bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonance Raman spectroscopy of arsanilazocarboxypeptidase A: Determination of the nature of the azotyrosyl-248·zinc complex
Authors: Scheule R. K. , Wart H. E. Van , Vallee B. L. , Scheraga H. A.
Published: May 2006

Resonance Raman spectra of arsanilazotryosyl-248 carboxypeptidase A (peptidyl-L-amino-acid hydrolase, EC 3.4.12.2) exhibit only the vibrational bands of its chromophoric azotyrosyl-248 residue uncomplicated by background interference from either water or other components of the protein. The resonance Raman spectra contain multiple, discrete bands which change as a function of pH, thereby demonstrating the existence of interconvertible species of the azotyrosine probe in solution. Spectra of model azophenols and of the apoazoenzyme establish the identity of these species. All conclusions about the azoenzyme based on the resonance Raman spectra, including the apparent pK values for the interconversion of these species, are in complete agreement with those drawn earlier from studies by absorption spectroscopy. In addition, the properties of resonance Raman bands that have been identified with the motions of specific atoms of azotyrosyl-248 provide details of the interactions of specific atoms of this chromophore with the catalytic zinc atom at the active site. In particular, this has allowed elucidation of the structure of the azotyrosyl-248-zinc coordination complex. Such experiments are also providing information on the effects of crystallization on the enzyme and on its interaction with inhibitors. The important potential of resonance Raman spectroscopy for the study of the structure of chromophoric components of active enzymatic sites and of metal complex ions is discussed.
Kinetics of processing of type I and type III procollagens in fibroblast cultures.
Authors: Goldberg B
Published: May 2006

The rates of conversion of types I and III procollagens to their respective collagens were compared in seven fibroblast culture systems of murine or human origin. During 24 hr of radioactive labeling or after shorter pulses followed by chases of 20-48 hr, no evidence was obtained for conversion of radiolabeled type III procollagen to insoluble collagen. In the same cultures and under the same conditions, native collagen was generated from radiolabeled type I procollagen. There was no evidence for proteolytic degradation of type III procollagen during the chase experiments. The results are ascribed to a lack of availability of the enzymes required for processing of type III procollagen.
Tripartite model for the photochemical apparatus of green plant photosynthesis.
Authors: Butler W L , Strasser R J
Published: May 2006

Equations for fluorescence and the rates of photochemistry of photosystem I and photosystem II are derived from a photochemical model for the photosynthetic apparatus that includes the various interactions of the light-harvesting chlorophyll a/b complex with photosystem I and photosystem II as specific photochemical rate constants. The degree of coupling between photosystem II and the chlorophyll a/b complex which is expressed as a product of two probability terms plays a central role in this three-pigment system. The cycling of excitation energy back and forth between photosystem II and the chlorophyll a/b complex increases the exciton density in both arrays of chlorophyll according to a simple analytical expression in the equations. These equations of the tripartite model provide new and credible insights into the photochemical apparatus of photosynthesis.
Interferon messenger RNA content of human fibroblasts during induction, shutoff, and superinduction of interferon production
Authors: Sehgal Pravinkumar B. , Dobberstein Bernhard , Tamm Igor
Published: May 2006

Translation of injected mRNA in oocytes of
Xenopus laevis
has been used as a highly sensitive and quantitative assay for interferon mRNA. Injection into oocytes of polyadenylylated RNA extracted from poly(I)·poly(C)-induced human diploid fibroblasts (FS-4) leads to the synthesis of biologically active human fibroblast interferon over a period of 24-32 hr. There is a linear relationship between the amount of mRNA injected and the interferon yield obtained over a range of 1-20 ng of injected RNA. Injection of 40-80 ng of mRNA into each of 15 oocytes, homogenized in 0.3 ml of incubation medium, gave a titer of 128-256 interferon reference units/ml of homogenate.

FS-4 cells at the peak of interferon production—i.e., approximately 2.5 hr after the beginning of induction with poly(I)·poly(C)—gave mRNA that yielded 24-48 interferon reference units/ml in the oocyte assay (30 ng of RNA injected per oocyte). An equivalent amount of mRNA from FS-4 cells in the shutoff phase, approximately 6 hr after induction, gave ≤4 interferon reference units/ml. In contrast, mRNA extracted from FS-4 cells that had been induced and maintained in the presence of 40 μM 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole for 6 hr produced 64-128 interferon reference units/ml. Polyadenylylated RNA obtained from uninduced FS-4 cells did not lead to detectable interferon synthesis (<4 interferon reference units/ml). These data provide a direct verification of the hypothesis that the shutoff of interferon production in FS-4 cells involves a regulatory event leading to the posttranscriptional inactivation or degradation of interferon mRNA. Because the inactivating mechanism is sensitive to inhibition by 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole, a selective inhibitor of nuclear heterogeneous RNA and mRNA synthesis, it is likely that synthesis of an RNA molecule is necessary for the shutoff of interferon production.
Embryologic development of a mouse sympathetic ganglion in vivo and in vitro.
Authors: Coughlin M D , Boyer D M , Black I B
Published: May 2006

