bluuebunny/crossref_metadata_2025 huggingface dataset:
Retinoic acid (vitamin A acid) induced transcriptional control of interferon production.
Authors: Blalock J E , Gifford G E
Published: May 2006

The production of interferon was used to study the site and mechanism of action of retinoic acid (vitamin A). The data are consistent with a site of action at the gene level, because it appears that interferon production is blocked at the transcriptional step by a retinoic acid-induced protein. (i) The effect of retinoic acid is probably on an early cellular function associated with interferon production rather than an effect on the inducer [virus or poly(I).poly(C)]. (ii) The suppression of interferon production by retinoic acid is blocked by cycloheximide, indicating that a newly synthesized protein (repressor) mediates the suppression. (iii) When allowances are made for the time required for the synthesis of the retinoic acid-induced protein, the time course of retinoic acid suppression of interferon production is superimposable on the time course of actinomycin D suppression because the slopes are parallel. These data provide evidence for transcriptional control of a specific protein (interferon) by retinoic acid. Additionally, they support the existence of transcriptional control of interferon production after addition of inducer.
New method for localizing proteins in periodic structures: Fab fragment labeling combined with image processing of electron micrographs.
Authors: Aebi U , ten Heggeler B , Onorato L , Kistler J , Showe M K
Published: May 2006

Fab fragments prepared from antisera directed against purified bacteriophage T4 structural proteins and head-related structures were used to label proteins on the surface of T-even giant phage capsids. Optically filtered electron micrographs of the Fab-labeled capsids reveal both the location of specific proteins within the capsomeres and differing conformational states of the protein subunits. We describe parameters affecting the utility of this technique for the study of molecular organization and protein conformation in periodic biological structures.
Evidence that pyrimidine dimers in DNA can give rise to tumors.
Authors: Hart R W , Setlow R B , Woodhead A D
Published: May 2006

The Amazon molly, Poecilia formosa, is a small fish that grows in clones. Hence, cells from one animal may be transplanted to another without danger of rejection. Cells from thyroid and adjacent tissue were irradiated with UV light in vitro and injected into the abdominal cavity of isogeneic recipients. At appropriate UV doses and numbers of cells injected, all recipients showed exuberant thyroid proliferation. We give arguments and data indicating that the proliferation is a tumor, not a goitrogenic response. If the UV irradiation is followed, but not preceded, by photoreactivating illumination, the yield of thyroid growths is markedly decreased. Because other investigations have shown that photoreactivation monomerizes UV-induced cyclobutylpyrimidine dimers in DNA and does not affect other photoproducts, our data indicate that pyrimidine dimers in DNA can give rise to tumors.
Transitions in collagen types during matrix-induced cartilage, bone, and bone marrow formation.
Authors: Reddi A H , Gay R , Gay S , Miller E J
Published: May 2006

The localization of types I, II, and III collagens during bone matrix-induced sequential differentiation of cartilage, bone, and bone marrow was studied by specific immunofluorescence. Subcutaneous transplantation of coarse powders of demineralized rat bone matrix into allogeneic recipients resulted in new bone formation. After a transient appearance of polymorphonuclear leukocytes in the implant, fibroblasts appeared in close continguity to the matrix on day 3. Type III collagen was then localized as a fine network around the invading fibroblasts. On days 4--6 smaller amounts of type I were also detected around these proliferating cells. With the onset of chondrogenesis, type II collagen was detected in the cartilage matrix on day 6 and persisted until the early stages of bone formation. Vascular invasion of the implant was accompanied by osteogenesis on day 10. Type I collagen was demonstrated in the newly deposited bone matrix coating the surfaces of cartilage spicules and particles of implanted bone powder. On day 17 and thereafter, type III collagen was localized as a fibrous array around nests of hematopoietic cells.
Feline oncornavirus-associated cell membrane antigen: evidence for an immunologically crossreactive feline sarcoma virus-coded protein.
Authors: Stephenson J R , Khan A S , Sliski A H , Essex M
Published: May 2006

The feline oncornavirus-associated cell membrane antigen (FOCMA) acts as a target for natural immuno-surveillance against tumor development in the cat. In the present study, mink and rat cells nonproductively transformed by feline sarcoma virus (FeSV) were shown to express FOCMA as well as 5'-terminal feline leukemia virus (FeLV) gag gene proteins, p15 and p12. In contrast, such cells lack detectable levels of other FeLV gag gene-coded proteins or the env gene product, gp70. FOCMA, p15, and p12 antigen expression is initially in the form of an 80,000-100,000 molecular weight precursor which, upon post-translational cleavage, gives rise to a 65,000 molecular weight component that contains FOCMA and a 25,000 molecular weight component containing p15 and p12. Feline lymphoma cells, including those from several tumors that lacked detectable levels of FeLV structural protein expression, were shown to be FOCMA-positive. These findings strongly suggest that FOCMA represents an FeSV-coded transformation specific protein and provide preliminary information regarding the position within the FeSV genome coding for its synthesis.
Amino acid sequence of the precursor region of MOPC-315 mouse immunoglobulin heavy chain.
Authors: Jilka R L , Pestka S
Published: May 2006

