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1.
Fox M  Boyle JM  Fox BW 《Mutation research》1976,35(2):289-309
Purine analogue resistant clones have been selected from the closely related Chinese hamster lines V79A and V79S. Clones were of either spontaneous origin or induced by EMS or ultraviolet light. The majority of clones selected in 8-azaguanine showed stable cross resistance to 6-thioguanine. Clones derived from V79A and selected for 6-thioguanine resistance were cross resistant to 8-azaguanine: however a group of 6-thioguanine resistant mutants selected from V79S cells were 8-azaguanine sensitive. All clones except two were unable to grow in HAT medium. The two exceptions were 8-azaguanine resistant, showed partial sensitivity to 6-thioguanine, and also differed in other biochemical characteristics. HGPRT activity was measurable in extracts of all clones under standard conditions. In many clones, HGPRT activity increased as the hypoxanthine concentration was reduced. Whole cell uptake of [14C] hypoxanthine was low in all cases examined and was not modified by incubation in the presence of amethopterin. The heat sensitivity and electrophoretic mobility of HGPRT in extracts of some clones was compared to that in wild-type extracts. All clones tested except one, which was consistently HAT positive, showed enhanced heat sensitivity and reduced electrophoretic mobility. None of the mutants reverted spontaneously at detectable frequency but some could be induced to revert by EMS. The presence of measurable enzyme with altered properties in all clones suggests that these revertable drug resistant clones represent missense mutants.  相似文献   

2.
Cultured mouse clonal cells, H-5, were treated with two different mutagens, ethyl methanesulfonate (EMS) and N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). Then two selective procedures using 8-azaguanine (8-AZ) or 6-thioguanine (6-TG) were compared in an effort to isolate hypoxanthine-guanine phosphoribosyl-transferase (HGPRT)-deficient cells containing different gene alterations. While many 8-AZ resistant cells were induced by EMS treatment, considerably more 6-TG resistant cells were induced by the same treatment. MNNG treatment induced many 8-AZ resistant mutants but induced hardly any 6-TG resistant mutants. After a fusion experiment of 91 sets involving 13 HGPRT-deficient mouse clones, 7 of which were resistant to 8 AZ and 6 of which were resistant to 6TG with subsequent selection on HAT medium, complementation occurred only in those hybrid mixtures formed between 8-AZ- and 6-TG-resistant clones, while it did not occur at all in hybrid mixtures formed between different 8-AZ-resistant clones and mixtures formed between different 6-TG-resistant clones. The clonally isolated HGPRT-positive cells, characterized by tetraploid karyology, had an apparent activity of HGPRT ranging from 25 to 30% of that of the wild-type parental cells. Heat-inactivation of HGPRT at 65 °C revealed that HGPRT from wild-type cells was heat stable and HGPRT from some 8-AZ-resistant clones were heat labile, while HGPRT from hybrid cells had intermediate stability. These results indicate that there would be alterations in the structural gene of HGPRT in the 8-AZ- or 6-TG-resistant mutants, and also that two selective procedures with 8-AZ or 6-TG alone can isolate different alterations in the structural gene of HGPRT. Moreover, this indicates that some of these gene alterations were mutually complementary. It is most likely that there would be at least 3 cistrons in the locus responsible for HGPRT activity in the mouse cells.  相似文献   

3.
Mutagenic effect of BUdR in diploid human fibroblasts   总被引:2,自引:0,他引:2  
It has only recently been possible to demonstrate the expected mutagenic effect of 5-bromodeoxyuridine (BUdR) in heteroploid hamster cells in culture. We have now extended this observation to diploid human fibroblasts utilizing techniques adapted from the work of Albertini and DeMars on X-ray mutagenesis at the hypoxanthine-guanine phosphoribosyltransferase (HGPRT) locus in these cells. In four separate experiments, fibroblasts from a female donor were exposed to 500 micrograms/ml ethylmethane sulfonate (EMS) or 3 micrograms/ml BUdR yielding survivals of 9% and 5%, respectively. After a 6-day expression period, survivors were plated in selection medium containing 0.3 micrograms/ml 8-azaguanine (8-AG). After 3-5 weeks, azaguanine-resistant colonies were isolated for characterization or stained for counting. The average spontaneous mutation rate/cell/generation was 0.6.10(-6). The average induced mutation rates for EMS and BUdR were 7.8.10(-6) and 6.3.10(-6)/cell/generation, respectively. Similar results were obtained in two experiments with an additional fibroblast line. Mutant colonies isolated following BUdR treatment demonstrated from 1.4 to 61.5% of the HGPRT activity of the parental line and showed at least 8% Barr bodies, excluding the possibility of contamination by Lesch-Nyhan cells. This demonstration of a BUdR effect comparable to that of an alkylating agent or X-irradiation opens the study of mutation due to base-analog substitution in diploid human cells.  相似文献   

