Publications

a role for asparaginyl-trna in the regulation of asparagine synthetase in a mammalian cell line.	the expression of asparagine synthetase activity [l-aspartate:ammonia ligase (amp-forming), ec 6.3.1.1] in cultured chinese hamster ovary (cho) cells is regulated by asparagine. after transfer of cho cells from an asparagine-supplemented medium to a medium lacking asparagine, activity increases 1.5- to 2-fold. if asparagine is added back to the medium, activity returns to control levels. to test the possible involvement of asn-trnaasn in regulating the levels of asparagine synthetase, we have ex ...	1977	18735
effect of ph on hyperthermic cell survival.	chinese hamster ovary cells incubated with various concentrations of co2, to obtain extracellular ph values in the range of 6.40-7.85, were heated at 45.5c for 5, 10, or 20 minutes. thermal sensitivity increased sharply from ph 7.35 to 6.65 (i.e., survival decreased from 1 x 10(-2) to 3 x 10(-5) for 20 minutes of heating), but remained constant from ph 7.35 to 7.85. the enhanced thermal sensitivity at ph values below pth 7.35 suggested that tumors should be preferentially destroyed by heat relat ...	1977	17014
reduced synthesis of [14c]mannosyl oligosaccharide-lipid by membranes prepared from concanavalin a-resistant chinese hamster ovary cells.	we compared the synthesis of mannosyl oligosaccharide-lipid by membranes of wild type and concanavalin a-resistant chinese hamster ovary cells during incubations with gdp-[14c]mannose and udp-n-acetylglucosamine. the membranes prepared from exponentially growing mutant cells incorporated 10- to 70-fold less [14c]mannose into oligosaccharide-lipid than did membranes of wild type cells. the lectin-resistant cells are temperature-sensitive for growth. using temperature-resistant revertants, we show ...	1977	863895
synaptonemal complex karyotyping in spermatocytes of the chinese hamster (cricetulus griseus). i. morphology of the autosomal complement in spread preparations.	using the counce-meyer spreading technique, in over 70 spermatocytes it was possible consistently to obtain whole, flattened nuclei containing complete sets of pachytene scs. the scs are visible in both the phase and electron microscopes. each sc is morphologically intact, preferentially stained, and attached to the nuclear envelope by a dense, terminal plaque. it is thus possible to trace each sc for its entire length. also, a structure representing the kinetochore is clearly visible in each au ...	1977	858262
lack of mutagenic effect of halothane or chloroform on cultured cells using the azaguanine test system.	halothane with and without nitrous oxide and chloroform alone were tested for mutagenic effects at the 8-azaguanine locus on the chromosomes of chinese hamster lung fibroblast cells in culture. no significant numbers of mutations were found after 24 h exposures to 1-3% of these anaesthetics, or to 75% nitrous oxide.	1977	911573
culture of pre-implantation chinese hamster (cricetulus griseus) embryos in vitro.	pre-implantation embryos from chinese hamsters (cricetulus griseus) were cultivated under completely defined conditions. the embryos were placed in drops of chemically defined medium under liquid paraffin and cultured in an atmosphere of 10% co2 in air. by this method, development will proceed in vitro from the two-cell stage up to the blastula within 72 h. it is possible to stop the cultivation at different stages of development, to fix the embryos and analyse the chromosomes. the method descri ...	1977	857153
segregation studies in cho hybrid cells: i. spontaneous and mutagen-induced segregation events of two recessive drug-resistant loci.	the process of segreation or phenotypic expression of two recessive drug-resistant loci from heterozygous chinese hamster ovary hybrid lines is examined. the spontaneous segregation rates of phytohaemagglutinin resistance (phar) and a temperature-dependent 8-azaguanine-resistant locus (azarts) from heterozygous quasitetraploid lines using luria-delbruck fluctuation analysis were 5 x 10(-5) and 10(-5) events/cell/generation, respectively. in quasihexaploid lines, the latter rates increased 40- an ...	1977	605380
the pericentriolar material in chinese hamster ovary cells nucleates microtubule formation.	the structure and function of the centrosomes from chinese hamster ovary (cho) cells were investigated by electron microscopy of negatively stained wholemount preparations of cell lysates. cells were trypsinized from culture dishes, lysed with triton x-100, sedimented onto ionized, carbon-coated grids, and negatively stained with phosphotungstate. the centrosomes from both interphase and dividing cells consisted of pairs of centrioles, a fibrous pericentriolar material, and a group of virus-like ...	1977	559676
cell cycle dependent changes in morphology. studied with a cold-sensitive mutant of chinese hamster ovary cells.		1977	558900
inactivation and mutation of cultured mammalian cells by aluminium characteristic ultrasoft x-rays. i. properties of aluminium x-rays and preliminary experiments with chinese hamster cells.	irradiation with ultrasoft x-rays produces electron tracks of short defined lengths in the irradiated material. this property is of particular interest in distinguishing between different models of radiation action on living organisms. the production, absorption and dosimetry of aluminium k characteristic x-rays of energy 1.5 kev are described. quantitative experiments on mammalian cells with these x-rays are possible, and they were found to be considerably more effective than gamma-rays in inac ...	1977	301864
microvascular lesions of gingival and cheek pouch tissue in the diabetic chinese hamster.		1977	266583
cyclic amp-protein-dna complex formation in mammalian cell-free systems.	a cytoplasmic protein fraction from kb and chinese hamster ovary cells (cho-kl) was shown to bind in vitro to camp and subsequently to dna-cellulose. this protein complex was not found in de-52 purified cho-k1 camp-dependent protein kinases. the complex appeared to exist as a small fraction of the total camp binding proteins, preferred native to denatured dna and exhibited multiple sedimentation coefficients in glycerol gradients. this complex, after elution from the dna cellulose column, was sh ...	1977	198443
[electron microscopic study of interphase in a culture of fibroblast-like cells].	the analysis of the ultrastructural changes of fibroblast-like cells of chinese hamster at different periods of the cell cycle demonstrates that the most reliable morphological criteria for identification of different periods of the interphase are changes of the nuclear chromatin and nucleolus and the dynamics of development of the daughter centrioles. no prominent changes of the morphology of the protein-synthesizing apparatus during interphase were noted.	1977	560735