Partially purified mRNA coding for the MOPC-315 heavy immunoglobulin alpha chain was translated in a reticulocyte lysate containing 20 labeled amino acids. Radiolabeled MOPC-315 heavy chain precursor protein, purified by preparative gel electrophoresis and immunoprecipitation, was sequenced by Edman degradation. The labeled phenylthiohydantoin amino acid obtained in each cycle was identified and quantitated by high-pressure liquid chromatography. The precursor sequence of 18 amino acids, Met-Lys-Val-Leu-Ser-Leu-Leu-Tyr-Leu-Leu-Thr-Ala-Ile-Pro-His-Ile-Met-Ser, preceded the sequence corresponding to the NH2 terminus of the mature secreted heavy chain.
Cultured aortic endothelial cells from pigs with von Willebrand disease: in vitro model for studying the molecular defect(s) of the disease.
Authors: Booyse F M , Quarfoot A J , Bell S , Fass D N , Lewis J C , Mann K G , Bowie E J
Published: May 2006

Aortic endothelial cells from normal pigs and pigs with von Willebrand disease have been established in long-term cultures. Both cultures appeared similar in terms of general growth characteristics, morphologic features and ultrastructure. Immunofluorescent staining of these cultures with chicken (or rabbit) antiporcine ristocetin-Willebrand factor sera (or IgG) resulted in extensive perinuclear staining of the cells in both cultures. Additionally, staining of semiconfluent cultures of normal cells for ristocetin-Willebrand factor revealed an extensive meshwork of distinct, immunologically identifiable ristocetin-Willebrand factor-containing filaments between cells. Immunoreactive material was considerably decreased and more diffuse between cells in semiconfluent cultures from affected pigs. Through immunocytochemical staining with peroxidase-coupled antiserum, the filaments (of indeterminate length) were found to have a diameter of approximately 300 A. Finally, washed porcine platelets interacted extensively with scrape-damaged cultures of affected endothelial cells. This interaction of platelets with damaged normal cultures was abolished by pretreatment of the cultures with rabbit antiporcine ristocetin-Willebrand factor IgG.
Heptadecapeptide gastrin in the vagal nerve.
Authors: Uvnäs-Wallensten K , Rehfeld J F , Larsson L I , Uvnäs B
Published: May 2006

Immunoreactive gastrin was present in vagal nerves from cats, dogs, and human beings. The abdominal portion of the vagus contained gastrin in amounts ranging from 16 to 273 pmol/g of nerve tissue (wet weight). The thoracic and cervical portion of the vagi contained only minute amounts of gastrin. Gel chromatography of extracts of human, canine, and feline abdominal vagi monitored by region-specific antisera against heptadecapeptide gastrin and triacontatriapeptide cholecystokinin revealed that the vagal gastrin immunoreactivity predominantly consisted of heptadecapeptide gastrin. In addition, the vagi contained small amounts of the NH2-terminal tridecapeptide gastrin fragment as well as of the putative biosynthetic gastrin precursors, components I and II. No cholecystokinin-like molecules were demonstrable. Immunocytochemical studies demonstrated gastrin-containing nerves in the intestinal wall. The nerves were found to be most numerous in the large and distal small intestine. These findings suggest that heptadecapeptide gastrin may represent a new vagal neurotransmitter.
Characterization and synthesis of volatile compounds from the defensive secretions of some "daddy longlets" (Arachnida: Opiliones: Leiobunum spp.).
Authors: Jones T H , Meinwald J , Hicks K , Eisner T
Published: May 2006

Analyses of the chief volatile constituents of the defensive secretions of three oplionids were carried out. Leiobunum nigripalpi produces three closely related C7 compounds: E-4-methyl-4-hexen-3-one(I), 4-methylhexan-3-one(II), and 4-methylhexan-3-ol(III), along with E-4-methyl-4-hepten-3-one(IV), E,E-2,4-dimethylhexa-2,4-dienal(IX), and a minor, unidentified component. L. leiopenis secretion contains E-4-methyl-4-hepten-3-one(IV), 4-methylheptan-3-one(V), E,E-2,4-dimethylhexa-2,4-dien-1-ol(VII), and E,E-2,4-dimethylhepta-2,4-dien-1-ol(VIII). L. calcar yields chiefly E-4,6-dimethyl-6-octen-3-one(VI) and E,E-2,4-dimethylhexa-2,4-dien-1-ol(VII). Six of these compounds are new natural products. The structures of these compounds, which can be regarded either as polyketide-derived or as modified isoprenoids, raise interesting biosynthetic questions.
Bovine papilloma virus: presence of virus-specific DNA sequences in naturally occurring equine tumors.
Authors: Lancaster W D , Olson C , Meinke W
Published: May 2006

Four of five spontaneous benign equine connective tissue tumors of unknown etiology and a bovine papilloma virus (BPV)-induced equine tumor contained BPV-specific DNA sequences as determined by DNA-DNA hybridization of DNA from tumors with BPV DNA labeled in vitro. Analysis of the kinetics of reassociation indicated that 20-75% of the BPV genome was present in the various tumors. The number of partial BPV genome equivalents ranged from 60 to 500 copies per diploid quantity of cellular DNA. Thermal denaturation profiles of duplexes formed between labeled BPV DNA and DNA from tumor cells indicated two tumors contained viral DNA with base sequences identical to BPV DNA. Three tumors (including DNA from the BPV-induced tumor) contained BPV-related DNA sequences that were less thermally stable. The decrease in thermal denaturation temperature may be due to the presence of (adenine + thymine)-rich regions of the BPV genome in the tumor cells.
Localization of bovine brain filament antibody on intermediate (100 A) filaments in guinea pig vascular endothelial cells and chick cardiac muscle cells.
Authors: Blose S H , Shelanski M L , Chacko S
Published: May 2006

