bluuebunny/crossref_metadata_2025 huggingface dataset:
Endoplasmic reticulum and autophagy in rat hepatocytes.
Authors: Novikoff A B , Shin W Y
Published: May 2006

Electron microscopy of hepatocytes in both normal rat liver and rat liver treated to induce hyperplasia of smooth endoplasmic reticulum shows that autophagic vacuoles and residual bodies (types of lysosomes) are continuous with endoplasmic reticulum.
Human milk stimulates DNA synthesis and cellular proliferation in cultured fibroblasts.
Authors: Klagsbrun M
Published: May 2006

Human milk contains a mitogenic factor that stimulates DNA synthesis and cell division in mouse and human fibroblasts in vitro. Milk at a concentration of 1% (vol/vol) is as active in stimulating DNA synthesis as is 5% (vol/vol) human serum and 10% (vol/vol) calf serum. The mitogenic activity of human milk is destroyed by incubation with trypsin and chymotrypsin. However, neither urea, guanidine hydrochloride-dithiothreitol, nor exposure to pH 1 will inactivate the milk-derived growth factor. Gel filtration and isoelectric focusing indicate that the mitogenic activity of human milk has a molecular weight between 14,000 and 18,000 and an isoelectric point between 4.4 and 4.7.
Sequence variability of immunoglobulins considered from the standpoint of population genetics
Authors: Ohta Tomoko
Published: May 2006

The probability of gene identity between members of a multigene family was investigated, assuming mutation, random genetic drift, and unequal crossing-over. The theoretical results on the equilibrium and transient behavior of the identity probability were applied to the analyses of sequence variability in the variable regions of immunoglobulins. The probability of amino acid identity between corresponding residue sites at different but homologous immunoglobulin sequences was computed both within and between species from data reported by other workers. The average probability of amino acid identity was obtained for the hypervariable regions and also for the framework regions. From statistical analyses based on population genetics theory it is concluded that somatic mutations cannot be the major cause of hypervariability and that the results can readily be explained by the germ line theory.
Teratocarcinoma cells as vehicles for introducing specific mutant mitochondrial genes into mice
Authors: Watanabe Tomomasa , Dewey Michael J. , Mintz Beatrice
Published: May 2006

The immediate purpose of the experiment was to establish a means of introducing specific mitochondrially encoded mutant genes into mice. Mouse teratocarcinoma stem cells were used as vehicles for the cytoplasmic markers because of their known capacity for normal somatic and germinal differentiation after injection into blastocysts. The mutation of choice, chloramphenicol resistance (CAP
R
), was first produced in a melanoma cell line by mutagenesis and selection. The CAP
R
trait was then transferred from a resistant melanoma cell to a sensitive (CAP
S
) teratocarcinoma cell by fusing to the latter only the cytoplasmic portion of the CAP
R
donor. This indirect route demonstrated the cytoplasmic provenance of the mutation. Protein synthesis in mitochondria isolated from the cybrid, or cytoplasmic hybrid, cells was barely affected by chloramphenicol, in contrast to the inhibitory influence of the drug on mitochondria of the parent teratocarcinoma line. Cells of the cybrid clone resembled teratocarcinoma cells and retained their ability to form diverse tissues in solid tumors produced from subcutaneous grafts. Cells from the tumors were retransplanted and were tested periodically by culture in chloramphenicol; they were found to be stably CAP
R
even after 16 weeks
in vivo
in the absence of the selective agent. The CAP
R
cybrids were microinjected into blastocysts of another inbred strain and, after transfer to foster mothers, mosaic mice were obtained. They comprised both cybrid- and blastocyst-derived cells in various tissues, as indicated by strain-specific nuclear markers. These results demonstrate successful normal differentiation of the CAP
R
lineage
in vivo
. Teratocarcinoma cybrids thus offer a practical portal of entry of preselected mitochondrial genes into mice. This will ultimately permit
in vivo
investigation of maternally transmitted traits, of mitochondrial genetic influences in specialized cells, and of possible roles of cytoplasmic genes in clinical and disease states.
Two HLA-linked loci controlling the fourth component of human complement.
Authors: O'Neill G J , Yang S Y , Dupont B
Published: May 2006

An electrophoretic polymorphism of the fourth component of human complement (C4) is described. Three patterns of bands of C4 were observed in EDTA plasma from a panel of unrelated blood donors and family members by using the technique of immunofixation electrophoresis. These patterns consisted of four fast-moving anodal bands (F), four slow-moving cathodal bands (S), or a combination of both the F and S bands (FS). The C4 patterns of bands were observed in EDTA plasma and not in serum. Family studies showed that this polymorphism of C4 did not segregate with HLA histocompatibility genes in a fashion governed by two codominant alleles at a single genetic locus. The family data are in agreement with the hypothesis that two different genetic loci control the electrophoretic patterns of C4. One locus controls the presence (F) or absence (f0) of the four anodal (F) bands and the other controls the presence (S) or absence (s0) of the four cathodal (S) bands. The C4F and C4S loci are both closely linked to HLA-B.
Changes in transmitter release induced by ion-containing liposomes.
Authors: Rahamimoff R , Meiri H , Erulkar S D , Barenholz Y
Published: May 2006