The morphologic and biochemical development of the embryonic mouse superior cervical ganglion was characterized in vivo and in tissue culture. From 13 days of gestation, when the superior cervical ganglion was first visible, to birth at 19 days, tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] activity increased 100-fold in vivo. Explants of ganglia from 14-day embryos exhibited abundant neurite outgrowth in basal medium without added nerve growth factor (NGF), and increases in tyrosine hydroxylase activity paralleled that observed in vivo. Ganglia from 14-day embryos elaborated neurites and exhibited 3-fold increases in enzyme activity in vitro in the presence of antiserum to NGF (anti-NGF) or NGF + anti-NGF. In direct contrast, ganglia from 18-day fetuses failed to grow without added NGF or in medium containing anti-NGF or NGF + anti-NGF: virtually no axon outgrowth occurred and tyrosine hydroxylase activity decreased by half. These observations suggest that developmental regulatory mechanisms change radically during embryologic and fetal life of mammalian superior cervical ganglion.
Murine leukemia virus morphogenesis: cleavage of P70 in vitro can be accompanied by a shift from a concentrically coiled internal strand ("immature") to a collapsed ("mature") form of the virus core.
Authors: Yoshinaka Y , Luftig R B
Published: May 2006

Disruption of Rauscher leukemia virus (RLV) with low levels of Nonidet P-40 yielded "immature" cores. These cores have a diameter of about 920 A, as opposed to the 1300-A diameter of RLV, possess knob-like protuberances, and contain a concentrically coiled internal strand apposed to the core shell. The two major polypeptide components of immature cores are (i) p30, the 30,000-dalton group-specific antigen, and (ii) a polypeptide that has the size and antigenic characteristics of P70, the 70,000-dalton precursor protein of the group-specific antigens of murine leukemia virus. Disruption of RLV at high ratios of Nonidet P-40 to virus yielded "mature" cores. These cores have an average diameter of 850 A, a smooth proteinaceous perimeter, and a collapsed internal strand, and they contain predominantly p30. Treatment of RLV with low levels of Nonidet P-40 for 16 hr at 22 degrees yielded cores that showed (I) a 70% decrease in the number of immature forms and concomitant increase in the number of mature forms, (II) a 60-90% decrease of P70, and (iii) a 30% increase in a 40,000- to 42,000-dalton protein. These results suggest that maturation of RLV cores is accomplished by cleavage of P70.
Biological properties of poliovirus encapsulated in lipid vesicles: antibody resistance and infectivity in virus-resistant cells.
Authors: Wilson T , Papahadjopoulos D , Taber R
Published: May 2006

We present evidence that poliovirus can be encapsulated in synthetic large phospholipid vesicles. The virus associated with the vesicles is found to be (i) resistant to antiserum against poliovirus and (ii) infectious for cells that are normally resistant to virus infection because of a membrane restriction. Our interpretation of these results is that the virus is entrapped in the interior aqueous space of the vesicles and that this vesicle-associated virus is introduced directly into the cytoplasm of the cells via fusion of the vesicles with the cellular plasma membrane, bypassing the surface receptor-mediated restriction.
Membrane-controlled depletion of complement activity by spin-label-specific IgM
Authors: Humphries Gillian M. K. , McConnell Harden M.
Published: May 2006

Complement depletion mediated by high molecular weight (IgM) rabbit antibodies specifically bound to spin-label lipid haptens dispersed in model membranes is controlled by various physical attributes of those membranes other than the total number of exposed determinants that they provide. Carrier lipids used at 32° were (
i
) a “fluid” phosphatidylcholine (PC), (
ii
) a “solid” PC, and (
iii
) a cholesterol/PC mixture. The concentration of hapten in the plane of the membranes (two-dimensional concentration) was varied while the overall hapten molarity (three-dimensional concentration) was kept constant.

Both specific binding and the efficiency of depletion by IgM are markedly enhanced by systematically decreasing the average distance between haptens (∞ → 26 A). Heterogeneous distribution was found to be more favorable than a random homogeneous distribution of the same number of haptens in the same total quantity of lipids. IgM efficiency is also markedly increased by the inclusion of cholesterol in PC membranes, an effect thought to result from enhanced projection of the determinant from the surface of the membrane and hence increased accessibility to the antibody-binding site. Furthermore, the efficiency of IgM was increased by using haptens dispersed in fluid rather than in solid PC membranes.

The results are consistent with the hypothesis that IgM molecules must be bound to a critical multiple of antigenic determinants at a membrane surface in order to induce complement-mediated attack and that subtle variation of the physical state of membrane antigens can be the crucial factor in determining the outcome of this type of efferent immune response.
Fatty liver induced in Zucker "fatty" (ff) rats by a semisynthetic diet rich in sucrose.
Authors: Novikoff P M
Published: May 2006

A new fatty liver model is described in which heredity plays a major role. A marked fatty liver develops when the homozygous mutant Zucker rat (ff or "fatty") is fed a semi-synthetic diet enriched in sucrose. Lean littermates do not develop fatty livers on this experimental diet. Even old ff rats do not develop fatty livers on chow; the experimental diet is required. The fatty liver is described, including light microscopic and preliminary electron microscopic observations.
Stimulation of human platelet guanylate cyclase by unsaturated fatty acid peroxides.
Authors: Hidaka H , Asano T
Published: May 2006

Guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] activity of human platelet homogenates was stimulated by the addition of phospholipase A2 or unsaturated fatty acids such as oleic, vaccenic, linoleic, linolenic, eicosenoic, eicosadienoic, and arachidonic acids. The addition of lipoxidase potentiated the fatty acid-induced stimulation of guanylate cyclase purified by DEAE-cellulose column chromatography. The extent of the stimulation was dependent on the concentration of the oxidized form of these fatty acids (peroxides). Saturated fatty acids such as stearic and arachidic acids had no effect on the guanylate cyclase activity in the presence or absence of lipoxidase, indicating that human plateletguanylate cyclase is stimulated by unsaturated fatty acid peroxides rather than by fatty acids.Hemoglobin prevented the enzyme stimulation produced by low concentrations of fatty acid peroxides, but enhanced stimulation of the enzyme activity with high concentrations of fatty acid peroxides. 2-Mercaptoethanol, dithiothreitol, and N-ethylmaleimide inhibited the guanylate cyclase activities both in the presence and absence of unsaturated fatty acidperoxide. The stimulation of guanylate cyclase activity by unsaturated fatty acid peroxidesis attributed to oxidation of sulfhydryl residues of the enzyme protein.
Isolation of an electrogenic K+/Ca2+ ionophore from an ionophoroprotein of beef heart mitochondria.
Authors: Blondin G A , Kessler R J , Green D E
Published: May 2006

A K+/Ca2+ electrogenic ionophore has been isolated from an ionophoroprotein of beef heart mitochondria and identified as a neutral peptide of molecular weight 1600. The amino acid composition and cationic specificity of the ionophore have been determined. The free ionophore was released from the ionophoroprotein as a consequence of tryptic digestion. The ionophoroprotein can be converted to an ionophoro peptide (molecular weight 5,100) by proteolysis without release of the free ionophore. The isolation of a K+/Ca2+ ionophore thus provides an introduction to the general technology of extracting ionophoro proteins and ofreleasing ionophores from these proteins by proteolytic digestion.
Nucleotide sequences of ribosome recgonition sites in messenger RNAs of vesicular stomatitis virus.
Authors: Rose J K
Published: May 2006

The ribosome recognition sites from vesicular stomatitis virus mRNAs have been isolated by ribosome protection of the mixture of viral mRNAs followed by complete separation of the protected sites by two-dimensional gel electrophoresis. The sites from the four major mRNAs each contain a single AUG initiation codon, indicating that they are true initiation sites, and the complete sequences of the N, NS, and G mRNA sites are reported. The sites do not all share common features nor do they have significant regions complementary to the known sequence at the 3'-terminus of 18S rRNA. The N and NS mRNAs show anine-nucleotide homology in the first eleven nucleotides extending from the capped 5'-end.
Secondary structure of heterogeneous nuclear RNA: Two classes of double-stranded RNA in native ribonucleoprotein
Authors: Calvet James P. , Pederson Thoru
Published: May 2006

Heterogeneous nuclear RNA (hnRNA) from HeLa cells contains intramolecular duplexes. Since hnRNA is associated with protein
in vivo
, it is possible that the double-stranded regions observed in deproteinized hnRNA form spontaneously upon the release of protein from single-stranded but potentially complementary sequences. We show here that this is not the case for a class of double-stranded sequences that is defined by resistance to RNases A + T
1
at high ionic strength. Exposure of HeLa hnRNA·ribonucleoprotein (hnRNP) particles to
Escherichia coli
RNase III, a double-strand-specific endoribonuclease, destroys most of the sequences resistant to RNases A + T
1
. This effect is completely blocked when hnRNP is exposed to RNase III in the presence of an excess of purified double-stranded RNA. In addition, we show that there exist two classes of double-stranded RNA in hnRNP at a salt concentration of 0.13 M. These are distinguished by their relative resistance to RNases A + T
1
. The more stable double-stranded sequences, which are resistant to RNases A + T
1
at 0.13 M, comprise 1.0-1.1% of the nucleotides in hnRNP. The less stable double-stranded sequences comprise an additional 1.5-2.0% of the nucleotides in hnRNP. These are sensitive to RNase III at 0.13 M, but are not resistant to RNases A + T
1
unless the salt concentration is raised to 0.63 M. The demonstration that double-stranded sequences resistant to RNases A + T
1
exist in native ribonucleoprotein and are not artifacts of deproteinization now makes it appropriate to seriously consider their possible functional role in hnRNA metabolism, perhaps as binding sites for regulatory proteins involved in mRNA processing.
Electron microscope studies of transient complexes formed between Escherichia coli RNA polymerase holoenzyme and T7 DNA.
Authors: Williams R C , Chamberlin M J
Published: May 2006

Electron microscopy was used to study the formation of random complexes between Escherichia coli RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) and a promoterless fragment (Mbo I-C) of bacteriophage T7 DNA, and to determine the location of the polymerase molecules bound at 3 degrees to the promoter-containing (Hinf)1100 fragment of the same DNA. The value of the Ka of random binding is about 3 times 10(4)M-1 when the enzyme is slowly diluted from its storage condition and is incubated with DNA for up to 2 min at 37 degrees. If dilution is rapid and occurs in a single step, or if incubation extends beyond 5 min, a substantial portion of RNA polymerase is converted to a form that binds randomly with a much greater affinity (about 10(8)M-1). Hence true random binding by RNA polymerase holoenzyme is much weaker than previously thought. However, great caution is required in assessing the extent of random binding where damage to the enzyme may occur. When RNApolymerase holoenzyme is incubated at 0 degrees with promoter-containing fragment (Hinf)1100, complexes form at the same promoter sites utilized at 37 degrees, although the highly stable "open" promoter complex is not formed under these conditions. However, the extent of binding is reduced as compared to promoter complexes formed at 37 degrees. This gives direct evidence for formation of complexes with promoter sites that have properties of the hypothetical "closed"complexes formed between RNA polymerase and duplex DNA.
5'-Terminal capping of RNA by guanylyltransferase from HeLa cell nuclei.
Authors: Wei C , Moss B
Published: May 2006

