| quantitative analysis of intercellular adhesive specificity in freshly explanted and cultured cells. | a new method is presented for the quantitative analysis of intercellular adhesive specificity. in this assay, two cell types are mixed, one unlabeled and the other labeled with the fluorescent dye, fluorescamine [4-phenylspiro(feran-2[3h],1'-phthalan)-3,3'-dione]. the resulting aggregates are analyzed by fluorescence microscopy to determine the number of labeled and unlabeled cells per aggregate. random (nonspecific) aggregation was characterized by a binomial distribution, and adhesive specific ... | 1981 | 6166626 |
| karyotyping chromosomes by electron microscopy. condensation-inhibition of g bands in human and chinese hamster chromosomes by a brdu-hoechst 33258 treatment. | a brdu-hoechst 33258 treatment of living cells, which selectively induced condensation-inhibition of g-band chromatin in human and chinese hamster chromosomes, is presented. as a consequence mitotic chromosomes showed high resolution r-banding patterns when examined by light and electron microscopy. besides each whole chromosome identification, this procedure also permitted the electron microscopic study of specific structures, such as satellites, secondary constrictions, telomeres, centromeres, ... | 1981 | 6169427 |
| eliminating mycoplasmas from contaminated cell cultures. | mycoplasmas are bothersome contaminants in cell cultures. cells derived from various sources are subject to contamination and although many procedures have been suggested to eliminate the contaminating mycoplasmas, there is no simple, rapid and effective method for eliminating them. we have devised a method for the selective killing of mycoplasmas based on the differences between the nucleic acid metabolism of mycoplasmas and that of tissue culture cells. whereas the nutritional requirements of ... | 1981 | 6169683 |
| comparative genetics of hamster amylases. | syrian (mesocricetus auratus) and chinese (cricetulus griseus) hamsters were phenotyped by electrophoresis for salivary and pancreatic amylases. syrian hamsters possess two salivary amylase electromorphs, the more anodal (fast) being invariant in 250 outbred and 17 representatives of 5 highly inbred lines. the slow electromorph had activity equal to that of the fast amylase (heavy), or had distinctly less activity (light), or was absent (null). the slow electromorph is inherited as an autosomal ... | 1981 | 6170291 |
| purification and characterization of hypoxanthine-guanine phosphoribosyltransferase from saccharomyces cerevisiae. | hypoxanthine-guanine phosphoribosyltransferase (hprt) was purified 12 000-fold to homogeneity from yeast by a three-step procedure including acid precipitation, anion-exchange chromatography, and guanosine 5' -monophosphate affinity chromatography. the enzyme is a dimer consisting of two, probably identical, subunits of mr 29 500. the enzyme recognized hypoxanthine and guanine, but not adenine or xanthine, as substrates. an antiserum against both native and denatured enzyme has been raised and s ... | 1981 | 6170313 |
| effects of the l isomer (+)-1,2-bis(3,5-dioxopiperazine-1-yl)propane on cell survival and cell cycle progression of cultured mammalian cells. | the effects of the l isomer (+)-1,2-bis(3,5-dioxopiperazine-1-yl)propane (icrf 159; nsc 169780) on cell viability, growth, and progression through the cell cycle were investigated in suspension cultures of murine leukemia (friend leukemia and l1210) cells and normal human lymphocytes stimulated with phytohemagglutinin and in adherent cultures derived from human neuroblastoma and chinese hamster ovary (cho) cells. cho cell colony formation was inhibited by 50% following either an 8.5-hr exposure ... | 1981 | 6171341 |
| isolation of special antibodies which react only with homologous enterotoxins from vibrio cholerae and enterotoxigenic escherichia coli. | cholera enterotoxin (ct) and heat-labile enterotoxin (lt) produced by enterotoxigenic escherichia coli share a common antigenic determinant. in addition, ct and lt each have a unique antigenic determinant. antisera were prepared by immunoaffinity chromatography against these unique antigenic determinants, that is, antiserum that reacted with ct but not with lt and antiserum that reacted with lt but not with ct. antiserum against the common antigenic determinant to ct and lt was also prepared by ... | 1981 | 6171516 |
| an autoradiographic method of detecting a. laidlawii and m. hyorhinis in cell cultures. | the autoradiographic investigation of l cells and chinese hamster cells for the presence of mycoplasmas (a. laidlawii and m. hyorhinis) using uridine/uracil (udr/u) testing is a rapid and reliable method suitable for the serial checking of even a small number of cells. it depends on a reduced incorporation of [3h]uridine and an increased uptake of [3h]uracil into the rna of mycoplasma-infected cells, shown in autoradiograms by the density of the grains and their distribution. results obtained by ... | 1981 | 6173306 |
| a comparison of induced sister chromatid exchange levels in chinese hamster ovary cells and cultured human lymphocytes. | human lymphocytes and chinese hamster ovary cells were exposed to dna damaging agents for two cell cycles, and the induced sister chromatid exchange (sce) rate was compared. cho cells showed a significant increase in sce following treatment with bleomycin and vincristine whereas human lymphocytes did not. both cho cells and lymphocytes showed an increase in sce with 5-bromodeoxyuridine (brdurd) and tritiated uridine (3h-urd) but the increase was greater in cho cells. sce levels were similar afte ... | 1982 | 6175512 |
| assignment of the gene for beta 2-microglobulin (b2m) to mouse chromosome 2. | we have assigned the gene (b2m) coding for murine beta 2-microglobulin (b2m) to mouse chromosome 2 by using a novel panel of chinese hamster-mouse somatic cell hybrid clones. because of 35 independent primary hybrids used in this study were derived from two types of feral mice, each with a different combination of robertsonian translocation chromosomes, as well as from mice with a normal complement of acrocentric chromosomes, analysis of 16 selected mouse enzyme markers provided data on the segr ... | 1982 | 6177004 |
| enhanced cell killing through the use of cell kinetics-directed treatment schedules for two-drug combinations in vitro. | kinetics-directed drug treatment schedules were tested in chinese hamster ovary cells. ten hr after treatment with 1,2:5,6-dianhydrogalactitol (dag) (at a dose lethal to less than 5% of the cells), a 150% enrichment of cells into the s phase of the cell cycle was observed. this blockade in s phase was reversible and was followed at 18 hr after an exposure to dag by a 200% increase in the fraction of cells in the g2-m phases of the cell cycle. bleomycin, known to be most effective against g2 + m ... | 1982 | 6177399 |
| flow cytometric characterization of a chinese hamster x man hybrid cell line retaining the human y chromosome. | a chinese hamster x man hybrid cell line (ch-y-vii) was established which retains a free human y chromosome. exponentially growing ch-y-vii cells were arrested with colcemid; metaphase chromosomes were isolated and stained with 33258 hoechst (ho) plus chromomycin a3 (ca3), or with ethidium bromide (eb). the ho/ca3-stained chromosomes were measured in a dual beam flow cytometer, and bivariate ho/ca3 flow karyotypes and univariate ho and ca3 flow karyotypes were established. eb-stained chromosomes ... | 1982 | 6179849 |