The changes in quantal transmitter release induced by egg phosphatidylcholine liposomes with different internal ionic composition were examined at the frog neuromuscular junction by using conventional electrophysiological techniques. It was found that liposomes containing calcium or sodium ions increase both evoked and spontaneous transmitter release, while liposomes containing potassium do not. The results suggest that phosphatidylcholine liposomes are able to transfer their aqueous medium into the presynaptic nerve terminal.
Three-dimensional structures of aspartate carbamoyltransferase from Escherichia coli and of its complex with cytidine triphosphate.
Authors: Monaco H L , Crawford J L , Lipscomb W N
Published: May 2006

X-ray diffraction studies to nominal resolutions of 3.0 A for unliganded aspartate carbamolytransferase (EC 2.1.3.2)(R32 crystal symmetry) and of 2.8 A for the complex of aspartate carbamoyltransferase with cytidine triphosphate (P321 crystal symmetry) have yielded traces of the polypeptide chains of the catalytic (C) and regulatory (R) chains in the hexameric C6R6 molecules. The independent molecular structures of the liganded and unliganded forms of the enzyme are very nearly identical. In the regulatory chain there is a CTP-binding domain that interacts with an adjacent regulatory subunit and a zinc-binding domain that interacts with the catalytic subunit. In the catalytic chain a polar domain shows interactions between adjacent pairs of C chains to form each trimer C3 while an equatorial domain shows intramolecular C3--C3 interactions. The active site is at or near the interface between adjacent C chains within the trimers. Probably each active center involves amino acid residues from adjacent C chains.
Filter-binding assay for covalent DNA-protein complexes: adenovirus DNA-terminal protein complex.
Authors: Coombs D H , Pearson G D
Published: May 2006

A rapid, simple, and quantitative filter-binding assay using glass fiber filters has been developed to detect the convalent adenovirus DNA-terminal protein complex. The assay is unusually sensitive because binding of protein-free DNA generally is less than 0.1%. Binding of the adenovirus complex to filters is mediated by terminal protein. We have found that: (i) the adenovirus complex binds maximally to filters in NaCl at concentrations higher than 0.2 M; (ii) noncovalent complexes between protein-free DNA and adenovirus proteins bind to filters in salt at concentrations lower than 0.4 M but not in concentrations higher than 0.7 M; and (iii) protein-free DNA alone binds to filters in guanidine.hydrochloride at concentrations higher than 0.8 M. By varying the ionic conditions, "all or none" modulation of these interactions can be achieved.
Sodium pyrophosphate inhibition of RNA.DNA hybrid degradation by reverse transcriptase.
Authors: Myers J C , Spiegelman S
Published: May 2006

Sodium pyrophosphate inhibits synthesis of anticomplementary DNA during a reverse transcriptase (RNA-directed DNA nucleotidyltransferase, EC 2.7.7.7) catalyzed reaction. In the presence of pyrophosphate, the complementary DNA remains stably complexed to the RNA template. In the absence of pyrophosphate, the DNA. RNA hybrid template is degraded and anticomplementary DNA is synthesized. High concentrations of additives containing phosphodiester bonds appear to inhibit the ribonuclease H activity (hybrid nuclease, EC 3.1.4.34) of the reverse transcriptase, therby preventing formation of RNA primers necessary for the synthesis of anticomplementary DNA.
Antipain inhibits thyroxine-induced synthesis of carbamyl phosphate synthetase I in tadpole liver.
Authors: Mori M , Cohen P P
Published: May 2006

The increased activity of carbamyl phosphate synthetase I [carbamoyl-phosphate synthase (ammonia); ATP: carbamate phosphotransferase (diphosphorylating), EC 2.7.2.5] in tadpole liver observed during thyroxine-induced metamorphosis was markedly inhibited by intraperitoneal injection of the microbial protease inhibitor antipain (0.1 micrometermol/g of body weight, twice daily). A somewhat less than maximal inhibition was seen when antipain was given only during the first 2 days of thyroxine treatment. On the other hand, little inhibition was observed when the inhibitor was given after the third or fourth day of thyroxine treatment. Antipain also inhibited thyroxine-induced increases of ornithine transcarbamylase (EC 2.1.3.3), arginase (EC 3.5.3.1), and succinate-cytochrome c reductase (EC 1.3.99.1) activities. Among other microbial protease inhibitors tested, chymostatin was nearly as effective as antipain, leupeptin was less effective, and pepstatin was ineffective. Analysis of the total liver protein and of the immunoprecipitate by sodium dodecyl sulfate/polyacrylamide gel electrophoresis showed that the inhibition was due to decreased amount of the enzyme protein. Antipain had no significant effect on leucine incorporation into total protein of tadpole liver. These results indicate the involvement of a proteolytic step in the pretranscriptional events in thyroxine-stimulated enzyme induction.
Catabolism of 2-deoxyglucose by phagocytic leukocytes in the presence of 12-O-tetradecanoyl phorbol-13-acetate.
Authors: Zabos P , Kyner D , Mendelsohn N , Schreiber C , Waxman S , Christman J , Acs G
Published: May 2006

