bluuebunny/crossref_metadata_2025 huggingface dataset:
Tissue-specific DNA methylation in a cluster of rabbit beta-like globin genes.
Authors: Shen C K , Maniatis T
Published: May 2006

The relationship between DNA methylation and differential expression of rabbit beta-like globin genes was studied by using restriction enzymes that cleave the sequence C-C-G-G but are differentially inhibited by the presence of 5-methylcytosine. The methylation frequency of 13 C-C-G-G sites that flank a set of four closely linked rabbit beta-like globin genes was determined. This analysis revealed that certain sites surrounding embryonic and adult globin genes are relatively undermethylated in DNA from embryonic and adult erythroid tissues, respectively. This pattern is most pronounced for three sites that are undermethylated in erythroid cells but are totally methylated in nonerythroid cells. We conclude that the degree of CpG methylation in the rabbit beta-like globin gene cluster is correlated with gene activity, but the effect is confined to relatively small regions of DNA.
Visualization of microtubules of cells in situ by indirect immunofluorescence.
Authors: Byers H R , Fujiwara K , Porter K R
Published: May 2006

Microtubule staining patterns can be visualized within cells in situ on the surface of fish scales from the squirrel fish, Holocentrus ascensionis, and the common goldfish, Carassius auratus, after incubation with antibodies to sea urchin tubulin and fluorescein-labeled goat antibodies to rabbit immunoglobulin G. Chromatophores in situ from both species reveal a radial microtubule framework that orients the alignment of pigment granules. Innervating fibers of erythrophores on the H. ascensionis scale can also be observed. In situ, pseudo-epithelial cells called scleroblasts show microtubule patterns with a remarkable degree of similarity within a selected region. Over 90% of the cells have a microtubule framework that is nearly superimposable from cell to adjacent cell. The microtubules in scleroblasts are few and form a simple radial framework with a localized microtubule organizing center (MTOC). Microtubules in scleroblasts in vitro emanate from localized MTOCs but are much less radially organized than in situ. Scleroblasts in situ on the scale of C. auratus show microtubules that curve abruptly into coalignment with phase striations on the fibrillary plate. The phase striations arise from the orthogonal plies of collagen in intimate association with the scleroblasts. The role of microtubules in scleroblasts may thus be to provide orientation for collagen fibrillogenesis, analogous to their role in orientation of cellulose fibers in plants. That cells in situ exhibit highly related and coordinated microtubule staining patterns reaffirms that the cytoskeleton plays an important role in the organization of differentiated tissues.
Glycosaminoglycans that bind cold-insoluble globulin in cell-substratum adhesion sites of murine fibroblasts.
Authors: Laterra J , Ansbacher R , Culp L A
Published: May 2006

Glycosaminoglycans (GAGs) and glycoprotein-derived glycopeptide from mouse BALB/c3T3 and simian virus 40-transformed 3T3 whole cells or their adhesion sites, which are left bound to the serum-coated tissue culture substratum after detachment of cells mediated by [ethylenebis-(oxyethylenenitrilo]tetraacetic acid (EGTA), were analyzed for specific binding to Sepharose columns derivatized with cold-insoluble globulin (CIg). CIg is the serum-contained form of fibronectin and is required for the adhesion of these fibroblasts to the substratum. Of the various GAGs present in these fractions of either cell type, only the highly N-sulfated sequences of heparan sulfate and a small subset of dermatan sulfate bind to CIg-Sepharose. There was no detectable binding of glycopeptide, undersulfated heparan sulfate, the various chondroitin species, or hyaluronate. Adhesion sites from newly attaching cells were greatly enriched in CIg-binding heparan sulfate when compared to long-term-growth adhesion sites or EGTA-detached cells. Various properties of binding were determined. The reference standard standard GAGs heparin (or heparan sulfate) and dermatan sulfate were able to displace bound radiolabeled adhesion site GAG from the column, whereas the other GAGs had no effect. CIg has been shown to be the only adhesion-promoting activity in the serum layer of this culture system. Because these fibroblast adhesion sites do not contain collagen, which could potentially mediate adhesion to the substratum-bound CIg, these data support other evidence that multivalent heparan sulfate proteoglycans mediate substratum adhesion of these cells by coordinate binding to fibronectin on the cell surface and CIg on the substratum.
Clone-specific cellular recognition in a sea anemone.
Authors: Lubbock R
Published: May 2006

A highly specific cellular recognition system, capable of distinguishing between syngeneic and allogeneic tissue, exists in Anthopleura elegantissima, a sea anemone that lives in clonal colonies and attacks foreign clones. During the attack, specialized surface protrusions (acrorhagi) are used for stinging. The recognition process was studied by presenting various tissues to the surface of inflated acrorhagi and observing whether nematocyst discharge occurred. Nematocyte excitation required direct contact of th acrorhagus with foreign tissue and is presumably mediated by cell surface receptors. Most foreign anthozoans were excitatory, but intact syngeneic individuals, organisms other than anthozoans, and inanimate objects consistently failed to elicit discharge. When the intact surface of an excised tentacle from one anemone was presented to the acrorhagus of another, discharge occurred in 101 of 102 allogeneic combinations; more than 50 tests with tentacles from clone mates (i.e., syngeneic combinations) were all negative. No evidence for specific immunological memory was found. It is suggested that clonal recognition depends upon genetically determined chemical markers in the surface membrane of the epithelial cells; these are assumed to differ between clones although, in rare cases, allogeneic clones may have similar markers.
Replication and meiotic transmission of yeast ribosomal RNA genes.
Authors: Brewer B J , Zakian V A , Fangman W L
Published: May 2006