| co-expression and amplification of dihydrofolate reductase cdna and the escherichia coli xgprt gene in chinese hamster ovary cells. | we have transformed chinese hamster ovary cells with a plasmid containing mouse dihydrofolate reductase (dhfr) cdna and the escherichia coli xanthine-guanine phosphoribosyl transferase (xgprt) gene under the control of the mouse mammary tumor virus and sv40 early promoters, respectively. selection for the expression of xgprt using the dominant selection scheme described by mulligan and berg yields clones that simultaneously express dhfr. growth of these cells in progressively increasing concentr ... | 1981 | 6180118 |
| hyperthermic potentiation of chromosome aberrations by anticancer antibiotics. | in view of the success of hyperthermia as a modality in cancer treatment, we have studied its effect on chromosomes in combination with anticancer antibiotics. three classes of chemicals, one with a non-delayed type of effect (adriamycin), one with a delayed type of effect (mitomycin c), and one with a truely radio-mimetic effect (bleomycin) were selected for study on human lymphocytes and chinese hamster k-1 cells. propane sultone was also included because its effect on plants is suppressed by ... | 1982 | 6180864 |
| assignment of snrna gene sequences to the large chromosomes of rat kangaroo and chinese hamster isolated by flow cytometric sorting. | chromosomes from a rat kangaroo (potorous tridactylus) cell line (ptk2) and from a chinese hamster (cricetulus griseus) cell line (chv79) were isolated by means of fluorescence activated flow cytometric sorting. dapi (4'-6-diamino-2-phenylindole) was used as the dna specific fluorescent dye. the karyotype of the ptk2 cells which exhibits 13 chromosomes was separated into 6, and the 22 chromosomes of the chv79 cells were resolved into 11 fractions. dna extracted from these chromosomal fractions w ... | 1982 | 6181947 |
| extracts from the brains of hibernating and alert ground squirrels: effects on cells in culture. | aqueous extracts were prepared from pulverized, acetone-dehydrated brains of hibernating and alert ground squirrels. addition of these extracts to chinese hamster ovary cells in suspension culture resulted in a decrease in the amount of [3h]thymidine incorporated into acid-precipitable material without affecting the transport or phosphorylation of the nucleoside. the inhibition was time- and dose-dependent and full recovery occurred about 2 hr after exposure of the cells to the active extract. t ... | 1982 | 6183661 |
| the analysis and interpretation of dna distributions measured by flow cytometry. | a principal use of flow cytometers is for the measurement of fluorescence distributions of cells stained with dna specific dyes. a large amount of effort has been and is being expended currently in the analysis of these distributions for the fractions of cells in the g1, s, and g2 + m phases. several methods of analysis have been proposed and are being used; new methods continue to be introduced. many, if not most, of these methods differ only in the mathematical function used to represent the p ... | 1982 | 6184208 |
| work in progress: the effect of heat on bleomycin cytotoxicity in vitro and on the accumulation of 57co-bleomycin in heat-treated rat tumors. | the cytotoxic effects of the sequence and timing in combined hyperthermia and bleomycin treatment were tested in vitro using v79 chinese hamster cells. the order of treatment was important; heat treatment followed by the administration of bleomycin yielded greater cytotoxicity than when the opposite order was used. to determine whether heat-treated tumors have an altered uptake of bleomycin, rat rhabdomyosarcoma (ba 1112) tumors were heated locally with rf current (43 degrees c, 90 min.), inject ... | 1983 | 6184743 |
| rna and dna content of isolated cell nuclei measured by multiparameter flow cytometry. | nuclei were isolated from various cell types including chinese hamster ovary (cho) and l1210 leukemia cell lines, primary cultures of fibroblasts, nonstimulated and stimulated human lymphocytes and mouse liver cells, by using different isolation techniques. the isolated nuclei were subsequently stained with acridine orange (ao) and their fluorescence was measured by flow cytometry. various procedures designed to stain dna versus rna differentially with ao were tested, and the staining of isolate ... | 1983 | 6185286 |
| toxicity of a male contraceptive, gossypol, in mammalian cell cultures. | gossypol, a substance extracted from cotton plants, is a potential male contraceptive. although human users reported only mild or no side effects, our study found gossypol to be cytotoxic to cultured mammalian cells. a dose dependent decrease in the number of viable cells and mitotic index was demonstrated with both chinese hamster ovary (cho) cells and human lymphocytes after the cultures received treatment of gossypol for various durations. cellular dna, rna, and protein synthetic activities w ... | 1983 | 6185412 |
| a family of repeated dna sequences, one of which resides in the second intervening sequence of the mouse dihydrofolate reductase gene. | one member of a repeated sequence family has been found in the second intron of the mouse dihydrofolate reductase gene. the family consists of approximately 20 members/haploid genome, two of which have been sequenced and found to contain a 480-base pair region of homology with a significant amount of sequence divergence. rat, chinese hamster, syrian hamster, and human dnas contain homologous repetitious elements, and the four rodent species have a member of this family associated with the dihydr ... | 1983 | 6185497 |
| constitutive, long-term production of human interferons by hamster cells containing multiple copies of a cloned interferon gene. | hybrid plasmids containing the mouse dihydrofolate reductase (dhfr) and a human interferon (either ifn-alpha 5 or ifn-gamma) coding sequence under the control of viral promoters were transfected into dhfr- chinese hamster ovary (cho) cells. dhfr+ colonies produced ifn at 10-1000 units x ml-1 x day-1. clones selected in methotrexate had a 20-50-fold increase in the ifn-alpha 5 and dhfr dna and mrna content and secreted ifn at 20,000-100,000 units x ml-1 x day-1. sds-polyacrylamide gel electrophor ... | 1983 | 6188107 |
| purification and some properties of a non-o1 vibrio cholerae enterotoxin that is identical to cholera enterotoxin. | cholera-like enterotoxin was isolated and purified from the culture supernatant of a non-o1 strain of vibrio cholerae, e8498, isolated from the environment. enterotoxin was purified by aluminum hydroxide absorption and elution and successive gel filtrations on sephadex g-100, bio-gel a-5m, and sephadex g-75. purified enterotoxin gave a single stained band on polyacrylamide gel disc electrophoresis, and the mobility was the same as that of cholera enterotoxin. the specific biological activity of ... | 1983 | 6188694 |
| chromosome mapping of human cell surface molecules: monoclonal anti-human lymphocyte antibodies 4f2, a3d8, and a1g3 define antigens controlled by different regions of chromosome 11. | monoclonal antibodies 4f2, a3d8, and a1g3, directed against cell surface antigens present on subsets of human cells, were used to identify the human chromosome regions that code for the antigenic determinants. human fibroblasts expressed all three antigens, and no cross-reactivity with chinese hamster or mouse cells was found. fourteen rodent x human somatic cell hybrids, derived from six different human donors and from two different chinese hamster and one mouse cell line, were studied simultan ... | 1983 | 6190235 |