We have found that phagocytic leukocytes exposed to the tumor-promoting agent, 12-O-tetradecanoyl phorbol-13-acetate, efficiently release carbon-1 of 2-deoxyglucose in the form of CO2 with concurrent intracellular accumulation of a phosphorylated 5-carbon intermediate. In the absence of 12-O-tetradecanoyl phorbol-13-acetate, these cells release barely detectable amounts of CO2 from 2-deoxyglucose. 12-O-Tetradecanoyl phorbol-13-acetate, at a concentration of 1 ng/ml, has an immediate effect on CO2 release, which is temperature-dependent and linear with time and cell number. The ability of a number of phorbol ester-like compounds to enhance this catabolic pathway for 2-deoxyglucose correlates with their ability to act as tumor promotors and inflammatory agents. Although this effect of phorbol esters appears to be restricted to granulocytes, monocytes, and macrophages, the possibility arises that other mammalian cells are capable of catabolizing or can be induced to catabolize-2-deoxyglucose. Thus, 2-deoxyglucose decarboxylation should be considered whenever this analog of mannose and glucose is used as an indicator for sugar transport, especially when pharmacodynamic agents are present.
Inhibition of growth of 3T3 cells by extract of surface membranes.
Authors: Whittenberger B , Raben D , Lieberman M A , Glaser L
Published: May 2006

The growth of Swiss 3T3 cells can be inhibited by the addition of a plasma membrane enriched fraction from 3T3 cells [Whittenberger, B & Glaser, L. (1977) Proc. Natl. Acad. Sci. USA 74, 2251--2255]. We report conditions for the extraction of the inhibitory components from the membranes with octylglucoside. The solubilized components reversibly inhibit the rate of cell division of 3T3 but not of simian virus 40-transformed 3T3 cells. The inhibitory activity is heat labile and nondialyzable. The inhibition observed with the soluble extract can be reversed by mitogenic factors present in serum.
Amino acid sequence of a progesterone-binding protein.
Authors: Popp R A , Foresman K R , Wise L D , Daniel J C
Published: May 2006

The amino acid sequence of blastokinin, also called uteroglobin, has been determined by a combined study of both the intact native molecule and the peptide fragments resulting from tryptic and chymotryptic digestions. Sequence analyses performed by automated methods and by sequential digestion with leucine aminopeptidase and carboxypeptidase Y demonstrate that blastokinin is a dimer of identical 69-amino acid subunits held together in parallel orientation by two disulfide bridges at positions 3 and 68. The polypeptide chains are further characterized by the absence of tryptophan residues and by single residues of histidine and tyrosine at positions 8 and 21, respectively. Six of eight amino acids, positions 17--24, near the progesterone binding site of blastokinin contain a hydroxyl group. Knowledge of the chemistry of this receptor site should allow better perspectives of the chemistry of molecules in normal tissues that are dependent on progesterone for growth and development, as well as compounds that could act as cancer antagonists for endocrine therapy of hormone-dependent tumors.
Fibronectin synthesis by epithelial crypt cells of rat small intestine.
Authors: Quaroni A , Isselbacher K J , Ruoslahti E
Published: May 2006

Synthesis of fibronectin in an epithelial cell line (IEC-6) established from rat small intestine was demonstrated by using immunofluorescence, radioimmunoassay, and collagen-binding. Internally labeled radioactive fibronectin isolated from the IEC-6 cells gave a single main band in sodium dodecyl sulfate/polyacrylamide gel electrophoresis under reducing conditions. Fibronectin isolated from rat plasma gave two closely spaced bands. The slower one had the same mobility as the epithelial cell fibronectin. The distribution of fibronectin in IEC-6 cells as detected by immunofluorescence was different from that described for fibroblasts and other cell types; fibronectin was present exclusively in regions of cell-to-cell contact. No fluorescence was detected on the surface membrane facing the culture medium or underneath the cells. This suggests that fibronectin may not be involved in the adhesion of the epithelial cells to the growth surface but could mediate cell-to-cell contacts. In microscopic sections of the small intestine, immunofluorescent staining with antifibronectin serum was strong in the basement membrane underlying the epithelial cells in the crypts. The in vitro synthesis of fibronectin by the crypt cells and its abundant presence in the basement membrane underlying the same cells in vivo suggests that fibronectin is a structural component of the basement membrane, and that it may be, at least in part, synthesized and deposited by the intestinal epithelium.
Naturally occurring promoter down mutation: nucleotide sequence of the trp promoter/operator/leader region of Shigella dysenteriae 16.
Authors: Miozzari G , Yanofsky C
Published: May 2006

The promoter/operator/leader region of the trp operon of Shigella dysenteriae 16 has single base pair differences from the corresponding region of Escherichia coli at positions -24 and -13. The difference at -13 was shown to be responsible for the 90% reduction in promoter function characteristic of the trp operon of S. dysenteriae. The base pair difference at position -13 also renders the operator partially constitutive. This allows the organism to maintain relatively high repressed levels of the trp enzymes and increases the relative importance of attenuation as a transcription control mechanism. These findings and the earlier observation that the trpE protein of S. dysenteriae is only slightly active explain the low in vivo expression of the trp operon of this organism. Nutritional studies suggest that operons involved in other amino acid biosynthetic pathways in S. dysenteriae 16 may be similarly partially inactivated.
Cytoplasmic transfer of resistance to antimycin A in Chinese hamster cells.
Authors: Harris M
Published: May 2006