The yeast Saccharomyces cerevisiae has approximately 120 genes for the ribosomal RNAs (rDNA) which are organized in tandem within chromosomal DNA. These multiple-copy genes are homogeneous in sequence but can undergo changes in copy number and topology. To determine if these changes reflect unusual features of rDNA metabolism, we have examined both the replication of rDNA in the mitotic cell cycle and the inheritance of rDNA during meiosis. The results indicate that rDNA behaves identically to chromosomal DNA: each rDNA unit is replicated once during the S phase of each cell cycle and each unit is conserved through meiosis. Therefore, the flexibility in copy number and topology of rDNA does not arise from the selective replication of units in each S phase nor by the selective inheritance of units in meiosis.
Involvement of calcium channels in short-term desensitization of muscarinic receptor-mediated cyclic GMP formation in mouse neuroblastoma cells.
Authors: El-Fakahany E , Richelson E
Published: May 2006

Incubation of mouse neuroblastoma cells (clone N1E-115) with Mn2+ resulted in a rapid and transient increase in cyclic GMP formation. This effect appears to be due to an increase in calcium influx because it did not occur in the absence of extracellular calcium or in the presence of verapamil, a calcium transport inhibitor. In addition, Mn2+ inhibited muscarinic receptor-mediated cyclic GMP responses. The ability of Mn2+ to increase cyclic GMP levels was markedly diminished in cells desensitized to the effects of carbamoylcholine, suggesting that this densensitization involves inactivation of calcium entry.
Dependence of in vitro myogenesis on a trophic protein present in chicken embryo extract.
Authors: Oh T H , Markelonis G J
Published: May 2006

A trophic protein (sciatin) purified from sciatic nerves has been shown to enhance the morphological development and to promote the maintenance of skeletal muscle cells in vitro [Markelonis, G. J. & Oh, T. H. (1979) Proc. Natl. Acad. Sci. USA 76, 2470-2474]. We have elicited a specific antiserum against purified sciatin in rabbits. By using this antiserum, we have examined whether sciatin is also required for the initial differentiation of avian myogenic cells in vitro. Sciatin was found to be a component of chicken embryo extract, a constituent of culture medium required for myogenesis in vitro, by an immunodiffusion assay and by NaDodSO4 gel electrophoresis of immunoprecipitates. The removal of sciatin from chicken embryo extracts by immunoprecipitation with antiserum against sciatin completely inhibited myogenesis. When myogenic cells were grown in culture medium from which sciatin had been removed, the cells failed to differentiate beyond the myoblast stage. However, when sciatin (25 microgram/ml) was added to the sciatin-absorbed culture medium, normal myogenesis ensued. Furthermore, myogenic cells underwent normal myogenesis in the absence of embryo extract if sciatin (25 microgram/ml) was added to the culture medium. These results demonstrate that sciatin is the component of chicken embryo extract required for myogenesis and that the protein influences the initial differentiation of myogenic cells in vitro.
Alternative male life histories in bluegill sunfish
Authors: Gross Mart R. , Charnov Eric L.
Published: May 2006

Male bluegill sunfish are shown to have two alternative mating strategies: cuckoldry or parental care. Cuckolder males first mature at age 2. They follow a developmental sequence of sneaking and then mimicking female behavior to deceptively gain access to spawnings. Males who become parentals (construct nests, attract females, provide brood care) delay maturation until age 7. The parental investment of these males is parasitized by the cuckolders. This system is an example of a truly parasitically dependent mating strategy in vertebrates. A natural selection model is developed to predict the equilibrium frequencies of the two male types. A preliminary test of the model provides qualitative agreement.
Energy transfer from PO excited states to alkali metal atoms in the phosphorus chemiluminescence flame
Authors: Khan Ahsan U.
Published: May 2006

Phosphorus chemiluminescence under ambient conditions of a phosphorus oxidation flame is found to offer an efficient electronic energy transferring system to alkali metal atoms. The lowest resonance lines,
2
P
3 / 2
,½→
2
S
½
, of potassium and sodium are excited by energy transfer when an argon stream at 80°C carrying potassium or sodium atoms intersects a phosphorus vapor stream, either at the flame or in the postflame region. The lowest electronically excited metastable
4
II

i

state of PO or the (PO[unk]PO)
*
excimer is considered to be the probable energy donor. The (PO[unk]PO)
*
excimer results from the interaction of the
4
II

i

state of one PO molecule with the ground
2
II

r

state of another. Metastability of the donor state is strongly indicated by the observation of intense sensitized alkali atom fluorescence in the postflame region.
Affinity labeling of rat liver thyroid hormone nuclear receptor.
Authors: Nikodem V M , Cheng S Y , Rall J E
Published: May 2006

