Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The structurally modified polyene antibiotic nystatin methyl ester (NME) has been utilized as a half-selection agent for isolating interspecific mouse--Syrian hamster hybrids. By using HAT media supplmented with NME we have isolated hybrid clones from polyethylene glycol-fused cultures of biochemically defective mouse (A9 or B82) and genetically normal Syrian hamster (KHK/C13) cells. Unfused parental cells were killed in HAT-NME media as a result of their genetic defect, absence of hypoxanthine guanine-phosphoribosyl transferase-HGPRT-(A9) or thymidine kinase--TK-(B82), or innate sensitivity to NME (BHK/C13). In contrast, hybrid cells proliferated and clones were isolated after 3 weeks growth in HAT-NME media, indicating the genetic complementation had occurred and polyene resistance was expressed as a dominant phenotypic property in the hybrids. The presently described technique is efficient in eliminating unfused parental cells and should prove useful in isolating other types of hybrids formed between genetically defective and normal parental cells.
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PMID:Selecting somatic cell hybrids with hat media and nystatin methyl ester. 70 4

The activity of thymidine kinase (TK) was studied in series of somatic cell hybrids between the mouse cell line 3T3-4E (TK-) and Chinese hamster cells M-15-1 (HGPRT-). Four groups of hybrid lines with different ratio of parental chromosome sets have been investigated: 1) three lines containing one hamster and one mouse chromosome set (1 hs+1 ms); 2) one line with 2 hs+1 ms; 3) one line containing 3 hs+1 ms and 4) one line containing 1 hs+2 ms. Mixtures of extracts from the parental cells were shown to possess the expected TK activity. The calculation of the activity per cell revealed that the 1 hs+1 ms and 2 hs+1 ms hybrid lines possessed about 50% of the initial hamster cell TK activity. The decreased TK activity in these hybrids might be due either to a loss of hamster chromosomes or to some inhibitory effect of mouse genome in cells with the studied ratio of parental sets. The enzyme activity in the 3 hs+1 ms hybrid was as expected, about three times greater than that of hamster cells.
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PMID:[Characteristics of somatic cell hybrids (mouse x Chinese hamster) with a different ratio of chromosome sets from the parent species. II. Thymidine kinase activity]. 124 40

5-Azacytidine (5-AzaC) induced mutation in the TK+/- human lymphoblastoid line, TK6, at both the thymidine kinase (tk) locus as measured by resistance to trifluorothymidine (F3TdR), and the hypoxanthine-guanine phosphoribosyltransferase (hgprt) locus, as measured by resistance to 6-thioguanine (6TG). F3TdRR and 6TGR mutant fractions induced by 5-AzaC were observed after a normal phenotypic expression time and remained stable. Interestingly, 5-AzaC was 5-10 times more mutagenic at the tk locus than the hgprt locus. However, F3TdRR colonies from 5-AzaC-treated cultures behaved like TK-deficient mutants induced by other chemical mutagens. The TK or HGPRT phenotype had no effect on the toxicity of 5-AzaC, thus eliminating differential toxicity as a potential cause for the observed higher mutability at the tk locus. 5-AzaC did not induce F3TdRR cells in the parental TK+/+ lymphoblastoid line, indicating that 5-AzaC-induced F3TdRR variants were not due to a dominant alteration in gene expression. 5-AzaC did not induce chromosomal aberrations in TK6 cells, eliminating clastogenic events as a potential cause for the higher mutability at the tk locus. 5-AzaC was also found to be mutagenic in a forward mutation assay to 8-azaguanine resistance in Salmonella typhimurium.
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PMID:Studies of mutagenicity and clastogenicity of 5-azacytidine in human lymphoblasts and Salmonella typhimurium. 242 Nov 58

We evaluated the ability of the antitumor agent 4-(9-acridinylamino)-methanesulfon-m-anisidide (amsacrine or m-AMSA) and its congener, o-AMSA, to induce specific-locus mutations at the heterozygous thymidine kinase (tk) locus of L5178Y/TK+/- -3.7.2C mouse lymphoma cells. These cells permit the recovery of mutants due to single-gene or chromosomal mutation. m-AMSA was highly mutagenic at the tk locus, producing approximately 3000 mutants/10(6) survivors at 10% survival; positive dose range 1-10 ng/ml; o-AMSA produced approximately 1500 mutants/10(6) survivors at 10% survival; positive dose range 0.1-2.5 micrograms/ml. Most of the TK mutants were small colonies, which suggests that m-AMSA and o-AMSA induce primarily chromosomal mutations as opposed to single-gene mutations. The potent clastogenicity of these agents was confirmed by cytogenetic analysis for chromosomal aberrations, which showed that m-AMSA (9 ng/ml, 10% survival) and o-AMSA (1 microgram/ml, 10% survival) produced 383 and 179 aberrations, respectively, per 100 metaphases (background = 3-4/100). The large-colony TK mutant frequencies produced by m-AMSA (67 - 112/10(6) survivors; background = 7/10(6); survival = 63 - 16%) were comparable to the published HPRT mutant frequencies produced by m-AMSA in V79 cells. Novobiocin (50 micrograms/ml), an inhibitor of mammalian DNA topoisomerase II and other enzymes, inhibited the mutagenic effects of m-AMSA, suggesting that DNA topoisomerase II (or another enzyme) may play a role in the mutagenic/clastogenic activity of m-AMSA.
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PMID:Mutagenicity of m-AMSA and o-AMSA in mammalian cells due to clastogenic mechanism: possible role of topoisomerase. 283 Apr 52