Guinea pig vascular endothelial cells contain naturally occurring rings of intermediate filaments that completely encircle the nucleus. Indirect immunofluorescence staining showed that these perinuclear rings bound antibody prepared against protein from bovine brain 9-nm filaments. In endothelial cells grown in the presence of 1 muM demecolcine (Colcemid) the perinuclear ring "coils" into a juxtanuclear "cap". Throughout this process we could demonstrate staining of the intermediate filaments. Chick cardiac muscle cells in culture stained diffusely with the antibody. After treatment for 24 hr with 1 muM demecolcine the cardiac cells accumulated large bands of intermediate filaments. These bands stained intensely with the antibody. Our findings suggest that intermediate filaments in guinea pig endothelial cells and those induced in chick cardiac muscle cells are antigenically similar to bovine brain filaments. The staining of these filaments is not affected by treatment with demecolcine.
Amino acid sequence of the NH2-terminal extra piece segments of the precursors of mouse immunoglobulin lambda1-type and kappa-type light chains.
Authors: Burstein Y , Schechter I
Published: May 2006

The mRNA molecules coding for mouse immunoglobulin light (L) chains direct the cell-free synthesis of precursors in which extra peptide segments precede the amino termini of the mature proteins. The results of amino acid sequence analyses of two precursors labeled with 20 radioactive amino acids enabled unambiguous determination of the complete primary structure of the extra piece segments. The complete sequences (and sizes) of the NH2-terminal extra pieces are: in MOPC-104E lambda1 L-chain precursor, Met-Ala-Trp-Ile-Ser-Leu-Ile-Leu-Ser-Leu-Leu-Ala-Leu-Ser-Ser-Gly-Ala-Ile-Ser (19 residues); in MOPC-41 kappa L-chain precursor, Met-Asp-Met-Arg-Ala-Pro-Ala-Gln-Ile-Phe-Gly-Phe-Leu-Leu-Leu-Leu-Phe-Pro-Gly-Thr-Arg-Cys (22 residues). The extra pieces in the precursors of MOPC-104E (lambda1), MOPC-41 (kappa), and MOPC-321 (kappa) L-chains differ extensively from each other in their amino acid sequence (65-73%). In addition to this sequence heterogeneity, the extra pieces are characterized by a high percentage of hydrophobic residues: 69% in the MOPC-104E lambda1 L-chain precursor (this report), 73-75% in the kappa L-chain precursors [Schechter, I. & Burstein, Y. (1976) Proc, Natl. Acad. Sci. USA 73, 3273-3277]. The marked hydrophobicity of the extra piece suggests that it may favor interaction of the precursor with cell membranes, in a manner similar to the function of the "hydrophobic domain" of membrane-bound proteins. We propose two possible targets for interaction: (i) the endoplasmic membranes, where the NH2-terminal extra piece is cleaved from the precursor to yield mature protein destined for secretion; (ii) the cell surface membrane, where the intact precursor is anchored by virtue of the hydrophobic extra piece to serve as the antigen-recognizing receptor.
Host-determined differences in expression of surface marker characteristics on human and simian lymphoblastoid cell lines transformed by Epstein-Barr virus.
Authors: Robinson J E , Andiman W A , Henderson E , Miller G
Published: May 2006

In an attempt to account for differences in the biologic behavior of Epstein-Barr virus in different primate species, we studied lymphocyte surface markers on primary and transformed cells. Among primary leukocytes, the distribution of cells with characteristics of bone-marrow-derived cells (B cells) was similar in humans, wooly monkeys, and cotton-top marmosets. However, after transformation by Epstein-Barr virus, cells from each species were characterically different. Transformed human umbilical cord cells expressed the complement receptor; monkey cells exhibited both this receptor and the receptor for IgG Fc (EA7S); and marmoset cells did not have either surface marker. We measured the transformation efficiency of human and marmoset leukocyte subpopulations enriched or depeleted in cells with the complement receptor. In both species the highest efficiencies of transformation were found in populations with the greatest numbers of cells with the receptor. The data therefore suggest that, in all species, a cell with the complement receptor is susceptible to transformation but that this receptor is not expressed on transformed marmoset cells. Thus, in Epstein-Barr virus-induced transformation it is necessary to distinguish between transformation of growth properties (immortalization) and transformation of cell surface properties.
Persistence of type 5 adenovirus DNA in cells transformed by temperature-sensitive mutant, H5ts125.
Authors: Mayer A J , Ginsberg H S
Published: May 2006

The characteristic of H5ts125, a temperature-sensitive DNA-minus mutant, to transform 3 to 8 times more rat embryo cells than wild-type 5 adenovirus was correlated with the persistence of an increased proportion of the viral genome in cells independently transformed at the nonpermissive (39.5 degrees) or semipermissive (36 degrees) temperature. Reassociation kinetics of the hybridization of 32P-labeled,HindIII restriction fragments of the viral genome and excess unlabeled, transformed cell DNA was used to measure the quantity of the viral genome in transformed cells. Three of four cell lines independently transformed and maintained at 36 degrees contained all regions of the viral genome; one line transformed at 39.5 degrees contained multiple copies representing all of the viral DNA; and one line contained a large proportion of the viral genome. The cell line transformed and maintained at 32 degrees contained a quantity of viral genome consistent with that usually found in cells transformed by wild-type 5 adenovirus.
Amino acid sequence for the peptide extension on the prolipoprotein of the Escherichia coli outer membrane.
Authors: Inouye S , Wang S , Sekizawa J , Halegoua S , Inouye M
Published: May 2006

