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)

A series of spontaneous and ethyl methanesulfonate-induced 6-thioguanine-resistant mutants were isolated in the CHO-10T5 cell line. This cell line was constructed by the introduction of a shuttle vector containing the Escherichia coli gpt gene into a hypoxanthine-guanine phosphoribosyltransferase deficient derivative of the Chinese hamster cell line CHO-K1. Shuttle vector sequences were recovered from many of the mutant cell lines by the COS cell fusion technique and the DNA base sequence of the gpt genes was determined whenever possible. The base sequences were determined for gpt genes recovered from 29 spontaneous mutants. Of these 29 mutants, 9 have single base substitutions, 1 has a small duplication, 17 have simple deletions, 1 has a deletion with additional bases inserted at the deletion site, and 1 has no change in the gpt coding sequence. Many of the deletions were less than 20 basepairs in length and several occurred in a region previously observed to be a hotspot for spontaneous deletions. The generation of the deletion/insertion mutation may have involved a quasi-palindromic intermediate. A total of 59 ethyl methansesulfonate-induced mutants were isolated and vector sequences were recovered from 50 mutants. All 50 mutants sequenced had single base substitutions and most (45) were G:C to A:T transitions. While there were no strong hotspots in this collection of mutations, the site distribution was obviously nonrandom. Many of the G:C to A:T transitions either produced a nonsense codon or occurred at glycine codons.
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PMID:DNA base sequence changes in spontaneous and ethyl methanesulfonate-induced mutations of a chromosomally-integrated gene in Chinese hamster ovary cells. 138 28

Recently, we have observed a small (36%), but significant, enhancement of the frequency of 6-thioguanine (6-TG)-resistant T-lymphocytes in blood from smokers. The molecular nature of 43 hypoxanthine-guanine phosphoribosyltransferase (hprt) mutant T-lymphocyte clones from nine smoking individuals was determined to investigate whether the increase in hprt mutant frequency would lead to a changed mutation spectrum. The types and distribution of hprt mutations in smokers was compared with those found in 55 6-TGr T-lymphocyte clones from 12 members of a control group of non-smokers. From this control group 25 hprt mutants were novel, whereas 31 have been described previously. Among smokers and non-smokers, a similar proportion of base substitutions (approximately 35%), mutations causing aberrant splicing (approximately 37%), frameshifts (approximately 16%) and deletions (approximately 9%) was found. In both groups, GC----AT base pair changes were found to be predominant among transitions. However, whereas all types of transversions were about equally represented in non-smokers, GC----TA transversions were not recovered among smokers. Investigation of the distribution of base substitutions over the hprt coding region showed no differences between the two groups. These data provide no clues on the nature of DNA adducts induced by smoking, which are thought to be responsible for the increased mutation frequency at the hprt locus in T-lymphocytes from smokers.
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PMID:Enhanced hprt mutant frequency but no significant difference in mutation spectrum between a smoking and a non-smoking human population. 139 47

Nuclear matrix organizes the mammalian chromatin into loops. This is achieved by binding of nuclear matrix proteins to characteristic DNA landmarks in introns as well as proximal and distal sites flanking the 5' and 3' ends of genes. Matrix anchorage sites (MARs), origins of replication (ORIs), and homeotic protein binding sites share common DNA sequence motifs. In particular, the ATTA and ATTTA motifs, which constitute the core elements recognized by the homeobox domain from species as divergent as flies and humans, are frequently occurring in the matrix attachment sites of several genes. The human apolipoprotein B 3' MAR and a stretch of the Chinese hamster DHFR gene intron and human HPRT gene intron shown to anchor these genes to the nuclear matrix are mosaics of ATTA and ATTTA motifs. Several origins of replication also share these elements. This observation suggests that homeotic proteins which control the expression level of many genes and pattern formation during development are components of the nuclear matrix. Thus, the nuclear matrix, known as the site of DNA replication, might sculpture the crossroads of the differential activation of origins during development and S-phase and the control of gene expression and pattern formation in embryogenesis.
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PMID:Homeotic protein binding sites, origins of replication, and nuclear matrix anchorage sites share the ATTA and ATTTA motifs. 142 78