A mutant subline of V79 Chinese hamster cells resistant to antimycin A (ANT) was obtained by treatment with ethyl methanesulfonate followed by serial selection in ANT-containing medium. Clonal derivatives of the resistant line are less susceptible than parent cells to growth inhibition by ANT in mass populations and show a higher plating efficiency in graded levels of inhibitor. Resistance to ANT is stable in drug-free medium and follows a pattern of incomplete dominance in hybrids between resistant and sensitive cells. No cross-resistance to chloramphenicol or other unrelated compounds was observed. Cytoplasmic transmission of ANT resistance can be readily demonstrated by fusing enucleated cytoplasts from resistant donors to sensitive recipient cells. The resulting cytohybrids ("cybrids") grow selectively in ANT but are identical karyotypically with the recipient cell type. As a putative mitochondrial marker, ANT resistance may be usefully combined with chloramphenicol resistance for studies on segregation and recombination in the mitochondrial genome of mammalian cells.
Model for evolution of Y chromosomes and dosage compensation.
Authors: Charlesworth B
Published: May 2006

Some difficulties with the classical model for the evolution of a genetically invert Y chromosome are discussed. An alternative model is proposed, which is based on the principle of Mullers ratchet; this involves the accumulation of chromosomes bearing deleterious mutant genes in a finite population in the absence of crossing-over. This process would result in the gradual increase, with time, in the number of mutant loci carried in an average Y chromosome, although the frequency of individual deleterious alleles at most loci remains low. It is shown that this creates a selection pressure for differentially increasing the activity of the X chromosome in heterogametic individuals at the expense of that of the Y, leading eventually to a genetically inert Y chromosome and to the evolution of dosage compensation.
Enhancement of banding patterns in human metaphase chromosomes by energy transfer
Authors: Sahar Elhanan , Latt Samuel A.
Published: May 2006

Intermolecular energy transfer between appropriately chosen pairs of dyes can be used to induce or enhance banding patterns in human metaphase chromosomes. Energy transfer, calibrated by fluorometric studies on soluble dye·DNA complexes, can also be detected by photometric measurements on cytological preparations of metaphase chromosomes stained with pairs of fluorochromes. If a fluorescent dye with one type of binding or quantum yield specificity (e.g., quinacrine, 33258 Hoechst, or chromomycin A
3
) is employed together with a counterstain (e.g., actinomycin D, 7-aminoactinomycin D, or methyl green) exhibiting a complementary base pair binding specificity and satisfying spectral overlap criteria for energy transfer, contrast in fluorescence from the first dye is enhanced in specific subsets of standard chromosome bands. Extensive energy transfer presumably suppress donor fluorescence except in chromosomal region containing clusters of at least 20 base pairs predominantly of one type, within which the donor but not the acceptor can bind and fluoresce. Quinacrine-bright polymorphic regions are especially resistant to fluorescence quenching by counterstains with G·C binding specificity, strengthening the evidence that these latter regions are highly enriched for A·T base pair clusters. The ability to highlight selectively many such polymorphic regions may prove of further, practical, utility in a number of cytogenetic problems.
Immunization against malaria with antigen from Plasmodium falciparum cultivated in vitro.
Authors: Reese R T , Trager W , Jensen J B , Miller D A , Tantravahi R
Published: May 2006

Aotus monkeys, which are generally killed when infected with the human malaria parasite Plasmodium falciparum, have been identified and grouped by karyotype. These animals were immunized with parasite material obtained from P. falciparum cultivated in vitro which had been maintained in culture for over a year. When sufficient amounts of this antigenic material were used with a synthetic muramyl dipeptide (MDP), protective immunity was induced without presenting the antigen in complete Freund's adjuvant.
Human antibodies reactive with purified envelope antigens of primate type C tumor viruses.
Authors: Kurth R , Mikschy U
Published: May 2006

Human sera from healthy individuals have been shown to react with viral antigens in preparations of detergent-disrupted C type viruses from monkeys. In this report, it is demonstrated that (populations of) these human antibodies react with highly purified envelope glycoproteins of the simian sarcoma virus-simian sarcoma-associated virus complex and the Friend leukemia virus complex. Several immunological parameters influencing human antibody binding to C type tumor virus antigens have been characterized. These parameters indicate that human antibodies tend to bind to what is probably a subset of the antigenic determinants on the virus envelope antigens and that different human sera recognize the same antigenic determinants on the virus envelope antigens tested. The possible origin of these antibodies is discussed.
Immunodiagnosis of infection with Schistosoma mansoni: enzyme-linked immunosorbent assay for detection of antibody to circulating antigen.
Authors: Kelsoe G H , Weller T H
Published: May 2006

A circulating antigen, a negatively charged polysaccharide from the trematode Schistosoma mansoni, was noncovalently bound to the surface of poly(L-lysine)-coated wells in polystyrene trays, which were then used in a micro-enzyme-linked immunosorbent assay (ELISA) test. The method provides an immunodiagnostic test for schistosomiasis of exceptional sensitivity with a high degree of specificity. Comparison of Bell egg counts and ELISA titers revealed a good correlation (r congruent to 0.80) in young individuals with low to moderate worm burdens, but this relationship was less marked in older individuals or those with high egg counts.
Brilliant total reflection from a liquid-liquid interface
Authors: Hildebrand Joel H.
Published: May 2006

In this paper I describe total reflection of great brilliancy that seems to indicate that an interface can be very thin.
Displacement and aberrant methylation in vitro of H-1 histone in rat liver nuclei after half-saturation of chromatin with polycations.
Authors: Byvoet P , Baxter C S , Sayre D F
Published: May 2006