The thyroid hormone receptor from rat liver nuclei has been covalently labeled with the N-bromoacetyl derivatives of L-thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3). Displacement binding studies showed that, in the presence of 100-fold molar excess of unlabeled N-bromoacetyl-T3 or T4, binding of [125I]T3 or [125I]T4 was nearly totally inhibited. Heat inactivation of the receptor (55 degrees C for 15 min) resulted in parallel losses in the binding of T3 (95%) and N-bromoacetyl-T3 (93%). These results indicated that T3 and T4 and their bromoacetyl derivatives compete for the same binding site. The nuclear receptor showed identical behavior in high-pressure liquid chromatography (HPLC) whether bound to T3 or T4 or covalently labeled with their bromoacetyl derivatives. HPLC provided a single-step 100-fold purification of the nuclear receptor. Na-DodSO4 gel electrophoresis of the nuclear receptor labeled with N-bromoacetyl derivatives of [125I]T3 or [125I]T4 showed one major radioactive component with a molecular weight of 56,000. Furthermore, in the absence of denaturant, the nuclear receptor either bound to [125I]T3 or covalently labeled with N-bromoacetyl-[125I]T3 showed identical mobility. These results suggested that the nuclear receptor is a single polypeptide chain and binds either T3 or T4. Nuclear receptors covalently linked with N-bromoacetyl derivatives of [125I]T3 or [125I]T4 may be useful as a marker for the preparative purification of receptor.
Nucleotide sequence and expression of Escherichia coli trpR, the structural gene for the trp aporepressor.
Authors: Gunsalus R P , Yanofsky C
Published: May 2006

The nucleotide sequence of trpR of Escherichia coli was determined. This gene codes for a polypeptide (Mr 12,356) that is 108 amino acid residues in length. NH2-terminal, COOH-terminal, and total amino acid analyses of purified aporepressor agree with the deduced amino acid sequence and establish the translation start and stop codons of the structural gene. The transcription start site for trpR mRNA synthesis in vitro was shown to be 56 base pairs prior to the translation start site. The nucleotide sequence on either side of the transcription start site is homologous to the trp operon operator. Purified trp aporepressor, when activated by L-tryptophan, protects restriction sites in this region, the presumed trpR operator, from cleavage by the respective restriction endonucleases. Bound RNA polymerase protects the same restriction sites. These findings and the additional observation that trp repressor inhibits transcription initiation in vitro establish that there is a functional overlap of operator and promoter sequences in the regulatory region of the trpR operon. These findings indicate that expression of trpR is autoregulatory.
Model for lactose repressor protein and its interaction with ligands.
Authors: Dunaway M , Manly S P , Matthews K S
Published: May 2006

A model is presented for the structure of the lactose repressor protein and for its interaction with inducer, operator DNA, and nonspecific DNA. The proposed structure is based on experimental evidence from this laboratory and from the literature and is offered as an integration of the available data on this system. Features unique to this model include: (i) interaction of the core region of the protein with the operator, (ii) primary effects of the conformational change in response to inducer on the core-operator interaction, (iii) contacts between all four subunits of the protein and the operator DNA, and (iv) qualitative differences in operator and nonspecific DNA binding.
Regulation of myosin self-assembly: phosphorylation of Dictyostelium heavy chain inhibits formation of thick filaments.
Authors: Kuczmarski E R , Spudich J A
Published: May 2006

Dictyostelium myosin is composed of two heavy chains and two pairs of light chains in a 1:1:1 stoichiometry. Myosin purified from amoebae grown in medium containing [32P]phosphate had two of the subunits labeled (0.2-0.3 mol of phosphate per mol of 210,000-dalton heavy chains and approximately 0.1 mol of phosphate per mol of 18,000-dalton light chain). Kinase activities specific for the 210,000-dalton and for the 18,000-dalton subunits have been identified in extracts of Dictyostelium amoebae, and the heavy chain kinase has been purified 50-fold. This kinase phosphorylated Dictyostelium myosin to a maximum of 0.5-1.0 mol of phosphate per mol of heavy chain. Heavy chain phosphate, but not light chain phosphate, can be removed with bacterial alkaline phosphatase. Actin-activated myosin ATPase increased 80% when phosphorylated myosin was dephosphorylated to a level of approximately 0.06 mol of phosphate per mol of heavy chain. This effect could be reversed by rephosphorylating the myosin. The ability of myosin to self-assemble into thick filaments was inhibited by heavy chain phosphorylation. For example, in 80-100 mM KCl, only 10-20% of the myosin was assembled into thick filaments when the heavy chains were fully phosphorylated. Removal of the heavy chain phosphate resulted in 70-90% thick filament formation. This effect on self-assembly could be reversed by rephosphorylating the dephosphorylated myosin. These findings suggest that heavy chain phosphorylation may regulate cell contractile events by altering the state of myosin assembly.
Radiosensitivity in ataxia-telangiectasia: a new explanation.
Authors: Painter R B , Young B R
Published: May 2006

The cause of increased radiosensitivity in ataxia-telangiectasia (AT) cells may be a defect in their ability to respond to DNA damage rather than a defect in their ability to repair it. Doses of x-radiation that markedly inhibited the rate of DNA synthesis in normal human cells caused almost no inhibition in AT cells and thus less delay during which x-ray damage could be repaired. The radioresistance of DNA synthesis in AT cells was primarily due to a much smaller inhibition of replicon initiation than in normal cells; the AT cells were also more resistant to damage that inhibited chain elongation. AT cells have been reported to undergo less radiation-induced mitotic delay than normal cells, which may cause them to move from G2 phase into mitosis before repair is complete and may result in the increased incidence of chromatid aberrations observed by others. Therefore, AT cells fail to go through those delays that allow normal cells to repair DNA damage before it can be expressed.
Evidence for an alternative nitrogen fixation system in Azotobacter vinelandii.
Authors: Bishop P E , Jarlenski D M , Hetherington D R
Published: May 2006