studies on adenosine 3',5'-phosphate-binding and adenosine 3',5-phosphate-dependent protein kinase activities associated with subcellular fractions of chinese hamster ovary cells.	both cyclic amp-binding and cyclic amp-dependent protein kinase activities exist in chinese hamster ovary cell extract. competition experiments demonstrate that the binding is specific for cyclic amp. all cellular elements including nucleus, mitochondria, plasma membrane, microsome, ribosome and cytosol contain both activities. binding activity is highest in the cytosol and lowest in the nucleus. each fraction contains endogenous protein kinase activity which is insensitive to cyclic amp activat ...	1977	200277
cell cycle variation associated with feeder effects in cultures of chinese hamster fibroblasts.		1977	913497
effect of distamycin a on chinese hamster chromosomes.		1977	71997
biochemical genetics of chinese hamster cell mutants with deviant purine metabolism: characterization of chinese hamster cell mutants defective in phosphoribosylpyrophosphate amidotransferase and phosphoribosylglycinamide synthetase and an examination of alternatives to the first step of purine biosynthesis.	activities of the first three enzymes in the de novo purine biosynthetic pathway have been measured in cell-free extracts of the chinese hamster ovary cell (cho-k1) and two purine-requiring auxotrophs of this cell. ade-a has been found to be defective in phosphoribosylpryophosphate (prpp) amidotransferase while ade-c has been found to be defective in glycinamide ribonucleotide (gar) synthetase. neither enzyme deficiency is due to the presence of an excess of diffusible inhibitor, and mixed extra ...	1977	564086
isolation of a lactic dehydrogenase-a-deficient cho-k1 mutant by nylon cloth replica plating.	a mutant chinese hamster ovary cell deficient in lactate dehydrogenase a activity has been isolated using a nonselective technique. the method uses histochemical staining to examine colonies directly for enzyme activity and nylon cloth replica plating to recover particular clones. the mutant cell has an apparent km (pyruvate to lactate) that is nearly tenfold higher than the parental cell, while its vmax has been reduced more than 80-fold. in mutant cell extracts with added porcine ldh-b enzyme, ...	1977	341374
selective loss of wheat germ agglutinin binding to agglutinin-resistant mutants of chinese hamster ovary cells.	the binding of 125i-labeled wheat germ agglutinin (wga) to parental and three distinct wga-resistant chinese hamster ovary cell lines possessing modified cell surface carbohydrate structures has been examined over a 10(6)-fold range of wga concentrations. the scatchard plot for wga binding to parental cells was complex and exhibited positively cooperative binding at the high affinity sites. one of the wga-resistant mutants (wgariii) was apparently not altered in its wga-binding ability compared ...	1977	270740
analysis of karyotype variation following carcinogen treatment of chinese hamster primary cell lines.	chinese hamster primary fibroblasts derived from several embryos were treated with the carcinogens benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene or n-methyl-n'-nitro-n-nitrosoguanidine. karyotype analysis, sister chromatid exchange frequency, evidence of transformation by growth in agar, cell morphology and reaction to cytocholasin b were tested at regular intervals over many culture passages. carcinogen treatment was found to shorten the time period before onset of permanent karyotypically cha ...	1977	924693
differential giemsa staining of sister chromatids after extraction with acids.	chromosomes of chinese hamster strain cells were air-dried on slides after brdu substitution for two or three rounds of replication. the preparations were treated with 20% pca at 55 degrees c for 20-30 min, or 5n hcl at 55 degrees c for 15-20 min. after staining with giemsa, unifilarly brdu-substituted chromatids stained faintly and bifilarly substituted chromatids stained darkly. such a pattern of sister chromatid differential staining was confirmed by the examination of metaphase cells grown w ...	1977	72637
a role for aminoacyl-trna synthetases in the regulation of amino acid transport in mammalian cell lines.	the regulation of neutral amino acid transport was examined utilizing two temperature-sensitive aminoacyl-trna synthetase mutants, by comparison of their transport activities at permissive and marginally permissive temperatures. when the temperature-sensitive leucyl-trna -synthetase mutant tsh1 was shifted from a normal growth temperature of 34 degrees to a marginally permissive temperature for growth of 38%, a significant enhancement in the initial rate of uptake of leucine and other l system a ...	1977	914817
the effect of cyclophosphamide on the centromere separation sequence in chinese hamster spermatogonia.	the sequence of centromere separation in spermatogonial chromosomes of untreated and cyclophosphamide-treated chinese hamsters is described. centromeres of chromosome 1 and 2 separated much earlier than all other chromosomes, especially 6-8. cyclophosphamide significantly inhibits the centromere separation in all chromosome groups but does not alter the sequence of separation.	1977	598845
tyzzer's disease in the chinese hamster (cricetulus griseus).		1977	599880
visualization of interphase chromosomes.	using a modified giemsa-banding technique we have observed what appear to be chromosomes during interphase in nuclei from allium cepa root tips and chinese hamster cells (cho line). during telophase through g1 chromosomes progressively uncoil and decondense. during s chromosomes are comparatively decondensed, but some segments have structure similar to chromosomes in g1 and g2. during g2 the chromosomes progressively recondense and coil in apparent preparation for prophase. although specific str ...	1977	562895
comparative investigations on cytogenetic effects of x-irradiation on the germinal epithelium of male mice and chinese hamsters.	in one short-term-experiment and one long-term-experiment spermatogonia of mice and chinese hamsters were compared for their sensitivity of x-ray induced chromosome aberrations. short-term-experiment: six hours after varying doses of x-rays the spermatogonia of both species were analysed and the number of induced chromatid breaks determined. at the dose range from 25-125 r the number of induced chromatid breaks per cell per roentgen is 0.01 in mice. in chinese hamsters this value is 0.0072. the ...	1976	1002141
