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)

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.
Mol Cell Biol 1992 Dec
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

Human diploid fibroblasts (strain VH-10) were exposed to the direct-acting alkylating agent, ethylene oxide (EtO), in vitro, and the frequency of HPRT mutants was evaluated by selection in medium containing 6-thioguanine. A dose-dependent increase of the mutant frequency was found in the dose range of 2.5-10 mMh of EtO. The EtO-induced mutant frequency increased 5-19 times the background frequency at low or moderately toxic doses, which indicates that EtO is a strong mutagen in human fibroblasts in vitro. The mutagenic potency was 9.8 x 10(-6) per mMh.
Environ Mol Mutagen 1992
PMID:Induction of 6-thioguanine-resistant mutants in human diploid fibroblasts in vitro with ethylene oxide. 154 Dec 59

The metabolic fate of labeled hypoxanthine and inosine, degradation products of adenine nucleotides, was studied in cultured beating cardiomyocytes, in order to assess the physiological significance of their contribution to salvage nucleotide synthesis in the heart. Inosine and hypoxanthine were found to be incorporated into nucleotides by a similar rate, but in the presence of 8-aminoguanosine, a potent inhibitor of purine nucleoside phosphorylase (EC 2.4.2.1), the rate of inosine incorporation into nucleotides was markedly reduced (by 75%), indicating that inosine incorporation to IMP (inosinic acid) occurs following its degradation to hypoxanthine. The proportion of hypoxanthine converted to IMP by hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) is markedly greater than that degraded to xanthine and uric acid by xanthine oxidase (EC 1.3.2.3). However, close to 50% of the IMP formed was degraded to inosine by IMP 5'-nucleotidase (EC 3.1.3.5). The results demonstrate the activity of the following futile cycle in the cardiomyocytes: hypoxanthine----IMP----inosine----hypoxanthine. The rational for the activity of this energy consuming cycle is yet unclear.
J Mol Cell Cardiol 1992 Feb
PMID:Metabolic fate of hypoxanthine and inosine in cultured cardiomyocytes. 158 1

We have investigated coelectroporation as a method for introducing minor genetic changes into specific genes in embryonic stem cells. A selectable marker (neo) and a targeting replacement vector designed to insert a 4-bp insertion into exon 3 of the mouse hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene were coelectroporated into embryonic stem cells and selected in G418 and 6-thioguanine (6-TG). HPRT-negative clones were obtained at a frequency of approximately 1 per 520 G418r clones. Southern analysis and the polymerase chain reaction were used to demonstrate that 3 of 36 of the 6-TG-resistant clones had the desired 4-bp insertion without any other disruption of the HPRT locus. Initial studies indicated that the other 33 6-TG-resistant clones probably resulted from the targeted integration of a concatemer containing both the targeting construct and the selectable neo gene.
Mol Cell Biol 1992 Jun
PMID:Investigation of coelectroporation as a method for introducing small mutations into embryonic stem cells. 158 68

We have established a comprehensive procedure based on the polymerase chain reaction (PCR) to analyze the molecular spectrum of mutations at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in Chinese hamster cells. The procedure includes direct sequencing of PCR-amplified hprt cDNA for locating point mutations in the expressed coding sequences, multiplex PCR amplification of the hprt exons for screening large deletions, and direct sequencing of PCR-amplified hprt exons and their flanking regions for detecting intronic mutations resulting in mRNA splicing errors. Using this procedure, we have identified different types of mutations among a representative collection of spontaneous and induced HPRT-deficient Chinese hamster cell mutants. This procedure is simple, rapid, accurate, and practical for a comprehensive study of the mutation spectrum in a large number of HPRT-deficient Chinese hamster cell mutants.
Environ Mol Mutagen 1992
PMID:Polymerase chain reaction-based comprehensive procedure for the analysis of the mutation spectrum at the hypoxanthine-guanine phosphoribosyltransferase locus in Chinese hamster cells. 160 Sep 52

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.
Somat Cell Mol Genet 1991 Nov
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.
Somat Cell Mol Genet 1990 May
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.
Mol Cell Biol 1990 Nov
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 enzyme hypoxanthine phosphoribosyltransferase (HPRT) catalyzes the metabolic salvage of the purine bases hypoxanthine and guanine. We previously characterized the genomic structure of the human HPRT gene and described its promoter sequence. In this report, we identify cis-acting transcriptional control regions of the human HPRT gene by linking various 5'-flanking sequences to the bacterial chloramphenicol acetyltransferase gene. The sequence from positions -219 to -122 relative to the translation initiation site is required for maximal expression of this gene, and it functions equally in both normal and reverse orientations. In addition, a cis-acting negative element is present in the region spanning from positions -570 to -388. This negative element can also repress promoters of heterologous genes, such as those of adenosine deaminase and dihydrofolate reductase, which are structurally and functionally similar to the human HPRT promoter. Furthermore, this repressor element functions independently of its orientation but appears to be distance dependent. In vivo competition assays demonstrated that the trans-acting factor(s) that binds to this negative element specifically inhibits human HPRT promoter activity. Taken together, these data localize cis-acting sequences important in the regulation of human HPRT gene expression and should allow the study of protein-DNA interactions which modulate the transcription of this gene.
Mol Cell Biol 1991 Aug
PMID:Functional characterization of the human hypoxanthine phosphoribosyltransferase gene promoter: evidence for a negative regulatory element. 171 4

We have analyzed the adenine phosphoribosyltransferase (APRT) enzyme from Chinese hamster ovary cells through the study of mutants that are able to grow in the presence of the toxic adenine analogue 8-azaadenine. The distribution of the amino acid alterations was analyzed in terms of the binding regions for the purine and phosphoribosylpyrophosphate substrates and a comparison was made with mutants known in human APRT and human, mouse and hamster hypoxanthine-guanine phosphoribosyltransferase. A number of mutants were found to cluster in several regions of the amino acid sequence. Residual enzyme activity with adenine was determined and this was correlated with substrate binding regions. A model of the secondary structure features is proposed.
J Mol Biol 1991 Sep 05
PMID:Mutational analysis of the structure and function of the adenine phosphoribosyltransferase enzyme of Chinese hamster. 171 94


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