A soluble extract prepared from HeLa cell nuclei has been shown to catalyze the 5'-terminal modification of RNA and synthetic polyribonucleotides to form m7G(5')pppA-and m7G(5')-pppG- structures referred to as caps. The reaction involves the transfer of a GMP moiety from GTP to the 5' end of an RNA molecule containing at least two terminal phosphates. Significantly, neither the beta nor the gamma phosphates of GTP are transferred and polynucleotides with no 5'-terminal phosphate or only one are not acceptors. In the absence of methyl donor, G(5')pppA- and G(5')pppG- structures were synthesized, indicating that methylation is not required for guanylylation. Cap formation was considered to occur by the following mechanism: (see article), in which AdoMet is S-adenosylmethionine, AdoHcy is S-adenosylhomocysteine, and (p)ppN- represents either the original 5' end of an RNA molecule or an internal site to which one or more phosphates were added after processing.
Binding of mouse interferon to polynucleotides.
Authors: De Maeyer-Guignard J , Thang M N , De Maeyer E
Published: May 2006

The polynucleotides poly(I) and poly(U), and to a lesser extent poly(G), are capable of desorbing mouse interferon from blue dextran-Sepharose columns, whereas poly(A) andpoly(C) are without effect. When covalently bound to agarose, poly(I), poly(U), and also poly(A) act as potent ligands for purification of interferon by affinity chromatography. Furthermore, poly(I) and poly(U) confer a significant degree of protection to interferon against thermal denaturation. Taken together, these observations point to a direct interaction of interferon with these polymers and suggest that interferon molecules have a polynucleotide attachment site. Possible implications for the concept of interferon induction are discussed.
Synthesis of collagen by chondrocytes in suspension culture: Modulation by calcium, 3′:5′-cyclic AMP, and prostaglandins
Authors: Deshmukh Kalindi , Sawyer Barry D.
Published: May 2006

Rabbit articular chondrocytes synthesize type II collagen [3α
1
(II)]
in vivo
and type I collagen [2α
1
(I)·α
2
] in monolayer cultures. In suspension culture the nature of phenotype depends on extracellular Ca
2+
. The relationship of Ca
2+
and 3′:5′-cyclic AMP (cAMP) in regulation of collagen synthesis has been investigated. In suspension culture, cAMP levels of chondrocytes increase by 2- to 3-fold and then reach basal values regardless of the presence or absence of extracellular Ca
2+
. The cells, however, synthesize primarily type II collagen in the absence of CaCl
2
in the medium and type I collagen in medium containing 1.8 mM CaCl
2
. If CaCl
2
is added when intracellular cAMP levels are low, the phenotype is type I collagen. These observations minimize the role of cAMP as a second messenger in the chondrocyte culture system. Increasing endogenous cAMP with a phosphodiesterase inhibitor or adding exogenous dibutyryl-cAMP leads the cells to synthesize type I collagen, although this effect is significantly less pronounced if the medium contains ethylene glycol bis(β-aminoethyl ether)-
N,N
′-tetraacetic acid (EGTA). Increased concentrations of cAMP may mobilize the intracellular calcium pools and activate the cells to switch their phenotypic expression. Prostaglandins E
2
and F
2
α, thought to be involved in rheumatoid arthritis and bone resorption, have no significant effect on cAMP content of chondrocytes and alter their collagen phenotype to a small extent.
Stable association of the human transgenome and host murine chromosomes demonstrated with trispecific microcell hybrids.
Authors: Fournier R E , Ruddle F H
Published: May 2006

Trispecific microcell hybrids were prepared by transferring limited numbers of chromosomes from a human/mouse gene-transfer cell line to a Chinese hamster recipient line. The donor cells employed were murine L-cells that stably expressed the human form of the enzyme hypoxanthine phosphoribosyltransferase. Karyotypic, zymographic, and back-selection tests of the resulting human/mouse/Chinese hamster microcell hybrids provided strong genetic evidence for a stable association of the human transgenome with host murine chromosomes in stable gene-transfer cell lines. This association, which may represent physical integration of the transgenome into the host cell genome, occurred at multiple chromosomal sites.
Expression of Ia-like antigen molecules on human granulocytes during early phases of differentiation
Authors: Winchester R. J. , Ross G. D. , Jarowski C. I. , Wang C. Y. , Halper J. , Broxmeyer H. E.
Published: May 2006

Human B lymphocyte antigens analogous to the murine Ia determinants were found on myeloblasts and promyelocytes but not on more mature granulocytes. This was apparent by fluorescent staining with both human alloantisera and rabbit antisera to the isolated Ia-like proteins. The cells of patients with chronic myelocytic leukemia showed this difference especially clearly. Separation of the myeloblasts and promyelocytes by multistep density gradient fractionation produced a marked enrichment of the positive cells. The remaining cells from higher density fractions were more-mature neutrophils that were essentially negative. In acute myeloid leukemia, in which myeloid cells early in differentiation predominate, the vast majority of cells were strongly positive. Similar results were obtained with normal bone marrow cells. Here also, only the early forms of the myeloid series separated by gradient centrifugation had Ia antigens. Evidence was also obtained for the presence of Ia determinants on cells with the appearance of early erythroid precursors. Support for the presence of the Ia determinants on granulocyte-macrophage committed stem cells was provided by the inhibition of granulocyte colony formation in agar cultures following preincubation of normal bone marrow with antiserum and complement.

