TitleAbstractYear(sorted ascending)
alpha-amanitin resistance of rna polymerase ii in mutant chinese hamster ovary cell lines.a number of mutant chinese hamster ovary (cho) cell lines resistant to the cytotoxic action of alpha-amanitin have been isolated. the alpha-amanitin sensitivity of the different mutant cell lines varied widely, but correlated well with the alpha-amanitin sensitivity of the rna polymerase ii activity in each of these mutant cell lines. in comparison with the rna polymerase ii of wild-type cells, three mutants, ama39, ama6, and amal, required respectively 2- to 3-fold, 8- to 10-fold, and about 800 ...19761262341
carcinogenic effects of different nitroso-compounds in chinese hamsters. ii. n-nitrosomorpholine and n-nitrosopiperidine.a total of 320 chinese hamsters (cricetulus griseus) (ch) were subcutaneously (s.c.) treated with 1/5, 1/10, or 1/20 ld50 of n-nitrosomorpholine (nm) or n-nitrosopiperidine (np). in the ch, nm and np both produced up to a 100% rate of papillomas of the cheek pouch, tongue, pharynx, esophagus and forestomach. occasionally squamous cell carcinomas also developed in these organs. a high rate of hepatomas was realized by np.1976132034
effects of ultraviolet irradiation on the rate and sequence of dna replication in synchronized chinese hamster cells.the effects of ultraviolet light (uv) irradiation on the rate of dna replication in synchronized chinese hamster ovary (cho) cells were investigated. a technique for measuring semiconservative dna replication was employed that involved growing the cells in medium containing 5-bromodeoxyuridine and subsequently determining the amount of dna that acquired hybrid buoyant density in cscl density gradients. one of the advantages of this technique was that it allowed a characterization of the extent o ...19761276380
galactokinase mutants of chinese hamster somatic cells resistant to 2-deoxygalactose.the growth of chinese hamster somatic cells was inhibited by 0.2 mg/cc of 2-deoxygalactose. mutants partially or fully resistant to 2-deoxygalactose were isolated in a single-step or two-step selection. some of them did not grow as well as the wild type; one of them which lacked galactokinase(ec. activity did not grow at all in galactose medium. the galactokinase kinetic properties (vmax & kmax of the other mutants and of the wild type were different. therefore resistance resulted either ...19761269916
a study of the morphological changes in the small intestine of the spontaneously diabetic chinese hamster.several morphological changes were observed microscopically in the small intestine of some diabetic chinese hamsters. although some alterations lacked statistical significance due to variation, most diabetics displayed a greater incidence and severity compared with nondiabetic controls. the following structural deviations were seen in the small intestines of some diabetics: increased surface area, elevated number of goblet cells per villus, decreased muscle thickness with connective tissue infil ...19761269845
modification of the response to actinomycin d-induced sublethal damage by simultaneous recovery from potentially lethal damage in mammalian cells.exponentially growing cells and cells that were allowed to enter a plateau or nondividing state of growth by depleting the medium of growth-essential nutrients were used in these studies. nondividing chinese hamster ovary cells in vitro are less sensitive to actinomycin d (amd) than are exponentially growing cells. the cells were tested for their ability to recover from amd-induced potentially lethal damage (pld) or sublethal damage. the proliferating and the nonproliferating cells do not recove ...19761268824
formation of thymidine kinase and deoxycytidylate deaminase in synchronized cultures of chinese hamster cells temperature-sensitive for dna synthesis.cytosol thymidine kinase (tk) and deoxycytidylate (dcmp) deaminase formation was investigated in synchronized cultures of k12 chinese hamster cells which have a temperature-sensitive lesion affecting the initiation of dna synthesis. enzyme formation was found to be cycloheximide-sensitive and also temperature-dependent. beginning at about six hours after addition of medium with 10% calf serum to serum-depleted k12 cultures, cytosol tk and dcmp deaminase activities increased when the cultures wer ...19761262406
isolation and partial characterization of three methotrexate-resistant phenotypes from chinese hamster ovary cells.three mechanisms for resistance to methotrexate (mtx) have been identified in chinese hamster ovary (cho) cells selected from resistance to this drug. first-step selections produce cells with either an apparent structural alteration in the enzyme dihydrofolate reductase (class i), or a decreased permeability to the drug (class ii). mutagenesis with ethyl methanesulfonate increases the proportion of mtx-resistant cells 5-10-fold. second-step selections to higher resistance using class i resistant ...19761028172