quantitative evaluation of somatotrophic cells (sc) in the adenohypophysis of normal and diabetic male chinese hamsters.	the pituitary of genetically diabetic chinese hamsters contains significantly (p less than 0.001) greater numbers of somatotrophes than pituitary of non-diabetics. this may play a role in the aetiopathology of diabetes in this species or at least contribute to the maintenance of hyperglycaemia.	1976	976637
investigations on the frequency of chromosome aberrations in bone marrow cells of chinese hamsters after simultaneous application of caffeine and cyclophosphamide.	the potentiating effect of caffeine (1,3,7-trimethylxanthine) on chemically induced chromosome aberrations was studied in bone marrow cells of chinese hamsters, exposed to the alkylating agent cyclophosphamide. four experimental series were performed: in the first two tests caffeine (200 mg/kg) or cyclophosphamide (40 mg/kg), respectively, were administered. a third and fourth test was performed with caffeine plus cyclophosphamide (200 + 40 mg/kg and 35 + 40 mg/kg, respectively) simultaneously. ...	1976	939563
the effect of hyperthermia on the repair of radiation damage in plateau phase cells.	hyperthermia (41 degrees c for 1 hr.) completely inhibited both sublethal and potentially lethal radiation damage repair by plateau phase cells taken from v79 chinese hamsters. this suggests that there may be disadvantages in combining x-ray and heat therapies for the treatment of tumors.	1976	1257447
metabolic effects and mortality rate in diabetic chinese hamsters after long-term treatment with 5-methoxyindole-2-carboxylic acid (mica).	chronic oral treatment of male diabetic chinese hamsters with 100 mg/kg/day 5-methoxyindole-2-carboxylic acid (mica) causes a depression of blood glucose in fasted animals and an improvement in the glucose profile in fed animals. glycogen levels in the liver and body weight are decreased. treated animals die at a higher rate than do controls. it is concluded that treatment with a potent inhibitor of gluconeogenesis like mica will not provide a useful tool in managing diabetes.	1976	989012
failure to detect chromosome damage in bone-marrow cells of mice and chinese hamsters exposed in vivo to some ergot derivatives.	a known chemical mutagen (trenimon, bayer), and three ergot derivatives (ergotamine tartrate, dihydroergotoxine mesylate, and methysergide hydrogen maleate) were tested in mice and chinese hamsters for mutagenic effects by means of the micronucleus test and the conventional chromosome method. in contrast to trenimon, which proved to be a powerful mutagen in these test systems, neither of the ergot derivatives showed an effect. it is concluded that these compounds, at subtoxic or therapeutic dose ...	1976	800380
genetic characterization of methotrexate-resistant chinese hamster ovary cells.	in a previous report, we described the selection and partial characterization of three methotrexate (mtx)-resistant chinese hamster ovary cells (cho) (1). class i cells contained an apparent structural alteration in dihydrofolate reductase. class ii cells had an alteration affecting the permeability of the drug. class iii cells, selected from class i cells, had an increased activity of the altered enzyme. in the work described here, it has been shown that the spontaneous mutation rate to class i ...	1976	1035580
a comparative study of different experimental protocols for mutagenesis assays with the 9-azaguanine resistance system in cultured chinese hamster cells.	both spontaneous and ems-induced mutant frequencies were determined in cultured cells from v79 chinese hamsters using three different experimental protocols. after optimal expression time was attained, mutation frequencies only remained constant when a protocol was used in whcih the cell density was maintained below critical values both before and during mutant selection. the identification of such a plateau allows, besides more reliable and reproducible estimates of mutation frequency, reductio ...	1976	794707
the cause of g2-arrest in chinese hamster ovary cells treated with anticancer drugs.	the nature of g2-arrest was studied in chinese hamster ovary cells after exposure to 4'-demethyl-epipodophyllotoxin 9-)4,6-0-2-thenylidene-beta-d-glycopyranoside (vm26), 1,3-bis(2-chloroethyl)-1-nitrosourea, 1,3-cis(2-chloroethyl)-1-nitrosourea, cis-4[[[(2-chloroethyl)-nitrosoamino] carbonyl] amino]- cyclohexane carboxylic acid, or neocarzinostatin. to determine whether this g2-arrest was due to a metabolic block or to damage to the genetic material, we employed the phenomenon of premature chrom ...	1976	137324
cytokinetic studies on the effect of hyperthermia on chinese hamster lung cells.		1976	976291
a microsurgical technique for orthotopic ovarian transplantation in the chinese hamster.	a microscopic surgical technique for the orthotopic transplantation of ovaries in the chinese hamster is described. the procedure, which uses microcauterization of the mesovarian stump and closure of the ovarian bursa with microvascular suture, resulted in a 75 to 80 percent surgical success rate in a series of 12 nondiabetic and 12 diabetic hamsters. applications include the production of prediabetic offspring, the study of intrauterine environmental effects on transplant-derived offspring, and ...	1976	982278
combinations of hyperthermia (40 degrees, 45 degrees c) with radiation.	incubation of chinese hamster cells at an elevated but sublethal temperature between fractions of radiation and/or pulses of hyperthermia at 45 degrees c strongly modified the effectiveness of cell killing. increasing the incubation temperature from 37 to 40 degrees c between fractions of hyperthermia at 45 degrees c followed by radiation substantially enhanced cell killing; while the opposite sequence (radiation leads to incubation at 40 degrees c leads to hyperthermia at 45 degrees c) resulted ...	1976	981627
effect of carbohydrates on growth inhibition by d-mannosamine of glucosamine-requiring mutant cells of chinese hamster lung cells.		1976	1026666
[telomeric chromosome fusion in cells treated with colcemid and 5-bromdeoxyuridine].	specific chromosomes with two or more centromeres were found in the tetraploid metaphases of the second mitotic division after combined treatment with coldemid (0.05 mug/ml) and 5-bromodeoxyuridine (50 mug/ml) for 24 hours in the aneuploid chinese hamster cell line. they were formed by telometric fusion of chromosomes and were absent in the cells treated with colcemid or 5-bromodeoxyuridine separately. a possible relation of this phenomenon to the telomeric association of chromosomes in the inte ...	1976	990480