Cross absorptions with purified preparations of immature cells provided evidence for the close similarity of the antigenic determinants on both myeloblasts and B cells. A 28,000-37,000-dalton bimolecular complex obtained from myeloblast membranes contained the Ia determinants and was similar to that obtained from peripheral blood B cell membranes.
Extraction of an actin-like protein from the prokaryote Mycoplasma pneumoniae.
Authors: Neimark H C
Published: May 2006

An actin-like protein has been identified in cell extracts from the prokaryote Mycoplasma pneumoniae. This protein bears a striking resemblance to actin from vertebrates: (i) the solubility of the protein during isolation is analogous to that of actin bound to myosin (soluble in high ionic strength salt solution and insoluble at low ionic strength), (ii) sodium dodecyl sulfate treatment of the partially purified M. pneumoniae extract produces a protein with an electrophoretic mobility very close to that of vertebrate actin in sodium dodecyl sulfate/polyacrylamide gels, (iii) treatment of preparations with ATP-Mg2+ allows separation of long curvilinear filaments, 5-6 nm wide, that closely resemble eukaryotic filamentous actin, and (iv) the prokaryotic filamentous actin binds vertebrate heavy meromyosin fragments to form hybrid compleexes with the characteristic shape of periodic repeating arrowheads, and no heavy meromyosin is bound in the presence of ATP.
Possibility of nonkinked packing of DNA in chromatin.
Authors: Sussman J L , Trifonov E N
Published: May 2006

The idea that DNA in chromatin can be packed smoothly, without breaking of base-stacking interactions, has been explored by both energetical estimations and stereochemical model building. A model of deformed DNA is built that fits reasonably to the known dimensions of a nucleosome. The model has slightly changed torsion angles in the sugarphosphate moieties relative to B DNA, varying gradually along the chains. The angle between planes of adjacent base pairs varies between 1 and 7 degrees. This model of deformed DNA does not have any unusually close nonbonded contacts and is evidently not the only possible model of smooth packing of DNA in chromatin. An energetical estimation of the critical radius of curvature of a smoothly bent DNA molecule is made using approximate potential functions for different van der Waals contracts in the B DNA structure. The critical radius of curvature of the deformed DNA-axis is close to the radius of a nucleosome (similar to 50 A). The smooth packing is a good alternative to models of kinked folding of DNA in nucleosomes.
Binding and release of eukaryotic initiation factor eIF-2 and GTP during protein synthesis initiation.
Authors: Trachsel H , Staehelin T
Published: May 2006

The eukaryotic initiation factor eIF-2 forms a ternary complex with Met-tRNAf and GTP. This complex binds to the 40S ribosomal subunit in the absence of mRNA and mRNA binding factors. Highly purified eIF-2 from rabbit reticulocytes was labeled with 125I by using the Bolton-Hunter reagent or with [gamma-32P]ATP by using the heme-regulated translational inhibitor protein kinase. The labeled eIF-2 was bound, together with equimolar amounts of Met-tRNAf and GTP, to the 40S subunit. In the presence of mRNA, mRNA binding factors, and 60S ribosomal subunits (complete initiation assay), eIF-2 was released from the 40S initiation complex in the subunit joining reaction. GTP also was released in this step and probably was hydrolyzed in the reaction that is dependent upon eIF-5 and the 60S subunit. The function of phosphorylated eIF-2 in initiation of protein synthesis is discussed.
Specific binding of messenger RNA and methionyl-tRNAfMet by the same initiation factor for eukaryotic protein synthesis.
Authors: Kaempfer R , Hollender R , Abrams W R , Israeli R
Published: May 2006

Affinity chromatography on columns containing globin mRNA, R17 phage mRNA, or double-stranded RNA linked to cellose is used to demonstrate unequivocally that the eukaryotic initiation factor (eIF-2) that forms a ternary complex with Met-tRNAf and GTP also binds tightly to these RNA species. Affinity chromatography of reticulocyte ribosomal wash yields over 100-fold purification of Met-tRNAf-binding factor. This factor is eluted as one of the most tightly bound proteins, and is active in protein synthesis even after passage over a column of double-stranded RNA-cellulose. eIF-2 binds mRNA and double-stranded RNA in distinctly different modes, protecting essentially all sequences in double stranded RNA, but very few in mRNA, against digestion with ribonuclease. Apparently, eIF-2 recognized the A conformation of double-stranded RNA, but not its sequence. By contrast, globin, Mengo virus, R17 and vesicular stomatitis virus mRNA are shown to possess a high-affinity binding site for eIF-2 that is absent in negative-strand RNA of vesicular stomatitis virus, an RNA that cannot serve as messenger. The results support the concept that eIF-2, the initiation factor that binds Met-tRNAf, recognizes an internal sequence in mRNA essential for protein synthesis.
Agonist-induced increase in apparent β-adrenergic receptor size
Authors: Limbird Lee E. , Lefkowitz Robert J.
Published: May 2006

The properties of digitonin-solubilized β-adrenergic receptors from frog erythrocyte membranes were studied by gel exclusion chromatography on AcA 34 Ultragel. β-Adrenergic receptor binding activity in these membranes can be identified by both an agonist ligand, [
3
H]hydroxybenzylisoproterenol, and the antagonist ligands, [
3
H]dihydroalprenolol and
125
I-labeled hydroxybenzylpindolol. Occupancy of the β-adrenergic receptors with the [
3
H]hydroxybenzylisoproterenol agonist prior to their solubilization from the membrane leads to an increase in apparent receptor size. Alterations in the molecular size of the receptor cannot be mimicked by occupancy of the binding site with the antagonist ligands. Exposure of frog erythrocyte membranes to [
3
H]hydroxybenzylisoproterenol agonist in the presence of 10 μM Gpp(NH)
p
, a guanyl nucleotide analog that exerts multiple regulatory effects on the catecholamine-sensitive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1] system, results in the elution of the [
3
H]hydroxybenzylisoproterenol radioligand in both the region characteristic of the agonist—receptor complex and the region characteristic of the antagonist—receptor complex.