| hyperthermia and bleomycin schedules on v79 chinese hamster cell cytotoxicity in vitro. | the effect of sequence and timing of hyperthermia (43 degrees) and bleomycin on chinese hamster cells (v79) has been investigated. hyperthermia preceding bleomycin treatment produced a greater cytotoxic effect than bleomycin treatment preceding hyperthermia. furthermore, it appears that the combination of hyperthermia and bleomycin becomes less effective if the application of bleomycin is delayed. the enhancement of cytotoxicity with hyperthermia first may be related to the effect of heat on the ... | 1983 | 6192905 |
| potentiation of mitomycin c, 6-mercaptopurine, bleomycin, cis-diamminedichloroplatinum and 5-fluorouracil by mycotrienins and mycotrienols. | mycotrienins i and ii and mycotrienols i and ii are ansamycin antibiotics containing a triene structure, isolated from streptomyces rishiriensis. an amphotericin b-resistant clone (ambr-1) derived from cultured chinese hamster v79 cells was cross-resistant to mycotrienins i and ii, but not to mycotrienol i or ii. these four ansamycin antibiotics were found to potentiate significantly the action of some anti-cancer agents including 5-fluorouracil, cis-diamminedichloroplatinum, bleomycin, mitomyci ... | 1983 | 6196249 |
| silver staining of the nucleolus-like bodies in postimplantation rat embryos and the nuage in chinese hamster oocytes. | | 1983 | 6196426 |
| evaluation of the genotoxic and embryotoxic potential of chlorpyrifos and its metabolites in vivo and in vitro. | the genotoxicity and embryotoxicity of chlorpyrifos (cpf) and two metabolites were evaluated using the chick embryo, chinese hamster ovary cells, and by examining blastocysts from superovulated cows crossed to chlorpyrifos-treated bulls. chlorpyrifos and metabolites were dissolved in acetone and administered to 3-day embryos by the air cell method. the ld50 was 1,500 micrograms/embryo when mortality was checked through and including 17 days of development. the metabolites were more embryotoxic t ... | 1984 | 6198172 |
| import of rat liver mitochondrial malate dehydrogenase. synthesis, transport, and processing in vitro of its precursor. | rat liver total rna was translated in a reticulocyte lysate, and the precursor of rat liver mitochondrial malate dehydrogenase was identified by a monospecific antibody against the denatured mature enzyme. the precursor is about mr = 1500 to 2000 larger than the monomeric form of the mature protein. the major spots of the two-dimensional peptide map of the two proteins were identical. the precursor was synthesized on free polysomes, but not membrane-bound polysomes. upon fractionation by molecul ... | 1984 | 6199356 |
| nitrilotriacetic acid does not induce sister-chromatid exchanges in hamster or human cells. | the effect of nitrilotriacetic acid on sister-chromatid exchanges (sces) in human peripheral blood lymphocytes and chinese hamster ovary cells was studied. the chemical did not increase the frequency of sces in either cell type. the negative response of these cells supports other evidence that nitrilotriacetic acid is not genotoxic and that its carcinogenicity to the urinary tract may involve an epigenetic mechanism. | 1984 | 6200412 |
| preparation of chromosome suspensions for flow cytometry. | certain variables in the preparation of chromosome suspensions for flow cytometric analysis have been investigated. the optimal conditions have been determined. the results of this series of experiments have been incorporated to yield a preparation protocol that gives chromosome profiles with a low amount of small particle debris and few chromosome clumps. the method reduces variability that results from sample preparation. chromosomes are optimally isolated in a hypotonic solution buffered to p ... | 1984 | 6201326 |
| tyrosyl kinases acquired from anchorage-independent cells by a membrane-enveloped virus. | tyrosyl kinase activity in vesicular stomatitis virus (vsv) acquired from host cells that differ in morphology was investigated. vsv grown in baby hamster kidney (bhk) cells with rounded morphology and a high efficiency of colony formation in soft agar (rous sarcoma virus [rsv]-transformed and suspension bhk cells) was compared with vsv grown in bhk cells with a flattened morphology and lower efficiency of colony formation in soft agar (rsv-infected revertant and control bhk cells). tyrosyl kina ... | 1984 | 6206078 |
| three human cell surface antigen systems determined by genes on chromosome 12. | the mouse monoclonal antibodies aba123, aba127, abk152, abm68, and abv1 were derived after immunization with cultured human tumor cells or melanocytes. antibodies aba123, aba127, and abk152 recognize human cell surface antigens expressed on most cultured human cells and show an identical pattern when tested on a panel of 47 human cell lines. they recognize at least two different epitopes on the same glycoprotein complex, designated a123/a127, which consists of 30,000-and 40,000-mol-wt glycopepti ... | 1984 | 6206575 |
| a comparison of genotoxicity of automotive exhaust particles from laboratory and environmental sources. | this research (1) ranked the genotoxicity of methylene chloride extracts of laboratory and environmentally collected particles and (2) evaluated the role of collection location and sample composition on genotoxic potency. samples of exhaust from a spark-ignition automobile, light-duty diesel automobile, and a heavy-duty diesel engine operated in a laboratory on a dynamometer were studied, as well as samples taken in a highway tunnel and outside the same tunnel. the tunnel samples were collected ... | 1984 | 6207015 |
| molecular cloning of cdna for rat and human carbamyl phosphate synthetase i. | recombinant plasmids with inserts complementary to the mrna for carbamyl phosphate synthetase i were identified from a rat liver cdna library by hybrid-selected mrna translation. four clones, the largest being 3100 base pairs, were identified for the rat liver enzyme. using the rat liver cdna as a probe, two homologous recombinant plasmids of approximately 1200 base pairs in length were isolated from a human liver cdna library. northern blot analysis of rat liver mrna and baboon liver mrna revea ... | 1984 | 6208196 |
| chromosomal assignments of three random rflp loci defined by base-pair changes in mspi sites. | three cloned single copy sequences isolated from a random partial plasmid library of human ecori-hindiii restriction fragments detect mspi site polymorphisms in human dna. since at least two of them have allele frequencies that make them suitable for family linkage studies, we have determined their chromosomal localizations. dna samples extracted from a panel of 31 chinese hamster x human somatic cell hybrids, that were derived from six different human donors, were analyzed for the presence of h ... | 1983 | 6209528 |
| [studies on the mechanism of drug resistance in tumor cells and a new antitumor antibiotic]. | characteristics of drug-resistant cell sublines l5178y: we isolated aclarubicin (acr)-, adriamycin (adm)-, bleomycin (blm-, and macromomycin (mcr)-resistant (r) cell sublines. the blmr cell line did not show cross-resistance to other drugs. the acrr and admr cell lines displayed cross-resistance to other anthracyclines. the drug-resistance of these cell lines was due to changes in membrane transport. all four resistant cell lines showed higher activity of membrane alkaline phosphodiesterase (apd ... | 1984 | 6210060 |
