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:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cones of thioguanine resistant K-BALB mouse cells wereisolated which were inducible for endogenous type C virus synthesis by cycloheximide and dexamethsone, but not 5-iododeoxyuridine. A comparison of the number of foci formed on NRK and SC-I cells suggested that the xenotropic virus was suppressed. The variants were not defective in the incorporation of thymidine or iododeoxyuridine or deficient in thymidine kinase, but were deficient in hypoxanthine-guanine phosphoribosyltransferase and the incorporation of hypoxanthine into nucleic acid. Because these cells are blocked at some point in the expression of endogenous virus, they may prove useful in establishing the steps involved in chemical activation of virus synthesis.
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PMID:Isolation of thioguanine resistant variants of K-BALB cells non-inducible for type C viruses by 5-iododeoxyuridine. 20 30

Mouse teratocarcinoma cells from the OTT6050 ascites tumor were established in tissue culture and selected for 5-bromodeoxyuridine (BrdUrd) resistance. The embryonal carcinoma cells grew without a feeder layer, remained deficient for thymidine kinase (EC 2.7.1.75), and differentiated like the original tumor into various tissues after subcutaneous injection into 129 mice. We fused the BrdUrd-resistant mouse teratocarcinoma cells with HT1080-6TG human diploid fibrosarcoma cells deficient in hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) and selected for hybrid cells in hypoxanthine/aminopterin/thymidine medium. The resulting hybrid cells segregated human chromosomes quickly and retained one to three human chromosomes including chromosome 17 that carries the human genes for thymidine kinase and galactokinase (EC 2.7.1.6). Single hybrid cells from five independent clones containing human chromosome 17 were injected into mouse blastocysts bearing several genetic markers that affect the coat color phenotype and strain-specific enzyme variants in order to detect tissue differentiation derived from the injected cells. After the injection of single hybrid cells into a total of 103 experimental blastocysts that had been surgically transferred to pseudopregnant foster mothers, 49 mice were born and 2 of them clearly revealed coat mosaicism. In 2 of 17 mice thus far analyzed, the injected hybrid cells proved to be capable of participating substantially in development of seven different organs. However, human gene products have not yet been detected unequivocally in those tissues and weak human-specific galactokinase activity could be recovered only from two mosaic tissues. Our results demonstrate that, after in vitro culture and selection, at least some of the human-mouse hybrid cells still retain their in vivo potential to differentiate and become functionally integrated in the living organism. It now seems feasible to cycle mouse teratocarcinoma cells carrying human genetic material through mice via blastocyst injection to study human gene expression during differentiation.
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PMID:Chimeric mice derived from human-mouse hybrid cells. 20 75

A simple method for the quick and accurate detection of cell fusion utilizing latex particles as cytoplasmic markers was developed and is reported here. The method is particularly useful for demonstrating human skin fibroblast heterokaryons. Ingestion of latex particles did not affect the growth of primary human and established BHK(21)/C(13) hamster fibroblasts. In addition, somatic cell hybridization between hypoxanthine phosphoribosyltransferase-deficient (HPRT-) and thymidine kinase-deficient (TK-) mutants of BHK(21)/C(13) was also unaffected by lates particle ingestion.
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PMID:Use of latex particles for analysis of heterokaryon formation and cell fusion. 35 91

Purified DNA from wild-type Chinese ovary (CHO) cells has been used to transform three hypoxanthine phosphoribosyltransferase (HPRT) deficient murine cell mutants to the enzyme positive state. Transformants appeared at an overall frequency of 5 x 10(-8) colonies/treated cell and expressed CHO HPRT activity as determined by electrophoresis. One gene recipient, B21, was a newly isolated mutant of LMTK- deficient in both HPRT and thymidine kinase (TK) activities. Transformation of B21 to HPRT+ occurred at 1/5 the frequency of transformation to TK+; the latter was, in turn, an order of magnitude lower than that found in the parental LMTK- cells, 3 x 10(-6). Thus both clonal and marker-specific factors play a role in determining transformability. The specific activity of HPRT in transformant extracts ranged from 0.5 to 5 times the CHO level. The rate of loss of the transformant HPRT+ phenotype, as measured by fluctuation analysis, was 10(-4)/cell/generation. While this value indicates stability compared to many gene transferents, it is much greater than the spontaneous mutation rate at the indigenous locus. The ability to transfer the gene for HPRT into cultured mammalian cells may prove useful for mutational and genetic mapping studies in this well-studied system.
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PMID:Transformation of the gene for hypoxanthine phosphoribosyltransferase. 39 22