isolation of mutants lacking branched-chain amino acid transaminase.variants of the chinese hamster ovary cell have been isolated which can no longer grow when valine, leucine, or isoleucine is replaced in the culture medium by its respective alpha-keto acid: alpha-ketoisovaleric acid, alpha-ketoisocaproic acid, or alpha-keto-beta-methylvaleric acid. these variants lack branched-chain amino acid transaminase activity. evidence is presented indicating these variants to be single gene mutants. genetic evidence is also presented confirming previous biochemical evid ...19761028171
biochemical genetics of chinese hamster cell mutants with deviant purine metabolism. iv. isolation of a mutant which accumulates adenylosuccinic acid and succinylaminoimidazole carboxamide ribotide.the production, isolation, and characterization of a new complementation group (ade-i) of adenine-requiring mutant of chinese hamster cells (cho-k1) is described. this mutant accumulates two intermediates of purine biosynthesis, both of which contain an aspartate moiety. one of these is shown to be adenylosuccinic acid (amps) by chromatographic analysis, while evidence is presented that strongly suggests the other intermediate is succinylaminoimidazole carboxamide ribotide (saicar). thus, ade-i ...19761028168
biochemical characterization of azetidine carboxylic acid-resistant chinese hamster cells.we have isolated variants of chinese hamster lung (chl) fibroblasts with decreased sensitivity to the toxic proline analog, l-azetidine-2-carboxylic acid (azca). resistance to azca is a stable characteristic of these cell lines since it is maintained after 40 generations in nonselective medium. two azca-resistant cell lines overproduce and excrete more proline than wild-type cells. furthermore, azca rapidly inhibits the synthesis of proline from glutamic acid in wild-type but not the resistant c ...1976954094
the rna polymerase ii of an alpha-amanitin-resistant chinese hamster ovary cell line.amal, an alpha-amanitin-resistant mutant of the chinese hamster ovary cell line, contains an rna polymerase activity which elutes from deae-sephadex at a salt concentration characteristic of an rna polymerase ii, but which is not sensitive to alpha-amanitin at levels where the polymerase ii of wild-type cells is strongly inhibited. this result suggests that amal owes its amanitin-resistant phenotype to a mutation affecting one of its genes for rna polymerase ii. to test this hypothesis, we purif ...1976954093
cytotoxicity, mutations and dna damage produced in chinese hamster cells treated with streptozotocin, its analogs, and n-methyl-n'-nitro-n-nitrosoguanidine.the activities of streptozotocin (sz), three structural analogs of sz, and n-methyl-n'-nitro-n-nitrosoguanidine (mnng) in producing cytotoxicity, mutations to 8-azaguanine (8-azg) resistance, and dna damage (single-strand breaks) in v79 chinese hamster cells have been examined. these three biological processes appear to be associated. mnng was about 10(3) times more active on a molar basis than sz, and the activities of the analogs fell within these extremes.1976130988
induction of stable protein-deoxyribonucleic acid adducts in chinese hamster cell chromatin by ultraviolet light.ultraviolet (uv)-light-mediated formation of protein-dna adducts in chinese hamster cell chromatin was investigated in an attempt to compare chromatin alterations induced in vitro with those observed in vivo. three independent methods of analysis indicated stable protein-dna associations: (1) a membrane filter assay which retained dna on the filter in the presence of high salt-detergent; (2) a sepharose 4b column assay in which protein eluted cincident with dna; and (3) a cscl density gradient e ...19765110
independent fluctuations of cytidine and adenosine diphosphate reductase activities in cultured chinese hamster fibroblasts.the activities of cdp and adp reductases were determined throughout the cell cycle of chinese hamster fibroblasts synchronized by partial deprivation of isoleucine. both enzyme activities were increased in s phase as compared to g1 phase. cdp reductase increased about 8-fold while adp reductase increased about 2.5-fold. the ratio of cdp to adp reductase was 0.26 at the g1 and early s phases of the cell cycle; the ratio was increased to 0.83 by late s phase. addition of actinomycin d or cyclohexi ...19761260052
carcinogenic effects of different nitroso-compounds in chinese hamsters. i. dimethylnitrosamine and n-diethylnitrosamine.three hundred and twenty chinese hamsters (cricetulus griseus) (ch) were treated (s.c.) with 1/5, 1/10 or 1/20 ld50 of dimethylnitrosamine (dmn) or n-diethylnitrosamine (den). these substances, in several respects, showed a different organotropy in this species than in both the syrian golden (sgh) and the european hamster (eh). in ch, den produced up to 100% squamous cell papillomata and occasionally also carcinomata of the cheek pouch, tongue, pharynix, oesophagus and forestomach. with den a hi ...19761268032
quantification of mitochondria during the cell cycle of chinese hamster cells. 19761261614
effects of laser uv-microirradiation (lambda = 2573 a) on proliferation of chinese hamster cells. 19761257404