We evaluated the ability of proflavin to induce specific-locus mutations at the heterozygous thymidine kinase (tk) locus of L5178Y/TK +/- -3.7.2C mouse lymphoma cells, which appears to permit the recovery of mutants due to single-gene and chromosomal mutations. Proflavin was highly mutagenic at the tk locus, producing 724-965 TK mutants/10(6) survivors (background = 56-85/10(6); survival = 29-32%). Most of the mutants were small colonies, which suggested that proflavin may induce chromosomal mutations. The potent clastogenicity of proflavin was confirmed by cytogenetic analysis for chromosomal aberrations. At the highest dose analyzed (1.5 micrograms/ml), proflavin produced 82 aberrations/100 metaphaes (background = 2/100). The large-colony TK mutant frequency produced by proflavin (48-109/10(6) survivors; background = 23/10(6); survival = 57-61%) was similar to published HPRT mutant frequencies produces by proflavin in L5178Y and CHO cells (50-100/10(6) survivors; background = 2-50/10(6); survival = 50-62%). These results lead to the conclusion that proflavin is a potent clastogen and induces a high frequency of small-colony TK mutants; however, it induces a low frequency of HPRT mutants and a low frequency of large-colony TK mutants.
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PMID:Mutagenicity and clastogenicity of proflavin in L5178Y/TK +/- -3.7.2.C cells. 334 81

Acrylamide was tested without exogenous activation in L5178Y/TK+/- -3.7.2C cells for mutation at the thymidine kinase locus and for clastogenicity. Acrylamide gave a positive induced mutagenic response (approximately 70 mutants/10(6) survivors) when tested at 600-650 micrograms/ml. The highest dose tested (850 micrograms/ml) resulted in an induced mutant frequency of approximately 380 mutants/10(6) survivors (survival = 13%). Acrylamide induced almost exclusively small-colony mutants, indicating that it might be acting by a clastogenic mechanism. As predicted, acrylamide was clastogenic, inducing both chromatid and chromosome breaks and rearrangements. A clearly positive clastogenic response was observed at both the 750 micrograms/ml and 850 micrograms/ml doses, which showed 16 and 64 aberrations per 100 cells, respectively (background = 3 aberrations per 100 cells). These studies indicate that the L5178Y/TK+/- mouse lymphoma assay can detect some chromosomal mutagens (clastogens) that show little activity in other single gene mutation assays, the CHO/HPRT and Salmonella.
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PMID:Mutagenicity and clastogenicity of acrylamide in L5178Y mouse lymphoma cells. 356 69

It has been shown that 5-azacytidine (5-Aza-Cyd) can reactivate genes on the inactive human X chromosome. It is assumed that the 5-Aza-Cyd acts by causing demethylation of the DNA at specific sites, but this cannot be demonstrated directly without a cloned probe. Instead, we have utilized the technique of DNA-mediated transformation to show that the 5-Aza-Cyd-induced reactivation occurs at the DNA level. DNAs from various mouse-human or hamster-human hybrid cell lines, deficient for mouse or hamster hypoxanthine phosphoribosyltransferase (HPRT, EC 2.4.2.8) and varying in whether they contained either an active or inactive human X chromosome, were used in transformation of HPRT- cells. DNA from the active human X chromosome-containing cell lines yielded HPRT+ transformants, whereas DNA from the inactive X chromosome-containing cells lines did not. The inactive X chromosomal DNA was able to transform thymidine kinase-deficient mouse cells, indicating that the DNA solution was normal. These results confirm that inactivation of the X chromosome involves a DNA modification. Furthermore, DNAs from three cell lines with a 5-Aza-Cyd-reactivated X chromosome also transform HPRT- cells, demonstrating that the 5-Aza-Cyd has altered the DNA structure and supporting the idea that methylation plays a role in X chromosome inactivation.
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PMID:Transformation with DNA from 5-azacytidine-reactivated X chromosomes. 617 98