The messenger RNA for the lipoprotein of the E. coli outer membrane was found to code for a putative precursor, prolipoprotein, which has 20 additional amino acid residues extending from the amino terminus of the lipoprotein. Using the prolipoprotein synthesized in an E. coli cell-free system directed by purified messenger RNA for the lipoprotein, the complete amino acid sequence of the amino-terminal precursor region was determined to be as follows: (formula: see text). It was also found that the prolipoprotein that accumulates in toluene-treated cells has the same sequence. The significance of the amino acid sequence is discussed in terms of the mechanism of biosynthesis and assembly of the lipoprotein in the E. coli outer membrane.
High-resolution proton magnetic resonance study of the secondary structure of the 3'-terminal 49-nucleotide fragment of 16S rRNA from Escherichia coli.
Authors: Baan R A , Hilbers C W , Van Charldorp R , Van Leerdam E , Van Knippenberg P H , Bosch L
Published: May 2006

The 3' terminus of 16S rRNA has been implicated in the recognition of mRNA's by the ribosome. A fragment containing the 3'-terminal 49 nucleotides cleaved from the rRNA by cloacin DF13 was isolated in a pure form. The secondary structure of this fragment has been studied by measuring the high-resolution proton magnetic resonance spectra. The resonances observed at low field can be assigned to hydrogen-bonded iminoprotons of base-pairs present in the fragment. From the data we conclude that the rRNA fragment, under the conditions used, exists as a hairpin consisting of eight intramolecular base-pairs, the 3'-terminal dodecanucleotide being unpaired. The implications of these findings with respect to the function of the ribosomal protein S1 are discussed.
Anionic glycopeptides and glycosaminoglycans synthesized by embryonic neural tube and neural crest.
Authors: Manasek F J , Cohen A M
Published: May 2006

Anionic glycopeptides and glycosaminoglycans synthesized by embryonic neural tube (epithelium) and neural crest (mesenchymal outgrowth) developing in vitro were examined. The profile of surface glycopeptides is relatively simple (two major ones for neural crest; four major ones for neural tube). There is one major glycopeptide found in the medium which is present only in trace amounts on the cells. Both hyaluronate and chondroitin sulfate are synthesized. Hyaluronate is predominantly cell associated; chondroitin sulfate is found predominantly in the medium. It is suggested that independent sorting of these relatively few glycopeptides can result in qualitative surface differences. Morphological state (epithelial or mesenchymal) and differentiated state may be related to these differences as well as to quantitative differences in surface glycosaminoglycans.
Changes in membrane microviscosity associated with phagocytosis: effects of colchicine.
Authors: Berlin R D , Fera J P
Published: May 2006

The effects of phagocytosis on plasma membrane microviscosity were studied by fluorescence depolarization techniques. It was shown that lipophilic probes are accumulated in intracellular vesicles to a significant degree in fibroblasts and neutrophils. Microviscosity was thus determined from the behavior of probes in isolated membranes. Phagocytosis of oil emulsions or polystyrene beads by rabbit polymorphonuclear leukocytes induces a marked decrease in plasma membrane microviscosity that parallels the extent of phagocytosis. Liposomes made from extracts of membrane lipid show qualitatively the same changes, indicating that the alteration of microviscosity results at least in part from changes in lipid composition. The decrease in microviscosity is abolished when colchicine is present during phagocytosis. Addition of colchicine to membranes previously isolated from control or phagocytic cells has no effect on their microviscosity. The results suggest that phagocytosis is accompanied by a microtubule-dependent reorganization of membrane lipids.
Intracellular binding of radioactive hydroxocobalamin to cobalamin-dependent apoenzymes in rat liver.
Authors: Mellman I S , Youngdahl-Turner P , Willard H F , Rosenberg L E
Published: May 2006

We identified previously an intracellular cobalamin (Cbl) binding protein(s) in cultured human fibroblasts, distinct from known Cbl "R" binders and absent from mutant cells deficient in the synthesis of the two Cbl coenzymes. In order to further characterize this binding activity, we have investigated its homologue in rat liver. After being transported to the liver by the serum protein transcobalamin II, [57Co]Cbl was bound by at least two distinct proteins, one cytosolic, the other mitochondrial. Labeled Cbl bound to cytosolic protein faster than or prior to the mitochondrial protein. With time there was a decline in radioactivity associated with the cytosolic binder and a coordinate increase in that associated with the mitochondrial binder. Although both proteins cochromatographed on Sephadex G-150 and had apparent molecular weights of 120,000, they were separated into two discrete components by polyacrylamide gel electrophoresis and by DEAE-cellulose chromatography. The cytosolic binder cochromatographed with N5-methyltetrahydrofolate:homocysteine methyltransferase activity (5-methyltetrahydropteroyl-L-glutamate:L-homocysteine S-methyltransferase, EC 2.1.1.13); the mitochondrial one with methylmalonyl CoA mutase activity (methylmalonyl-CoA CoA-carbonylmutase, EC 5.4.99.2). These proteins were distinguished further by the chemical forms of [57Co]Cbl found with them, hydroxocobalamin and methylcobalamin with the cytosolic protein and adenosylcobalamin with the mitochondrial one. These results suggest that intracellular Cbl binding activity in rat liver can be accounted for by attachment of Cbl to the two known Cbl-dependent apoenzymes, methylmalonyl CoA mutase and methyltetrahydrofolate methyltransferase. The mechanism and significance of the observered binding protein deficiency in mutant human fibroblasts must, therefore, be re-evaluated.
Covalent linkage of a protein to a defined nucleotide sequence at the 5'-terminus of virion and replicative intermediate RNAs of poliovirus.
Authors: Flanegan J B , Petterson R F , Ambros V , Hewlett N J , Baltimore D
Published: May 2006