| assignment of the human gene for muscle-type phosphofructokinase (pfkm) to chromosome 1 (region cen leads to q32) using somatic cell hybrids and monoclonal anti-m antibody. | human phosphofructokinase (pfk; ec 2.7.1.11) is under the control of three structural loci which encode muscle-type (m), live-type (l), and platelet-type (p) subunits; human diploid fibroblasts and leukocytes express all three loci. in order to assign human pfkm locus to a specific chromosome we have analyzed human x chinese hamster somatic cell hybrids for the expression of human m subunits, using an anti-human m subunit-specific mouse monoclonal antibody. in 18 of 19 hybrids studied, the expre ... | 1982 | 6213050 |
| species specific differences in the toxicity of mithramycin, chromomycin a3, and olivomycin towards cultured mammalian cells. | three structurally related anticancer drugs, mithramycin, chromomycin a3, and olivomycin, showed large unexpected differences (up to more than 1000 fold) in their toxicity towards cultured cells from various species (human, chinese hamster, syrian hamster, and mouse). among the cell types examined, human cells (both a diploid fibroblast cell strain and hela cells) were maximally sensitive to all these drugs, followed by the syrian hamster kidney cells (bhk 21). the mouse (lmtk- cells) and chines ... | 1982 | 6215417 |
| rapid, one step staining procedures for analysis of cellular dna and protein by single and dual laser flow cytometry. | detailed, simplified techniques are described for simultaneous staining and analysis of dna and protein in a number of mammalian cell types. cell staining involves the addition of appropriate dye mixtures to unfixed or ethanol-fixed cells and subsequent analysis of cell populations in the staining reagents generally within 10 to 20 minutes. the approach is novel in that no centrifugation steps are involved during the staining procedure, thus, eliminating cell clumping and cell loss and making th ... | 1982 | 6216083 |
| somatic cell genetic approaches to down's syndrome. | somatic cell genetic analysis of mutants of chinese hamster ovary cells with deficient purine synthesis and of hybrids between these mutants and human cells is described. data are presented substantiating that two genes for enzymes of purine synthesis, adec and adeg, can be coordinately regulated in mammalian cells. analysis of a human-hamster hybrid cell, ade c/21, which contains a normal complement of hamster chromosomes and human chromosome 21 as its only human genetic component recognizable ... | 1982 | 6217778 |
| composition and synthesis during g1 and s phase of a high mobility group-e/g component from chinese hamster ovary cells. | a perchloric acid soluble protein from the sedimented chromatin of blended chinese hamster ovary (line cho) cells has been isolated by guanidine hydrochloride gradient chromatography on bio . rex-70 ion exchange resin. the amino acid composition of the protein (designated as cho hmg-e/g) is similar to that of mouse hmg-e, but it differs from that of bovine hmg-14 and hmg-17 or any possible mixture of the two. cho hmg-e/g incorporates [32p]phosphate like hmg-14 and hmg-17 class proteins from othe ... | 1983 | 6218827 |
| characterization of a chinese hamster ovary cell line resistant to uncouplers. | the chemiosmotic theory of oxidative phosphorylation and the action of uncouplers was examined by characterizing a clone, uh5, of chinese hamster ovary (cho tk-) cells resistant to 5-chloro-3-tert-butyl-2'-chloro-4'-nitrosalicylanilide (s-13), a potent uncoupler of oxidative phosphorylation. about 9-times and 4-times more s-13 was required to effect growth and respiration respectively of uh5 cells compared to the parental cho tk- cells. uh5 cells were cross-resistant to the uncouplers sf-6847 (3 ... | 1983 | 6223814 |
| comparative genotoxicity of adriamycin and menogarol, two anthracycline antitumor agents. | adriamycin and menogarol are anthracyclines which cause more than 100% increase in life span of mice bearing p388 leukemia and b16 melanoma. unlike adriamycin, menogarol does not bind strongly to dna, and it minimally inhibits dna and rna synthesis at lethal doses. adriamycin is a clinically active drug, and menogarol is undergoing preclinical toxicology at national cancer institute. in view of the reported mutagenicity of adriamycin, we have compared the genotoxicity of the two drugs. our resul ... | 1983 | 6225515 |
| isolation and preliminary characterization of the chinese hamster thymidine kinase gene. | the chinese hamster thymidine kinase (tk) gene has been isolated from a recombinant phage library constructed with genomic dna from mouse ltk- cells transformed to tk+ by transfection with chinese hamster genomic dna. the phage library was screened by the benton-davis plaque hybridization technique, using as probes, subclones of recombinant phage that were isolated from mouse ltk+ transformants by the trna suppressor rescue method. the chinese hamster tk gene is contained within 13.2 kilobases o ... | 1983 | 6227808 |
| infidelity of dna synthesis as a cause of mutagenesis. | the concept underlying these studies is that a major determinant of mutagenesis involves perturbations in the fidelity of dna replication. i.e., the accuracy by which dna polymerases copy dna templates. to investigate this relationship, we have designed in vitro assays to measure the accuracy of dna replication and used these systems to screen for and to quantitate factors that promote errors in dna synthesis. using dna polymerase from bacteria, the frequency of mistakes with phi x174 dna as a t ... | 1983 | 6228545 |
| deficient humoral antibody response of the spontaneously diabetic chinese hamster. | the antibody responses of spontaneously diabetic chinese hamsters to sheep erythrocytes was investigated. after primary challenge, total antibody production of the diabetics was only 50% or less than that of nondiabetic controls, and little or no switchover to igg production occurred. after second challenge, total antibody of diabetics was still reduced compared with controls. some switchover to igg did occur after second challenge but was only 40% that of controls. poor antibody response was no ... | 1984 | 6229797 |
| human dihydrofolate reductase gene organization. extensive conservation of the g + c-rich 5' non-coding sequence and strong intron size divergence from homologous mammalian genes. | the complete human dihydrofolate reductase (dhfr) gene has been cloned from four recombinant lambda libraries constructed with the dna from a methotrexate-resistant human cell line with amplified dhfr genes. the detailed organization of the gene has been determined by restriction mapping of the cloned fragments and dna sequencing of all the protein coding regions and adjacent intron segments, and shown to correspond to that of the native human dhfr gene. the gene spans a length of approximately ... | 1984 | 6235374 |
| a dominant mutation to ricin resistance in chinese hamster ovary cells induces udp-glcnac:glycopeptide beta-4-n-acetylglucosaminyltransferase iii activity. | a biochemical basis for the lec10 mutant phenotype of chinese hamster ovary cells has been identified. independent lec10 mutants, originally selected for resistance to the toxicity of ricin, have been shown to exhibit reduced binding of 125i-ricin at the cell surface. although this is indicative of structural changes in cell-surface carbohydrates, labeling of plasma membranes with galactose oxidase/[3h]borohydride revealed no significant differences between mutant and parental cells. alterations ... | 1984 | 6238035 |