selection of temperature-sensitive chl asparagyl-trna synthetase mutants using the toxic lysine analog, s-2-aminoethyl-l-cysteine.	we developed a procedure, using the toxic lysine analog s-2-aminoethyl-l-cysteine (thialysine) as the selective agent, to obtain mutant chinese hamster lung (chl) fibroblasts with temperature-sensitive defects affecting protein synthesis. the procedure is efficient, rapid, and simple. using this selective system, we isolated six temperature-sensitive mutants that fail to grow (plating efficiencies less than 10-5) and synthesize protein at 39 degrees c. the temperature-sensitive phenotype of five ...	1976	1017011
the effect of adriamycin and radiation on g2 progression.	the effect of the dna-intercalating antibiotic adriamycin on the progression of chinese hamster ovary cells into mitosis, and on the delay induced by ionizing radiation, was studied using the mitotic cell selection procedure to monitor the rate of cell division. following the addition of adriamycin, the mitotic rate remained unaltered for a refractory period and then decreased to zero. this effect was concentration dependent with transition points between the s-g2 boundary for 0.1 mug/ml and lat ...	1976	975085
nature of 3,6-bis(5-chloro-2-piperidinyl)-2,5-piperazinedione-induced cytotoxicity in chinese hamster ovary cells.	we sutdied the effect of 3,6-bis(5-chloro-2-piperidinyl)-2,5-piperazinedione (bcp) on various parameters of the replication cycle and cell grwoth on monolayer cultures of chinese hamster ovary cells. the results indicated that bcp had no effect on the g-s transition or the passage of cells from metaphase to g. however, bcp prolonged s- and g-phases because of its retarding effect on dna synthetis. bcp was more toxic to s-phase cells than to g or mitotic cells. as with other alkylating agents, ch ...	1976	1003560
rate of rna synthesis as a function of temperature in chinese hamster lung fibroblasts (v-79).		1976	1001370
repair of potentially lethan radiation damage: comparison of neutron and x-ray rbe and implications for radiation therapy.	experiments with chinese hamster cells have shown that neutron irradiation does not result in repair of potentially lethal damage (pld), i.e., that which can be influenced by changes in environmental conditions following irradiation. since pld is presumed to be repaired in tumors but not in normal tissues, this absence of differential sparing of tumor cells relative to normal tissues--a feature characteristic of irradiation with x rays--represents an advantage of neutrons in addition to their re ...	1976	981675
decreased cyclic amp and insulin responses to glucose in pancreatic islets of diabetic chinese hamsters.	the dose as well as the time kinetics of insulin and adenosine-3',5'-monophosphate (cyclic amp) responses to glucose were compared in pancreatic islets isolated from normal and diabetic chinese hamsters. the insulin content in diabetic islets was about one-half that in normal islets. insulin release in diabetic islets incubated for 10 min with glucose 60-1000 mg/100 ml was from one-third to one-half that in normal islets. glucose 1000 mg/100 ml stimulated three-fold increases in insulin release ...	1976	187518
a correlation between membrane glycopeptide composition and losses in concanavalin a agglutinability induced by db-camp in chinese hamster ovary cells.		1976	187438
identification of late dna-replicating regions in chinese hamster chromosomes using a brdu-giemsa technique.	asynchronous chinese hamster cells were labelled with brdu for 3 h prior to harvesting the metaphase cells. the late dna replicating sites became unifilarly brdu-substituted as compared to the earlier replicating sites having a normal dna constitution. those late replicating sites were identified by pale coloration or dot formation after treatment with 1.0 m na-phosphate solution (adjusted to ph 9.0 with supersaturated amount of nahco3 and at a temperature of 69-75 degrees c) and staining with g ...	1976	1001156
differential rates of sister chromatid exchanges between euchromatin and heterochromatin.	in two rodent species, the chinese hamster and the montane vole (microtus montanus), the rate of sister chromatid exchange was lower in constitutive heterochromatin than in euchromatin.	1976	793794
[changes in the cytochemical properties of chromatin after stimulating proliferation in a stationary culture of chinese hamster cells].	the first part of the prereplicative period in stimulated for cell proliferation steady-state culture of chinese hamster cells was studied cytochemically. investigation of the binding pattern of basic dye acridine orange and actinomycin d with cell nuclei and the melting profile of chromatin in situ suggests that one of the early events occurring in the course of stimulation of cell proliferation in steady-state culture is chromatin activation, i.e. changes in its physicochemical properties resu ...	1976	1034988
mutant alleles for hypoxanthine phosphoriboxyltransferase: codominant expression, complementation, and segregation in hybrid chinese hamster cells.	chinese hamster ovary cell mutants resistant to the purine analogs 6-thioguanine or 8-azaguanine have been isolated following mutagenesis with ethyl methane sulfonate. the activities of hypoxanthine phosphoribosyltransferase (hprt) in three such mutants have been found to exhibit an increased km for the substrate 5-phosphoribosyl-1-pyrophosphate. the isoelectric point of the mutant enzyme activity has also changed in two mutants. hybrid cells containing one mutant and one wild-type allele expres ...	1976	1027153
the isolation and preliminary characterization of somatic cell mutants resistant to the protein synthesis inhibitor-emetine.	emetine reversibly inhibits protein synthesis in chinese hamster ovary (cho) cells. stable mutants which are 20-80 fold more resistant to the cytotoxic action of the drug can be isolated in a single step at a frequency of about 2-5 x 10(-7). the frequency of such mutants is increased 30-50 fold by ethyl methane sulphonate mutagenesis, and the spontaneous rate of mutation to emetine resistance as measured by luria-delbruck fluctuation analyses is 4.9 x 10(-7) mutations per locus per generation. p ...	1976	975243
effects of halothane on dna synthesis and the presynthetic phase (g 1) in dividing fibroblasts.	the effects of halothane on deoxyribonucleic acid (dna) synthesis and events preceding dna synthesis have been examined in chinese hamster fibroblasts in culture.dna synthesis was studied by the uptake of 3h-thymidine during short periods of incubation that minimized effects on cells in the presynthetic phase (g1). halothane produced slight but significant dose-related depression of 3h-thymidine uptake (20 per cent depression with 2 per cent halothane). in a separate series of experiments, synch ...	1976	973693