Radiomethyl incorporation in vitro into Nepsilon-methyllysine of histones from rat liver nuclei incubated in the presence of S-adenosyl[methyl-3H]methionine is stimulated if the polycations polylysines, protamines, or histones are added to the incubation mixture. Maximal stimulation occurs at a cation/nucleotide ratio of 0.5. Past this point stimulation drops, except in the case of very lysine-rich histone H-1, for which the maximal level of incorporation remains constant upon further addition of this histone. Bio-Gel P-10 chromatography, differential precipitation, and gel electrophoresis of radiomethylated histones indicate that although the usual incorporation of radiomethyl into histone H-3 is not affected, active methylation of H-1 occurs in the presence of polycations. Column chromatographic amino acid analysis reveals that the methylation of H-1 will specifically generate Nepsilon-monomethyllysine. Except for this condition, H-1 is never methylated in vivo or in incubated cell nuclei. Because H-1 is the weakest bound histone in chromatin, the above phenomena may be explained by assuming that, within the chromatin, polycations displace the lysine-rich histone towards the nucleosome, which results in its abberant methylation, assuming that the native nucleosome is the seat of the histone lysine methyltransferase.
Isolation and characterization of ColE1-derived plasmid copy-number mutant.
Authors: Gelfand D H , Shepard H M , O'Farrell P H , Polisky B
Published: May 2006

The plasmid pBGP120 is a ColE1 derivative that contains elements of the Escherichia coli lac operon and the Tn3 transposon. We have selected and isolated a copy-number mutant of pBGP120. In exponentially growing cultures, the copy-number mutant, pOP1, represents approximately 30% of total intracellular DNA compared to about 5% for pBGP120. Plasmid-encoded beta-galactosidase monomer can represent 50% of newly synthesized protein in cells carrying pOP1. pOP1 is structurally unstable in certain genetic backgrounds and under certain growth conditions, breaking down to a smaller sized plasmid that retains the DNA overproducer phenotype and the Tn3 transposon. The smaller overproducer plasmid, pOP1delta6, is generated by a continuous deletion of sequences located between one end of the Tn3 transposon and a site about 630 nucleotides from the EcoRI site in the beta-galactosidase structural gene of pOP1. pOP1delta6 retains the ColE1 origin of replication but has lost the lac promotor and operator and most of the beta-galactosidase structural gene. pOP1delta6 exists at approximately 210 copies per chromosome in exponentially growing cells.
Specific RNA sequences and gene products of MC29 avian acute leukemia virus
Authors: Mellon Pamela , Pawson Anthony , Bister Klaus , Martin G. Steven , Duesberg Peter H.
Published: May 2006

The 28S RNA of the defective avian acute leukemia virus MC29 contains two sets of sequences: 60% are hybridized by DNA complementary to other avian tumor virus RNAs (group-specific cDNA) and 40% are hybridized only by MC29-specific cDNA. Specific and group-specific sequences of viral RNA, defined in terms of their large RNase T
1
-resistant oligonucleotides, were located on a map of all large T
1
oligonucleotides of viral RNA. Oligonucleotides representing MC29-specific sequences of viral RNA mapped between 0.4 and 0.7 unit from the 3′-poly(A) end. Oligonucleotides of group-specific sequences mapped between 0 and 0.4 and between 0.7 and 1 map unit. Cell-free translation of viral RNA yielded three proteins with approximate molecular weights of 120,000, 56,000, and 37,000, termed P120
mc
, P56
mc
, and P37
mc
. P120
mc
contained both MC29-specific peptides and serological determinants and peptides of the conserved, internal group-specific antigens of avian tumor viruses. P120
mc
is translated only from full-length 28S RNA. Furthermore, MC29 RNA contains sequences related to the group-specific antigen gene (
gag
), near the 5′ end, which are followed by MC29-specific sequences. We conclude that this protein is translated from the 5′ 60% of the RNA, and that it includes a segment translated from the specific sequences. It is suggested that the transforming (
onc
) gene of MC29 may consists of the specific and some group-specific RNA sequences and that P120
mc
, which is also found in transformed cells, may be the
onc
gene product.
Resolution of cytochrome oxidase into two component complexes.
Authors: Fry M , Vande Zande H , Green D E
Published: May 2006

Cytochrome c oxidase (ferrocytochrome c: oxygen oxidoreductase, EC 1.9.3.1) has been resolved into a pair of complexes of unequal molecular weight. The larger complex (electron transfer complex) contains exclusively the oxidation-reduction proteins characteristic of cytochrome oxidase; the smaller complex (ion transfer complex) shows exclusively the capability for cation-dependent induction of the fluorescence of 8-anilino-1-naphthalenesulfonic acid--a capability demonstrable in preparations of cytochrome oxidase. The duplex nature of cytochrome oxidase has important implications for the mechanism of energy coupling.
Compartmentalization of cyclic AMP-dependent protein kinases in human erythrocytes.
Authors: Dreyfuss G , Schwartz K J , Blout E R
Published: May 2006

The human erythrocyte contains two types of cyclic AMP-dependent protein kinase. The membrane-associated protein kinase holoenzyme can be released intact by hypotonic treatment at alkaline pH. Chromatography on DEAE-cellulose and molecular weight determinations demonstrate that this enzyme is a type I cyclic AMP-dependent protein kinase, while the predominant cyclic AMP-dependent protein kinase found in the cytoplasm is type II. The catalytic subunits of the two types of kinase found in the erythrocyte are identical, but the regulatory subunits, which distinguish the two types of kinase, determine their localization within the cell. It is proposed that the regulatory subunit of the type I enzyme, in addition to binding the catalytic subunit, interacts specifically with one or more membrane proteins and that this interaction may serve to position the kinase in preferential proximity to protein substrates.
Initiation of HeLa cell DNA synthesis in a subnuclear system.
Authors: Brun G , Weissbach A
Published: May 2006