| transfer of chinese hamster chromosome 1 to mouse cells and regional assignment of 7 genes: a combination of gene transfer and microcell fusion. | we have used a combination of chromosome-mediated gene transfer and microcell fusion techniques to transfer chinese hamster chromosome 1 to mouse cells. microcell hybrids containing a single hamster chromosome were analyzed to map genes on this chromosome. we have confirmed the assignment of seven markers (gsr, np, est-d, adk, pep-s, pgm2, and pep-b) to hamster chromosome 1. segregation among the linked markers was induced by x irradiation followed by selection for the retention or loss of human ... | 1984 | 6239397 |
| cloning the complete human adenine phosphoribosyl transferase gene. | we have isolated a clone from a human genomic lambda library which cross-hybridises with the cloned hamster adenine phosphoribosyl transferase gene (aprt). after restriction mapping and further hybridisation to the hamster gene, a series of putative human aprt-containing fragments has been isolated and tested for ability to transform adenine phosphoribosyl transferase-deficient (aprt-) strains of chinese hamster ovary (cho) cells to aprt proficiency. transforming activity was detected in a 48-kb ... | 1984 | 6241170 |
| molecular mechanisms involved in the production of chromosomal aberrations. ii. utilization of neurospora endonuclease for the study of aberration production by x-rays in g1 and g2 stages of the cell cycle. | chinese hamster ovary cells (cho) were x-irradiated in g1 and g2 stages of the cell cycle and subsequently neurospora endonuclease (ne) (e.c.3.1.4), an enzyme which is specific in cleaving single-stranded dna, was introduced into the cells, after making the cells permeable by treatment with inactivated sendai virus. with this treatment all classes of x-ray-induced chromatid aberrations increased in g2 cells, whereas in g1 cells an increase in chromosome type of aberrations was found, associated ... | 1980 | 6244487 |
| distribution of endogenous murine leukemia virus dna sequences among mouse chromosomes. | we used mouse-chinese hamster somatic cell hybrids which lose mouse chromosomes to examine the distribution of murine leukemia virus dna sequences in the genome of a/hej mice. we analyzed total cellular dna from various hybrid clones for the presence of viral sequences by molecular hybridization and used the southern blot hybridization procedure to identify viral dna in cellular restriction endonuclease fragments. our results show that murine leukemia virus dna sequences are distributed among ma ... | 1980 | 6245275 |
| ubiquitous, interspersed repeated sequences in mammalian genomes. | dna base sequence comparisons demonstrate that the principal family of 300-nucleotide interspersed human dna sequences, the repetitive double-strand regions of hela cell heterogeneous nuclear rna, and specific rna polymerase iii in vitro transcripts of cloned human dna sequences are all representatives of a closely related family of sequences. a segment of approximately 30 residues of these sequences is highly conserved in mammalian evolution because it is also present in the interspersed repeat ... | 1980 | 6246492 |
| the synergistic effects of sv40 and budr on induction of gene mutations and chromosomal aberrations in chinese hamster cells. | the induction of chromosomal aberrations and gene mutations was studied in chinese hamster cells after separate and combined treatment with budr and sv40. separate treatment of cells with budr or virus infection increased the yield of chromosomal aberrations and reversions from glutamine requirement, expressed at 40 degrees c (a ts mutant), to prototrophy. the combined effect of the incorporation of budr into one dna strand, and a subsequent infection by sv40 was additive as regards the percenta ... | 1980 | 6247650 |
| atp enhances cyclic amp accumulation by intact p388 mouse lymphoma cells. | one of the characteristics of malignant cells is a poor response to hormones and a low level of cyclic amp. whilst this is true of intact p388 mouse lymphoma cells, high levels of adenylate cyclase (atp pyrophosphate-lyase (cyclizing), ec 4.6.1.1) activity can be measured in particulate preparations of these cells. when atp is added to the incubation medium of intact lymphoma cells, the cyclic amp level is enhanced. this effect of atp is not mediated by adenosine, nor is it enhanced by naf. the ... | 1980 | 6248129 |
| alteration of the membrane lipid composition and infectivity of vesicular stomatitis virus by growth in a chinese hamster ovary cell sterol mutant and in lipid-supplemented baby hamster kidney clone 21 cells. | the cholesterol and phospholipid composition of the membrane of vesicular stomatitis (vs) virus was altered by growth in a sterol auxotroph chinese hamster ovary (cho mi) host cell and by infection of cho mi and baby hamster kidney (bhk)-21 cells supplemented with fatty acids and dimethylethanolamine. vs virus released from infected cho mi sterol auxotroph cells grown in delipidated serum had a 50% lower ratio of cholesterol to phospholipid and an 80% drop in infectivity measured by plaque forma ... | 1980 | 6249809 |
| cytopathogenic mechanisms of entamoeba histolytica. | cinemicrography of entamoeba histolytica destruction of chinese hamster ovary (cho) cells shows that ameba cytopathogenicity consists of separate components: a contact-dependent cytolethal effect, and phagocytosis. cells not in contact with amebae remain intact. quantitation of ameba destruction of cho cells by applying the one-hit hypothesis confirms that the cytoethal effect of amebae is contact dependent. studies with 111indium oxine-labeled cells provide further evidence of extracellular kil ... | 1980 | 6249882 |
| integration of the simian virus 40 genome into cellular dna in temperature-sensitive (n) and temperature-insensitive (a) transformants of 3t3 rat and chinese hamster lung cells. | we studied the pattern of integration of the simian virus 40 (sv40) genome into the cellular dna of n-transformants (temperature sensitive) and a-transformants (temperature insensitive) derived from 3t3-fisher rat and chinese hamster lung cells. the sv40 dna was covalently linked to the cellular dna in both types of transformants. in the rat cells, most n-transformants contained sv40 sequences integrated at a single site; most a-transformants contained sv40 sequences integrated at two to five si ... | 1980 | 6251267 |
| replication of chinese hamster embryo cells transformed by temperature-sensitive t-antigen mutants of simian virus 40. | chinese hamster embryo cells transformed by simian virus 40 temperature-sensitive t-antigen mutants replicated when confluent at 40.5 degrees c, regardless of the selection method, selection temperature, or virus strain used. | 1980 | 6251272 |
| comparative analysis of proteins selectively released from cell nuclei of different eukaryotic species under conditions of mild hydrolysis by nucleases. | nuclei of cultured chinese hamster fibroblasts, dechoryonized eggs of drosophila melanogaster, calf thymocytes and mouse spleen were digested with micrococcal nuclease or dnase i under conditions when about 15-20% of nuclear dna is hydrolyzed. proteins released from the nuclei with this dna were analyzed by electrophoresis in polyacrylamide gels in the presence of sds and the most prominent components were purified in each case. it is shown that these components derived from different species ha ... | 1980 | 6251362 |
| transformation of mammalian cells with an amplifiable dominant-acting gene. | we have transferred a mutant hamster gene coding for an altered dihydrofolate reductase to wild-type cultured mouse cells by using total genomic dna from methotrexate-resistant chinese hamster ovary a29 cells as donor. by demonstrating the presence of hamster gene sequences in transformants we have provided direct evidence for gene transfer. transformants selected for increased resistance to methotrexate contain increased amounts of the newly transferred gene. we have used this mutant dhfr gene ... | 1980 | 6251468 |