chromosome breakage associated with organic mercury in chinese hamster cells in vitro [proceedings].		1976	972628
chromosome aberrations in oocytes of nmri mice and bone marrow cells of chinese hamsters induced with 3,4-benzpyrene.	this paper deals with mutagenicity tests with 3,4-benzpyrene in mice oocytes of the strain nmri and chinese hamster bone-marrow cells. the mutagenic effect of this hydrocarbon was observed in both test systems. investigations of bone-marrow chromosomes clearly show dose-response curves.	1976	972619
purine uptake by azaguanine-resistant chinese hamster cells.	in this study the resistance of a number of lines of chinese hamster ovary cells to azaguanine is examined. those which are drug resistant by virtue of a deficiency of hypoxanthine-guanine phosphoribosyltransferase (hprt) fail to take up any exogenous hypoxanthine or azaguanine. a second class of drug resistant cells which grow in the reverse selective hat medium and have levels of hprt in the range of the wild type parent line take up these purines at lower rates than the nonresistant cells and ...	1976	972164
fragmentation of chromatin with 125i radioactive disintegrations.	the dna in chinese hamster cells was labeled first for 3 h with [3h]tdr and then for 3 h with [125i]udr. chromatin was extracted, frozen, and stored at -30 degrees c until 1.0 x 10(17) and 1.25 x 10(17) disintegrations/g of labeled dna occurred for 125i and 3h respectively. velocity sedimentation of chromatin (dna with associated chromosomal proteins) in neutral sucrose gradients indicated that the localized energy from the 125i disintegrations, which gave about 1 double-strand break/disintegrat ...	1976	963201
use of lipid vesicles as carriers to introduce actinomycin d into resistant tumor cells.	unilamellar lipid vesicles have been used as a carrier vehicle to enhance the uptake of actinomycin d into an actinomycin d-resistant chinese hamster tumor cell line (dc-3f/adx). the dc-3f/adx cell line is resistant to actinomycin d as a result of its decreased capacity to transport actinomycin d across the plasma membrane and is able to grow in the presence of concentrations of actinomycin d that are cytotoxic for the sensitive parent cell line (dc-3f). incubation of resistant dc-3f/adx cells w ...	1976	975068
dotted chromosomes produced in sodium phosphate solution supersaturated with nahco3.	dotted chromosomes were consistently produced in both brdu and non-brdu substituted chinese hamster cells after treatment with 1.0 m na-phosphate solution, adjusted to ph 9.0 with a supersaturating amount of nahco3, and at a temperature of 80--95 degrees c. -- a series of changes in chromosome morphology was produced as the temperature of the solution was progressively increased. in brdu-treated cells, g-banding and differentially stained sister chromatids were sequentially produced prior to the ...	1976	63362
effects of tritiated thymidine on cell population kinetics.	this paper reports growth-kinetic data of chinese hamster tissue culture cells exposed at various times to differnt activities (0.05 muci/ml up to 10.0 muci/ml of tritiated thymidine. the analysis of the results aims at the determination of colony-size distribution and to the cellular capacity of reproduction after treatment which is reflected in the cell division spectrum within dialy intervals. the results of the growth-curves represented were converted into integrated curves of colony-size di ...	1976	968927
chinese hamster purine-nucleoside phosphorylase: purification, structural, and catalytic properties.	purine-nucleoside phosphorylase (ec 2.4.2.1; purine-nucleosideorthophosphate ribosyltransferase) was purified to apparent homogeneity from chinese hamster liver and kidneys and from v79 tissue culture cells. the enzymes from both sources appear to have identical structural and catalytic properties. a simple rapid radioisotope assay capable of detecting 0.1 nmol of product for both directions of the purine-nucleoside phosphorylase reaction is described using bio-rad cu2+ chelex in pasteur pipet c ...	1976	825137
chain elongation and joining of dna synthesized during hydroxyurea treatment of chinese hamster cells.	we have previously presented evidence that hydroxyurea treatment of synchronized g1 chinese hamster cells did not prevent the entry of cells into the dna synthetic period but that the dna synthesized during this period (in which total dna synthesis was severely depressed) was quite small (walters, r.a., tobey, r.a. and hildebrand, c.e. (1976) biochem. biophys. res. com. 69, 212-217). in view of the reported effects of hydroxyurea on deoxyribonucleoside metabolism and possible relationship to con ...	1976	963081
effects of ionizing radiation of rna metabolism in cultured mammalian cells. iii. specific reduction in mrna synthesis during resumed division and plateau phases following exposure to 800 rads of x irradiation.	the cell growth response of cultured chinese hamster ovary cells, line cho, to 800 rads of x irradiation involves a period of division delay, followed by a period of resumed division which terminates in a plateau phase. over 95% of the cells die eventually. no direct effects of rna or protein metabolism are evident during the delay period. during the resumed division and beginning of plateau phases, however, a specific and relatively constant reduction in mrna synthesis relative to messenger-lik ...	1976	963053
the effect of nitroimidazole and nitroxyl radiosensitizers on the post-irradiation synthesis of dna.	the modification of dna damage by three radiosensitizing drugs, present during gamma-irradiation of hypoxic chinese hamster cells, was investigated. both 2-methyl-5-nitroimidazole-1-ethanol (metronidazole) and 1-(2-nitro-1-imidazole)-3-methoxy-2-propranol (ro-07-0582) were found to cause large increases in the yield of dna single-strand breaks (ssb); triacetoneamine-n-oxyl (tan) was found to have only a small effect on ssb production. the three drugs tested did not inhibit the rejoining of ssb. ...	1976	1086839
cell volume growth after cell cycle block with chemotherapeutic agents.	the effects of various chemotherapeutic agents on the volume of chinese hamster v79 fibroblasts and murine lymphoma l5178y cells were studied by electronic volume spectroscopy. cells arrested in the division cycle by a chemotherapeutic block continued to grow in volume resulting in abnormally large cells unable to reduce their volume by cell division. this was observed in cells treated with colcemid, vinblastine, excess thymidine, hydroxyurea, ara-c, 5-fluorouracil, actinomycin-d and bleomycin, ...	1976	58726