Somatic cell hybrids between mouse and human cell lines have been used to identify the specific chromosome that governs the synthesis of type I procollagen. Fourteen hybrid clones and subclones were derived independently from crosses between mouse parents [LM (thymidine kinase-negative) or A9 (hypoxanthine phosphoribosyltransferase-negative)] and human cells (human diploid lung fibroblasts WI-38 or diploid skin fibroblasts GM5, GM17, and GM9). The cultures were labeled with [(3)H]proline in modified Eagle's medium without serum. Radioactive procollagens were purified from the medium by the method of Church et al. [(1974) J. Mol. Biol. 86, 785-799]. DEAE-cellulose chromatography was used to separate collagen and type I and type III procollagen. Human type I procollagen was assayed by double immunodiffusion analysis with type I procollagen antibodies prepared by immunizing rabbits with purified human type I procollagen. These analyses combined with karyology and isozyme analyses of each hybrid line have produced evidence for the assignment of the gene for human type I procollagen to chromosome 17. A human microcell-mouse hybrid cell line containing only human chromosome 17 was positive for human type I procollagen, lending further support to the assignment of the human type I procollagen gene to chromosome 17. Finally, by using a hybrid line containing only the long arm of human chromosome 17 translocated onto a mouse chromosome, the type I procollagen gene can be assigned more specifically to the long arm of chromosome 17.
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PMID:Genetics of the connective tissue proteins: assignment of the gene for human type I procollagen to chromosome 17 by analysis of cell hybrids and microcell hybrids. 41 88

The availability of systems which permit the selective elimination of marsupial cells from fused cultures is an essential requirement for the production of marsupial X eutherian somatic cell hybrids. Such hybrids have particular advantages for genetic studies of mammalian cells. We describe the isolation and characterization of several drug-resistant marsupial cell strains. We have selected strains resistant to concentrations of 10 micrograms/ml of the purine analogues 8-azaguanine and 6-thioguanine. Several of these strains were found to be deficient in the enzyme hypoxanthine phosphoribosyltransferase and consequently sensitive to hypoxanthine-aminopterin-thymidine (HAT) selective medium. We have also isolated marsupial cell strains resistant to concentrations of 22 micrograms/ml of the thymidine analogue 5-bromodeoxyuridine. These strains were thymidine kinase deficient and HAT sensitive. Drug resistance was a stable characteristic maintained for many generations in the absence of the drug. However, inhibition of growth of these drug-resistant strains was strongly density dependent, a factor that caused difficulties in the selection of hybrids. We have also developed selective systems which exploit differences between marsupial and eutherian cells in sensitivity to growth in ouabain, and in adhesiveness and other growth properties. Marsupial cells were found to be naturally much more sensitive to ouabain than rodent cells, a phenomenon that should be useful in the selection of marsupial X rodent cellular hybrids. We discuss a number of difficulties associated with the derivation and use of variant marsupial cell strains.
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PMID:Fusion and hybridization of marsupial and eutherian cells. V. Development of selective systems. 56 74

A new selective medium has been developed for cells containing the enzyme deoxycytidine deaminase. This medium contains hypoxanthine, aminopterin, and 5-methyldeoxycytidine (HAM medium). To survive in the presence of the aminopterin, the cells must utilize deoxycytidine deaminase to convert the 5-methyldeoxycytidine to thymidine. The cells must also have thymidine kinase and hypoxanthine phosphoribosyltransferase. A mouse cell line deficient in deoxycytidine deaminase has been isolated from a deoxycytidine kinase-deficient line, using 5-bromodeoxycytidine as the selective agent. A hybrid line between this double mutant and a human diploid fibroblast was isolated in HAM medium. The hybrid line contains the chromosomes expected of a human-mouse hybrid. The deoxycytidine deaminase isozyme patterns on cellogel show that the human-mouse hybrid cell line produces an enzyme with an electrophoretic mobility intermediate between that of the human and that of the mouse.
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PMID:A human-mouse somatic hybrid line selected for human deoxycytidine deaminase. 123 1