The 5'-terminus of poliovirus polyribosomal RNA is pUp. A candidate for the 5'-terminus of poliovirion RNA was recovered as a compound migrating toward the cathode when 32P-labeled virion RNA was completely digested with ribonucleases T1, T2 and A and analyzed by paper ionophoresis at pH 3.5. Treatment with proteinase K reversed its direction of migration, indicating the presence of protein. Treatment with venom phosphodiesterase liberated all of the radioactivity as pUp, suggesting that poliovirion RNA has a protein-pUp 5'-terminus. Treatment of virion RNA with T1 ribonuclease alone generated a proteinase K-sensitive oligoribonucleotide. Analysis of the oligoribonucleotide using ribonucleases A and U2 showed its structure to be protein-pU-U-A-A-A-A-C-A-G. Digests of replicative intermediate RNA contained sufficient protein-pUp to suggest that this structure is at the 5'-end of most nascent poliovirus RNA molecules. We suggest that a protein-nucleotide structure acts as a primer for initiating synthesis of poliovirus RNA.
Excision repair of benzo[a]pyrene-deoxyguanosine adducts in baby hamster kidney 21/C13 cells and in secondary mouse embryo fibroblasts C57BL/6J.
Authors: Shinohara K , Cerutti P A
Published: May 2006

The formation and excision of benzo[a]pyrene-deoxyguanosine adducts in metabolizing baby hamster kidney cells (21/C13) and secondary mouse embryo fibroblasts (C57BL/6J) was investigated. Both diastereomeric adducts, N2-(10-(7beta,8alpha,9alpha-trihydroxy-7, 8, 9, 10 tetrahydrobenzo[a]-7,8,9,10-tetrahydrobenzo[a]pyrene)yl)deoxyguanosine, were detected in both cell lines and both cell lines were capable of excising these lesions, albeit with low efficiency.
Nucleotide sequence surrounding a ribonuclease III processing site in bacteriophage T7 RNA.
Authors: Rosenberg M , Kramer R A
Published: May 2006

We have determined a nucleotide seuqence of 87 residues surrounding a ribonuclease III (endoribonuclease III; EC 3.1.4.24) processing site in the bacteriophage T7 intercistronic region between early genes 0.3 and 0.7. The structural requirements necessary for proper recognition and cleavage by RNase III are discussed. In addition, other structural features characteristic of this intercistronic boundary are described.
Rotational relaxation of 70S ribosomes by a depolarization method using triplet probes.
Authors: Lavalette D , Amand B , Pochon F
Published: May 2006

Rotational relaxation on the microsecond time scale has been followed by a depolarization technique using the properties of the long-lived triplet state of covalently bound labels. Two triplet probes, which efficiently bind to ribosomal proteins, are described. The rotational correlation time of 70S ribosomes of Escherichia coli has been measured. The average hydrodynamic radius of the functionally active 70S particle in solution has been estimated to 147 A. A concentration dependence of the correlation time has been observed, which may result from an association of the 70S ribosomes to form 100S dimers.
Invariance and heterogeneity in the major structural and regulatory proteins of chick muscle cells revealed by two-dimensional gel electrophoresis.
Authors: Izant J G , Lazarides E
Published: May 2006

A two-dimensional gel electrophoresis system is used to investigate some of the properties of desmin, the major subunit of the 100-A filaments from chick muscle cells, and to compare these properties to those of the other major contractile and regulatory proteins of muscle. Desmin from embryonic and adult smooth, skeletal, and cardiac muscle cells is resolved into two isoelectric variants, alpha and beta, which possess slightly different electrophoretic mobilities in sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Both the alpha and the beta variants from all six preparations appear to be identical in isoelectric point and apparent molecular weight. The alpha and beta desmin are present in approximately equal amounts in all three types of muscle, suggesting that both isoelectric variants of desmin serve as the structural subunits of the 100-A filaments in chick muscle cells. Tropomyosin also can be resolved into two subunits, alpha and beta, in all three types of muscle. However, in each type of muscle both subunits differ from their counterparts in the other types of muscle, either by molecular weight or by isoelectric point. These results indicate that, with regard to apparent isoelectric point and molecular weight, desmin, a major muscle structural protein, is invariant, while tropomyosin, a major muscle regulatory protein, exhibits heterogeneity in the three types of muscle.
Selective scattering spectra as an approach to internal structure of granal and agranal chloroplasts.
Authors: Bialek G E , Horváth G , Garab G I , Mustárdy L A , Faludi-Dániel A
Published: May 2006

Selective scattering spectra of granal and agranal chloroplasts were measured in the red spectral region and compared with calculations based on the Mie theory. The spectra were influenced considerably by the intactness and ultrastructural pattern of the chloroplasts. It was demonstrated that the spectra consist of two components: one attributable to grana and the other, to single lamellae. The dependence of the selective scattering spectra on the ultrastructural characteristics offers a convenient method for monitoring the quality of chloroplast preparations by a procedure much faster than electron microscopy.
Unified mechanism for relay and oscillation of cyclic AMP in Dictyostelium discoideum.
Authors: Goldbeter A , Segel L A
Published: May 2006