4.
Chinese hamster cells were treated with ethyl methanesulfonate or N-methyl-N'-nitro-N-nitrosoguanidine, and mutants resistant to 8-azaguanine were selected and characterized. Hypoxanthine-guanine phosphoribosyltransferase activity of sixteen mutants is extremely negative, making them suitable for reversion to HGPRTase(+). Ten of the extremely negative mutants revert at a frequency higher than 10(-7) suggesting their point mutational character. The remaining mutants have demonstrable HGPRTase activity and are not useful for reversion analysis. Five of these mutants have < 2% HGPRTase and are presumably also HGPRTase point mutants. The remaining 14 mutants utilize exogenous hypoxanthine for nucleic acid synthesis poorly, and possess 20-150% of wild-type HGPRTase activity in in vitro. Their mechanism of 8-azaguanine resistance is not yet defined.  相似文献   

5.
Michel Caboche 《Genetics》1974,77(2):309-322
5-bromodeoxyuridine resistance mutations induced by mutagenesis were studied. The average expression time for induced mutations varied with the concentration of the mutagen ethyl methanesulfonate (EMS). However, a constant number of two generation times was necessary for half maximal expression of induced mutations. Also, induced mutation rates were compared under optimal expression conditions for bromodeoxyuridine, fluorodeoxyuridine and azaguanine resistance markers. Ten independent bromodeoxy-uridine-resistant clones were tested for reversion. Two clones reverted-one spontaneously and the other after mutagenesis. The spontaneous rate of mutation to bromodeoxyuridine resistance, estimated by the fluctuation test, was high in revertant clones (4 x 10(-6) / cell / generation) and low in the wild-type cells (< 3.5 x 10(-8) / cell / generation). A comparison of induced mutation frequencies at variable EMS concentrations showed a single-hit curve for revertant clones and a multihit curve for the wild-type cells. Thymidine kinase activities of resistant clones were usually less than 2% of that of the wild-type clone. Inducibility, thermal stability and intracellular localization of the thymidine kinases of the wild-type cells and of a revertant clone were identical. A low, but significant (P < 0.10), Km discrepancy was observed between enzyme extracts of these lines. The genetic implications of these results are discussed.  相似文献   

6.
Mutants of a diploid human lymphoblast line resistant to 6-thioguanine (6TG) appear 6--16 generations after treatment with any of a diverse group of mutagents: methylnitrosourea (MNU), methylnitrosoguanidine (MNNG), ICR-191, 5-bromodeoxyuridine (BUdR). A hypothesis is advanced that expression of the 6-thioguanine-resistant state may require the removal of essentially all pre-existing hypoxanthine--guanine phosphoribosyl transferase (HGPRT) molecules via division, dilution, and protein turnover. Design of protocols for quantitative mutation assays requires attention to this phenomenon.  相似文献   

7.
Factors affecting the efficiency of selection of “reverants” of salvage pathway mutants in media containing amethopterin have been examined. Our V79 Chines hamster cell line was found to require a significantly higher level of thymidine for optimal growth in such media than has been reported for other cell lines. Hypoxanthine (but not glycine) was also required for reversal of amethopterin toxicity, but levels did not differ significantly from those reported elsewhere. Growth in HAT was also dependent on plating density and serum batch. Our modification (VHAT) was compared with published HAT recipies in back selection reconstruction experiments. A sharp fall in EOR (efficiency of recovery) of wild type cells from mixtures with mutants at plating densities greater than 3500 cells/cm2 (105 cells/6 cm dish) was observed for VHAT. EOR with other HAT recipes was lower still, and was affected also by the particular mutant used in the mixture.EMS induced “revertants” were isolated from three 8AZr mutants by plating in VHAT. All. revertants were however amethopterin resistant, they were also 8AZ resistant and the mobility of residual HGPRT (as measured by polyacrylamide gel electrophoresis) was similar to that of their 8AZr parents i.e. dissimilar from that in wild type. The modal chromosome number of V79 wild type cells was 21. No significant deviation from this mode was detected in any of the mutant lines examined. The data indicate that the recovery of colonies in HAT from 8AZr mutants does not necessarily indicate that a back mutation in the structural gene for HGPRT has occurred. Thus, the frequency of HAT+ colonies cannot be taken as a direct indication of reversion frequencies.  相似文献   