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

In 1956, I decided to apply my experience in microbial genetics to developing analogous systems for human cell lines, including the selection of mutants with either a loss or gain of a biochemical function. For instance, mutants resistant to azahypoxanthine showed a loss of the HPRT enzyme (hypoxanthine phosphoribosyl transferase), whereas gain of the same enzyme was accomplished by blocking de novo purine biosynthesis with aminopterin, while supplying hypoxanthine and thymine (HAT selection). Using HAT selection, we: (i) genetically transformed HPRT- mutant cells to HPRT+ wild type by using DNA extracted from HPRT+ cells, and (ii) selected HPRT+ hybrid cells by fusing HPRT- D98/AH2 cells with skin cells. These approaches, which we dubbed in 1962 as a 'first step toward gene therapy', contributed to the later development of (i) cell fusion techniques, (ii) the development of monoclonal antibodies, (iii) routine transformation of mammalian cells with cloned genes, and (iv) methods for creating transgenic organisms.
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PMID:Use of the HPRT gene and the HAT selection technique in DNA-mediated transformation of mammalian cells: first steps toward developing hybridoma techniques and gene therapy. 144 89

Dosage compensation of X-linked genes in male and female mammals is accomplished by random inactivation of one X chromosome in each female somatic cell. As a result, a transcriptionally active allele and a transcriptionally inactive allele of most X-linked genes reside within each female nucleus. To examine the mechanism responsible for maintaining this unique system of differential gene expression, we have analyzed the differential binding of regulatory proteins to the 5' region of the human hypoxanthine phosphoribosyltransferase (HPRT) gene on the active and inactive X chromosomes. Studies of DNA-protein interactions associated with the transcriptionally active and inactive HPRT alleles were carried out in intact cultured cells by in vivo footprinting by using ligation-mediated polymerase chain reaction and dimethyl sulfate. Analysis of the active allele demonstrates at least six footprinted regions, whereas no footprints were detected on the inactive allele. Of the footprints on the active allele, at least four occur over canonical GC boxes or Sp1 consensus binding sites, one is associated with a potential AP-2 binding site, and another is associated with a DNA sequence not previously reported to interact with a sequence-specific DNA-binding factor. While no footprints were observed for the HPRT gene on the inactive X chromosome, reactivation of the inactive allele with 5-azacytidine treatment restored the in vivo footprint pattern found on the active allele. Results of these experiments, in conjunction with recent studies on the X-linked human PGK-1 gene, bear implications for models of X chromosome inactivation.
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PMID:Multiple in vivo footprints are specific to the active allele of the X-linked human hypoxanthine phosphoribosyltransferase gene 5' region: implications for X chromosome inactivation. 144 69

Fluoranthene (FA) was studied with respect to possible mechanisms of its high mutagenicity but low carcinogenicity, in comparison with the corresponding properties of benzo[a]pyrene (BaP), and with regard to the synergism of these two compounds shown by van Duuren and Goldschmidt (J Natl Cancer Inst 56, 1976, 1237). FA and BaP activated by S9 from Aroclor 1254 (PCB)-treated rats induce HPRT mutations in CHO cells with about equal effectiveness at the same exposure doses, which also lead to the same frequencies of repairable DNA adducts, enzyme-induced strand breaks being used as an indirect measure of adducts to DNA. FA was also shown to be an efficient inducer of SCE in human peripheral lymphocytes cocultivated with PCB-treated HepG2 cells or with liver cells from PCB-pretreated rats. For the induction of SCE, FA and BaP were shown to act additively. From metabolic studies with liver microsomes from C57Bl/6 mice it is concluded that, whereas BaP induces the metabolism of BaP to the mutagenic epoxide, neither BaP nor FA is able to induce the metabolism of FA. In mutation experiments with V79 cells (XEM2) constitutive for P450 IA1 activity, BaP 7,8-diol but not FA 2,3-diol provokes a high frequency of HPRT mutations. In cells constitutive for P450 IA2 enzymatic activity FA and BaP are but weakly mutagenic and practically nonmutagenic, respectively. Due to the additivity of the genotoxic effects of FA and BaP, induction of an error-prone condition by the latter compound seems to be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:On the bioactivation and genotoxic action of fluoranthene. 146 88