A modified version of an allosteric model for adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] previously analyzed for sustained oscillations of adenosine 3':5'-cyclic monophosphate (cAMP) in Dictyostelium discoideum [Goldbeter, A. (1975) Nature 253, 540-542] is examined to see whether it can account for the relay of cAMP pulses. Oscillations occur around a nonequilibrium, unstable stationary state when system parameters are in a certain domain. It is found that relay can occur outside this domain, in a restricted set of parameter values for which the solution ultimately tends to a stable steady state. A suprathreshold level of extracellular cAMP is needed to elicit relay which consists in a pulsatory synthesis of intracellular cAMP. Theoretical predictions are compared with the results of experiments on cAMP relay and oscillation in aggregation-competent cells of D. discoideum. The model suggests an explanation for the emergence of aggregation centers and for a sequence of developmental events observed in interphase amoebae.
Differences in removal of acetylaminofluorene and pyrimidine dimers from the DNA of cultured mammalian cells.
Authors: Amacher D E , Elliott J A , Lieberman M W
Published: May 2006

The rate and extent of disappearance of two DNA lesions (pyrimidine dimers and covalently bound acetylaminofluorene), both thought to be removed by the so-called wide-patch (approximately 100 nucleotides) repair process, were studied in a variety of cultured mammalian cells. With the exception of mouse cells, dimers were removed more rapidly and extensively than covalently bound acetylaminofluorene. In human cells, for example, about 50% of the dimers were excised from DNA in 1 hr while only 25-50% of the chemically induced lesions were excised from DNA after 48 hr. Surprisingly mouse cells, which remove few dimers, were about as competent as control human fibroblasts at removing acetylaminofluorene lesions; however, xeroderma pigmentosum cells (group D) removed fewer N-acetoxy-2-acetylaminofluorene-induced lesions than control human cells. Our data raise the possibility of separate repair processes for these two types of lesions and suggest that their expression may be under similar genetic control in human cells.
Quantitative determination of transformed cells in a mixed population by stimultaneous fluorescence analysis of cell surface and DNA an individual cells.
Authors: Hawkes S P , Bartholomew J C
Published: May 2006

Cell-surface labeling with fluorescamine indicates that the fluorescence of Balb 3T3 A31 cells in considerably decreased after both viral and chemical transformation. This phenomenon, coupled with the technique of flow microfluorometry, enabled nontransformed and transformed cells to be distinguished. A second fluroescent probe, propidium iodide, which intercalates into DNA, was used in combination with fluorescamine in order to obtain a ratio of cell-surface labeling to DNA content. This manipulation allowed enhanced resolution of two populations and the detection of small numbers of transformants in a predominantly normal population.
Immunoprevention of x-ray-induced leukemias in the C57BL mouse.
Authors: Peters R L , Sass B , Stephenson J R , Al-Ghazzouli I K , Hino S , Donahoe R M , Kende M , Aaronson S A , KElloff G J
Published: May 2006

An attempt to prevent irradiation-induced thymic lymphomas in C57BL mice was made by inducing active immunity to endogenous type-C virus with inactivated Rauscher murine leukemia virus (MuLV) or inactivated Gross MuLV or by transferring passive immunity to endogenous type-C virus with goat anti-Gross MuLV IgG. Control groups received the following immunogen or treatment: inactivated simian sarcoma virus, complete Freund's adjuvant, normal goat IgG, and diluent, in both irradiated and nonirradiated C57BL mice Active immunity to the 70,000 molecular weight glycoprotein AKR-gp70 by immunization with Rauscher MuLV and passive immunity to AKR-gp70 by passive transfer of goat anti-Gross-MuLV IgG was measurable throughout some of the latent period of tumor development; in these two groups a significant reduction in tumor incidence was observed, as compared to the other experimental and control groups. Thus, the present findings support the concept of a type-C virus etiology of irradiation-induced leukemias and demonstrate the applicability of immunologic techniques directed against the endogenous type-C virus in the prevention of this disease.
5'-deoxypyridoxal as a potential anti-sickling agent.
Authors: Benesch R , Benesch R E , Edalji R , Suzuki T
Published: May 2006

5'-Deoxypyridoxal, which reacts specifically with the terminal amino groups of the alpha chains of hemoglobin, increases the oxygen affinity of hemoglobin solutions as well as of dilute suspensions of normal and sickle red cells and whole blood. As a result, the proportion of deoxyhemoglobin (which is responsible for sickling) is decreased at venous oxygen tensions and this is reflected by a sharply reduced sickle cell count in this range of oxygen pressures.
Voltage-dependent facilitation of Ca2+ entry in voltage-clamped, aequorin-injected molluscan neurons.
Authors: Eckert R , Tillotson D , Ridgway E B
Published: May 2006

Voltage-clamp experiments were performed on giant neurons of the nudibranch Anisodoris nobilis injected with the Ca-sensitive photoprotein, aequorin. Depolarization beyond -10 to +5 m V produced an aequorin signal, the amplitude of which depended on the extracellular Ca2+ concentration, the amplitude of the depolarization, and its duration. In paired pulse experiments, the amplitude of the aequorin signal produced in response to the second of two identical depolarizing pulses was larger than that produced during the first, resulting from an increased entry of Ca2+ during the second pulse. The increment in Ca conductance inferred from the augmented signal during the second pulse was independent of Ca2+ influx during the first pulse but, instead, was related to the amplitude and duration of the first pulse.
Regulation of growth hormone messenger RNA by thyroid and glucocorticoid hormones.
Authors: Martial J A , Baxter J D , Goodman H M , Seeburg P H
Published: May 2006