8.
Exposure of V79 cells to azaguanine (7-21 microM for 2-7 weeks) had little effect on growth or plating efficiency but resulted in gradual acquisition of resistance to 8-azaguanine (AZ) and 6-thioguanine (TG) and loss of ability to grow in HAT. The rate of evolution of the resistant phenotype was dependent on the concentration and duration of exposure to AZ. The increase in proportion of resistant cells was paralleled by a rise in phosphatase activity (pH optimum 7.0-7.5) expressed by intact cells and this preceded the fall in HGPRT activity. Elevated phosphatase activity and a resistant phenotype were stably expressed in clones isolated and cultured in the absence of AZ. Hypoxanthine guanine phosphoribosyl transferase (HGPRT) activity in cell extracts of three resistant clones ranged from 18 to 43% of wild-type levels but was unaltered with respect to substrate affinity and electrophoretic mobility. Mg2+-dependent activity dephosphorylated inosine 5'monophosphate (IMP), guanine 5'monophosphate (GMP), adenosine-5-monophosphate (AMP) and p-nitrophenylphosphate (PNPP) and was also elevated with respect to wild-type levels in resistant cell extracts. Purine nucleoside phosphorylase levels were similar in sensitive and resistant cell extracts. Cross-sensitivity studies with other purine analogues suggest that the elevated phosphatase activity does not contribute to the resistant phenotype. No karyotypic changes were observed in the resistant cell lines.  相似文献   

9.
The mutagenic action of SV40 in permanent lines of Chinese hamster cells (CHO-K1 and V79) was investigated with the aid of different resistance markers. The markers studied had resistance to 8-azaguanine (25 and 30 mug/ml), aminopterin (3.3--5.5X10(-3) mug/ml), colchicine (6.5 and 7.0X10(-2) mug/ml) and 5-bromodeoxyuridine (50--120 mug/ml), respectively. After virus infection the mutation frequencies were increased by one (azaguanine, aminopterin) and two (colchicine) orders of magnitude as compared with spontaneous mutation frequencies. In contrast, it was not possible to enhance the frequency of mutation to BUdR resistance. On the other hand, the ability to proliferate in HAT medium was induced in three of five BUdR-resistant cell clones by infection with SV40. The resistance induced by SV40 was stable when isolated clones were cultured under non-selective conditions. Mechanisms are proposed that may be responsible for the mutagenic action of SV40.  相似文献   

10.
Dibutyryl adenosine 3',5'-phosphate (Bt2cAMP)-sensitive (Bt2cAMPS) revertants were isolated from a resistant S49 cell mutant carrying a structural gene lesion in the regulatory subunit of cAMP-dependent protein kinase (cA-PK). This was accomplished with a counter-selection in which, first, Bt2cAMP was used to reversibly arrest revertants, and then a sequence of treatments with bromodeoxyuridine, 33258 Hoechst dye, and white light was used to kill cycling mutant cells. Reversion rates in nonmutagenized cultures could not be accurately measured, but spontaneous revertants do occur and with frequencies of less than 10(-7) to 10(-5). The mutagens ethyl methane sulfonate (EMS), N-methyl-N'-nitro-N-nitro-soguanidine (MNNG), and ICR191 increased the reversion frequency. In all cases, reversion to Bt2cAMP sensitivity was associated with restoration of wild-type levels and apparent activation constant for cAMP of cA-PK. MNNG induced revertants whose cell extracts contained cA-PK activity distinguishable from that of wild type by thermal liability. EMS did not. The counter-selection effectively isolates rare phenotypes and is therefore a useful tool in further somatic genetic experiments. The association of reversion with alterations in cA-PK function supports all previous data from this and other laboratories implicating cA-PK as the intracellular mediator of cAMP effects. Reversion is probably the result of a mutational event. Induction of reversion by ICR191 suggests the existence of a novel mechanism for generating revertants in somatic cells.  相似文献   

11.
8-azaguanine and 6-thioguanine were both toxic to non-dividing liver cells in primary cultures. In addition, these agents were toxic to an established line of liver-derived epithelial cells brought to growth arrest by serum deprivation. These observations demonstrate that the toxicity of 8-azaguanine and 6-thioguanine can occur at least in part through mechanisms that do not involve effects on DNA synthesis or incorporation of the analogs into DNA.Abbreviations AG 8-azaguanine - ARL adult rat liver epithelial cell line - HGPRT hypoxanthine-guanine phosphoribosyl transferase - WME Williams Medium E  相似文献   