Two Azotobacter vinelandii strains capable of growing on N2(Nif+) were isolated from two different mutant strains that lacked dinitrogenase activity (Nif-). Extracts of N2-grown cells of the two Nif+ strains lacked significant amounts of the "conventional" dinitrogenase protein subunits, as determined by two-dimensional gel electrophoresis. Instead, the extracts contained at least four new proteins that appeared to be ammonia-repressible (i.e., they were not detected in extracts of ammonia-grown cells). Based on the results of genetic backcrosses, the two Nif+ strains were shown to be pseudorevertants. Both Nif+ pseudorevertant strains were able to grow in N-free media lacking molybdenum but containing tungsten (conditions that prevented growth of the wild-type strain). The four new proteins were observed in extracts of N2-fixing cells of the Nif+ pseudorevertants regardless of whether the cells were grown in the presence of molybdenum-starved wild-type A. vinelandii cells grown under N2-fixing conditions. Under conditions of molybdenum deprivation, Nif- mutant strains of several different phenotypic classes underwent phenotypic reversal to Nif+, as shown by their ability to incorporate 15N2 and to grow in N-free media. These results provide evidence that A. vinelandii possesses an alternative N2-fixation system that is expressed during conditions of molybdenum deficiency.
Analysis of the mechanism of fast axonal transport by intracellular injection of potentially inhibitory macromolecules: evidence for a possible role of actin filaments.
Authors: Goldberg D J , Harris D A , Lubit B W , Schwartz J H
Published: May 2006

Although actin is thought to participate in several types of cell motility other than muscle contraction, no direct evidence has linked it to the force-generating mechanism for fast axonal transport. We have obtained evidence for the involvement of actin by microinjecting, into the serotonergic giant cerebral neuron of Aplysia, two preparations that have been shown to depolymerize actin filaments. One is a fraction of rabbit serum containing a heat-labile gamma globulin that affects actin polymerization in a manner similar to that of cytochalasin and several proteins that are thought to regulate the length of actin filaments. The other is bovine pancreatic DNase I which binds to actin stoichiometrically. Both preparations substantially decreased the transport of storage vesicles containing [3H]serotonin. Phalloidin, a toxic fungal peptide that binds to actin filaments but stabilizes rather than depolymerizes them, did not inhibit transport. We have not yet determined whether the inhibition od transport occurs during export of [3H]serotonin from the cell body into the axon or during translocation along the axon. Nevertheless, these observations provide a promising experimental indication that actin is involved in fast axonal transport.
Release of enkephalins and enkephalin-containing polypeptides from perfused beef adrenal glands.
Authors: Kilpatrick D L , Lewis R V , Stein S , Udenfriend S
Published: May 2006

Enkephalins and enkephalin-containing polypeptides were released from perfused bovine adrenal glands by nicotine and Ba2+, agents that release catecholamines. All the enkephalin-containing polypeptides that are normally found in the adrenal medulla were released by the two secretagogues in approximately the same proportions as are present in adrenal chromaffin granules.
Increased mutation in crosses between geographically separated strains of Drosophila melanogaster.
Authors: Thompson J N , Woodruff R C
Published: May 2006

Mutator activity associated with the common male recombination (MR) chromosomes in Drosophila melanogaster appears to be suppressed in natural populations. Crosses between geographically separated populations, however, lead to the release of mutator activity as measured by a significant increase in visible mutations. Such an increase in mutation in hybrid individuals may be a powerful factor in inducing or releasing variation in nature, and in more extreme instances may contribute to the separation of microdifferentiated populations.
Complete amino acid sequence of pooled papain-solubilized HLA-A, -B, and -C antigens: relatedness to immunoglobulins and internal homologies.
Authors: Trägärdh L , Rask L , Wiman K , Fohlman J , Peterson P A
Published: May 2006

Pooled, papain-solubilized HLA-A, -B, and -C antigens, derived from a large number of individuals and comprising several allelic forms, have been subjected to amino acid sequence determination. Despite the heterogeneity of the material, a main sequence representing all of the 273 amino acid residues could be established. The primary structure encompasses two immunoglobulin-like disulfide loops. The single carbohydrate moiety is attached to asparagine-86. Computer analyses demonstrated that the COOH-terminal one-third of the sequence, called H3, display statistically significant homology with members of the immunoglobulin family. The NH2-terminal two-thirds of the molecule, called H1 and H2, are not significantly homologous to any of the immunoglobulin sequences. However, H1 and H2 exhibit a distant relatedness to each other but no obvious similarity to the H3 region.
Inhibition of the initiation of translation by a factor isolated from Escherichia coli cells.
Authors: Clark V L
Published: May 2006

A low molecular weight factor isolated from Escherichia coli cells was found to inhibit protein synthesis in vitro directed by RNA of bacteriophage R-17. The factor also inhibited poly(U)-directed translation, but higher concentrations were required. When the factor was added after R-17 RNA-directed translation was initiated, the onset of inhibition was delayed. Initiation-independent translation of polysomes was not inhibited. The factor inhibited the binding of N-formylmethionyl-tRNAfMet to 70S ribosomes to form the 70S initiation complex, and it released the N-flrmylmethionyl-tRNAfMet from preformed complexes. The factor did not prevent the formation of N-formylmethionylpuromycin. It was concluded that the factor inhibits specifically the initiation of translation.
Phospholipid methylation: a biochemical signal modulating lymphocyte mitogenesis.
Authors: Hirata F , Toyoshima S , Axelrod J , Waxdal M J
Published: May 2006