the effect of combined treatment with a platinum complex and ionizing radiation on chinese hamster ovary cells in vitro.cis-dichlorobis(cyclopentylamine)platinum ii (dbcp) belongs to the group of platinum complexes which have recently been reported to have anti-tumour activity. its cytotoxic activity in cho cells is not cell-age-dependent, but enhancement of the effect of ionizing radiation is both dose-and cell cycle phase-dependent. in asynchronous cell populations dbcp acts as a dose-modifying factor for ionizing radiation. doses of dbcp reducing survival of cho cells to 26% and 4% applied 1 h before irradiati ...1976944586
chromosome analyses in cell cultures of the chinese hamster after application of cadmiumsulphate.cell cultures of a chinese hamster cell line were treated with cdso4 in concentrations of between 10(-4) and 10(-8) mol/l for different time periods. after a treatment of 16 h the mitotic index was reduced. strong stickiness and pycnosis of chromosomes occurred at the highest concentrations. a treatment period of 3 h with concentrations of 10(-5) and 10(-4) mol/l without additional application of colcemid and hypotonic solution yielded a stathmokinetic effect. the mitotic index increased, mitose ...1976934175
sequence of centromere separation of mitotic chromosomes in chinese hamster.chromosome preparation in late metaphase cells from bone marrow of colcemid treated male chinese hamsters were used to analyse the sequence of separation of sister centromeres. chromatids of chromosomes 2 and 1 are the first ones to separate at centromeres, followed by members of group b, d and c. some acrocentric chromosome is always the last one to separate at the centromere. the data point to a possible correlation between the position of a centromere in the separation sequence in the genome ...19761253649
hydroxyurea does not prevent synchronized g1 chinese hamster cells from entering the dna synthetic period. 19761259759
g2 block in chinese hamster cells induced by x-irradiation, hyperthermia, cycloheximide, or actinomycin-d. 19761265214
x-ray-induced mutants resistant to 8-azaguanine. ii. cell cycle dose response.synchronous chinese hamster ovary cells were irradiated in g1 or s phase. colony survival in alpha mem medium with dialyzed serum was determined with or without 15 mug/ml 8-azaguanine (ag). an expression period of over three generations (multiplicity of 20) was utilized, with expression times ranging from 58 to 114 h. both g1 and s phase were practically identical in sensitivity to x-ray-induced mutations, with mutant frequency/viable cell/rad ranging from 1 x 10(-7) (75-100 rad) to 8 x 10(-7) ( ...19761264111
x-ray-induced mutants resistant to 8-azaguanine. i. effects of cell density and expression time.asynchronous chinese hamster ovary cells were irradiated and colony survival in alpha mem medium with dialyzed serum was determined with or without 15 mug/ml 8-azaguanine (ag). data indicated that a reproducible assay for the system was dependent upon controlling cell density at least two days prior to induction as well as throughout the expression period. generally, spontaneous and radiation-induced mutant frequencies decreased when cell densities exceeded a critical density of 3-6 x 10(4) cell ...19761264110
selection and characterization of chinese hamster ovary cells resistant to the cytotoxicity of lectins.chinese hamster ovary (cho) cells selected in a single step for resistance to the cytotoxicity of the lectin from red kidney beans (pha) behave as authentic somatic cell mutants. the pha-resistant (phar) phenotype is stable in the absence of selection; its frequency in a sensitive-population is increased several-fold by mutagenesis; and it behaves recessively in somatic cell hybrids. the activity of a specific glycosyl transferase which transfers n-acetylglucosamine (glcnac) to terminal alpha-ma ...19761262042
non-histone protein synthesis during g1 phase and its relation to dna replication.the kinetics of non-histone chromosomal protein (nhcp) synthesis were studied in chinese hamster ovary (cho) plateau phase cells stimulated to proliferate and were compared to nhcp synthesis kinetics in two populations of synchronous g1 traversing cells. in all cases, nhcp synthesis rates increase 3- to 5-fold as cells traversed g1 and attained maximum values one hour before semi-conservative dna replication began. similar to results in synchronous g1 cells, the molecular weight distributions of ...19761254652
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 ...19761253338
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 ...19761253180
negative pion irradiation of mammalian cells. 1. survival characteristics of monolayers and spheroids of chinese hamster lung cells.monolayers and spheroids of chinese hamster cells (v79) were subjected to negative pion irradiation under aerobic conditions. r.b.e. values in the pion peak of 1-8 and 1-5 were obtained for monolayers and spheroids, respectively, whereas the r.b.e. for the plateau was found to be slightly higher than 1. in addition, it was observed that the higher resistance of the v79 spheroid cells than the monolayers to gamma-irradiation is not diminished in the pion peak, suggesting that the underlying pheno ...19761083848