Mammalian cells are known to synthesize DNA in discrete stages, the first of which seems to be the formation of DNA pieces 150--200 nucleotides in length that have a s20 value of about 4 S. We have reconstructed a system derived from HeLa cell nuclei that carries out RNA-primed initiation of the synthesis of small (4S) DNA fragments. This synthesis is resistant to high concentrations of alpha-amanitin and sensitive to antibody directed against RNA polymerase I, suggesting that this enzyme may be involved in the initiation step. The formation of small DNA fragments in this system also requires DNA polymerase alpha, heat-labile nuclear factor(s), and at least one other nuclear protein.
Thiostrepton-resistant mutants exhibit relaxed synthesis of RNA.
Authors: Smith I , Paress P , Pestka S
Published: May 2006

Spontaneous mutants of Bacillus subtilis resistant to thiostrepton (TSP) exhibit relaxed synthesis of RNA when starved for required amino acids. Intact cells of tsp mutants cannot synthesize the regulatory nucleotides, ppGpp and pppGpp, after amino acid deprivation. Because ribosomes isolated from spontaneous revertants to thiostrepton sensitivity and from wild-type stringent strains can synthesize (p)ppGpp whereas ribosomes isolated from tsp strains cannot synthesize these regulatory nucleotides in the presence of stringent factor, it appears that the lesion is expressed at the level of the ribosome. Genetic mapping, via three-factor transformational crosses, has shown that tsp is closely linked to rif, in the order cysA14, tsp, rif-I, strA. The phenotype of the tsp mutants indicates that they are of the relC type. Their map position indicates that they are different from a previously described B subtilis rel mutation. Ribosomes from the latter strain can synthesize (p)ppGpp in cell-free extracts.
Repair of O6-methylguanine in adapted Escherichia coli.
Authors: Schendel P F , Robins P E
Published: May 2006

Cells exposed to sublethal concentrations of simple alkylating agents develop resistance to their mutagenic effects. This results from the induction of a system that we have called the adaptive response. During exposure to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), Escherichia coli cells induced for the adaptive response accumulate substantially less O6-methylguanine in their DNA than control cells. If O6-methylguanine does form, adapted cells possess a repair system for removing it from their DNA. The capacity of this system is limited and the system ceases to function when too much alkylation has occurred. From this point onwards O6-methylguanine starts to accumulate, and the cells begin to develop mutations at a rate directly proportional to their rate of O6-methylguanine accumulation. Our data support the idea that the O6 methylation of guanine accounts for most MNNG-induced mutagenesis.
Construction of bacterial plasmids that contain the nucleotide sequence for bovine corticotropin-beta-lipotropin precursor.
Authors: Nakanishi S , Inoue A , Kita T , Numa S , Chang A C , Cohen S N , Nunberg J , Schimke R T
Published: May 2006

mRNA that encodes the common peptide precursor for the hormones corticotropin and beta-lipotropin was purified from the neurointermediate lobe of bovine pituitaries, and double-stranded cDNA species synthesized from this template were cloned in Escherichia coli X1776 by inserting them into the Pst I endonuclease cleavage site of the pBR322 plasmid using poly(dG)poly(dC) homopolymeric extensions. Certain of the cloned cDNA inserts contain nucleotides corresponding to the complete amino acid sequence of bovine corticotropin and a coding sequence that corresponds to at least the first portion of bovine beta-lipotropin. The nucleotide sequences coding for corticotropin and beta-lipotropin are separated on the cDNA by a 6-base-pair sequence encoding lysine and arginine, indicating that the carboxyl terminus of corticotropin is connected on the precursor peptide with the amino terminus of beta-lipotropin by these two amino acids. In addition, the cloned cDNA insert is characterized by an unusually high C+G nucleotide base content as well as by a number of DNA sequence duplications.
Application of higher derivative techniques to analysis of high-resolution thermal denaturation profiles of reassociated repetitive DNA.
Authors: Cuellar R E , Ford G A , Briggs W R , Thompson W F
Published: May 2006

We have analyzed high-resolution denaturation profiles of reassociated repetitive DNA sequences by using a combination of higher derivative analysis and curve-fitting techniques. Procedures originally used for resolution of components in complex absorption spectra were found to be applicable to high-resolution analysis of melting profiles of reassociated repetitive DNA sequences from pea DNA. Under conditions that eliminate the base composition effect on thermal stability (2.4 M tetraethylammonium chloride), such an anlysis can distinquish "thermal classes" of repetitive DNA duplexes exhibiting different amounts of base pair mismatch. Only a single thermal class is observed in reassociated Escherichia coli DNA whereas at least five classes can be reproducibly distinguished in pea and mung bean DNAs.
Variable and constant regions are separated in the 10-kbase transcription unit coding for immunoglobulin kappa light chains.
Authors: Gilmore-Herbert M , Hercules K , Komaromy M , Wall R
Published: May 2006