12.
Isolation of ouabain-resistant human diploid fibroblasts   总被引:17,自引:0,他引:17  
R Mankovitz  M Buchwald  R M Baker 《Cell》1974,3(3):221-226
Seventeen clones resistant to the cytotoxic action of ouabain were isolated in culture by direct selection from 5 independent strains of diploid human fibroblasts. Resistant clones were recovered at frequencies on the order of 10?7 per wild type cell selected from populations treated with the mutagen EMS, but no resistant cells were detected among 108 unmutagenized cells. Most selected clones remained ouabain-resistant following further propagation in the absence of drug. The growth of wild type cells was inhibited by 50% at ouabain concentrations of 2–5 × 10?8 M, while resistant clones required 15–180 fold higher drug concentrations to cause equivalent inhibition. Ouabain-resistant clones showed increased resistance of K+ transport function to ouabain inhibition that paralleled their increased resistance to growth inhibition. Initial experiments suggest that under selective conditions the resistant diploid fibroblasts differ significantly from wild type in binding of 3H-ouabain per unit surface area. The ouabain-resistant cells were similar to wild type in transport properties unrelated to ouabain inhibition. Resistant cells had normal karyotypes and senesced with a lifespan similar to control clones. The ouabain-resistant phenotypes of these diploid human fibroblast isolates apparently reflect point mutations that specifically affect the Na+/K+ transport ATPase with respect to ouabain-binding and/or response to bound ouabain.  相似文献   

13.
The stability of the 8-azaguanine resistance marker during the number of cell generations has been analyzed for 63 clones of Chinese hamster cells. The resistant clones analyzed were spontaneous or induced after the treatment of parent cells by 5-BUdR, EMS, or histone H1. The clones have revealed different levels of AG-resistance as well as different ability to maintain the above level, under the cultivation in the drug-free medium. Subclones, isolated from the unstable clone, were found to be different in both the resistance level and the stability of resistant state.  相似文献   

14.
The human lymphoblast line MGL8 was treated with HAT and subsequently "mutagenized" with EMS (200 microgram/ml) to give 15% survival, and 6-thioguanine-resistant cells were selected by cloning in soft agarose containing the drug (1 microgram/ml). Eighteen sublines of independently derived resistant clones were isolated and studied in detail. One subline had a low residual HGPRT activity of about 1% of the parental cells. The HGPRT of this subline had a higher Km for PRPP, was more sensitive to heat, and was degraded faster by trypsin than the enzyme in extracts of MGL8 cells. This resistant subline and three others contained CRM levels of 1--38%, compared to the wild-type, so they probably represent true structural mutants of the HGPRT gene. All the variants maintained the karyotype of the parental line (46, XY, 6p-).  相似文献   

15.
Five clones of mouse neuroblastoma cells able to grow in hypoxanthine-aminopterin-thymidine containing medium were isolated from a hypoxanthine-guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8; IMP: pyrophosphate phosphoribosyltransferase) deficient cell line. These hypoxanthine-aminopterin-thymidine resistant revertant clone had 45-55% of wild-type cell HGPRT activity. Kinetic studies indicated that the HGPRT in revertant clones had a reduced maximal velocity as compared to wild type cells based on cell protein. Apparent Km values of HGPRT for hypoxanthine and 5-phosphoribosyl-1-pyrophosphate were similar in wild-type and revertant cells. Heat inactivation studies demonstrated a similar heat lability for HGPRT in revertant and wild-type cells. An antibody fraction prepared from serum of rabbits immunized with HGPRT partially purified from mouse liver was used to measure the amount of cross-reacting material in normal and revertant clones. The revertant clones had one-half the amounth of cross-reacting material present in wild-type cells, based on a given amount of cell protein. These data indicate that the revertant cells may contain fewer HGPRT molecules with unaltered catalytic activity.  相似文献   

16.
B P Kopnin  A V Gudkov 《Genetika》1983,19(6):872-880
The influence of some agents on gene amplification in Djungarian hamster and mouse cells was studied. The tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA), the epidermal growth factor (EGF), insulin, and 5-bromodeoxyuridine (BUdR) increase the incidence of colchicine-resistance, connected with amplification of the genes, which probably encode the polypeptide p22. The highest frequency of gene amplification was observed after the pretreatment of cells with TPA, which enhanced the number of colchicine-resistant colonies 44-200-fold. Mitostatic agents colchicine and colcemid increased the number of methotrexate-resistant cells, 2.0-6.5 times. These cells usually arise as the result of amplification of dihydrofolate reductase genes. Dexamethasone and ethidium bromide did not change the portion of cells resistant to colchicine. Ethylmethane sulfonate (EMS) decreased the number of colchicine-resistant cells. The cells of two Djungarian hamster colchicine-resistant clones obtained after treatment with TPA did not differ from those of spontaneously derived colchicine-resistant clones. Both have similar survival patterns in the medium with different colchicine concentrations, unstable inheritance of the drug resistance, the additional chromosome 4 and small chromatin bodies-the structures containing the amplified genes. Possible mechanisms of the induction of gene amplification by the agents used are discussed.  相似文献   