Phospholipid methylation in murine T lymphocytes but not B cells was stimulated by mitogenic lectins such as concanavalin A and phytohemagglutinin, and the methylation was then returned to the control level by the concomitant activation of phospholipase A2. A parallelism between dose-response curves of concanavalin A for phospholipid methylation and thymidine incorporation was found. Inhibition of either synthesis or degradation of methylated phospholipids resulted in a decrease in the thymidine incorporation. Although prostaglandins such as the E and F series were the main products of arachidonic acid released by phospholipase A2 activation, inhibition of synthesis of these compounds by indomethacin did not reduce the thymidine incorporation significantly. These results suggest that the mitogenesis of murine T lymphocytes is triggered by the activation of both phospholipid methyltransferase(s) and phospholipase A2.
Hydrolysis of GTP on elongation factor Tu.ribosome complexes promoted by 2'(3')-O-L-phenylalanyladenosine.
Authors: Campuzano S , Modolell J
Published: May 2006

In the presence of Escherichia coli ribosomes and elongation factor EF) Tu, 2'(3')-O-L-phenylalanyladenosine (AdoPhe), the 3'-terminal portion of Phe-tRNAPhe, promotes the hydrolysis of GTP. The reaction requires the presence of both 30S and 50S ribosomal subunits and of proteins L7/L12 on the 50S subunit, is unaffected by mRNA [poly(uridylic acid)], and is strongly stimulated by EF-Ts. It is proposed that the AdoPhe-dependent GTP hydrolysis, like that promoted by aminoacyl-tRNA, is mediated by a ternary complex with EF-Tu and GTP; however, in contrast to aminoacyl-tRNA, AdoPhe is probably not retained by ribosomes after GTP hydrolysis. Phe-tRNAPhe or N-acetyl-Phe-tRNAPhe bound to the ribosomal acceptor site do not inhibit, but even stimulate, GTP hydrolysis by AdoPhe.EF-Tu.GTP. Thus, the binding site for EF-Tu on the ribosome is probably available for interaction with AdoPhe.EF-Tu.GTP regardless of whether the nearby acceptor site is vacant of occupied with aminoacyl-tRNA or peptidyl-tRNA. The results demonstrate the critical role of the 3'-terminal region of aminoacyl-tRNA in activating the EF-Tu- plus ribosome-dependent GTPase.
Structural details of membrane-bound acetylcholine receptor from Tropedo marmorata.
Authors: Zingsheim H P , Neugebauer D C , Barrantes F J , Frank J
Published: May 2006

A projection, at 15- to 20-A resolution, is presented of the structure of the membrane-bound acetylcholine receptor protein from Torpedo marmorata. The projection has its axis perpendicular to the membrane plane; its main contribution originates from a hydrated portion of the protein, which extends from the membrane into the aqueous medium. The structure is distinctly asymmetric, with individual morphological subunits barely resolvable. These results have been obtained by noncrystallographic averaging, using correlation functions, applied to electron micrographs of receptor-rich membrane fragments. The micrographs had been taken with minimal beam exposure in a scanning transmission electron microscope.
Synthesis and insertion of cytochrome P-450 into endoplasmic reticulum membranes.
Authors: Bar-Nun S , Kreibich G , Adesnik M , Alterman L , Negishi M , Sabatini D D
Published: May 2006

Treatment of rats with phenobarbital leads to a substantial increase in levels of translatable liver cytochrome P-450 mRNA. This mRNA is primarily associated with ribosomes bound to endoplasmic reticulum membranes which in an in vitro system synthesized approximately 10 times more cytochrome P-450 than did free polysomes from the same animals. Cytochrome P-450 synthesized by rough microsomes in vitro appears to be directly inserted into the membranes because it was not released by a treatment with low detergent concentrations that released albumin and other microsomal content proteins. The amino-terminal amino acid sequence of cytochrome P-450 synthesized in an mRNA-dependent system resembles in hydrophobicity the signal segment of presecretory proteins and therefore may serve to insert the polypeptide into the membrane during synthesis. In contrast to the situation with secretory proteins and several other membrane proteins, however, the putative insertion signal of cytochrome P-450 is not removed by a membrane-associated peptidase and remains in the mature polypeptide.
International Ultraviolet Explorer satellite observations of seven high-excitation planetary nebulae
Authors: Aller L. H. , Keyes C. D.
Published: May 2006

Observations of seven high-excitation planetary nebulae secured with the International Ultraviolet Explorer (IUE) satellite were combined with extensive ground-based data to obtain electron densities, gas kinetic temperatures, and ionic concentrations. We then employed a network of theoretical model nebulae to estimate the factors by which observed ionic concentrations must be multiplied to obtain elemental abundances. Comparison with a large sample of nebulae for which extensive ground-based observations have been obtained shows nitrogen to be markedly enhanced in some of these objects. Possibly most, if not all, high-excitation nebulae evolve from stars that have higher masses than progenitors of nebulae of low-to-moderate excitation.
Index theory for the boundaries of complex analytic varieties
Authors: Yau Stephen S.-T.
Published: May 2006

A result of boundary
p
-index is presented for a vector bundle on a complex analytic variety with boundary. A characterization of which odd-dimensional, real submanifolds of [unk]

N

are boundaries of complex subvarieties (respectively submanifolds) in [unk]

N

is given.
Membrane lipid physical state and modulation of the Na+,Mg2+-ATPase activity in Acholeplasma laidlawii B.
Authors: Silvius J R , McElhaney R N
Published: May 2006