UV transcription mapping with recombinant DNA probes containing immunoglobulin kappa light chain mRNA sequences has been used to determine the size of the transcription unit coding for kappa light chain m RNA and to establish the arrangement of variable and constant regions in this transcription unit. In relation to ribosomal RNA standards, the transcription of kappa light chain constant region sequences into nuclear RNA exhibits a UV target size of 9.6 kbases (kb). The kappa light chain variable region exhibits a UV target size of 7.6 kb indicating that it is separated by approximately 2.0 kb from the constant region in the kappa light chain transcription unit. The size of the primary transcript (i.e., the direct, unprocessed RNA product of transcription) predicted from the constant region target size concurs with our previous pulse-labeling results which showed that the largest presumptive nuclear RNA precursor to kappa light chain mRNA is approximately 10 kb. In addition, the UV target size of cytoplasmic kappa mRNA is indistinguishable from the target size of constant region sequences in nuclear RNA. These results suggest that the kappa light chain transcription unit is copied directly into a 10-kb nuclear RNA precursor in which the kappa variable and constant regions are separated by approximately 2 kb. Accordingly, it is proposed that the joining of immunoglobulin kappa light chain variable and constant regions occurs in the post-transcriptional processing of this large nuclear RNA precursor into kappa light chain mRNA.
Loss of proliferative calcium dependence: simple in vitro indicator of tumorigenicity.
Authors: Swierenga S H , Whitfield J F , Karasaki S
Published: May 2006

The proliferative activities of three lines of "normal" epithelioid rat liver cells and six tumorigenic liver cell lines in the presence of a wide range of calcium concentrations were measured by a simple colony forming assay. The proliferative activities of the normal cells and, to a lesser extent, of the cells of a marginally tumorigenic line were directly proportional to the extracellular calcium concentration. The proliferative activities of the cells of the strongly tumorigenic lines, on the other hand, were either uninfluenced by or inversely proportional to the extracellular calcium concentration. Thus, the proliferative response to the extracellular calcium concentration is a sensitive indicator of the carcinogenic potential of liver cells.
Infection with paramyxoviruses stimulates synthesis of cellular polypeptides that are also stimulated in cells transformed by Rous sarcoma virus or deprived of glucose
Authors: Peluso Richard W. , Lamb Robert A. , Choppin Purnell W.
Published: May 2006

Infection of several types of cultured cells with the paramyxoviruses simian virus 5 and Sendai virus stimulates synthesis of four polypeptides (I-IV) with molecular weights of approximately 99,000, 97,000, 86,000, and 78,000, respectively. That these are host polypeptides encoded in cellular mRNAs has been shown by the inhibition of their synthesis by actinomycin D and by the similarity of the peptide maps of them and of polypeptides with the same electrophoretic mobility from uninfected cells. Peptide mapping as well as identical migration in polyacrylamide gels has also indicated that polypeptides I, II, and IV are the same as plasma membrane polypeptides whose synthesis is enhanced in cells transformed by Rous sarcoma virus and in normal cells by glucose deprivation or treatment with 2-deoxyglucose. Polypeptides I and II appear to be the same polypeptides, with the observed differences in migration reflecting the glycosylation of polypeptide I, a relationship previously shown to exist between polypeptides in glucose-deprived and glucose-fed cells. Infection with paramyxoviruses does not significantly increase the transport of glucose by cells, and the maintenance of a high concentration of glucose in the medium does not prevent the enhanced synthesis of these polypeptides. This is in contrast to the situation in transformed cells in which stimulation of synthesis of these polypeptides is secondary to depletion of glucose in the medium due to increased glucose uptake by the cells. Thus, although paramyxovirus infection and transformation by Rous sarcoma virus result in stimulation of the synthesis of the same membrane polypeptides, the mechanism of stimulation differs.
Pituitary somatotrophs contain [Met]enkephalin-like immunoreactivity.
Authors: Weber E , Voigt K H , Martin R
Published: May 2006

Serial sections from epoxy resin-embedded rat anterior pituitaries were sequentially immunostained for endorphin, [Met]enkephalin, and growth hormone, respectively. We found that [Met]enkephalin immunoreactivity was confined to the growth hormone producing cells. Corticotropin/endorphin cells in the anterior pituitary from both normal and adrenalectomized rats did not contain any [Met]enkephalin immunoreactivity. When anterior pituitary cells were maintained in monolayer culture for 10 days, [Met]enkephalin immunoreactivity was still located in the growth hormone-producing cells although the staining was weaker than in the somatotrophs in pituitary tissue fixed immediately after death of the animals. This suggested that somatotrophs synthesize [Met]enkephalin. However, this cannot be proved conclusively until biosynthesis experiments have been performed. The following conclusions were drawn from these findings. (i) Anterior pituitary [Met]enkephalin is not an extraction artifact derived from beta-endorphin with which it shares the NH2-terminal pentapeptide sequence. (ii) In the anterior pituitary, beta-endorphin is not the precursor to [Met]enkephalin. [Met]Enkephalin in somatotrophs may be of brain origin and in the somatotrophs may be bound to intracellllar receptors as has been shown for luteotropin releasing hormone in gonadotropic cells.
Cholesterol monohydrate growth in model bile solutions.
Authors: Toor E W , Evans D F , Cussler E L
Published: May 2006