17.
Chinese hamster V79 cells were mutagenized with ethyl methanesulfonate at various concentrations. Clones resistant to 8-azaguanine (20 and 80 micrograms/ml) or 6-thioguanine (4 micrograms/ml) were selected at different times after the treatments. The total yield of induced mutations was only slightly affected by the kind and concentration of purine analog used in the selection. However, full phenotypic expression of the mutants selected with 8-azaguanine was achieved earlier than that of mutants resistant to 6-thioguanine. This result seems to be best explained by the reported lower affinity of 8-azaguanine for the wild-type HGPRT enzyme, thus providing evidence that, in this gene-mutation assay, the phenotypic expression time has a physiological component.  相似文献   

18.
Spontaneous mutagenesis and mutagenesis induced by chemical mutagens in culture Chinese hamster cells were investigated. Appearance of mutations controlling the resistance to 6-mercaptopurine (6M) and reverse mutations to sensitivity was studied. The rate of spontaneous mutations of 6M resistance in cells studied was found to be sufficiently stable: it was independent on the repeated freezing of these cells and the duration of their cultivation. 5-bromodeoxyuridine (BUdR) has been shown to induce mutations to 6M resistance in cells of the 237i clone; the rate of induced mutations in some experiments as compared to the rate of spontaneous mutations was 1-2 orders higher. No clear-cut delay of phenotypic expression of BUdR-induced mutations was found. Seven independently arisen mutant clones were isolated. Five of them appeared spontaneously and two clones were induced by BUdR. Three spontaneously arisen clones were found to be reversible to sensitivity. The rate of reverse mutations in cells of the other four clones, did not exceed (2,3-3,5)-10(-6) per cell per generation. The rate of spontaneous reverse mutations in these clones was less at least one order lower as compared to the rate of spontaneous mutations to 6M-resistance. The attempts to induce reverse mutations to sensitivity by N-nitrosomethylurea in spontaneously reversible resistant cells and by BUdR in mutant cells arisen as a result of the treatment with the same agent proved unsuccessful. A method of estimation of experiment's resolving power is described for cases, when no expected events (in our study reverse mutations) were observed.  相似文献   

19.
The ability of 5 independently isolated thymidine kinase-deficient clones of mouse lymphoma P388 to revert has been examined. We were unable to detect spontaneous revertants in any of the 5 clones. Treatment with the hypomethylating agent 5-azacytidine induced reversion in 4 of the clones, but the frequency of revertants was very low (less than 10(-6). The response was not dose-dependent. The mutagen EMS was capable of inducing reversion in 3 of the clones with a variable level of response. The activity of thymidine kinase in 16 revertants was determined. In half of these the level of enzyme activity was considerably greater than the original P388 cell line. The high frequency loss of thymidine kinase that occurs in these cells may represent a stable inactivation of gene activity rather than an alteration in the DNA base sequence.  相似文献   

20.
Summary A clone of Vero cells resistant to up 20 μg/ml 8-azaguanine was isolated. This clone (designated Vero 153) has a doubling rate of approximately 24 h and a maximum cell density of 10,000/mm2. Deficiency of the enzyme hypoxanthine guanine phosphoribosyl transferase (HGPRT) in Vero 153 was demonstrated by methods of radiochromatography. Vero 153 is susceptibletto hypoxanthine-thymidine-aminopterin (HAT) medium and its resistance to 8-azaguanine seems to be nonreversible. Like parenal cells, Vero 153 was also incapable of interferon production when challenged with Newcastle disease virus (NDV) or poly(inosinic acid) poly(cytidylic acid) (poly I:C). Similar chromasome complements (majority range 56 to 57) and band patterns were observed in cells harvested at Passages 10, 20, and 50. The potential use of Vero 153 for somatic cell hybridization for purposes of gene mapping, virus rescue, and the control of inteferon production is discussed. This project was supported by grant from the Medical Research Council, Canada (MT-1615).  相似文献   

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