mutagenic mechanism of 5-bromodeoxyuridine in chinese hamster cells.	resistance to 6-thioguanine was induced by 5-bromodeoxyuridine (budr) in synchronous chinese hamster cells. the yield of mutant colonies was not proportional to the amount of budr incorporated into dna; thus mutants were not due to mispairing of budr with guanine during replication. few mutants were induced until budr concentrations exceeded that of the intracellular thymidine triphosphate pool and mutant yield was depressed by addition of thymidine to the medium. these data suggest that budr ex ...	1976	958231
the influence of serum components on the growth and mutation of chinese hamster cells in medium containing 8-azaguanine.	low concentrations (less than or equal 20 mug/ml) of 8-azaguanine are 1000 fold more toxic to v79 chinese hamster cells in medium containing 10% dialyzed fetal calf serum than in medium containing 10% undialyzed serum. serum enzyme activity that converts ag to nontoxic 8-azaxanthine degrades ag at the same rate, whether or not the serum is dialyzed. however, cytotoxicity results similar to those obtained with us were produced in medium containing ds and 2.5 mug of hypoxanthine (hx)/ml (dsh). the ...	1976	958230
biochemical genetics of chinese hamster cell mutants with deviant purine metabolism: isolation, selection, and characterization of a mutant lacking hypoxanthine-guanine phosphoribosyltransferase activity by nutritional means.	mutants of the chinese hamster ovary cell derived from cho-k1 have been selected for lack of hypoxanthine-guanine phosphoribosyltransferase (ec 2.4.2.8) (hgprt) without the use of a drug-resistance protocol. the procedure depends on the use of a parental strain carrying a mutation making it unable to synthetize purines and thus dependent upon exogenously added purines for growth. the standard "budr-visible-light" procedure is then used to select those cells which can use adenine but cannot use h ...	1976	800293
energy metabolism in respiration-deficient and wild type chinese hamster fibroblasts in culture.	this paper presents a comparison of energy metabolism in wild type and respiration-deficient chinese hamster cells. from previous work (defrancesco et. al., '75) it was concluded that the mutant satisfies essentially all of its energy requirements from glycolysis and in this study we measure precisely the amount of glucose consumed and lactate produced per milligram increment of protein in exponentially growing cultures. from these measurements we calculate the amount of atp derived from glycoly ...	1976	8468
evaluation of the mutagenic potential of cyclohexylamine on spermatogonia of the chinese hamster.	in a cytogenetic study on the spermatogonia of chinese hamster, cyclohexylamine (neutral sulphate) was evaluated for mutagenic effects in comparison with an untreated control group and a group treated with the mutagenic compound cyclophosphamide, by assessing spermatogonial metaphases of treated chinese hamster for chromosomal structural changes. each test group comprised 8 male hamsters selected at random. approximately 100 metaphases from each animal were assessed. the doses were 5 x 150 mg cy ...	1976	958236
the significance of dna damage in the cell cycle sensitivity of chinese hamster ovary cells to bleomycin.	chinese hamster ovary cells have been treated with bleomycin at various stages in the cell cycle. mitotic cells, which exhibit least survival, show the greatest amount of dna strand breakage and a marked inhibition of dna replication in the subsequent s phase. strand-rejoining experiments suggest that this is primarily due to differences in the amount of damage produced in the dna but does not exclude the possibility that cells at the various cell stages also differ in their ability to repair th ...	1976	58718
hypoxanthine transport by cultured chinese hamster lung fibroblasts.	the uptake of hypoxanthine by chinese hamster lung fibroblasts grown in tissue culture was studied in wild type clones and 8-azaguanine-resistant mutant clones devoid of hypoxanthine-guanine phosphoribosyltransferase. wild type fibroblasts rapidly accumulate [3h]hypoxanthine from the medium and over 80% of the intracellular radioactivity is found in acid-soluble nucleotides. the phosphoribosyltransferase-deficient clones accumulate much lower levels of hypoxanthine and over 85% of the intracellu ...	1976	182679
a respiration-deficient chinese hamster cell line with a defect in nadh-coenzyme q reductase.	we have recently described a chinese hamster cell line with a greatly reduced rate of respiration. in this report we conclude that the defects is in nadh-coenzyme q reductase (nadh oxidase), the first part of the electron transport chain. the conclusion is based on the following observations. (a) in this and in the earlier report we determined that the relevant enzymes of the krebs cycle are present and active. (b) oxygen consumption by isolated mitochondria is normal when driven by succinate an ...	1976	947896
chemical transformation of chinese hamster cells: ii. appearance of marker chromosomes in transformed cells.	the chromosomes of 12 samples of cultured chinese hamster kidney and prostate cells (4 normal and 8 transformed), whose tissue culture properties have already been described (kirkland, 1976) have been examined for numerical change and for the appearance of abnormal markers. six transformed kidney subclones contained a consistent telocentric marker not present in the normal parental cell, and giemsa banding demonstrated this to be the centromere and the long (q) arm of the number 4 chromosome in ...	1976	986826
chemical transformation of chinese hamster cells. i. a comparison of some properties of transformed cells.	fifty-one subclones from carcinogen-treated cells of 3 tissues (kidney, liver and prostate) of the male chinese hamster have been studied to determine the relationships of 3 criteria of in vitro transformation: morphological change, increased plating efficiency and growth in soft agar. there was no correlation between increased plating efficiency and the other 2 parameters. morphological change was not always easily recognisable, particularly in cells derived from liver, and was not always a sta ...	1976	962992