| identification of 5-methylcytosine in dna fragments immobilized on nitrocellulose paper. | a method to identify 5-methylcytosine (m5cyt) in dna immobilized on nitrocellulose paper by using antibody against m5cyt raised in rabbits is described. immobilized restriction fragments of dna are incubated first with purified antibody against m5cyt and then with goat anti-rabbit igg labeled with 125i. restriction fragments containing m5cyt are visualized by autoradiography. by using this method, a heavily methylated fragment of about 1700 base pairs was identified in nuclear dna fom chinese ha ... | 1980 | 6251470 |
| comparative gene mapping: order of loci on the x chromosome is different in mice and humans. | for comparative studies we have used the somatic cell hybridization approach to regionally map genes on the mouse x chromosome. fibroblasts from a mouse with the balanced reciprocal translocation t(xd;16b5)16h were fused with a chinese hamster cell line (v79/380-6) deficient in activity of the enzyme hypoxanthine phosphoribosyltransferase (hprt). interpecific cell hybrids were initially selected for retention of the mouse translocation chromosome carrying the hprt gene. subsequently, hybrid clon ... | 1980 | 6251472 |
| dna of simian virus 40 mutates chinese hamster cells. | infection of chinese hamster cells with sv 40 dna gives rise to mutants resistant both to s-axaguanine (ag) and aminopterin (ap). this mutagenic effect can be raised when facilitating dna uptake of cells by a helper agent. the extent of muyagenic action depends further on the concentration of dna applied to the cells, with 2 micrograms/ml being more effective than 10 micrograms/ml, as well as on the period of incubation of infected cells before onset of mutant selection (mutation expression time ... | 1980 | 6251786 |
| the specific organisation of satellite dna sequences on the x-chromosome of mus musculus: partial independence of chromosome evolution. | dna was isolated from a chinese hamster/mouse hybrid cell line containing a single mouse chromosome, the x-chromosome, and digested with a variety of restriction endonucleases known to cut mouse satellite dna. after agarose gel electrophoresis and transfer to nitrocellulose, hybridisation was carried out to a radioactive mouse satellite dna probe. in this manner the organisation of satellite sequences at an individual chromosome was determined. we have found that the organisation of centromeric ... | 1980 | 6253924 |
| altered synthesis and processing of oligosaccharides of vesicular stomatitis virus glycoprotein in different lectin-resistant chinese hamster ovary cell lines. | to determine the particular intracellular steps in the glycosylation of the vesicular stomatitis virus (vsv) glycoprotein that were altered in several lectin-resistant cho cell lines, vsv-infected parental and mutant cells were pulse-labeled for 30 and 120 min with [3h]mannose and [3h]glucosamine. cell-associated viral glycopeptides were analyzed by gel filtration combined with specific glycosidase digestions and compared with the corresponding mature virion oligosaccharides. the intracellular g ... | 1980 | 6255177 |
| simian virus 40-chinese hamster kidney cell interaction. v. cooperative effect of 5-iodo-2'-deoxyuridine and mitomycin c in the enhancement of virus replication in infected cells. | a cooperative effect of 5-iodo-2'-deoxyuridine and mitomycin c which amplified (10- to 50-fold) their stimulating effect on simian virus 40 replication was obtained in infected chinese hamster kidney cells. the results indicate that these drugs act at different levels to modify the permissiveness of cells to simian virus 40. | 1980 | 6255213 |
| structure and organization of the highly repeated and interspersed 1.3 kb ecori-bg1ii sequence family in mice. | ecori digestion of total mouse dna yields a prominant 1.3 kb fragment amounting to between 1 and 2% of the mouse genome. the majority of the 1.3 kb ecori fragments have a single bg1ii site 800 bp from one end. this ecori-bg1ii sequence family shows hindiii and haeiii sequence heterogeneity. we have cloned representatives of the ecori-bg1ii gene family in charon 16a and studied their structure and organization within the genome. the cloned 1.3 kb fragments show the expected restriction enzyme pat ... | 1980 | 6255440 |
| control of sv40 replication by a simple chromosome in monkey-hamster cell hybrids. | somatic cell hybrids produced between cercopithecoid monkey and chinese hamster cells were used to assay susceptibility to sv40 viral infection in an attempt to define the primate factors that determine permissiveness to viral replication. these cell hybrids, which differed in their primate chromosome complement, were found to differ also in their ability to sustain viral replication. a correlation was found between an elevated sv40 viral replication and the presence of the chromosomes 11 in the ... | 1980 | 6255616 |
| enhanced sensitivity of tumorigenic cells to rapid rounding induced by phenylalaninol. | this study describes a rounding reaction induced in mammalian cells by the addition of phenylalaninol. in the chinese hamster ovary tsh1 line the rounding occurred rapidly with a half time of 1 min at 25 mm phenylalaninol. after the removal of phenylalaninol, the rounding was reversed, leading to the reflattening of the cells with a half-time of 3.5 min. rounding was inhibited by dibutyryl-camp and testosterone, and reflattening by cytochalasin b. either in the case of the tsh1 line and its grow ... | 1980 | 6257353 |
| structure of the abelson murine leukemia virus genome and the homologous cellular gene: studies with cloned viral dna. | circular double-stranded dna produced after infection of mouse cells with abelson murine leukemia virus (a-mulv) was isolated and cloned in the phage vector charon 21a. the resulting clones of the a-mulv genome show homology to the ends of moloney mulv and to a 3.5 kb central region containing sequences unique to abelson virus. a 2.3 kb restriction fragment containing only a-mulv-specific sequences was subcloned in the plasmid vector pbr322 and used as a probe for the cellular gene that had been ... | 1980 | 6257398 |
| chromosomes involved in production of infectious sv40 particles in mouse/sv40-transformed chinese hamster cell hybrids. | the clone 6d hybrid, capable of expressing the virus-specific t-antigen but unable to produce infectious virus particles after superinfection, presented a complete mouse (3t3-4e) chromosome complement and a significant loss of chinese hamster (chk/svlp ag) chromosomes. similar properties were displayed by a budr-resistant derivative of the cl 6d hybrid (cl 6d.6bu). three independent superhybrid clones (cl 10b, cl 10c, cl 11a) isolated after backcross of the cl 6d.6bu hybrid with a nontransformed ... | 1981 | 6258123 |
| temporal regulation of the rate of vesicular stomatitis virus mrna translation during infection of chinese hamster ovary cells. | | 1981 | 6258290 |
| studies on the cytopathogenicity of entamoeba histolytica. | we have explored the interaction of virulent and avirulent e. histolytica (hm1 and 303 respectively) with human polymorphonuclear leukocytes (pmns) and chinese hamster ovary (cho) cells. pmns exhibit chemotaxis to both hml and 303. on contact with hml, pmns degranulate and die (trypan blue uptake); incubation at a ratio of 100 pmns per ameba for 40 minutes revealed 70 per cent pmn death with 84 per cent hml viability. 303s are often ingested by pmns on contact; after incubation as above, only 1 ... | 1980 | 6258505 |