Chinese hamster ovary (CHO) cell lines heterozygous at both the adenine phosphoribosyltransferase (aprt) and thymidine kinase (tk) loci were used for single-step selection of spontaneous and induced mutants resistant to 8-azaadenine (AAr), 6-thioguanine (TGr), ouabain (OUAR), or 5-fluorodeoxyuridine (FUdRr). Mutation data are reported for direct mutagens (EMS, ethyl methanesulfonate; MNNG, N-methyl-N'-nitro-N-nitrosoguanidine; NQO, 4-nitroquinoline 1-oxide) and promutagens (DMN, dimethylnitrosamine; BP, benzo[a]-pyrene) activated by rat-liver homogenates. Optimal plating densities were established for AAr, TGr, OUAR and FUdRr. The induced mutant frequencies as a function of relative cell survival after treatment with EMS, DMN or BP were 2--4 d for AAr, 6--8 d for TGr, 3 d for OUAR, and 1--3 d for FUdRr. The induced mutant frequencies as a function of relative cell survival after treatment with EMS, DMN or BP showed locus-specific differences in sensitivity. Of 61 clonal isolates resistant to AA and assayed for APRT activity, 87% had less than or equal to 5% wild-type activity; of 30 TGr clones assayed, 83% had less than or equal to 5% wild-type HGPRT activity. Of 42 FUdRr clones assayed, 98% had less than or equal to 1% wild-type TK activity. 50 clones selected in medium containing FUdR displayed cross-resistance to 5-bromodeoxyuridine (BUdR) and trifluorothymidine (TFT) and all were sensitive to HAT (hypoxanthine--amethopterin--thymidine) medium. The tk locus showed the largest mutational response as a function of cell survival after mutagen treatment. The rapid expression kinetics for FUdRr and the possibility that the locus detects a broader spectrum of genetic lesions than the other drug-resistance markers are discussed in terms of a sensitive screening assay for detecting potential mutagens.
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PMID:Mutagenicity testing in mammalian cells. II. Validation of multiple drug-resistance markers having practical application for screening potential mutagens. 644 64

The efficiency of DNA-mediated transfer of the gene (hprt) for hypoxanthine phosphoribosyltransferase (HPRT; IMP: pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) is dependent upon the recipient cell used. hprt has been transferred into mouse TG8 or Chinese hamster CHTG49 cells at a high frequency, similar to the frequency of the gene (tk) for thymidine kinase (TK; ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21) transfer into mouse LMTK- cells (i.e., 10(-6)). In contrast, the frequency of transfer of hprt into mouse A9 cells was about two orders of magnitude less. The identification of efficient recipient cells for hprt transfer permits the use of DNA-mediated transfer as a bioassay for the gene. Cotransfer of the linked tk gene and the gene (galk) for galactokinase (ATP: D-galactose 1-phosphotransferase, EC 2.7.1.6) to LMTK- cells has been detected once among 87 tk transferrents. This suggests that the distance between the tk and galk genes in the Chinese hamster genome may be smaller than was previously thought. Significant differences between chromosome-mediated and DNA-mediated gene transfer were observed with respect to both the size of the transferred functional genetic fragment and the recipient cell specificity.
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PMID:Cotransfer of linked eukaryotic genes and efficient transfer of hypoxanthine phosphoribosyltransferase by DNA-mediated gene transfer. 692 11

The regional gene assignments for human porphobilinogen deaminase (PBGD; EC 4.3.1.8) and esterase A4 (ESA4; EC3.1.1.1) chromosome 11 have been determined with somatic cell hybridization and immunologic, electrophoretic, and cytogenetic techniques. Dimethyl sulfoxide-induced erythroid differentiation of hybrid clones derived from the fusion of tetraploid Friend murine erythroleukemia (2S MEL) cells deficient in thymidine kinase and human Lesch--Nyhan fibroblasts (HLN) deficient in hypoxanthine phosphoribosyltransferase (HPRT-; EC 2.4.2.8) were examined for expression of human PBGD, ESA4, and lactate dehydrogenase A (LDHA; EC 1.1.1.27). Human PBGD was detected by rocket immunoelectrophoresis with rabbit anti-human PBGD IgG and by isoelectric focusing. The human chromosome complement of each clone was determined by cytogenetic and enzyme marker analyses. Of the five primary 2S MEL--HLN clones examined, three were positive for human PBGD. These were subcloned to yield a total of 10 secondary, tertiary, or quaternary clones. Analyses of these subclones permitted the regional assignment of human PBGD and ESA4 to the long arm of chromosome 11. Finer regional assignment of the loci for human PBGD and ESA4 was facilitated when two 2S MEL (HPRT-)--human fibroblast (HX/11) hybrids, each containing the X chromosome--autosome translocation (der11), t(X;11)(q25-26;q23) as the only human chromosome, were examined for expression of human PBGD, ESA4, and LDHA. One clone, HX/11-2, contained the intact X/11 translocated chromosome; in the other, HX/11-3, 11p was deleted, and the human X/11 derivative was translocated onto a mouse chromosome. HX/11-2 expressed human LDHA, but HX/11-3 did not, verifying that the latter human 11/X derivative did not include 11pter leads to 11p12; PBGD and ESA4 were not detected in either hybrid. These results confirm the location of the gene for human PBGD on chromosome 11 and establish the assignment of the loci for PBGD and ESA4 in the region 11q23 leads to 11qter.
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PMID:Regional gene assignment of human porphobilinogen deaminase and esterase A4 to chromosome 11q23 leads to 11qter. 694 13


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