Thyroid and glucocorticoid hormones stimulate growth hormone synthesis in cultured rat pituitary cells (GC). We have compared changes in growth hormone production and mRNA in these cells. Triiodothyronine (10 nM) and dexamethasone (1 micron) stimulated increases in growth hormone production by 2.5- and 3.8-fold, respectively. There were corresponding increases in the capacity of RNA from hormone-treated cells to direct synthesis of pregrowth hormone in a wheat germ cell-free translation system, suggesting hormone-regulated increases in growth hormone mRNA. Hormone-induced changes in mRNA were also demonstrated by determining the kinetics of hybridization of a cDNA probe prepared from RNA enriched (about 70%) for growth hormone translational activity with RNA from control and hormone-treated cells. These results suggest that thyroid and glucocorticoid hormones can regulate growth hormone production by influencing the levels of its mRNA.
Neurotensin: specific binding to synaptic membranes from rat brain.
Authors: Kitabgi P , Carraway R , Van Rietschoten J , Granier C , Morgat J L , Menez A , Leeman S , Freychet P
Published: May 2006

The binding of neurotensin to synaptic membranes from rat brain was studied at 24 degrees with the use of [3H]neurotensin. The binding was found to be highly specific, saturable, and reversible. Values for KD of 2 nM and 0.9 nM were derived from equilibrium and kinetic experiments, respectively. Virtually no degradation of neurotensin was observed in the incubation medium after exposure to synaptic membranes under the conditions of the binding studies. Competitive inhibition of [3H]neurotensin binding by partial sequences of neurotensin revealed that the addition of the residue arginine-8 to the neurotensin-(9-13)-pentapeptide increases about 500-fold the relative binding potency, whereas the remaining portion of the NH2-terminal region is mainly responsible for full pharmacological potency; the COOH-terminal leucyl residue is essential for binding.
Inhibition of transcription and translation of globin messenger RNA in dimethyl sulfoxide-stimulated Friend erythroleukemic cells treated with interferon.
Authors: Rossi G B , Dolei A , Cioé L , Benedetto A , Matarese G P , Belardelli F
Published: May 2006

The addition of appropriate doses of interferon (IF) to cultures of Friend erythroleukemic cells inhibits dimethyl sulfoxide (Me2SO)-stimulated erythroid differentiation. In this study, the synthesis of heme, hemoglobin, and globin mRNA in Me2SO-stimulated cultures, with or without IF added, was compared. Although the hemoglobin content in Me2SO+IF-treated cultures was reduced 6- to 9-fold compared to that of cultures treated with Me2SO alone, there was less than a 2-fold decrease in the amount of heme accumulated. Globin mRNA, although unchanged in size or base sequence, was reduced in content in the Me2SO+IF cultures. The level of reduction of globin mRNA was insufficient to account for the lack of globin synthesis. Thus, it appears that IF may operate on two levels--one involving the transcription of globin mRNA and the other involving its translation.
High-fidelity transcription of 5S DNA injected into Xenopus oocytes.
Authors: Brown D D , Gurdon J B
Published: May 2006

Purified DNA, from Xenopus erythrocytes, containing genes for 5S ribosomal RNA (58 DNA) is transcribed faithfully when it is injected into the nucleus of a Xenopus oocyte. Full length 5S RNA of the correct sequence is transcribed from the injected DNA, and the newly synthesized transcripts hybridize predominantly with the coding strand of 5S DNA. The majority of transcripts hybridize with the gene region as opposed to the spacer region of the coding strand. Accurate transcription starts within the first 3 hr and continues for up to 4 days after injection of 5S DNA. Radioactive 5S RNA is detected in as short a labeling time as 1 hr.
Isolation of troponin-like complex from bovine brain cortex.
Authors: Mahendran C , Berl S
Published: May 2006

A troponin-like complex has been isolated from bovine brain cortex. This tropinin-like complex, with brain tropomyosin, confers Ca2+ sensitivity to the actin-activated myosin adenosinetriphosphatase (ATP phosphohydrolase, EC 3.6.1.3). That is, the Mg2+-stimulated ATPase activity generated by the interaction of purified muscle actin with muscle myosin is inhibited in the absence of Ca2+ but not in the presence of Ca2+ as a result of the addition of both brain tropomyosin and troponin-like complex. The troponin-like complex contains three components, one of which is similar in molecular weight to the troponin-T of skeletal actomyosin.
Isolation of a chloroplast N,N'-dicyclohexylcarbodiimide-binding proteolipid, active in proton translocation.
Authors: Nelson N , Eytan E , Notsani B E , Sigrist H , Sigrist-Nelson K , Gitler C
Published: May 2006

The N,N'-dicyclohexylcarbodiimide-binding proteolipid from lettuce chloroplast membranes has been purified by a novel, rapid technique involving I-butanol extraction and ether precipitation. Reconstitution of this proteolipid into liposomes composed of chloroplast lipids and subsequent incorporation of bacteriorhodopsin resulted in the formation of liposomes exhibiting a light-dependent accumulation of protons. This accumulation was significantly enhanced upon addition of N,N'-dicyclohexylcarbodiimide at concentrations similar to those that inhibit chloroplast adenosinetriphosphatase activity. Radioactively labeled N,N'-dicyclohexylcarbodiimide was found to be incorporated essentially into the proteolipid of the reconstituted liposomes. These results suggest that the functional unit responsible for proton channeling in the chloroplast membrane has been isolated and reconstituted in the native state.
Heteroploid conversion of human skin cells by methylcholanthrene.
Authors: Freeman A E , Lake R S , Igel H J , Gernand L , Pezzutti M R , Malone J M , Mark C , Benedict W F
Published: May 2006