| inefficient internalization of receptor-bound low density lipoprotein in human carcinoma a-431 cells. | human epithelioid carcinoma a-431 cells are known to express unusually large numbers of receptors for the polypeptide hormone epidermal growth factor. the current studies demonstrate that this cell line also expresses 5- to 10-fold more low density lipoprotein (ldl) receptors per cell than either human fibroblasts or chinese hamster ovary (cho) cells. as visualized with an ldl-ferritin conjugate, the ldl receptors in a-431 cells appeared in clusters that were distributed uniformly over the cell ... | 1981 | 6259181 |
| isolation and characterization of a pseudomonas aeruginosa mutant producing a nontoxic, immunologically crossreactive toxin a protein. | nitrosoguanidine mutagenesis of pseudomonas aeruginosa strain pao-1 yielded a mutant strain, pao-pr1, which produced a protein that was immunologically indistinguishable from native toxin a and was nontoxic for cultured chinese hamster ovary cells. in contrast to native toxin, the cell-associated and extracellular crossreactive material (crm), designated "crm protein," possessed no adenosine diphosphate-ribosylating activity. this crm protein comigrated with native toxin a on sodium dodecyl sulf ... | 1980 | 6261247 |
| rat bladder cell-mediated mutagenesis od chinese hamster v79 cells and metabolism of benzo[a]pyrene. | primary rat bladder epithelial cells were cocultivated with chinese hamster v79 cells in the presence of carcinogens, and the induction of 6-thioguanine resistance in the v79 cells was used as a marker of cell-mediated mutagenesis. the carcinogens dimethylnitrosamine, 7,12-dimethylbenz[a]anthracene, and benzo[a]pyrene (bp) were mutagenic to v79 cells in the presence of bladder cells but not in their absence. analysis of bp metabolites formed by bladder cells indicated that 7,8-dihydro-7,8-dihydr ... | 1981 | 6262559 |
| passage of an integral membrane protein, the vesicular stomatitis virus glycoprotein, through the golgi apparatus en route to the plasma membrane. | the intracellular pathway of biogenesis of the vesicular stomatitis virus transmembrane glycoprotein was investigated in situ by using indirect immunofluorescence of whole infected chinese hamster ovary cells and immunoelectron microscopy of ultrathin frozen sections of infected cells. transport of the glycoprotein was synchronized by using the temperature-sensitive virus mutant orsay-45 and a temperature shift-down protocol. sequential appearance of the glycoprotein in the rough endoplasmic ret ... | 1981 | 6262824 |
| titration of integrated simian virus 40 dna sequences, using highly radioactive, single-stranded dna probes. | nick-translated simian virus 40 (sv40) [32p]dna fragments (greater than 2 x 10(8) cpm/micrograms) were resolved into early- and late-strand nucleic acid sequences by hybridization with asymmetric sv40 complementary rna. both single-stranded dna fractions contained less than 0.5% self-complementary sequences; both included [32p]-dna sequences that derived from all regions of the sv40 genome. in contrast to asymmetric sv40 complementary rna, both single-stranded [32p]dnas annealed to viral [3h]dna ... | 1981 | 6264104 |
| cytopathogenicity of entamoeba histolytica: trophozoite homogenates modulate dna synthesis in a mammalian cell line. | we examined the effect of total trophozoite homogenates from four axenized strains of entamoeba histolytica (hk9, hm1, hm2, and hm3) on the dna synthesis of subconfluent cultures of chinese hamster ovary (cho) cells incubated at low (0.1%) serum concentration. hm1, hm2, and hm3 extracts increased [3h]thymidine incorporation to acid-insoluble material in cho cells up to a maximum of 2.5, 1.5, and 1.5 times respectively, at doses of amebal protein ranging from 16 to 125 micron/ml. hm1 and hm2 extr ... | 1981 | 6264701 |
| chromosome aberrations in chinese hamster embryonal fibroblasts after exposure to rous sarcoma virus. | | 1981 | 6266887 |
| surface changes in cell membranes of chinese hamster embryo fibroblasts, normal and transformed by rous sarcoma virus, infected with influenza virus a2-texas. | | 1981 | 6266888 |
| gonadotropin stimulation of pregnenolone metabolism in chinese hamster ovary cells in culture. | to determine if chinese hamster ovary (cho) cells in culture are able to metabolize steroids, cho cells were incubated in defined medium with [14c]pregnenolone. as shown, [14c]pregnenolone is metabolized to progesterone and other delta 53 beta steroids; this steroidogenic response is appreciably enhanced upon exposure of the cells to 50 nm gonadotropins (human chorionic gonadotropin and follicle-stimulation hormone). the primary metabolites that accumulate in the medium upon treatment with gonad ... | 1981 | 6267080 |
| sensitive determination of pyrimidine dimers in dna of uv-irradiated mammalian cells. introduction of t4 endonuclease v into frozen and thawed cells. | endonuclease v from e. coli infected with phage t4 was used to evaluate the frequency and the removal of pyrimidine dimers from dna in cultured mammalian cells. cellular membranes were made permeable to the enzyme by two cycles of rapid freezing and thawing. the number of endonuclease-sensitive sites in dna was assayed by sedimentation in alkaline sucrose gradients upon which the cells were lysed directly. comparison of the frequency of endonuclease-sensitive sites with the frequency of pyrimidi ... | 1981 | 6267456 |
| the mannose 6-phosphate receptor of chinese hamster ovary cells. compartmentalization of acid hydrolases in mutants with altered receptors. | the localization of acid hydrolases was examined in chinese hamster ovary cells with defective mannose 6-phosphate receptors; these mutants had been shown to exhibit reduced uptake and altered binding of exogenously added acid hydrolase (robbins, a. r., myerowitz, r., youle, r. j., murray, g. j., and neville, d. m., jr. (1981) j. biol. chem. 256, 10618-10622). cells were grown in the presence of [3h]mannose, alpha-l-iduronidase and beta-hexosaminidase were immunoprecipitated sequentially, electr ... | 1981 | 6270123 |
| characterization of a membrane-associated receptor from bovine liver that binds phosphomannosyl residues of bovine testicular beta-galactosidase. | a receptor that binds the phosphomannosyl recognition marker of bovine testicular beta-galactosidase (beta-d-galactoside galactohydrolase, ec 3.2.1.23) was isolated from bovine liver membranes. the receptor was extracted from crude plasma membrane preparations with triton x-100 and immunoprecipitated as a receptor--beta-galactosidase complex with anti-beta-galactosidase. the receptor was dissociated from the precipitate with mannose 6-phosphate, labeled with 125i, and purified on a beta-galactos ... | 1981 | 6270668 |
| requirement of the human chromosome 11 long arm for replication of herpes simplex virus type 1 in nonpermissive chinese hamster x human diploid fibroblast hybrids. | somatic cell hybrids between chinese hamster (ch) lung cells (v79/380-6), nonpermissive for productive infection by herpes simplex type 1 (hsv-1), and permissive human diploid cells support productive hsv-1 infection as long as they retain human chromosome 11. human chromosome 3 has been reported to complement nonpermissivity in (ch) don cells (1). intraspecies hybrids between don/a3 and v79/380-6 cells, however, did not support hsv-1 replication, indicating lack of complementation. the block in ... | 1981 | 6270835 |