Careful analysis of the Arrhenius plot of the Na+,Mg2+-ATPase (ATP pyrophosphohydrolase, EC 3.6.1.8) activity in Acholeplasma laidlawii B membranes of varying fatty acid composition has been combined with differential thermal analysis of the membrane lipid phase transitions to evaluate the effects of membrane lipid properties on the enzyme activity. Our results indicate that the enzyme is active only in association with liquid-crystalline lipids, exhibiting a significant heat capacity of activation, delta Cp++, for the ATP hydrolytic reaction in this case. Quantitative analyses of Arrhenius plots for the enzyme activity in membranes whose lipids exhibit a gel-to-liquid-crystalline phase transition in the physiological temperature range suggest that the ATPase is inactivated when its boundary lipids undergo a phase transition that is driven by the bulk lipid phase transition but is less cooperative than the latter. Our results suggest that the familiar "biphasic linear" Arrhenius plots obtained for many membrane enzymes may in fact have a more complex shape, analysis of which can furnish useful information regarding the behavior of the enzyme molecule.
Three-dimensional crystals of membrane proteins: bacteriorhodopsin.
Authors: Michel H , Oesterhelt D
Published: May 2006

The intrinsic membrane protein bacteriorhodopsin has been crystallized by salt precipitation after solubilization by octyl glucoside. Two different crystal forms were obtained, depending on the nature of the salt used and the pH. Needles formed in the presence of sodium phosphate and in ammonium sulfate solutions above pH 4.8. Cubes appeared in sodium citrate solutions or ammonium sulfate. Unlike the cubic crystals, the birefringent needles showed strong linear dichroism, which allowed determination of the orientation of the chromophore's transition moment. The procedure described here may be of general use in crystallographic studies of membrane proteins.
Native ribonucleoprotein is an efficient transcriptional complex of avian myeloblastosis virus.
Authors: Chen M , Garon C F , Papas T S
Published: May 2006

A native ribonucleoprotein (RNP) complex of avian myeloblastosis virus was prepared under conditions that gave optimal cDNA synthesis. The complex was an autonomous transcriptional unit capable of synthesizing DNA complementary to the RNA virus genome in the absence of exogenous reverse transcriptase (RNA-dependent DNA nucleotidyltransferase), genomic RNA, and primer. The RNA of the RNP complex cannot be translated in an in vitro cell-free translational system. The RNP contains intact viral RNA, the two subunits of the reverse transcriptase (beta and alpha), the p32 polypeptide resulting from the cleavage of the beta subunit into the alpha subunit, and p12. The principal polypeptide constituent of the RNP complex is the highly basic protein p12, which occurs at a molar ratio of 40:1 in relation to the beta subunit of the polymerase. When examined by the electron microscope, the RNP complex appears similar to the beaded structure of chromatin fiber. A significant portion of these molecules are circular, with headlike structures attached. The circular nature of the proviral DNA and the ability of the RNP complex to generate large intact cDNA copies from the natural primer end suggest that the 5' and 3' ends of the viral RNA are in proximity when in the RNP complex.
Mitochondria and sarcoplasmic reticulum as model targets for neurotoxic and myotoxic phospholipases A
2
Authors: Ng Ronald H. , Howard Bruce D.
Published: May 2006

Certain neurotoxins and myotoxins from snake venoms have phospholipase A
2
activity (phosphatide 2-acylhydrolase, EC 3.1.1.4), which appears to be necessary for their toxicity. Several of these toxins inhibit the net uptake of Ca
2+
into sarcoplasmic reticulum vesicles and brain mitochondria. We have obtained evidence that the ability to inhibit this Ca
2+
uptake is a mechanistically relevant correlate of the toxicity of these proteins rather than being just a nonspecific consequence of their phospholipase A
2
activity. Two of the toxins, β-bungarotoxin and notexin, had 5% and 50%, respectively, of the phospholipase A
2
activity of IVa phospholipase A
2
(a nontoxic enzyme), but β-bungarotoxin was as effective as IVa in inhibiting Ca
2+
uptake into brain mitochondria and notexin was more effective. Each of the myotoxic enzymes substantially inhibited Ca
2+
uptake into sarcoplasmic reticulum, notexin being the most effective in this regard. This ability correlated better with their myotoxic potency than with their phospholipase A
2
activity. β-Bungarotoxin lost its toxicity but not its measurable phospholipase A
2
activity after modification with ethoxyformic anhydride in the presence of dihexanoylphosphatidylcholine. The modified toxin also lost most of its ability to inhibit Ca
2+
uptake into sarcoplasmic reticulum and brain mitochondria. Sarcoplasmic reticulum vesicles reconstituted from solubilized sarcoplasmic reticulum retained their sensitivity to notexin.
Structure of the alpha-fetoprotein gene in the mouse.
Authors: Gorin M B , Tilghman S M
Published: May 2006

The mouse alpha-fetoprotein mRNA is the product of a single-copy gene whose mRNA coding sequences are represented discontinuously in the genome. Several EcoRI genomic fragments which contain portions of the alpha-fetoprotein gene have been cloned using the EK2 vector lambda gt WES . lambda B. In addition, a mouse genomic library has been screened to obtain a 15.75-kilobase segment of DNA that includes more than 85% of the alpha-fetoprotein coding sequence. Analyses by restriction endonuclease mapping and electron microscopy showed that the mRNA sequence is interrupted by at least 11 intervening sequences which occupy 90% of the cloned DNA.
Inhibition of preprotein processing in ascites tumor lysates by incorporation of a leucine analog
Authors: Hortin Glen , Boime Irving
Published: May 2006