cytological evidence for switches in polarity of chromosomal dna.from the types of ring chromosomes induced in x-irradiated chinese hamster ovary (cho) cells, we deduce the existence of switches in the polarity of chromosomal dna; if there is a continuous dna double helix along the full length of the chromosome then the polarity switches imply 3'-3' and 5'-5' phosphodiester linkages. the resolution of the method is such that we estimate that there is one polarity switch for every 10(9) normal 3'-5' phosphodiester bonds.19761062800
dna strand breaks, repair, and survival in x-irradiated mammalian cells.the yields of unrepairable single-and double-strand breaks in the dna of x-irradiated chinese hamster cells were measured by low-speed neutral and alkaline sucrose density gradient sedimentation in order to investigate the relation between these lesions and reproductive death. after maximal single-strand remoining, at all doses, the number of residual single-strand breaks was twice the number of residual double-strand breaks. both double-strand and unrepairable single-strand breaks were proporti ...19761062792
biochemical selection systems for mammalian cells: the essential amino acids.the essential amino acid requirement of cultured mammalian cells can be satisfied by 19 amino acid derivatives. this finding (a) confirms the results of animal nutritional studies and (b) identifies 19 essential amino acid derivatives and should permit the isolation of a new class of auxotrophic mutants. five naturally occurring auxotrophic markers have been detected in this survey; namely, inability to utilize cystathionine and citrulline in chinese hamster ovary (cho) cells, inability to metab ...19761028167
isolation and characterization of temperature-sensitive mutants of chinese hamster ovary cells after treatment with uv and x-irradiation.the isolation of ten conditionally lethal temperature-sensitive mutants of the chinese hamster ovary cell (cho-kl, pro-) by the budr-visible light selection procedure described. treatment with radiation at doses known to cause single gene mutation in mammalian cells increases the mutation frequency by a factor of at least 14. these mutants will grow with normal plating efficiency at 34.5 degrees but will not grow at 39.5 degrees. complementation analysis by two independent methods indicates that ...19761028162
carcinogenic effects of different nitroso-compounds in chinese hamsters: n-dibutylnitrosamine and n-nitrosomethylurea.three hundred and twenty chinese hamsters (cricetulus griseus) (ch) were subcutaneously (s.c.) treated with 1/5, 1/10 or 1/20 the mean lethal dose (ld50) of n-dibutylnitrosamine (dbn) or n-nitrosomethylurea (nmu). in several respects these two substances produced the same organotropy in the ch as in the syrian golden (sgh) and european hamsters (eh). dbn prolonged lung tumours and neoplasms of the injection site. nmu induced tumours of the injection site only.19761016942
comparative investigations on cytogenetic effects of x-irradiation on the germinal epithelium of male mice and chinese 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 ...19761002141
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.1976976637
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. ...1976939563
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.19761257447
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.1976989012
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 ...1976800380
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.1977598845
tyzzer's disease in the chinese hamster (cricetulus griseus). 1977599880
effects of ultraviolet light on synchronized chinese hamster ovary cells; potentiation by hydroxyurea.we have examined the effects of hydroxyurea on u.v.-irradiated chinese hamster cho-ki cells. ultraviolet irradiation followed by incubation with hydroxyurea causes only slight disruption of dna and chromosome structure in cho-ki cells compared with hela cells. there is, however, a clear potentiation by hydroxyurea of the u.v. killing of cho-ki cells, which is most pronounced at those points in the cycle which are reported to have small dna precursor pools. this potentiation is reduced when dna p ...1977599176
pesticide induced ouabain resistant mutants in chinese hamster v79 cells.the effect of 3 insecticides (chlordane, dieldrin and carbaryl) and one herbicide (2,4-d-fluid) was studied on the induction of ouabain-resistant mutants in chinese hamster v79 cells at concentrations approaching the environmental protection agency (epa) tolerance limits. the kinetics and dose range for cytotoxicity were determined by colony formation assay. results showed that these compounds enhanced the number of ouabain-resistant mutants and acted as weak mutagens.1977413633
retention of the glycocalyx after cell detachment by egta.chinese hamster ovary cells were examined ultrastructurally following several detachment procedures. alterations in the surface glycoproteins were observed by using ruthenium red in the fixation procedure. trypsin removed a major portion of the cells glycocalyx and formed spherical cellular configurations. egta detached cells were also spherical, however, their glycocalyx appeared to remain although redistributed over the cell surface. kinetic studies showed no alterations in subsequent populati ...1977411829