The growth of cholesterol monohydrate from solutions of bile salt, lecithin, and small electrolytes has been studied by microscopy and with the Coulter Counter. The crystal forms found by microscopy are the same as those seen in human gallstones and in squirrel monkey cholesterol microliths. The cholesterol growth rates determined with the Coulter Counter vary slowly with cholesterol concentration at low degree of supersaturation but become exponential at higher cholesterol concentrations. Growth is accelerated by the presence of calcium and magnesium but inhibited by potassium. These results can be combined with previous measurements of cholesterol dissolution rates to give a more accurate picture of the dynamics of gallstone formation.
In vitro segregation of different cell lines with neuronal and glial properties from a stem cell line of rat neurotumor RT4.
Authors: Tomozawa Y , Sueoka N
Published: May 2006

A clonal stem cell line, RT4-AC, of the rat peripheral neurotumor RT4 differentiates in culture into morphologically distinct cell types RT4-B, RT4-D, and RT4-E (cell type conversion). The multipotential stem cell type RT4-AC and cell type RT4-D produce a glial marker, S100 protein, but RT4-B and RT4-E do not. The stem cells also show a small but significant response to veratridine on voltage-dependent Na+ influx. Cell types RT4-B and RT4-E show a clear response of voltage-dependent Na+ influx to veratridine, typical of neuronal cells, whereas cell type RT4-D is completely negative. These results indicate that (i) the stem cell type RT4-AC shows both neuronal and glial properties, (ii) cell types RT4-B and RT4-E have a neuronal property, and (iii) cell type RT4-D has a glial property. Therefore, cell type conversion of stem cell RT4-AC to RT4-B and RT4-E cells seems to result in differentiation towards neuronal cell types, and cell type conversion of RT4-AC to RT4-D results in differentiation towards a glial type in culture.
Generalizing Fisher's “reproductive value”: “Incipient” and “penultimate” reproductive-value functions when environment limits growth; linear approximants for nonlinear Mendelian mating models
Authors: Samuelson Paul A.
Published: May 2006

In the usual Darwinian case in which struggle for existence leads to density limitations on the environment's carrying capacity, R. A. Fisher's reproductive-value concept reduces to zero for every initial age group. To salvage some meaning for Fisher's notion, two variant reproductive-value concepts are defined here: an “
incipient
reproductive-value function,” applicable to a system's early dilute stage when density effects are still ignorable; and a “second-order
penultimate
reproductive-value function,” linking to a system's initial conditions near equilibrium its much later small deviations from carrying-capacity equilibrium. Also, slowly changing age-structured mortality and fertility parameters of Lotka and Mendelian mating systems are shown to suggest linear reproductive-value surrogates that provide approximations for truly nonlinear diploid and haploid models.
Blockade of neuromuscular transmission by enzymatically active and inactive beta-bungarotoxin.
Authors: Livengood D R , Manalis R S , Donlon M A , Masukawa L M , Tobias G S , Shain W
Published: May 2006

beta-Bungarotoxins have been shown to be presynaptic blockers of neuromuscular transmission. This paper reports experiments using the most positively charged beta-bungarotoxin that elutes from a CM-Sephadex C-25 column. The toxin is shown to be a single polypeptide with a molecular weight of approximately 11,000 and has phospholipase A2 activity. The application of the enzymatically active toxin to the frog sciatic nerve-sartorius muscle preparation results in an initial decrease in the average endplate potential amplitude followed by a temporary rebound in endplate potential amplitude, and finally a complete inhibition of endplate potentials. Similarly, minature endplate potential frequency is initially reduced upon toxin application but then increases dramatically. After the phospholipase A2 of the toxin is inactivated, treatment with the toxin results in only the initial decrease in transmitter release. There results suggest that this beta-bungarotoxin acts in two functionally separate steps: (i) by binding to a specific presynaptic site possibly associated with calcium entry, and (ii) by perturbing the presynaptic membrane by its enzyme action, which results in an increase and then a failure in transmitter release.
Variation of isomer distribution in electrophilic nitration of toluene, anisole, and
o
-xylene: Independence of high regioselectivity from reactivity of reagent
Authors: Olah George A. , Lin Henry C. , Olah Judith A. , Narang Subhash C.
Published: May 2006

The nitration of toluene and anisole was studied with nitrating systems of varying reactivity. High regioselectivity of
ortho-para
over
meta
substitution was maintained in all nitrations, regardless of the reactivity of the nitrating system. At the same time, the amount of
meta
substitution stayed low (3% or less), even when the fast reactions may have reached the encounter-controlled limit. Because the nitration of
o
-xylene, in which both ring positions are activated by the effect of a methyl group, also does not show any diminishing of regioselectivity, the possibility of a dual mechanistic pathway, in which the activated position would react by a fast, encounter-controlled path, whereas the nonactivated
meta
position by a slower σ-type path, can be ruled out. The data unambiguously prove that the high regioselectivity of electrophilic aromatic nitration is independent of the reactivity of the reagent, because no significant increase of
meta
substitution of toluene or anisole was observed, regardless of the activity of the nitrating system. No selectivity-reactivity relationship is thus evident and the
ortho-para
directing effect of primary substituents over
meta
substitution is always maintained. The variation in the amount of the
meta
isomer, up to the observed limit of about 3% in the case of toluene and <2% for anisole, is probably significant but, at the present time, cannot be quantitatively evaluated with the ±0.5% overall reproducible accuracy of the nitrations. Steric factors, such as increasing bulkiness of the nitrating agent, also can affect the
ortho-para
isomer ratios but are not considered to be the only reason for the observed variations, which reflect the specific nitrating systems, affecting the nature and position of the transition state of highest energy on the reaction pathway.