The precise molecular interactions responsible for the agonist-induced increase in apparent β-adrenergic receptor size are still unresolved. However, the low concentrations of agonist that are capable of altering apparent receptor size and the sensitivity of this effect to guanyl nucleotides suggest that these phenomena may be intimately involved in eliciting the physiological effects of β-adrenergic catecholamines at the molecular level.
Mutant RNA polymerase of Escherichia coli terminates transcription in strains making defective rho factor.
Authors: Guarente L P , Beckwith J
Published: May 2006

We have isolated a rifampicin-resistant mutant of Escherichia coli RNA polymerase that restores transcription termination in strains with a defective rho protein. In such strains, the mutant RNA polymerase terminates transcription at normally rho-dependent sites at the end of the trp operon, in bacteriophage lambda, and within the lac operon. In addition, a strain with this mutant RNA polymerase remains viable with an amber mutation in rho, whereas a strain with wild-type RNA polymerase does not. These results suggest that the mutant RNA polymerase can terminate transcription at normally rho-dependent sites in the absence of rho.
Combined immunofluorescence and high-voltage electron microscopy of cultured mammalian cells, using an antibody that binds to glutaraldehyde-treated tubulin.
Authors: Eckert B S , Snyder J A
Published: May 2006

An antibody against tubulin that binds specifically to microtubules in glutaraldehyde-fixed cells has been prepared. Sodium dodecyl sulfate-denatured tubulin treated with glutaraldehyde was used to immunize rabbits. In glutaraldehyde-fixed cells the fluorescent image of this antibody reveals a fine lattice of microtubules around the nucleus of PtK1 (Potorous tridactylis) cells and many uniformly fluorescent microtubules in the peripheral cytoplasm. In cells fixed with formaldehyde the microtubules appear to have a similar distribution, but the fluorescent image is much less uniform. Combined high-voltage electron microscopy and immunofluorescent studies reveal that microtubules are found in the cytoplasm in the same region as the fluorescent antibody stain.
Multiple forms of sarc gene proteins from Rous sarcoma virus RNA.
Authors: Kamine J , Burr J G , Buchanan J M
Published: May 2006

In a previous study we were able to identify two proteins of 25,000 and 18,000 daltons that were made from RNA of transforming virions of Rous sarcoma virus (RSV) and that were missing from the translation products of a transformation-defective deletion mutant of RSV. In the present study we have separated RSV virion RNA on sucrose gradients and have determined that the two putative sarc gene products are synthesized as doublets from an mRNA of approximately 18 S. There also appear to be several other sizes of virion mRNA that direct the synthesis of other viral proteins. These data are discussed in terms of the structure of the RSV genome. In addition to the 25,000- and 18,000-dalton doublets, there also is a 60,000-dalton protein whose synthesis is directed by 18S viral RNA from transforming virion of RSV. Peptide mapping has shown that the 60,000- and 25,000-dalton doublet are structurally related. In addition, the use of two-dimensional gel electrophoresis has allowed us to resolve both bands of the 25,000-dalton doublet into several differently charged species.
Cell lineages of the embryo of the nematode Caenorhabditis elegans.
Authors: Deppe U , Schierenberg E , Cole T , Krieg C , Schmitt D , Yoder B , von Ehrenstein G
Published: May 2006

Embryogenesis of the free-living soil nematode Caenorhabditis elegans produces a juvenile having about 550 cells at hatching. We have determined the lineages of 182 cells by tracing the divisions of individual cells in living embryos. An invariant pattern of cleavage divisions of the egg generates a set of stem cells. These stem cells are the founders of six stem cell lineages. Each lineage has its own clock--i.e., an autonomous rhythm of synchronous cell divisions. The rhythms are maintained in spite of extensive cellular rearrangement. The rate and the orientation of the cell divisions of the cell lineages are essentially invariant among individuals. Thus, the destiny of cells seems to depend primarily on their lineage history. The anterior position of the site of origin of the stem cells in the egg relates to the rate of the cell cycle clock, suggesting intracellular preprogramming of the uncleaved egg. We used a technique that allows normal embryogenesis, from the fertilized egg to hatching, outside the parent under a cover glass. Embryogenesis was followed microscopically with Nomarski interference optics and high-resolution video recording.
A geometric model describing a quasi-equilibrium of energy flow in populations of stream insects
Authors: Vannote Robin L.
Published: May 2006

Studies of growth, population structure, and metabolism for the mayfly nymph
Ephemerella dorothea
suggest that in natural streams this species maintains a nearly uniform weight-specific metabolic rate from the time of hatching (0.002 mg) to maturity (4.0 mg) as average stream temperature increases from 0.5° to 15°. The observed homeostasis represents a central tendency between two opposing factors that affect metabolism (size and temperature) and is achieved because any increase in metabolic rate due to warming of streams from winter to late spring is almost completely compensated by the increase in nymphal size from hatching to emergence. Results indicate that natural selective processes have favored individuals whose growth rates are proportional to seasonal changes in temperature. The model suggests a possible mechanism for explaining synchronous larval growth, pulsed adult emergence, and progressive decreases in adult weight of individuals emerging after the main cohort.
Decision procedure for indefinite hypergeometric summation
Authors: Gosper R. William
Published: May 2006