a search for allelic recombination in chinese hamster cell hybrids.mutants resistant to 6-thioguanine were selected from cho cells which were either temperature sensitive or proline requiring. these mutants were stable and had low levels of hypoxanthine guanine phosphoribosyl transferase (hgprt). hybrids were selected which were heteroallelic at the hgprt locus and complementation between the mutants used was not observed. interallelic recombination at this locus would generate hgprt+ cells which could be selected in littlefield's hat medium. selection experime ...1977600266
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 ...1977924693
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 ...197772637
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 ...1977914817
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 ...1977200277
histone composition of nucleosomes isolated from cultured chinese hamster cells.nuclei isolated from cultured chinese hamster cells were treated with micrococcal nuclease and lysed, and the resulting chromatin subunit classes (nucleosomes) were purified by sedimentation and resedimentation through isokinetic sucrose gradients. nucleosomes isolated from [3h]thymidine-labeled cells were analyzed for dna size using both polyacrylamide gel and electron microscopic techniques. nucleosomes isolated from [14c]lysine-labeled cells were analyzed for protein content using a sodium do ...1977911804
properties of carbohydrate utilising variants of chinese hamster cells.variants of chinese hamster ovary cells (cho-k1) have been isolated which can grow on one of the following carbohydrates: lactose, sucrose, ribose or lactate. the ribose+ clones grow at the same rate on glucose as the parental cells whereas the others grow more slowly. with the exception of one ribose+ clone all excrete lactic acid while growing on glucose; none excrete significant amounts of lactic acid while growing on the alternative energy source. wild-type cells and the variants accumulate ...1977610885
a method for the isolation of chinese hamster cell variants with an altered ability to utilise carbohydrates.chinese hamster ovary cells (cho-k1) are able to utilise only a few carbohydrates for growth such as glucose, mannose, fructose and galactose. they do not grow on ribose, lactose, sucrose, glycerol, lactate, pyruvate, citrate, succinate, fumarate or malate nor on glycogenic or ketogenic amino acids. after mutagenesis and selection in glucose free medium supplemented with various, individual, growth substrates, we have isolated single-cell derived clones which are now able to grow on one of the f ...1977610884
induction of sister chromatid exchanges in chinese hamster cells by carcinogenic mutagens requiring metabolic activation. 1977593288
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 ...1977564086
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, ...1977341374
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 ...1977270740
cell cycle variation associated with feeder effects in cultures of chinese hamster fibroblasts. 1977913497
effect of distamycin a on chinese hamster chromosomes. 197771997
a quantitative assay of mutation induction at the hypoxanthine-guanine phosphoribosyl transferase locus in chinese hamster ovary cells (cho/hgprt system): development and definition of the assay is described for the measurement of mutation induction at the hypoxanthine-guanine phosphoribosyl transferase (hgprt) locus in chinese hamster ovary (cho) cells utilizing resistance to 6-thioguanine (tg). optimal selection conditions are defined for such parameters as phenotypic expression time prior to selection, and tg concentration and cell density which permits maximum mutant recovery. the nature of the tg-resistant mutants is characterized by several physiological and biochemical m ...1977917038
effect of caffeine on sister chromatid exchanges and chromosomal aberrations induced by mutagens in chinese hamster cells. 1977917034
effect of tumor promoting agents on mutation frequencies in cultured v79 chinese hamster cells. 1977917033
mutagenic and epigenetic influence of caffeine on the frequencies of uv-induced ouabain-resistant chinese hamster cells.caffeine, given as a post-treatment to uv-irradiated chinese hamster cells in vitro, modified the frequency were increased when caffeine was added only for the dna repair and mutation fixation period. when caffeine was added after the dna repair and mutation fixation period, or immediately after dna damage and for the entire repair and selection period, mutation frequencies were reduced. a hypothesis, given to explain both results, is that caffeine, by blocking a constitutive "error-free" postre ...1977917032
forward and reverse mutations affecting the kinetics and apparent molecular weight of mammalian hgprt.chinese hamster cells selected for resistance to 8-azaguanine following mutagenesis have hypoxanthine-guanine phosphoribosyltransferase (hgprt; e.c. with characteristics compatible with different mutations in the structural gene for that enzyme. using immunopurification and sds-polyacrylamide electrophoresis, mutants producing antigenically active forms of the enzyme can be analyzed for changes in the molecular weight of hgprt. enzyme subunits from mutants rjk3 and rjk39 are reduced in ...1977912745