We have analyzed the organization, structure, and function of the murine T-cell receptor C alpha/C delta region. This region spans 94.6 kb of DNA and contains the C alpha and C delta genes, as well as the V delta 5, J delta 2, and 50 different J alpha gene segments. Within this sequence we have identified 15 new J alpha gene segments, 40 new 5' RNA splice signals, and 40 new DNA rearrangement signals for the J alpha gene segments. The murine C alpha/C delta sequence contains an exceptionally high level of coding sequence with over 5.7% of the total sequence found in the exons. This is much more than that found in the beta-globin locus and the HPRT locus. Using the sequence data obtained from the C alpha/C delta region, we have designed simple assays to test for J alpha gene segment transcription and to determine the level of polymorphism for simple repeat sequences among different inbred strains of mice using the polymerase chain reaction. Furthermore, comparisons of this 95 kb of sequence with the available sequence from homologous regions of other species have led to the identification of a highly conserved sequence that is present throughout vertebrates and in the mouse binds lymphocyte-specific nuclear proteins. Comparisons of a 10-kb region, which includes the C alpha gene in human and mouse, average 66% sequence similarity. These studies support the contention that large-scale DNA sequencing projects of homologous regions of mouse and human will provide powerful new tools for studying the biology and evolution of loci such as the T-cell receptor and for identifying and posing new questions about the functions of conserved sequences.
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PMID:Organization, structure, and function of 95 kb of DNA spanning the murine T-cell receptor C alpha/C delta region. 150 54

The effects of the reaction photosensitized by 4'-hydroxymethyl-4,5'-8-trimethylpsoralen (HMT) on a mouse lymphoma cell line have been examined. Using the hypoxanthine phosphoribosyltransferase (HPRT) locus as target gene, a mutagenic effect of the photoreaction can be detected concomitantly with a loss of cell viability. Isolation of HPRT deficient clones has permitted a molecular characterization of the mutational pattern induced by the photosensitization reaction mediated by HMT. Southern blotting analysis demonstrated that the HPRT deficiency could not be correlated with gene deletions larger than 300 bp. Using polymerase chain reaction on both DNA and cDNA, amplification products have been cloned into M13mp18 and sequenced. Base transversions targeted on thymine residues have been located in exon 2, 3, 8 and 9 together with spontaneous frameshift mutations occurring in a run of guanine residues in exon 3. HPRT deficiencies owing to mutations arising in the HPRT promoter region have also been observed. Dot and Northern blot analysis revealed that the photoreaction could lead to either a reduced level of gene transcription or to a complete absence of HPRT m-RNA. Using polymerase chain reaction (PCR) amplification and agarose gel electrophoresis, deletions in the HPRT promoter have been observed and correlated to deficient enzyme expression.
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PMID:Molecular analysis of mutations induced by 4'-hydroxymethyl-4,5',8-trimethylpsoralen and UVA in the mouse HPRT gene. 154 88

The change in DNA responsible for partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency in three brothers has been determined by polymerase chain amplification and sequencing. An A-to-G substitution at base 155 in exon 3 predicts a change in aspartic acid 52 to glycine. Allele-specific polymerase chain amplification verified the presence of the mutation in genomic DNA and provides a means of direct diagnostic assay.
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PMID:The point mutation of hypoxanthine-guanine phosphoribosyltransferase (HPRTEdinburgh) and detection by allele-specific polymerase chain reaction. 155 76


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