Leucine analogs were tested in the Krebs II ascites cell-free translation system for the ability to inhibit preprotein cleavage by replacing leucine in nascent chains of bovine preprolactin, rat preprolactin, human placental prelactogen (pre-hPL), and pre-α subunit of human chorionic gonadotropin (α-hCG). In the absence of analog, ascites microsomal membranes cleaved these preproteins to their mature forms and sequestered the processed products. Also, two asparagine residues in α-hCG were glycosylated. When 4 mM β-DL-hydroxyleucine was added to the lysate instead of L-leucine, cotranslational processing and sequestration of both species of preprolactin and pre-hPL were inhibited. Sequential Edman degradation confirmed that pre-hPL was not cleaved. The inhibition of processing by β-hydroxyleucine resulted from its incorporation into protein. This was shown by reversal of the effect by addition of leucine and by inhibition of [
3
H]leucine incorporation into protein. Of significance, the processing of pre-α-hCG was less sensitive to β-hydroxyleucine because its prepeptide contains only four scattered leucine residues, whereas the presegments of hPL and the prolactins contain six to eight clustered leucine residues. These experiments demonstrate that translocation and processing of secretory proteins require structural features determined by the primary amino acid sequence.
Biosynthesis and assembly of the proton-translocating adenosine triphosphatase complex from chloroplasts
Authors: Nelson Nathan , Nelson Hannah , Schatz Gottfried
Published: May 2006

The H
+
-translocating ATPase complex of chloroplasts consists of at least eight nonidentical subunits. Five of these (α, β, γ, δ, and ε subunits) collectively constitute the globular extramembranous CF
1
portion of the complex. The remaining three subunits (I-III) represent the membrane-embedded portion. Biosynthesis and assembly of these subunits were studied by pulse-labeling isolated spinach chloroplasts in the presence of cycloheximide or chloramphenicol and by translating total leaf RNA in a rabbit reticulocyte system. The labeled products were analyzed by immunoprecipitation with subunit-specific antisera or by isolating the entire H
+
-translocating ATPase complex in a nearly pure state. We found that chloroplasts synthesize the α, β, γ, and ε subunits of CF
1
, the membrane-embedded subunit I, and probably also the membrane-embedded subunit III. The δ subunit (and probably also subunit II) are imported from the cytoplasm via larger precursor forms. After isolated chloroplasts are labeled in the presence of cycloheximide, the chloroplast-made H
+
-ATPase subunits are assembled into a complex that is indistinguishable from the authentic H
+
-ATPase complex. This assembly indicates that isolated chloroplasts contain excess pools of the cytoplasmically made subunits.
Selenium-containing tRNAs from Clostridium sticklandii: cochromatography of one species with L-prolyl-tRNA.
Authors: Chen C S , Stadtman T C
Published: May 2006

75Se-Labeled tRNAs were synthesized by Clostridium sticklandii cultures supplemented with 1 microM sodium [75Se]selenite or [75Se]selenocysteine. This process is highly specific for selenium; it occurred in the presence of 1.2 mM sodium sulfide and was not decreased by the further addition of a 500-fold molar excess of cysteine. The 75Se in these tRNAs was located in the polynucleotide portion of the molecules and not in esterified (alkali-labile) selenocysteine. Inhibition of cell multiplication by antibiotics that block either protein synthesis or DNA-dependent RNA synthesis did not prevent this 75Se incorporation. Three [75Se]tRNAs were separated from C. sticklandii cells labeled in the presence of chloramphenicol and were partially purified by chromatography on benzoylated DEAE-cellulose and DEAE-Sephadex A-50 columns. These were designated seleno-tRNAs I, II, and III according to their elution sequence from benzoylated DEAE-cellulose. Cochromatography of purified seleno-tRNA II on DEAE-Sephadex A-50 with an L-proline-accepting species suggests that it is a selenium-containing L-prolyl-tRNA.
During ontogeny, Ia-bearing accessory cells are found early in the thymus but late in the spleen.
Authors: Lu C Y , Beller D I , Unanue E R
Published: May 2006

The ontogeny of Ia-bearing accessory cells was studied in mice. Ia-bearing adherent cells from the thymus, consisting predominantly of macrophages, were found from birth. These adherent cells were able to present antigen, as measured by their ability to induce immune T-cell proliferation. In contrast, Ia-bearing adherent cells from the spleen were not found until the second week of life, and their antigen-presentation function was not present until later. The differential ontogeny of Ia-bearing accessory cells at these sites may be important in both development of immune competence and the restriction of autoimmunity.
Electron density functions for simple molecules
Authors: Pearson Ralph G. , Palke William E.
Published: May 2006

Trial electron density functions have some conceptual and computational advantages over wave functions. The properties of some simple density functions for H
+
2
and H
2
are examined. It appears that for a diatomic molecule a good density function would be given by ρ =
N
(
A
2
+
B
2
), in which
A
and
B
are short sums of
s, p, d
, etc. orbitals centered on each nucleus. Some examples are also given for electron densities that are appropriate for excited states.
Benzocyclobutene—
o
-xylylene valence tautomerization: Oxygen and sulfur analogs
Authors: Mao Yuh-Lin , Boekelheide V.
Published: May 2006

Gas phase pyrolysis of
o
-hydroxybenzyl alcohol at 750°C gave
o
-quinonemethide, which, on isolation, formed a mixture of the corresponding dimer and trimer. However, pyrolysis of
o
-hydroxy-[1-(4-pentenyl)]benzyl alcohol permitted intramolecular trapping of the intermediate
o
-quinonemethide, giving 3,4-trimethylene-3,4-dihydrobenzochroman. In contrast, gas phase pyrolysis of
o
-mercaptobenzyl alcohol readily gave benzo[
b
]thiete in good yield. The pyrolysis makes this interesting highly strained molecule readily available for study and synthetic application. Preliminary results showed that benzo[
b
]thiete readily undergoes thermal dimerization, ring-opening reactions with nucleophiles, and a variety of Diels-Alder reactions.
Analytical approximation to the accessible surface area of proteins
Authors: Wodak Shoshana J. , Janin Joël
Published: May 2006