action of a platinum complex [cis-dichlorobis (cyclopentylamine)-platinum (ii)] on chinese hamster ovary cells in vitro.	cis-dichlorobis(cyclopentylamine)platinum (ii) (dbcp) treatment of chinese hamster ovary (cho) monolayer cell cultures was found to cause: (1) growth inhibition due to an impaired g1 leads to s transition and formation of a non-cycling compartment; (2) delayed cell death (with a maximum at 72 h after treatment); (3) decrease of [14c] tdr incorporation into dna. part of the surviving cell population was subject to non-lethal damage. the do values of the dose--survival curves were 9.2 and 14 mug/m ...	1976	954143
evidence for the formation of hybrid dna during mitotic recombination in chinese hamster cells.	direct evidence is provided for the formation of hybrid dna during mitotic recombination in cho cells. the cells were labeled for one round of replication in medium containing budr, so that the density of the dna was heavy light (hl) and then returned to light medium. further dna synthesis, during either repair or chromosome replication, can only result in hl or fully light (ll) dna; however, the formation of hybrid dna as part of the process of recombinational repair will produce some fully hea ...	1976	954106
configurational changes in chromatids from helical to banded structures.	induction of configurational changes in the helical chromatids of air dried chromosomes was used to explore the mechanism of g-banding. from the water-giemsa stained metaphase spreads of chinese hamster cells, chromosomes having clearly helical chromatids were selected and photographed. then the chromosomes were decolorized, treated with trypsin, and restained with saline-giemsa (1x ssc). such procedures were repeatedly carried out upon the same chromosomes. subsequent examination of the chromos ...	1976	976013
effect of hoechst 33258 on chinese hamster chromosomes.	cells of the chinese hamster strain c-125 were treated for different time intervals with h 33258, a bibenzimidazole derivative. the same compound was used to stain fixed cells of the same strain. h 33258 induced in cells in culture specific areas of reduced spiralization on the metaphase chromosomes of some cells. these probably correspond to dna segments rich in a-t bases interspersed along the chromosomes. probably h 33258 acts during s period of cell cycle. the banding obtained by staining wi ...	1976	61845
effects of actinomycin d and puromycin on colchicine-induced endoreduplication in chinese hamster cells in vitro.	experiments were carried out to study the events through which the process of endoreduplication occurs after treatment with colchicine in chinese hamster cells cultivated in vitro, and to analyse the differences between the processes leading to normal mitosis and those leading to endoreduplication. chinese hamster cells (line c-125) were treated with colchicine (10(-4) m) for 1 h, in order to induce endoreduplication. before and after colchicine treatment the cultures were treated at various int ...	1976	954141
temporal sequence of mutation for 6-thioguanine resistance in synchronised chinese hamster cells.	the temporal sequence of mutation to 6-thioguanine resistance was studied in chinese hamster ovary cells synchronised in s phase. the number of resistant mutants induced following exposure to pulses of bromodeoxyuridine and subsequent selection was significantly greater if budr pulses were administered during the first, rather than the second half of s phase. the results are interpreted as indicating that the gene responsible for 6-thioguanine resistance is replicated during the first half of s ...	1976	21369911
enhancement of postreplication repair in chinese hamster cells.	alkaline sedimentation profiles of pulse-labeled dna from chinese hamster cells showed that dna from cells treated with n-acetoxy-acetylaminofluorene or ultraviolet radiation was made in segments smaller than those from untreated cells. cells treated with a small dose (2.5 mum) of n-acetoxy-acetylaminofluorene or (2.5 j-m-2) 254-nm radiation, several hours before a larger dose (7-10 mum) of n-acetoxy-acetylaminofluorene or 5.0 j.m-2 of 254 nm radiation, also synthesized small dna after the secon ...	1976	1065893
the selection of chinese hamster cells deficient in oxidative energy metabolism.	a selection scheme based on the nutritional requirements of a previously described respiration-deficient chinese hamster line has been used to isolate new mutants defective in oxidative energy metabolism. three of the primary characteristics of this type of mutant are (1) a strict dependency on the continued presence of glucose for survival; (2) a drastic reduction in the rate of oxygen consumption; (3) an inhibition of krebs cycle activity resulting in auxotrophy for asparagine and carbon dioxi ...	1976	1027147
the ultra-fast repair of single-strand breaks in dna of gamma-irradiated chinese hamster cells.		1976	1087297
modulation of membrane drug permeability in chinese hamster ovary cells.	the kinetics of colchicine uptake into chinese hamster ovary cells have been investigated and found to be consistent with an unmediated diffusion mode. a variety of compounds such as local anesthetics and non-ionic detergents as well as drugs such as vinblastine, vincristine, daunomycin and actinomycin d potentiate the rate of colchicine uptake into these cells and into colchicine resistant mutants. in all cases, higher concentrations of these compounds were required to stimulate colchicine upta ...	1976	999943
carbon-13 nuclear magnetic resonance spectroscopy of suspensions of chinese hamster ovary cells specifically enriched with (methyl-13c)choline.		1976	999821
altered leucyl-transfer rna synthetase from a mammalian cell culture mutant.	altered leucyl-trna synthetase from a mammalian cell culture temperature-sensitive mutant, tshl, was compared with enzyme from normal wild type chinese hamster ovary cells. the mutant enzyme had a km for leucine four times larger than that of wild type and enzyme levels 3-10% that of wild type. the presence of trna was necessary during in vitro heating of the mutant enzyme to allow expression of thermolability while the presence of trna protected wild type enzyme against thermal inactivation. th ...	1976	11833
the effect of fractionated exposure to thio-tepa upon chinese hamster cells in vitro.	the dependence of the surviving fraction of chinese hamster cells in vitro upon the concentration of thio-tepa, upon the duration of drug exposure and upon fractionation of drug exposure has been studied. given a constant exposure time, the surviving fraction decreased according to a "shoulder" curve with increasing concentration. given a constant concentration, the surviving fraction decreased exponentially with increasing exposure time. splitting exposure of 60 min into two 30 minutes' exposur ...	1976	138276
