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)

If excision repair-proficient human cells are allowed time for repair before onset of S phase, the premutagenic lesions formed by (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy- 7,8,9,10-tetrahydrobenzo[a]pyrene (benzo[a]pyrene diol epoxide, BPDE) are lost from the transcribed strand of the hypoxanthine (guanine) phosphoribosyltransferase (HPRT) gene faster than from the nontranscribed strand. No change in strand distribution is seen with repair-deficient cells. These results suggest strand-specific repair of BPDE-induced DNA damage in human cells. To test this, we measured the initial number of BPDE adducts formed in each strand of the actively transcribed HPRT gene and the rate of repair, using UvrABC excinuclease in conjunction with Southern hybridization and strand-specific probes. We also measured the rate of loss of BPDE adducts from the inactive 754 locus. The frequencies of adducts formed by exposure to BPDE (1.0 or 1.2 microM) in either strand of a 20-kilobase fragment that lies entirely within the transcription unit of the HPRT gene were similar; the frequency in the 14-kilobase 754 fragment was approximately 20% lower. The rates of repair in the two strands of the HPRT fragment differed significantly. Within 7 hr after treatment with 1.2 microM BPDE, 53% of the adducts had been removed from the transcribed strand, but only 26% from the nontranscribed strand; after 20 hr, these values were 87% and 58%, respectively. In contrast, only approximately 14% of the BPDE adducts were lost from the 754 locus in 20 hr, a value even lower than the rate of loss from the overall genome (i.e., 38%). These results demonstrate strand-specific and preferential repair of BPDE adducts in human cells. They suggest that the heterogeneous repair of BPDE adducts in the human genome cannot be accounted for merely by the greatly increased rate of the repair specific to the transcribed strand of the active genes, and they point to a role for the chromatin structure.
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PMID:Preferential repair and strand-specific repair of benzo[a]pyrene diol epoxide adducts in the HPRT gene of diploid human fibroblasts. 160 50

We have determined the nucleotide sequences of 10 intragenic human HPRT gene deletion junctions isolated from thioguanine-resistant PSV811 Werner syndrome fibroblasts or from HL60 myeloid leukemia cells. Deletion junctions were located by fine structure blot hybridization mapping and then amplified with flanking oligonucleotide primer pairs for DNA sequence analysis. The junction region sequences from these 10 HPRT mutants contained 13 deletions ranging in size from 57 bp to 19.3 kb. Three DNA inversions of 711, 368, and 20 bp were associated with tandem deletions in two mutants. Each mutant contained the deletion of one or more HPRT exon, thus explaining the thioguanine-resistant cellular phenotype. Deletion junction and donor nucleotide sequence alignments suggest that all of these HPRT gene rearrangements were generated by the nonhomologous recombination of donor DNA duplexes that share little nucleotide sequence identity. This result is surprising, given the potential for homologous recombination between copies of repeated DNA sequences that constitute approximately a third of the human HPRT locus. No difference in deletion structure or complexity was observed between deletions isolated from Werner syndrome or from HL60 mutants. This suggests that the Werner syndrome deletion mutator uses deletion mutagenesis pathway(s) that are similar or identical to those used in other human somatic cells.
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PMID:Nucleotide sequence analysis of human hypoxanthine phosphoribosyltransferase (HPRT) gene deletions. 163 4

We have determined the genetic stability of three independent intragenic human HPRT gene duplications and the structure of each duplication at the nucleotide sequence level. Two of the duplications were isolated as spontaneous mutations from the HL60 human myeloid leukemia cell line, while the third was originally identified in a Lesch-Nyhan patient. All three duplications are genetically unstable and have a reversion rate approximately 100-fold higher than the rate of duplication formation. The molecular structures of these duplications are similar, with direct duplication of HPRT exons 2 and 3 and of 6.8 kb (HL60 duplications) or 13.7 kb (Lesch-Nyhan duplication) of surrounding HPRT sequence. Nucleotide sequence analyses of duplication junctions revealed that the HL60-derived duplications were generated by unequal homologous recombination between clusters of Alu repeats contained in HPRT introns 1 and 3, while the Lesch-Nyhan duplication was generated by the nonhomologous insertion of duplicated HPRT DNA into HPRT intron 1. These results suggest that duplication substrates of different lengths can be generated from the human HPRT exon 2-3 region and can undergo either homologous or nonhomologous recombination with the HPRT locus to form gene duplications.
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PMID:Molecular structure and genetic stability of human hypoxanthine phosphoribosyltransferase (HPRT) gene duplications. 163 5