We propose an analytical substitute to the geometrical construction that is commonly used in calculating the protein surface area that is accessible to the solvent. A statistical approach leads to an expression of accessible surface areas as a function of distances between pairs of atoms or of residues in the protein structure, assuming only that these atoms or residues are randomly distributed in space but not penetrating each other. This function gives good estimates of the accessible surface area and of the area buried in subunit contacts for a number of proteins. Its evaluation is very fast, and the function can be differentiated, which opens the way to new applications of accessibility measurements in the study of proteins. As an example, we show that the presence of domains is easily detected by an automatic procedure based on surface areas only.
Sizes, locations, and directions of transcription of two genes on a cloned maize chloroplast DNA sequence
Authors: Link Gerhard , Bogorad Lawrence
Published: May 2006

mRNA for the large subunit (LS) of ribulose-1,5-bisphosphate carboxylase [3-phospho-D-glycerate carboxylase (dimerizing), EC 4.1.1.39] of
Zea mays
is complementary to an uninterrupted 1600-base-pair-long chloroplast DNA sequence that has been mapped precisely within the 4350-base-pair-long chloroplast DNA fragment
Bam
9 to which it had been traced earlier [Bedbrook, J. R., Coen, D. M., Beaton, A. R., Bogorad, L. & Rich, A. (1979)
J. Biol. Chem.
254, 905-910]. An additional 1400-base-pair-long uninterrupted region that is colinear with a chloroplast RNA has been detected on
Bam
9. The transcript from this region is part of a 2200-nucleotide-long RNA. The remainder of the DNA sequence for the 2200-base-pair RNA maps outside
Bam
9. The 1600-base-pair
LS
gene and the gene for the 2200-nucleotide transcript are close to one another. They are separated by an untranscribed intercistronic “gap” about 330 base pairs long. These two closely packed genes are inverted on the chromosome—i.e., their 3′ termini are at opposite ends of the untranscribed gap and they map on opposite strands.
Thermally induced biosynthesis of 2'-O-methylguanosine in tRNA from an extreme thermophile, Thermus thermophilus HB27.
Authors: Kumagai I , Watanabe K , Oshima T
Published: May 2006

The contents of 2'-O-methylguanosine and 1-methyladenosine in unfractionated tRNA obtained from Thermus thermophilus HB27 were found to increase significantly when the bacterium was grown at a higher temperature (80 degrees C). S-Adenosyl-L-methionine-dependent tRNA (guanosine-2')-methyltransferase (EC 2.1.1.34) and tRNA (adenine-1)-methyltransferase (EC 2.1.1.36) were detected in a cell-free extract of the thermophile, and both of them were partially purified. tRNA (guanosine-2')-methyltransferase specifically catalyzed the methylation of the guanylate residue at position 19 from the 5' end of Escherichia coli tRNAMetf. The amounts of these methyltransferases in the cells and their thermal characteristics seemed to be independent of the growth temperature of the bacterial cells from which the enzymes were extracted. It was inferred that the temperature dependence of the methylation process in vivo is accounted for, not by temperature dependence of enzyme formation, but by that of the enzyme activity.
Fujinami sarcoma virus: An avian RNA tumor virus with a unique transforming gene
Authors: Lee Wen-Hwa , Bister Klaus , Pawson Anthony , Robins Terry , Moscovici Carlo , Duesberg Peter H.
Published: May 2006

The oncogenic properties and RNA of the Fujinami avian sarcoma virus (FSV) and the protein it encodes were investigated and compared to those of other avian tumor viruses with sarcomagenic properties such as Rous sarcoma virus and the acute leukemia viruses MC29 and erythroblastosis virus. Cloned stocks of FSV caused sarcomas in all chickens inoculated and were found to contain a 4.5-kilobase (kb) and an 8.5-kb RNA species. The 4.5-kb RNA was identified as the genome of defective FSV because it was absent from nondefective FSV-associated helper virus and because the titer of focus-forming units increased with the ratio of 4.5-kb to 8.5-kb RNA in virus preparations. This is, then, the smallest known tumor virus RNA with a transforming function. Comparisons with other viral RNAs, based on oligonucleotide mapping and molecular hybridization, indicated that 4.5-kb FSV RNA contains a 5′
gag
gene-related sequence of 1 kb, an internal specific sequence of about 3 kb that is unrelated to Rous sarcoma virus, MC29, and erythroblastosis virus, and a 3′-terminal sequence of about 0.5 kb related to the conserved C region of avian tumor viruses. The lack of some or all nucleotide sequences of the essential virion genes,
gag, pol
, and
env
, and the isolation of FSV-transformed nonproducer cell clones indicated that FSV is replication defective. A 140,000-dalton,
gag
-related non-structural protein was found in FSV-transformed producer and nonproducer cells and was translated
in vitro
from full-length FSV RNA. This protein is expected to have a transforming function both because its intracellular concentration showed a positive correlation with the percentage of transformed cells in a culture and because FSV is unlikely to code for major additional proteins since the genetic complexities of FSV RNA and the FSV protein are almost the same. It is concluded that the transforming
onc
gene of FSV is distinct from that of Rous sarcoma virus and other avian tumor viruses with sarcomagenic properties. Hence, multiple mechanisms exist for sarcomagenic transformation of avian cells.