Given a summand

a
n

, we seek the “indefinite sum”
S
(
n
) determined (within an additive constant) by [Formula: see text] or, equivalently, by [Formula: see text] An algorithm is exhibited which, given

a
n

, finds those
S
(
n
) with the property [Formula: see text] With this algorithm, we can determine, for example, the three identities [Formula: see text] [Formula: see text] and [Formula: see text] and we can also conclude that [Formula: see text] is inexpressible as
S
(
m
) -
S
(0), for any
S
(
n
) satisfying Eq. 2.
Distinct protein components from Torpedo marmorata membranes carry the acetylcholine receptor site and the binding site for local anesthetics and histrionicotoxin.
Authors: Sobel A , Heidmann T , Hofler J , Changeux J P
Published: May 2006

Highly purified subsynaptic membrane fragments prepared from Torpedo marmorata electric organ (specific activity, greater than 4 mumol of Naja nigricollis alpha-[3H]toxin per mg of protein) exhibit, on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, two major protein bands of apparent molecular weight 40,000 and 43,000, respectively. Dissolution of these membranes by the nondenaturing detergents Triton X-100 and Berol 043 followed by standard fractionation yielded (i) the 9S acetylcholine-receptor protein which still binds the alpha-[3H]toxin and after further purification yielded, in the presence of sodium dodecyl sulfate, the 40,000-dalton component, covalently labeled by the affinity reagent 4-(N-maleimido)phenyl[3H]trimethylammonium; only serine was found as the NH2-terminal amino acid of this protein; and (ii) a high molecular weight aggregate named 43,000 protein which was resolved in denaturing gels almost exclusively as the 43,000-dalton band, In the absence of detergents, the 43,000 protein binds compounds known to interact with the acetylcholine ionophore: a fluorescent local anesthetic quinacrine and histrionicotoxin (apparent dissociation constant, 7 +/- 1 X 10(-7) M). The regulation of quinacrine fluorescennce by carbamylcholine, observed in the intact membrane, no longer occurs with the isolated 43,000 component.
Sound transmission in the salamander ear.
Authors: Wever E G
Published: May 2006

The mode of stimulation of the ear by sounds is considered in Amphibia, in which it differs among the three Recent orders. Of special interest is the order Caudata, in which this stimulation takes a unique form: sounds applied to the oval window of one ear produce a path of vibratory motion that passes through the brain cavity to the oval window on the opposite side. In this course the vibratory movements traverse both right and left amphibian papillae, and both basilar papillae also in species that contain these endorgans. Thus, in the salamander the hearing is invariably binaural.
Physical organization of the
ilvEDAC
genes of
Escherichia coli
strain K-12
Authors: McCorkle George M. , Leathers Timothy D. , Umbarger H. E.
Published: May 2006

We have determined the physical location of the
ilvEDAC
genes on the restriction cleavage map of the
ilv
region of
Escherichia coli
K-12 by two methods: (
i
) heteroduplex and endonuclease cleavage analysis of hybrid phages carrying genetically defined parts of the
ilv
cluster and (
ii
) complementation analysis and enzyme assays to determine
ilv
gene expression from hybrid plasmids containing DNA restriction fragments of the transducing phage λh80d
ilv
. The
ilvEDA
and
ilvC
operons occupy 2.4 and 0.9 megadalton sequences of DNA, respectively, and are separated by a region of 0.6-0.75 megadalton. The
ilvD
region, specifying dihydroxy acid dehydrase, has a maximum coding capacity of about 55,000 daltons of polypeptide. Our results confirm that
ilvC
is transcribed clockwise on the
E. coli
K-12 map, in the same direction as
ilaEDA
. A secondary λ attachment site within
ilvC
has been located on a small (0.45 megadalton)
Eco
RI fragment. Our results are compared to other physical studies of
ilv
DNA.
Chemical determination of the m1 Moloney sarcoma virus pP60gag gene order: evidence for unique peptides in the carboxy terminus of the polyprotein.
Authors: Oskarsson M K , Elder J H , Gautsch J W , Lerner R A , Vande Woude G F
Published: May 2006

The gene order of the ml Moloney sarcoma virus (mlMSV) specific pP60gag (P60) was determined by direct chemical analysis of the polyprotein. P60 was cleaved with cyanogen bromide (CNBr) into eight partial and complete fragments ranging in mass from 10,000 daltons to 58,000 daltons. Peptide maps of these fragments were compared to maps of p15, p12, and three CNBr fragments of p30. The polarity of p15 and p12 in a CNBr fragment of P60 was determined by carboxypeptidase A digestion; likewise the CNBr fragments of p30 were ordered by aminopeptidase digestion. The linear arrangement of P60 CNBr fragments gave the gene order of NH2-p15-p12-p30-COOH. The m3 isolate of MSV expresses a P70 gag polyprotein. Peptide maps of 48,000-dalton CNBr fragments of m3 P70 and ml P60 were similar and suggested that both polyproteins were similar through the NH2-terminal two-thirds of p30. However, the presence of peptides unique to the 10,500-dalton COOH-terminal fragment of m1MSV p30 and not present in the p30 of either m3MSV or Moloney leukemia virus suggested that the gag gene deletion in the m1 isolate begins in the p30 reading frame.
Specific transcription of eukaryotic tRNA genes in Xenopus germinal vesicle extracts.
Authors: Schmidt O , Mao J I , Silverman S , Hovemann B , Söll D
Published: May 2006