| lung and liver cell-mediated mutagenesis systems: specificities in the activation of chemical carcinogens. | a liver and lung cell-mediated-v79 cell mutagenesis system using intact cells as metabolic activation systems was employed to study the relative ability of cells from these organs to activate chemical carcinogens. primary cultures of liver and lung cells from male sprague dawley rats were used to metabolically activate the chemicals and the mutation of chinese hamster v79 cells to ouabain resistance used to detect mutagenic intermediates. 7,12-dimethylbenz[a]anthracene and 3-methylcholanthrene, ... | 1981 | 6271413 |
| monoclonal antibodies to the low density lipoprotein receptor as probes for study of receptor-mediated endocytosis and the genetics of familial hypercholesterolemia. | monoclonal antibodies directed against the low density lipoprotein (ldl) receptor have been prepared by immunization of mice with a partially purified receptor from bovine adrenal cortex. spleen cells from the mice were fused with the sp2/0-ag14 line of mouse myeloma cells. the most extensively studied monoclonal antibody, designated immunoglobulin-c7, reacts with the human and bovine ldl receptor, but not with receptors from the mouse, rat, chinese hamster, rabbit, or dog. 125i-labeled monoclon ... | 1981 | 6271765 |
| role of adherence in cytopathogenic mechanisms of entamoeba histolytica. study with mammalian tissue culture cells and human erythrocytes. | the enteric pathogen, entamoeba histolytica, appears to cause disease by adhering to and then destroying mucosal barriers. using an in vitro method of studying the interaction of e. histolytica with target cells (chinese hamster ovary [cho] and human erythrocytes [rbc]), we examined the mechanism of amebic adherence and its role in lysis of target cells. killing and phagocytosis of target cells by amebas ceases at 4 degrees c, allowing observation of adherence. amebas adhere to cho cells at 4 de ... | 1981 | 6271810 |
| targeted killing of cultured cells by receptor-dependent photosensitization. | this paper describes a method, designated "receptor-dependent photosensitization," by which the receptor-mediated endocytosis of low density lipoprotein (ldl) can be used to deliver a photosensitizing agent, pyrene, to cultured human and animal cells. the hydrophobic core of ldl is extracted and replaced with pyrene covalently coupled to cholesteryl oleate. this reconstituted ldl enters cells in significant amounts only when the cells express ldl receptors, resulting in the accumulation of pyren ... | 1981 | 6272315 |
| methotrexate-resistant chinese hamster ovary cells have amplified a 135-kilobase-pair region that includes the dihydrofolate reductase gene. | for the eventual purpose of isolating and studying a single animal cell replicon, we have developed a methotrexate-resistant chinese hamster ovary cell line that has amplified an early-replicating dna sequence approximately 500 times; this sequence includes the gene coding for dihydrofolate reductase (dhfr; tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:nadp+ oxidoreductase, ec 1.5.1.3). dhfr composes 30% of the cytoplasmic protein in this cell line, and dhfr mrna represents 25% of the ... | 1981 | 6273843 |
| carcinogen-mediated amplification of viral dna sequences in simian virus 40-transformed chinese hamster embryo cells. | exposure of simian virus 40 (sv40)-transformed chinese hamster embryo cells to various chemical and physical carcinogens induced sv40 dna synthesis. although the carcinogen-mediated amplification of sv40 dna is regulated by the viral a gene, the induction of viral dna synthesis does not result in the rescue of infectious virus or the formation of complete viral dna molecules. instead, a heterogeneous collection of dna molecules containing sv40 sequences was generated by treatment with 7,12-dimet ... | 1981 | 6273853 |
| morphologic study of the internalization of a lysosomal enzyme by the mannose 6-phosphate receptor in cultured chinese hamster ovary cells. | the binding and internalization of a model lysosomal enzyme, beta-galactosidase, was visualized by use of rabbit anti-beta-galactosidase and goat anti-rabbit igg; the second antibody was labeled with rhodamine or fluorescein (for detection by fluorescence) or with horseradish peroxidase (for electron microscopy). chinese hamster ovary cells were incubated with beta-galactosidase at 4 degrees c, and then were washed and sequentially incubated in the cold with the two antibodies. the beta-galactos ... | 1981 | 6273898 |
| the cloning and reintroduction into animal cells of a functional cad gene, a dominant amplifiable genetic marker. | rodent cells resistant to pala, a specific inhibitor of the aspartate transcarbamylase activity of the multifunctional cad protein, overproduce cad as a result of amplification of the cad gene. we cloned a functional cad gene from syrian hamster cells using a cosmid vector. two independently isolated cosmids containing cad genes have inserts 40 and 45 kb long. we introduced the cloned genes into cad-deficient chinese hamster ovary (cho) cell mutants by fusing them with protoplasts of escherichia ... | 1981 | 6277500 |
| potentiation of cell killing by inhibitors of poly(adp-ribose) polymerase in four rodent cell lines exposed to n-methyl-n-nitrosourea or uv light. | the sensitivities (do-values) of the cytotoxic effect of mnu on four rodent cell lines were: mouse l1210, 0.07 mm; rat yoshida sarcoma, 0.52 mm; chinese hamster v79a, 0.70 mm and the uv sensitive, x-ray sensitive v79/79, 0.35 mm. the abilities of maximum non-toxic doses of the poly-(adp-ribose) polymerase inhibitors, 5-methyl nicotinamide (5men), 3-methoxybenzamide (3mba) and caffeine to potentiate this cytotoxicity and that of uv light in v79a and v79/79 was measured. the degree of potentiation ... | 1982 | 6277522 |
| j chain is encoded by a single gene unlinked to other immunoglobulin structural genes. | immunoglobulin j chain mediates the polymerization of both igm and iga immunoglobulins. its synthesis is closely regulated in b lymphocytes, apparently at the level of rna transcription. to define the genetic bases of this regulation, we have determined the location and number of j chain genes in the mouse. analysis of dna from a group of somatic cell hybrids containing various mouse chromosomes on a constant background of chinese hamster chromosomes indicated that this gene is located on mouse ... | 1982 | 6278047 |
| metabolism of benzo(a)pyrene in epidermal keratinocytes and dermal fibroblasts of humans and mice with reference to variation among species, individuals, and cell types. | the metabolism of benzo(a)pyrene (bp) in epidermal keratinocytes and dermal fibroblasts of humans and mice was investigated with emphasis on variation among species, individuals, and cell types. human epidermal and dermal cells were isolated from the skin of normal subjects by trypsinization at 4 degrees overnight, followed by separation of the epidermis from the dermis with forceps. in confirmation of previous studies metabolic activity of human epidermal cells on bp was consistently demonstrat ... | 1982 | 6279285 |
| carcinogen-mediated amplification of specific dna sequences. | a model experimental system based on sv40-transformed chinese hamster embryo cells and a highly sensitive in situ hybridization procedure was designed. exposure of the cells to different categories of chemical and physical carcinogens resulted in the induction of sv40 dna synthesis in the treated cells. although the carcinogen-mediated amplification of sv40 dna sequences is regulated by the viral "a" gene, neither infectious virus nor complete viral dna molecules were rescued from the treated ce ... | 1982 | 6279687 |