A convenient system for gene targeting that uses hypoxanthine phosphoribosyltransferase (HPRT) minigenes as the selectable marker in HPRT-deficient mouse embryonic stem (ES) cells is described. Improvements to the expression of HPRT minigenes in ES cells were achieved by promoter substitution and the provision of a strong translational initiation signal. The use of minigenes in the positive-negative selection strategy for gene targeting was evaluated and the smaller minigenes were found to be as effective as a more conventional marker--the herpes simplex virus thymidine kinase gene. Minigenes were used to target the DNA repair gene ERCC-1 in ES cells. A new HPRT-deficient ES cell line was developed that contributes with high frequency to the germ line of chimeric animals. The ability to select for and against HPRT minigene expression in the new HPRT-deficient ES cell line will make this system useful for a range of gene-targeting applications.
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PMID:Gene targeting using a mouse HPRT minigene/HPRT-deficient embryonic stem cell system: inactivation of the mouse ERCC-1 gene. 144 55

This paper examines the mechanism by which 5-bromodeoxyuridine (BrdUrd) induces a high frequency of transient trifluorothymidine (F3TdR)-resistant variants in the TK6 human lymphoblast cell line (a TK +/- heterozygote). This phenomenon has previously been termed 'pseudomutation' (Liber et al., 1985). We now report that 5-azacytidine (5-AzaC), an inhibitor of DNA methylation, reverses BrdUrd-induced pseudomutation in a dose-dependent manner. The inhibition by 5-AzaC is highly specific and does not appear to involve nucleotide pool perturbations. 5-AzaC inhibits the pseudomutagenic effect (transient trifluorothymidine resistance in a thymidine kinase heterozygote), but not the stable mutagenic effect (stable 6-thioguanine resistance or trifluorothymidine resistance in a hypoxanthine-guanine phosphoribosyltransferase-proficient cell) induced by BrdUrd. 5-AzaC did not affect the induction nor expression of mutation induced by several other chemical mutagens at either the tk or hgprt loci. Inhibition of pseudomutation by 5-AzaC did not appear to be caused by a number of potential confounding factors. Although significant changes in the levels of DNA methylation were detected by HPLC analysis in BrdUrd-treated cells, the dose response for inhibition of pseudomutation by 5-AzaC was correlated with a significant decrease in 5-methylcytidine levels. These results and additional data in the literature have led us to postulate a novel mechanism in which the substitution of BrdUrd in a TpG dinucleotide(s) may serve as a substrate for non-heritable methylation and hence transiently inactivate tk gene expression.
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PMID:5-Azacytidine inhibits the induction of transient TK-deficient cells by 5-bromodeoxyuridine. A novel hypothesis for the facilitation of hypermethylation by 5-bromodeoxyuridine. 170 44

Chinese hamster ovary (CHO) cells were subjected to electroporation in the presence of 5-methyl deoxycytidine-triphosphate. This treatment increases by 10 to 100-fold the frequency of cells lacking thymidine kinase, hypoxanthine-guanine phosphoribosyltransferase, or adenine phosphoribosyltransferase. The inactivation of the genes coding for these enzymes is thought to occur following the direct incorporation of the methylated nucleotide triphosphate into DNA. The enzyme-deficient clones were stable, but almost all were reactivated at high frequency by the demethylating agent 5-azacytidine, to produce derivatives with enzyme activity. The results indicate that there is a direct relationship between DNA methylation and gene silencing.
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PMID:Gene silencing in mammalian cells by uptake of 5-methyl deoxycytidine-5'-triphosphate. 172 91


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