Cloned tRNA genes from Drosophila and from yeast have been transcribed faithfully in extracts prepared from Xenopus germinal vesicles. The newly formed RNA is composed of precursor tRNAs (of 5S RNA size) and of tRNAs. The plasmid pCIT12 carries genes for Drosophila tRNALys, tRNAArg, and tRNAAsn, Nucleotide analysis of one RNA species transcribed from pCIT12 DNA showed it to be identical to Drosophila tRNALys; it even contained some of the modified nucleotides expected for this tRNA. This RNA species is formed in the germinal vesicle extract via a larger precursor tRNA molecule that does not contain nucleotide modifications. This simple transcription system should aid studies aimed at defining the regulatory DNA regions responsible for eukaryotic gene transcription. In addition, it may provide tRNA precursors that are needed for detailed investigations of eukaryotic tRNA biosynthesis.
Ovalbumin gene: evidence for a leader sequence in mRNA and DNA sequences at the exon-intron boundaries.
Authors: Breathnach R , Benoist C , O'Hare K , Gannon F , Chambon P
Published: May 2006

Selected regions of cloned EcoRI fragments of the chicken ovalbumin gene have been sequenced. The positions where the sequences coding for ovalbumin mRNA (ov-mRNA) are interrupted in the genome have been determined, and a previously unreported interruption in the DNA sequences coding for the 5' nontranslated region of the messenger has been discovered. Because directly repeated sequences are found at exon-intron boundaries, the nucleotide sequence alone cannot define unique excision-ligation points for the processing of a possible ov-mRNA precursor. However, the sequences in these boundary regions share common features; this leads to the proposal that there are, in fact, unique excision-ligation points common to all boundaries.
Mechanism of action of the pyruvate dehydrogenase multienzyme complex from
Escherichia coli
Authors: Angelides Kimon J. , Hammes Gordon G.
Published: May 2006

The extent of cooperativity among the polypeptide chain components in the overall reaction catalyzed by the pyruvate dehydrogenase multienzyme complex from
Escherichia coli
has been studied. Selective inactivation of the pyruvate dehydrogenase component with thiamin thiazolone pyrophosphate demonstrates that no cooperativity between this component and the overall catalytic reaction occurs: the amount of overall complex activity is directly proportional to the fraction of active pyruvate dehydrogenase component. The transacetylase component has two lipoic acid residues on each of its polypeptide chains that can be modified by
N
-[
3
H]ethylmaleimide in the presence of pyruvate and thiamin pyrophosphate. The kinetics of the loss of overall complex activity due to modification of the lipoyl residues on the transacetylase component by maleimide reagents shows that not all lipoic acids are coupled into the overall catalytic reaction and that acyl-group and electron pair transfer involving two or more lipoic acids per catalytic cycle must occur. Finally, full complex activity is found when only half the normal flavin content is present. The results indicate that extensive communication among lipoic acids in acyl-group and electron pair transfer must exist in the normal catalytic mechanism. These results are consistent with the average distances between catalytic sites measured by energy transfer experiments.
Identification of tubulin from the yeast Saccharomyces cerevisiae.
Authors: Baum P , Thorner J , Honig L
Published: May 2006

A tubulin-like protein was identified in the lower eukaryote Saccharomyces cerevisiae. The following criteria were used: (i) copolymerization of the 35S-labeled yeast protein with porcine brain tubulin; (ii) immunoprecipitation of the 35S-labeled yeast protein with antiflagellar tubulin antibody; (iii) the presence of the yeast protein as a constituent of isolated yeast nuclei; and (iv) splitting of the yeast protein in a gel electrophoretic system containing sodium dodecyl sulfate that resolved the alpha- and beta-tubulin chains from other sources. This protein did not appear to have significant affinity for the plant alkaloid, Colcemid.
Induction of ornithine decarboxylase activity in a temperature-sensitive cell cycle mutant of Chinese hamster cells.
Authors: Landy-Otsuka F , Scheffler I E
Published: May 2006

We have investigated the induction of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activity in a temperature-sensitive cell cycle mutant of Chinese hamster fibroblasts. This activity is not induced at the nonpermissive temperature, although the synthesis of the majority of proteins is normal. From a combination of studies with inhibitors of mRNA synthesis and maturation (alpha-amanitin, and cordycepin) and of proteins synthesis (cycloheximide, diphtheria toxin, and emetine), we conclude that the temperature-sensitive block is at the level of translation of one or more specific mRNAs.
Epidermal growth factor: morphological demonstration of binding, internalization, and lysosomal association in human fibroblasts.
Authors: Gorden P , Carpentier J L , Cohen S , Orci L
Published: May 2006

Using a quantitative electron microscopic autoradiographic technique, we have localized the initial binding step of 125I-labeled epidermal growth factor (125I-EGF) to the plasma membrane of the human fibroblast. After initial binding, labeled EGF is internalized progressively by the cell in a time- and temperature-dependent fashion; when cell-associated radioactivity comes to steady state, approximately 1/3 of the autoradiographic grains are related to the plasma membrane and approximately 2/3 have been internalized. Under these conditions the internalized grains are almost exclusively related to lysosomal structures. When 125I-EGF associates with the cells for 2 hr at 4 degrees or 2 min at 37 degrees, 34% of grains localize to coated regions of the membrane. These coated regions make up less than 2% of the membrane surface. These data directly confirm kinetic studies and suggest that saturable binding of EGF is followed by adsorptive pinocytosis and cellular degradation of the ligand and possibly its cell surface receptor.