The V79 Chinese hamster cell mutant V-B11 has previously been assigned to a new complementation group (group 7) of UV-sensitive rodent mutants. The D10 for cell survival is approximately 6 J/m2 for V-B11, compared with approximately 15 J/m2 for the parental V79 cell line. The removal of (6-4) photoproducts from the genome overall is not impaired in V-B11, and the level of unscheduled DNA synthesis measured 2 h after UV irradiation is similar to that observed in the parental V79 cells. DNA repair replication measured as a function of UV dose is approximately 50% reduced in V-B11 in comparison with V79, when measured during the first 6 h after UV irradiation. Furthermore, in V-B11 the rate of cyclobutane dimer removal from the HPRT gene is slower than in wild-type cells. Despite the observed defects no effect on the UV-induced frequency of mutants at two loci: Na+/K(+)-ATPase and HPRT was found in V-B11 cells. The properties of V-B11 are compared with those of other UV-sensitive mutants.
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PMID:DNA repair characteristics and mutability of the UV-sensitive V79 Chinese hamster cell mutant V-B11 (complementation group 7). 165 76

Cells of the human lymphoblast line WI-L2 and its derivative TK-6 were synchronized by centrifugal elutriation and cell-cycle dependent mutation to 6TGR (HPRT) and OUAR (Na+, K+ ATPase) measured. Bromodeoxyuridine induced 6TGR and OUAR mutations within S phase while butylmethyl-sulfonate induced mutation displayed no cell-cycle dependence. The data indicate that centrifugal elutriation is a facile means to obtain a useful degree of synchrony for these cell lines.
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PMID:Cell-cycle dependent mutation of human lymphoblasts: bromodeoxyuridine and butyl methanesulfonate. 165 42

We have shown previously a good correlation between etoposide-induced sister chromatid exchanges (SCE) and cytotoxicity. A semisynthetic derivative of podophyllotoxin, etoposide is also called Vepesid (Bristol; code designation VP-16-213, abbreviated VP-16). Since SCE represent DNA recombinational events, we hypothesized that VP-16-induced SCE might result in nonhomologous recombination in which segments of DNA were either deleted or added, leading to an alteration of gene sequences responsible for essential cell proteins. Alterations of such essential genes and consequent interference with formation of their products could consequently lead to cell death. To evaluate whether VP-16 treatment caused sufficient levels of DNA sequence alterations to interfere with gene product formation, we isolated hypoxanthine (guanine) phosphoribosyltransferase (HPRT)-deficient mutants from Chinese hamster V79 cells grown in the presence or absence of VP-16. DNA from 3 spontaneous mutants and 10 VP-16-induced mutants was analyzed by Southern blot hybridization to a full-length hamster HPRT cDNA probe. Most of the VP-16-induced mutants showed partial deletions and/or rearrangements of the HPRT gene. In contrast, spontaneous mutants showed negligible deletions or rearrangements. These results provide strong support for our hypothesis that deletion of genetic sequences may constitute an important component of the mechanism of VP-16-induced cell death.
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PMID:Etoposide (VP-16-213)-induced gene alterations: potential contribution to cell death. 168 41

Fanconi anemia (FA) is an autosomal recessive disorder characterized by chromosomal instability and abnormalities in the processing of DNA lesions induced by cross-linking agents. We previously reported that after photoaddition of psoralen derivatives the frequency of HPRT- mutants was significantly lower in FA than in normal human lymphoblasts. The hypomutability in FA cells was shown to be associated with an increased deletion frequency at the HPRT gene level. Further characterization of 70 unrearranged mutants (without detectable changes in restriction enzyme fragment length) according to the HPRT gene expression is reported here. Northern blot hybridization analysis demonstrates considerable differences in mRNA phenotyping between normal and FA cells. In normal cells, the minority of spontaneous (31%) and psoralen-induced mutants (0% and 14% according to treatment) arise from mutations that alter the HPRT gene transcription. In contrast to normal cells, in the majority of mutants isolated from FA cells, HPRT gene expression is found to be affected. Indeed a large proportion of either spontaneous (67%) or psoralen-induced (56% and 46%) mutants did not produce detectable amounts of mRNA. These results suggest that the mutagenic processing of spontaneous and psoralen-photoinduced lesions differs in normal and FA cells.
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PMID:HPRT gene expression differs in mutants derived from normal and Fanconi anemia cells: analysis of spontaneous and psoralen-photoinduced mutants. 168 31