discrete electrophoretic products of mitochondrial protein synthesis in the chinese hamster ovary cell line.mitochondrial proteins labelled with [35s]methionine for 1 h in whole chinese hamster ovary (cho) cells in the presence of cycloheximide or emetine, known inhibitors of cytosolic protein synthesis, have been enumerated and characterized by their electrophoretic mobility in sodium dodecyl sulfate slab gel electrophoresis. ten distinct electrophoretic bands were observed. the components were relatively stable during a 2 h postlabelling period. the same 10 bands were also seen with the cho cell lin ...1977912598
sensitivity of different cell lines and of different phases in the cell cycle to hyperthermia.the sensitivity of different cell lines (chinese hamster ovary, hela, l1210, and p388) to 43 degrees was compared chinese hamster ovary and hela cells were much less temperature sensitive than were l1210 or p388 cells. this difference persisted even when hela and l1210 cells were grown in the same medium and suggested that this was an inherent difference between the cell lines. of all the cell lines, 7-day l1210 ascites, maintained by transfer in mice, were the most sensitive. the greater sensit ...1977561655
nucleolar chromatin in chinese hamster ovary cells. topographical distribution of ribosomal dna sequences and isolation of ribosomal transcription complexes. 1977913418
spontaneous lesions in chinese hundred and fifty-seven chinese hamsters (cricetulus griseus) from the lovelace foundation inhalation toxicology research institute colony had pulmonary granulomas, nodular hyperplasia of the liver, granulocytic bone marrow hyperplasias and myelogenous leukemia, nephrosclerosis and uterine adenocarcinomas. these chinese hamsters had a median life span of 1 075 days. the long life span and information on naturally-occurring diseases suggest that this species might be more widely used for toxi ...1977919235
induction of thioguanine- and ouabain-resistant mutants and single-strand breaks in the dna of chinese hamster ovary cells by 3h-thymidine.cultured chinese hamster cells were labeled with 6-3h-thymidine or 5-methyl-3h-thymidine and allowed to accumulate damage from 3h decays for various periods of time while frozen. the frequencies of cells resistant to 6-thioguanine or ouabain and the amount of dna damage (i.e., number of single-strand breaks) were determined and compared with the mutation frequencies resulting from x and ultraviolet light irradiation. whereas 3h decays and x rays made only 6-thioguanine-resistant mutants, ultravi ...1977914028
somatostatin in the pancreas, stomach and hypothalamus of the diabetic chinese hamster. 1977908469
abnormalities in pelvic visceral nerves. a basis for neurogenic bladder in the diabetic chinese order to determine whether bladder dysfunction and hydronephrosis in diabetic chinese hamsters are associated with nerve pathology, the pelvic visceral nerves of diabetic and normal hamsters were examined with histochemical and electron microscopic techniques. acetylcholinesterase activity was reduced in the nerves and on smooth muscle fibers in the urinary bladder of diabetic hamsters when compared to controls. depression of enzyme staining was most marked in those hamsters with the most sev ...1977903213
repair of potentially lethal damage in chinese hamster cells after x and alpha irradiation. 1977897087
distribution of uv-induced unscheduled dna synthesis in metaphase chromosomes of chinese hamster cells. 1977891651
repair following combined x-ray and heat at 41 degrees in plateau-phase mammalian cells.plateau-phase v79 chinese hamster cells maintained at 37 degrees following x-irradiation demonstrated both sublethal damage repair and potentially lethal damage repair. when cells were kept at 41 degrees for 1 hr following irradiation, no sublethal damage repair was seen. in contrast, irradiated cells maintained at 41 degrees for 1 hr and then returned to 37 degrees were capable of repairing both sublethal and potentially lethal radiation damage; hyperthermic (41 degrees) inhibition of radiation ...1977884682
repair of the sublethal and mutational damage induced by x-rays in chinese hamster hai cells in vitro.the ability of chinese hamster hai cells to repair damage related to cell death and mutational change induced by x-rays were examined by using a sensitive forward mutation system from prototrophic ch-hai cl 23 cells to auxotrophs. the results obtained from the split dose experiments seem to suggest that chinese hamster hai cells have the repair mechanisms for the sublethal and mutational damage induced by x-rays and that the repair mechanisms act in common for the repair of both cases of damage.1977608187
[replication of chromosomal dna in chinese hamster cells, cultivated at different temperatures].dna fiber autoradiography was used to measure the rate of replication and the size of replication units in chinese hamster cells cultured at 34, 37 and 39 degrees c. the average rate of dna replication per single fork is 0.6 mcm/min at 34 degrees and 0.8 mcm/min at 37 and 39 degrees. in contrast to the change in the rate of dna replication, no change was found in the size of replication units, which are more than 200 mcm at 31, 37 and 39 degrees. the change of the length of the s phase at variou ...1977563118