Cultured epithelial cells from human skin generally had 3- to 30-fold more hydrocarbon-metabolizing activity than fibroblasts from skin of the same donor. This activity was constant for up to 55 days in primary culture but was lost rapidly upon physical subdivision of the cultures. Treatment of primary mixed fibroblasts and epithelial cell cultures with methylcholanthrene, but not phenanthrene, led to development of actively growing fibroblastic cultures with many heteroploid cells. Unique marker chromosomes, stable over a number of cell population doublings, were identified in several of the heteroploid cell strains. Pure cultures of fibroblasts from the same donors did not undergo heteroploid conversion in response to methylcholanthrene. Spontaneously occurring heteroploidy in logarithmic phase human fibroblasts is a rare event; thus, heteroploid conversion may be a useful marker for chemical transformation of human cells. Because methylcholanthrene seems to have little transforming effect on human skin fibroblasts, human skin epithelial cells, because of their hydrocarbon-metabolizing activity, may serve to convert methylcholanthrene from a distal to an ultimate carcinogenic form.
Studies of streptozotocin-induced insulitis and diabetes.
Authors: Rossini A A , Like A A , Chick W L , Appel M C , Cahill G F
Published: May 2006

Multiple small injections of streptozotocin produce a delayed, progressive increase in plasma glucose in mice within 5-6 days after the injections, in association with pronounced insulitis and induction of type C viruses within beta cells. Multiple subdiabetogenic doses of streptozotocin in rats and multiple injections of another beta cell toxin, alloxan, in mice did not induce insulitis although hyperglycemia followed the injection of larger quantities of both agents. In mice, the prior injection of 3-O-methyl-D-glucose (3-OMG) or nicotinamide attenuated the diabetic syndrome produced by streptozotocin; however, 3-OMG was more protective. Rabbit antimouse lymphocyte serum, alone, provided partial protection but, when given together with either 3-OMG or nicotinamide, effectively prevented the streptozotocin-induced diabetic syndrome. Cessation of these preventive treatments was followed by the appearance of insulitis and diabetes. These findings suggest that multiple injections of streptozotocin induce, in susceptible hosts, the triad of direct beta cell cytotoxicity, virus induction within beta cells, and cell-mediated autoimmune reaction. These factors, acting separately or in concert, appear to induce a destructive insulitis and severe diabetes. The relative importance of each component and the factors governing host susceptibility remain to be clarified.
Superiority of interconvertible enzyme cascades in metabolic regulation: analysis of monocyclic systems.
Authors: Stadtman E R , Chock P B
Published: May 2006

A theoretical analysis of monocyclic cascade models shows that the steady-state fraction of covalently modified interconvertible enzyme is a function of 10 different cascade parameters. Because each parameter can be varied independently, or several can be varied simultaneously, by single or multiple allosteric interactions of ligands with one or more of the cascade enzymes, interconvertible enzymes are exquisitely designed for the rigorous control of key metabolic steps. Compared with other reglatory enzymes, they can respond to a greater number of allosteric stimuli, they exhibit greater flexibility in overall control patterns, and they can generate a greatly amplified response to primary allosteric interactions of effectors with the converter enzymes. Contrary to earlier views, the decomposition of ATP associated with cyclic coupling of the covalent modification and demodification reactions is not a futile process. ATP decomposition supplies the energy needed to maintain concentrations of modified enzyme at steady-state levels that are in excess of those obtainable at true thermodynamic equilibrium.
Specific radiolabeling of a cell surface receptor for epidermal growth factor.
Authors: Das M , Miyakawa T , Fox C F , Pruss R M , Aharonov A , Herschman H R
Published: May 2006

A photoreactive derivative of epidermal growth factor (EGF) has been used to identify and specifically label a membrane receptor for EGF on mouse 3T3 cells. Photoactivable EGF, labeled with 125I, was incubated with 3T3 cells and then photolyzed in situ to generate a nitrene capable of reacting with a wide variety of chemical bonds. Analysis of the system by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed, besides the band of EGF, only one other major radioactive band, at a position indicating an apparent molecular weight of 190,000. This band was absent when a nonresponsive and nonbinding variant of 3T3 was used. A direct proportionality between binding activity and crosslinked complex formation was demonstrated using a variety of binding conditions. "Down regulated" cells, in which EGF binding activity was greatly reduced by prolonged incubation with an appropriate concentration of EGF, also had a decrease in covalent complex formation proportional to the decrease in EGF binding activity.
Source of oxygen in the CO
2
produced in the bioluminescent oxidation of firefly luciferin
Authors: Shimomura Osamu , Goto Toshio , Johnson Frank H.
Published: May 2006

Incorporation of
18
O into the CO
2
produced in the bioluminescent oxidation of firefly luciferin was studied. In H
2
16
O medium with
18
O
2
gas, the product CO
2
contained up to 75% C
16
O
18
O, showing that one O of the product CO
2
arose from the O
2
that oxidized luciferin. This result is consistent with a dioxetane mechanism. Analysis of the mass spectral data of the CO
2
obtained in high-enrichment H
2
18
O medium with
16
O
2
gas indicated the presence of about 20% contaminating CO
2
, which contributes approximately 70% of the total incorporated
18
O. Thus the values of incorporated
18
O in H
2
18
O medium with
16
O
2
gas have no significance in the present context. Data obtained with luciferases of the American firefly
Photinus
and Japanese firefly
Luciola
were similar.