cytotoxic effects of hyperthermia and adriamycin on chinese hamster cells.	chinese hamster cells, exposed to simultaneous hyperthermia (43 degrees c) and adriamycin (adm), were intially sensitized to the cytotoxic activity of adm. if the duration of the combined treatment exceeded about 30 minutes, however, the cells became refractory to additional killing by adm. if heat was applied before adm exposure, the cells also could be rendered insensitive; this state persisted so that 24 hours after a 50-minute exposure to 43 degrees c, the cells still showed considerable res ...	1976	1003542
laser uv microirradiation of interphase nuclei and post-treatment with caffeine. a new approach to establish the arrangement of interphase chromosomes.	laser uv microirradiation of chinese hamster interphase cells combined with caffeine post-treatment produced different patterns of chromosome damage in mitosis following irradiation of a small area of the nucleus that may be classified in three categories: i)intact metaphase figures, ii)chromosome damage confined to a small area of the metaphase spread, iii)mitotic figures with damage on all chromosomes. category iii might be the consequence of a non-localized distortion of nuclear metabolism. b ...	1976	1002167
carbohydrate energy sources for chinese hamster cells in culture.		1976	995956
stimulation of informosomal rna synthesis in cultured chinese hamster cells exposed to low levels of cadmium.		1976	992074
a surface glycoprotein modulating drug permeability in chinese hamster ovary cell mutants.	chinese hamster ovary cells selected for resistance to colchicine display pleiotropic cross-resistance to a wide range of amphiphilic drugs. the drug-resistant phenotype is due to a membrane alteration which reduces the rate of drug permeation. surface labelling studies reveal that drug-resistant chinese hamster ovary cell membranes possess a carbohydrate-containing component of 170 000 daltons apparent molecular weight which is not observed in wild type cells. through studies of the metabolic i ...	1976	990323
quantized generation time in mammalian cells as an expression of the cellular clock.	the distribution of possible generation times in mammalian cells does not appear to be continous within the limits of range for each cell type; rather, generation time is quantized in multiples of 3-4 hr. synchronous cultures of chinese hamster v79 cells were prepared using manual and automated methods to select and stage mitotic cells. using synchronous cultures and time-lapse video tape microscopy, it was possible to show that generation times within a population of mitotically selected cells ...	1976	1069287
5-bromodeoxyuridine-dna strand symmetry and the repair of photolytic breaks in chinese hamster cell chromosomes.	experiments described in this report quantiate the black light sensitivities of chinese hamster lung (chl) cells containing brdurd-dna of defined composition. cesium chloride equilibrium gradient centrifugation provides estimates both of the percent thymidine replacement by brdurd and of the symmetry (unifilar versus bifilar) of brdurd incorporation into the chromosomal dna duplexes. radiation damage to brdurd-substituted chl cell dna and its repair in situ also have been assessed by alkaline su ...	1976	1069276
isolation and characterisation of chinese hamster cells resistant to 5-fluorodeoxyuridine.		1976	130246
inhibition by caffeine of post-replication repair in chinese hamster cells treated with cis platinum (ii) diamminedichloride: the extent of platinum binding to template dna in relation to the size of low molecular weight nascent dna.	treatment of chinese hamster lung v79-379a cells with the anti-tumour agent cis platinum (ii) diamminedichloride, (cis pt(ii)), resulted in an immediate recuction in the rate of dna synthesis. sedimentation of newly synthesised dna through alkaline sucrose gradients revealed it to be approximately the same size as that obtained from untreated cells. in contrast, in the presence of 0.75 mm caffeine, the rate of dna synthesis rapidly returned to control levels, although sedimentation analysis show ...	1976	1253338
increased cell killing by metronidazole and nitrofurazone of hypoxic compared to aerobic mammalian cells.	nitromidazole and nitrofuran derivatives comprise a large family of compounds, some of which have been shown to be hypoxic cell specific radiosensitizers in vivo and in vitro. the effects of metronidazole (2-methyl-5-nitroimidazole-1-ethanol) and nitrofurazone (5-nitro-2-furaldehyde semicarbazone) were studied on cell viability in vitro in the presence of air or nitrogen in the absence of radiation. exponential-phase chinese hamster ovary cells were placed in suspension culture in complete mediu ...	1976	1253180
[damaging effect of 3h-uridine on tissue culture cells during the logarithmic and stationary phases of growth].	the chinese hamster fibroblasts entered the stationary phase of growth after 5.5 days of cultivation. the induction of the culture proliferation occurred within the first 4 hrs of cultivation in the fresh nutrient medium. after addition of 3h-uridine in high concentration and with high specific activity (75 micron cu/m and 23 cu/mm), in the stationary phase a lesser number of cells with aberrations and a higher mitotic index were noted than in the logarithmic phase. 3h-uridine injured the cells ...	1976	1036114
[development of spontaneous mutations in somatic mamalian cells and dna replication. ii. expression of gene mutations in cultured cells].	the dependence of spontaneous rate and phenotypic expression of 6-mercaptopurine resistance mutations of dna replication synthesis was studied in cultured chinese hamster cells. spontaneous mutations arising with a constant rate per cell per time unit independently on dna replication rate were shown to be expressed only in the course of subsequent cell divisions. the frequency of n-nitrosomethylurea induced mutations in cells with reduced and normal dna replication rate is approximately the same ...	1976	1034583
biochemical genetics of chinese hamster cell mutants with deviant purine metabolism iii. isolation and characterization of a mutant unable to convert imp to amp.	the isolation and characterization of a new mutant of chinese ovary cells (cho-k1) is described. this mutant, ade-h, has the following properties: (1) it forms a new genetic complementation group; (2) it specifically requires adenine for growth and will not grow on aminoimidazole carboxamide (aic) or hypoxanthine; (3) it accumulates imp; (4) it cannot synthesize adenine nucleotides; (5) its phenotype can be mimicked by treatment of cho-k1 (the wild type parental strain) with hadacidin, an inhibi ...	1976	1028159