clonal growth of chinese hamster cell lines in protein-free media.a protein-free synthetic medium, mcdb 301, has been developed for clonal growth of chinese hamster ovary cell lines. medium f12 was developed originally for that purpose, but later failed to support good growth without small amounts of serum protein. growth was restored by the addition of nonphysiological amounts of commercially prepared thyroxine or smaller amounts of the trace element selenium. the thyroxine preparation was shown to contain sufficient selenium to account for all of its growth- ...1977562838
chromosome loss is responsible for segregation at the hprt locus in chinese hamster cell hybrids.the phenomenon of segregation of gene expression has been examined in intraspecific somatic cell hybrids. specifically, segregation at the hypoxanthine guanine phosphoribosyltransferase (hprt) locus has been studied in hybrids of chinese hamster cell lines. the role of chromosome segregation, or other chromosomal events has been assessed by detailed comparison of karyotypes in the 6-thioguanine resistant segregants with those of the parental hybrid lines. the results clearly demonstrate that los ...1977562539
the control of cell proliferation by preformed purines: a genetic study. i. isolation and preliminary characterization of chinese hamster lines with single or multiple defects in purine "salvage" pathways.sublines with single or multiple defects in purine "salvage" enzymes were isolated from the chinese hamster fibroblastic line gma32 through single or successive one-step selections for resistance to purine analogs. they were examined for their ability to incorporate purine bases and nucleosides into macromolecules, for their sensitivity to growth inhibitory purines, and for their rescue by exogenous purines from deprivation imposed by metabolic inhibitors of endogenous synthesis. the results sho ...1977199954
cytochemical study of glucose-6-phosphatase in chinese hamster testis. 1977196695
biochemical genetic analysis of pyrimidine biosynthesis in mammalian cells: i. isolation of a mutant defective in the early steps of de novo pyrimidine synthesis.the isolation and characterization of a new mutant of chinese hamster ovary cells is described. this mutant, urd-a, shows an absolute requirement for exogenously added pyrimidines for growth. complementation analysis indicates that the lesion in this mutant is recessive. revertants can be isolated at frequencies suggesting that it is a single gene alteration. biochemical analysis of cell-free extracts of cho-k1 (urd+) and urd-a revealed that urd-a possesses no more than 10% of wild-type levels o ...197721463
variations in the length of s-phase related to the time cells are blocked at the g1-s interface.the inhibition of dna synthesis with hydroxyurea or 5-fluorode-oxyuridine decreases the duration of s-phase of synchronously growing chinese hamster cultures. - the observed drug effects are discussed in relation to an alteration of programmed dna replication.1977144048
the interaction of hoechst 33258 and brdu substituted dna in the formation of sister chromatid exchanges.sister chromatid exchanges (sces) are induced in cultured chinese hamster cells by treatment with 5-bromodeoxyuridine (brdu) or with hoechst 33258 (h33258) plus brdu. the sce frequencies depend upon the number of h33258 molecules available per cell (or per base pair) and the number of brdu molecules available per cell, and not solely upon molarity. in addition, h33258 and brdu act synergistically to induce sces. at low brdu concentrations h 33258 induces very few sces. at high brdu concentration ...197771978
action of heparin on mammalian nuclei. i. differential extraction of histone h1 and cooperative removal of histones from chromatin.heparin interacts strongly with the histone component of chromatin, forming heparin-histone complexes which resist dissociation by 0.2 m h2so4. heparin treatment of unfractionated histones isolated from nuclei of chinese hamster cells indicates that the affinities of the histone classes for heparin appear in the order from greatest to least: (h3, h4) greater than (h2a, h2b) greater than h1. however, when isolated nuclei are treated with heparin, h1 is released from the chromatin more readily tha ...1977884118
dna replication kinetics in x-irradiated chinese hamster ovary cells. 1977897075
a radioprotective effect of vitamin c observed in chinese hamster ovary cells.vitamin c at high concentrations was found to inhibit the growth of cho clone a cells in culture. it had a radioprotective effect, giving a maximum increase in cell survival of a factor of seven under the experimental conditions used. the protective effect was mainly but not exclusively attributable to an increase in the do, the maximum increase observed being the order of 1.4.1977890235
no mutagenic effect of enflurane on cultured cells.enflurane was tested by the 8-azaguanine system for any evidence of mutagenic effects. no significant increase in the number of mutant colonies compared with controls was found after 24 h of exposure of chinese hamster cells to 1.5-6.5% enflurane and no damaged chromosomes were seen in metaphase cells on slides. studies of inhibition of growth rate by enflurane show that in this respect its effects were similar in magnitude to other commonly used inhalation anaesthetic agents, but with regard to ...1977889666