To determine the methylation status of female germ cells in reference to the programmed reversal of X chromosome inactivation in these cells, we examined human fetal ovaries at developmental stages from the time germ cells initiate meiosis to when they cease to synthesize DNA (8-21 weeks gestation). Using methylation-sensitive restriction enzymes, we analyzed 57 MspI sites (32 sites in the CpG islands, and 25 nonclustered sites) from five X-linked housekeeping genes (HPRT, G6PD, P3, PGK, and GLA) and two tissue specific genes (X-linked F9 and autosomal EPO). Methylation patterns were compared to those of male germ cells, sperm, and somatic tissues of both sexes. All 32 MspI sites in CpG islands were unmethylated in germ-cell fractions of fetal ovary and adult testes, which could explain the reversibility of X inactivation in these tissues. However, whereas male meiotic germ cells were extensively methylated outside the islands (in the body of genes) and the methylation patterns resembled those of most somatic tissues, none of the 25 nonclustered CpGs was methylated in DNA contributed by the germ-cell component of fetal ovaries. The presence of faint MspI-like fragments in HpaII digests of fetal testes as well as fetal ovary prior to the onset of meiosis suggests that DNA of primordial germ cells is unmethylated in both sexes. Our observations of meiotic germ cells suggest that the female germ cells remain unmethylated, but that methylation in male germ cells occurs postnatally, prior to or during the early stages of spermatogenesis. In any event, the striking sex difference in methylation status of endogenous single-copy genes in meiotic germ cells could provide a molecular basis for parental imprinting of the mammalian genome.
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PMID:Sex difference in methylation of single-copy genes in human meiotic germ cells: implications for X chromosome inactivation, parental imprinting, and origin of CpG mutations. 169 9

Early embryonic development in Xenopus laevis is programmed in part by maternally derived mRNAs, many of which are translated at the completion of meiosis (oocyte maturation). Polysomal recruitment of at least one of these mRNAs, G10, is regulated by cytoplasmic poly(A) elongation which, in turn, is dependent upon the cytoplasmic polyadenylation element (CPE) UUUUUUAUAAAG and the hexanucleotide AAUAAA (L. L. McGrew, E. Dworkin-Rastl, M. B. Dworkin, and J. D. Richter, Genes Dev. 3:803-815, 1989). We have investigated whether sequences similar to the G10 RNA CPE that are present in other RNAs could also be responsible for maturation-specific polyadenylation. B4 RNA, which encodes a histone H1-like protein, requires a CPE of the sequence UUUUUAAU as well as the polyadenylation hexanucleotide. The 3' untranslated regions of Xenopus c-mos RNA and mouse HPRT RNA also contain U-rich CPEs since they confer maturation-specific polyadenylation when fused to Xenopus B-globin RNA. Polyadenylation of B4 RNA, which occurs very early during maturation, is limited to 150 residues, and it is this number that is required for polysomal recruitment. To investigate the possible diversity of factors and/or affinities that might control polyadenylation, egg extracts that faithfully adenylate exogenously added RNA were used in competition experiments. At least one factor is shared by B4 and G10 RNAs, although it has a much greater affinity for B4 RNA. Additional experiments demonstrate that an intact CPE and hexanucleotide are both required to compete for the polyadenylation apparatus. Gel mobility shift assays show that two polyadenylation complexes are formed on B4 RNA. Optimal complex formation requires an intact CPE and hexanucleotide but not ongoing adenylation. These data, plus additional RNA competition studies, suggest that stable complex formation is enhanced by an interaction of the trans-acting factors that bind the CPE and polyadenylation hexanucleotide.
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PMID:Maturation-specific polyadenylation and translational control: diversity of cytoplasmic polyadenylation elements, influence of poly(A) tail size, and formation of stable polyadenylation complexes. 170 Feb 72

The Chinese hamster ovary (CHO) assay, which measures newly induced mutations at the hypoxanthine-guanine phosphoribosyltransferase (hgprt) locus, has been widely used for mutagenesis testing. The insensitivity of the standard assay to some genotoxic agents has been speculated to be due to the relatively small number of cells used in the assay. In the present study, we have compared the standard monolayer assay with a suspension adapted CHO assay that uses cell numbers comparable to that of the L5178Y mouse lymphoma assay. Nine compounds, ethyl methanesulfonate (EMS), methyl methanesulfonate (MMS), 2-methoxy-6-chloro-9-[3-(ethyl-2-chloroethyl)-aminopropylamino]-acridine 2HCl (ICR 170), methyl acrylate, ethyl acrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, 2-ethylhexyl acrylate and dicyclopentenyloxyethyl methacrylate were evaluated in the monolayer and suspension assays. Both assays gave the same overall qualitative results for the test compounds. There were some quantitative differences in the mutant frequency for the three compounds found to be mutagenic (EMS, MMS and ICR 170). The acrylates (many of which appear to exert their genotoxic effect through a clastogenic mechanism) were negative in both test systems. The use of the suspension assay did not improve the ability of the hgprt locus to detect the genotoxicity of the acrylates. Thus, increasing the number of cells does not improve the ability of the CHO/HGPRT assay to detect compounds that act primarily by a clastogenic mechanism.
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PMID:Comparison of mutagenicity results for nine compounds evaluated at the hgprt locus in the standard and suspension CHO assays. 171 14


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