density lipoprotein by normal human fibroblasts and by fibroblasts from a case of homozygous familial hypercholesterolemia.
Authors: Stein O , Weinstein D B , Stein Y , Steinberg D
Published: May 2006

Skin fibroblasts from a patient with homozygous familial hypercholesterolemia (HFH) were compared with normal skin fibroblasts with regard to binding, internalization, and degradation of iodinated human low density lipoprotein (LDL). Like other cell lines from HFH patients, the mutant cells showed no suppression of sterol synthesis by LDL. Surface binding, measured at 0 degrees to eliminate the appreciable internalization that was shown to occur at 37 degrees, was on the average slightly less for HFH cells than normal cells at low LDL concentrations but comparable or even greater at high LDL concentrations (greater than 60 mug of LDL protein per ml). A major defect observed was in the rate of internalization of LDL at 37 degrees, which was only 1-10% of that in normal cells. LDL degradation was also markedly reduced but not to the same extent. Thus, a larger fraction of the LDL taken up appeared to be degraded by the mutant cells. The most striking defect observed, then, was not in surface binding of LDL but in rate of LDL internalization. While this might be secondary to a defect in specific binding sites of LDL, the magnitude of the observed differences in binding at low temperature seems too small to account for the huge differences in internalization (13- to 115-fold).
Reiteration frequency of immunoglobulin light chain genes: further evidence for somatic generation of antibody diversity.
Authors: Tonegawa S
Published: May 2006

Methods have been developed for preparing mouse immunoglobulin light chain mRNA of better than 90% purity. Hybridization of both lambda and kappa mRNAs to excess liver DNA yielded results compatible with gene reiteration frequencies of two to three. There was no evidence of hybridization of these highly purified mRNAs to reiterated DNA, and, in fact, the kinetics of hybridization were very similar to that of purified globin mRNA. Purified lambda mRNA from tumors producing structurally different lambda chains were used in competition hybridization experiments. An unlabeled lambda mRNA competed with another, labeled lambda mRNA to the same extent as homologous unlabeled lambda mRNA. That is, base sequence homology among lambda mRNAs is so high that any lambda mRNA should cross-hybridize with all germ line variable (Vlambda) genes at least for those V-regions which are represented among myelomas. From amino-acid sequence data, it is argued that there are probably more than 25 different lambda V regions. Hence it is concluded that the number of germ line genes is too small to account for the diversity of lambda chains. A similar conclusion is drawn for kappa chains.
Isoimmunization against human chorionic gonadotropin with conjugates of processed beta-subunit of the hormone and tetanus toxoid.
Authors: Talwar G P , Sharma N C , Dubey S K , Salahuddin M , Das C , Ramakrishnan S , Kumar S , Hingorani V
Published: May 2006

The immunogenicity of the conjugate prepared from "processed" beta-subunit of human chorionic gonadotropin (choriogonadotropin, HCG) and tetanus toxoid has been studied in animals and a human subject. The conjugate elicited the formation of high-affinity (Ka = 10(9)-10(11) M-1) anti-HCG and anti-tetanus antibodies. On primary immunization, the antibody, response lasted for several months. Repeat injection of the conjugate in the declining phase of antibody titers produced a booster response without a lag period. The antibodies reacted with the beta-subunit of HCG and the complete HCG molecule but were devois of significant crossreactivity with human growth hormone, placental lactogen, follicle-stimulating hormone, thyroid-stimulating hormone, and luteinizing hormone at tonic and surge levels. The antibodies were competent for neutralizing the biological activity of HCG in the mouse uterine weight gain assay, the ventral prostate weight gain assay, and the radioligand assay for binding of 125I-labeled HCG to receptors on corpus luteum. HCG (5000 international units) administered to an immunized subject was completely bound by circulating antibodies. Administration of HCG (in contrast to conjugate) was without booster effect on anti-HCG titers.
Antigen related to mammalian type-C RNA viral p30 proteins is located in renal glomeruli in human systemic lupus erythematosus.
Authors: Mellors R C , Mellors J W
Published: May 2006

An antigen related to mammalian type-C RNA viral p30 proteins was shown by the use of anti-p30 sera and the indirect immunofluorescence method to be present in the kidneys and spleen in a fulminant fatal case of human systemic lupus erythematosus and to be located in the glomeruli, the site of active lupus diffuse glomerulonephritis.
Interacting quantum fields and the chronometric principle
Authors: Segal I. E.
Published: May 2006

A form of interaction in quantum field theory is described that is physically intrinsic rather than superimposed via a postulated nonlinearity on a hypothetical free field. It derives from the extension to general symmetries of the distinction basic for the chronometric cosmology between the physical (driving) and the observed energies, together with general precepts of quantum field theory applicable to nonunitary representations. The resulting interacting field is covariant, causal, involves real particle production, and is devoid of nontrivial ultraviolet divergences. Possible physical applications are discussed.
Glycosylation of hemoglobin in vitro: affinity labeling of hemoglobin by glucose-6-phosphate.
Authors: Haney D N , Bunn H F
Published: May 2006

To determine the mechanism for the formation of hemoglobin A1c (Hb A1c) in vivo, we incubated human hemoglobin with glucose and metabolites of glucose. [14C]Glucose-6-phosphate (G6P) reacted readily with deoxyhemoglobin, and formed a covalent linkage. The reaction rate was considerably reduced in the presence of carbon monoxide or 2,3-diphosphoglycerate (2,3-DPG). Purified G6P hemoglobin had a lowered oxygen affinity and decreased reactivity with 2,3-DPG compared to Hb A. G6P behaved as a 2,3-DPG analog and reacted specifically at the NH2-terminal amino group of the beta chain. In contrast, the interaction of hemoglobin with glucose was much slower, and was unaffected by carbon monoxide or 2,3-DPG. Neither glucose-1-phosphate, fructose-6-phosphate, nor fructose-1,6-diphosphate formed a reaction product with hemoglobin. G6P behaves as an affinity label with the phosphate group forming electrostatic bonds at the 2,3-DPG binding site and the aldehvde group reacting with the NH2-terminal amino group of the beta chain. Thus, G6P hemoglobin may be an intermediate in the conversion of Hb A to Hb A1c.