the adhension of chinese hamster cells. i. effects of temperature, metabolic inhibitors and proteolytic dissection of cell surface macromolecules. 1977881433
the organization of repeated nucleotide sequences in the replicons of mammalian dna.chinese hamster ovary cells were irradiated with 100-5,000 rads of x-rays and inhibition of the initiation of replicons after irradiation was demonstrated by analyzing nascent dna sedimented in alkaline sucrose gradients. the renaturation kinetics of dna synthesized during 60 min of incubation after irradiation was compared with that of dna synthesized during the 60 min after sham irradiation and with that of parental dna. nascent dna from cells whose replicon initiation was inhibited renatured ...1977880330
quantitative analysis of biological marker synthesis in tumor cell cycle.a quantitative relationship between tumor cell number and biologic marker concentration has been investigated and characterized by the previously developed discrete-time kinetic model for the study of cell kinetics. here, this model is further expanded to cope with both cell cycle kinetics and biologic marker synthesis. a synchronized tumor-cell population is examined to determine the time course of the synthesis of markers in relation to cell cycle. the dna content distributions, measured by fl ...1977872404
effects of mercuric chloride on synchronized chinese hamster ovary cells: survival and dna replication.chinese hamster ovary (cho) cells in vitro were treated with hgcl2 at various stages in the cell cycle and the effects of this chemical on cell survival, dna replication, and cell division were observed. in terms of survival the early g1 cells were the most sensitive to treatment, followed by late g1 and early s, while mid s and late s-g2 treated cells were the least sensitive. treatment with hgcl2 also resulted in reduced rates of dna replication and delays in cell division. the early g1 treate ...1977560920
the response of chinese hamster ovary cells to fast-neutron radiotherapy beams. ii. sublethal and potentially lethal damage recovery capabilities. 1977408868
adhesion of phospholipid vesicles to chinese hamster fibroblasts. role of cell surface proteins.the adhesion of artificially generated lipid membrane vesicles to chinese hamster v79 fibroblasts in suspension was used as a model system for studying membrane interactions. below their gel-liquid crystalline phase transition temperature, vesicles comprised of dipalmitoyl lecithin (dpl) or dimyristoyl lecithin (dml) absorbed to the surfaces of edta- dissociated cells. these adherent vesicles could not be removed by repeated washings of the treated cells but could be released into the medium by ...1977407233
transfer of codominant markers by isolated metaphase chromosomes in chinese hamster ovary cells.codominant mutations to methotrexate and ouabain resistance in chinese hamster ovary cells can be transferred to recipient chinese hamster ovary cells by isolated metaphase chromosomes. for methotrexate, both the structural change and the increased activity of dihydrofolate reductase (5,6,7,8-tetrahydrofolate:nadp+ oxidoreductase ec, characteristic of the donor cells, are observed in the transferents (cells that carry and express functions derived by chromosome transfer). the transferen ...1977269408
strategies for choosing a deoxyribonucleic acid stain for flow cytometry of metaphase chromosomes.requirements for flow cytometry of metaphase chromosomes stained with three deoxyribonucleic acid (dna)-specific fluorescent dyes--hoechst 33258, chromomycin a3, and ethidium bromide--are reviewed. fluorescence properties of these three stains when bound to mitotic cells or to chromosomes in suspension are measured and compared with fluorescence properties when bound to dna in solution. conditions are given for high resolution flow cytometry of chinese hamster chromosomes stained with each of th ...197770463
mutants of cho cells resistant to the protein synthesis inhibitors, cryptopleurine and tylocrebrine: genetic and biochemical evidence for common site of action of emetine, cryptopleurine, tylocrebine, and tubulosine.stable mutants resistant to the protein synthesis inhibitors cryptopleurine and tylocrebine can be isolated in chinese hamster ovary (cho) cells, in a single step. the frequency of occurrence of cryptopleurine (cryr) and tylocrebrine (tylr) resistant mutants in normal and mutagenized cell populations is similar to that observed for emetine resistant (emtr) mutants. the cryr, tylr, and emtr mutants exhibit strikingly similar cross-resistance to the three drugs used for selection, to tubulosine an ...1977560858
a reduction in the degree of h4 acetylation during mitosis in chinese hamster cells. 1977883971
chinese hamster cell mutant with defective mitochondrial protein synthesis. 1977196202
the recovery of normal dna replication kinetics in ultraviolet-irradiated chinese hamster cells. 1977895752
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