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)

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

Spontaneous thioguanine-resistant mutants were derived from populations of finite-life-span, diploid human fibroblasts by means of a fluctuation analysis. cDNA was prepared from mutant HPRT mRNA and amplified by the polymerase chain reaction, and the sequence of the product was analyzed. Exon deletions, which very likely arose from mutations in the intron splice site consensus sequences, were found in 10 of the 37 mutants examined (27% of the total). Among the 28 mutations in the coding sequence, base pair substitutions predominated (89%). With the exception of one base pair involved in a tandem mutation, all base pair substitutions resulted in alterations in the predicted amino acid sequence of the protein. In addition there were three frameshift mutations, consisting of the deletion of one or two base pairs. Although mutations occurred throughout the coding sequence, 50% (14/28) were found in the 5' portion of exon 3.
Somat Cell Mol Genet 1991 Sep
PMID:Kinds and locations of mutations arising spontaneously in the coding region of the HPRT gene of finite-life-span diploid human fibroblasts. 176 87

We describe a highly efficient stable gene transfection procedure for Chinese hamster ovary (CHO) cells using a modification of the calcium phosphate-DNA coprecipitation method. We have found that treatment of CHO cells with chloroquine increases the efficiency of gene transfer by up to 20-fold (from approx. 0.01% to approx. 0.2%) when transfection is done using the pSV2-neo plasmid. The optimized transfection procedure requires that CHO cells to be incubated with calcium phosphate-DNA coprecipitate and chloroquine (100 microM) for a total of 16 h. By using high-molecular-weight human genomic DNA as a DNA source for transfection, we show that this procedure is equally efficient for stably transferring a much larger gene, such as the 49-kb human hypoxanthine phosphoribosyltransferase gene.
Somat Cell Mol Genet 1991 Sep
PMID:High-efficiency stable gene transfection using chloroquine-treated Chinese hamster ovary cells. 176 89

Epidemiologic application of the human in vivo hypoxanthine-guanine phosphoribosyltransferase (hprt) mutation assay requires screening of mutant colonies to differentiate independent from clonal origin. Previously, sibship was defined by Southern blot analysis of T cell receptor gene rearrangements. We report here a more expedient method to determine these rearrangements utilizing the polymerase chain reaction (PCR) and a DNA single-strand conformation polymorphism technique. The results are consistent with those obtained by Southern blotting in that sibship can be defined easily. A major advantage is that cells may be taken directly from the microtiter plate, eliminating the necessity to expand the clones and isolate genomic DNA. Cell lines which have not undergone receptor gene rearrangements cannot serve as PCR templates and do not interfere with this analysis. Furthermore, background from the large number of nonmutant lymphocytes present in the well does not hinder the analysis of the T cell receptor pattern of a mutant. This technique facilitates rapid screening of a large number of clones in a shorter time than Southern blotting, and is useful for the study of in vivo mutation and the clonal expansion of mutants in populations of T cells.
Mutagenesis 1991 Sep
PMID:Single-strand conformation polymorphisms can be used to detect T cell receptor gene rearrangements: an application to the in vivo hprt mutation assay. 179 41

To better understand the mechanism of homologous recombination in mammalian cells that facilitates gene targeting, we have analyzed the recombination reaction that inserts a plasmid into a homologous chromosomal locus in mouse embryonic stem cells. A partially deleted HPRT gene was targeted with various plasmids capable of correcting the mutation at this locus, and HPRT+ recombinants were directly selected in HAT medium. The structures of the recombinant loci were then determined by genomic Southern blot hybridizations. We demonstrate that plasmid gaps of 200, 600, and 2,500 bp are efficiently repaired during the integrative recombination reaction. Targeting plasmids that carry a double-strand break or gap in the region of DNA homologous to the target locus produce 33- to 140-fold more hypoxanthine-aminopterin-thymidine-resistant recombinants than did these same plasmids introduced in their uncut (supercoiled) forms. Our data suggest that double-strand gaps and breaks may be enlarged prior to the repair reaction since sequence heterologies carried by the incoming plasmids located close to them are often lost. These results extend the known similarities between mammalian and yeast recombination mechanisms and suggest several features of the insertional (O-type) gene targeting reaction that should be considered when one is designing mammalian gene targeting experiments.
Mol Cell Biol 1991 Sep
PMID:Double-strand gap repair in a mammalian gene targeting reaction. 187 28

Targeted recombination in murine embryonic stem cells promises to be a powerful tool for introducing specific mutations into target genes to study development in mice and to create animal models of human disease. Gene targeting also holds potential for correcting genetic defects as an approach to human gene therapy. To precisely modify target genes, homologous recombination must proceed with high fidelity. However, several results have suggested that targeted recombination may be highly mutagenic. To test the accuracy of gene targeting we analyzed 44 independent targeted recombinants at the hypoxanthine phosphoribosyltransferase (HPRT) locus in a human fibroblast cell line and in mouse embryonic stem cells. We surveyed 80 kilobases around the sites of recombination by using chemical cleavage of mismatches. Only two mutations were found: a T----G transversion and a thymidine deletion. Thus, gene targeting in mammalian cells can be extremely accurate. These results demonstrate the feasibility of generating precise modifications of mammalian genomes by gene targeting.
Proc Natl Acad Sci U S A 1991 Sep 15
PMID:Fidelity of targeted recombination in human fibroblasts and murine embryonic stem cells. 189 53

Accumulated data using functional, morphologic, and histochemical analysis suggests that follicular proliferations in the thyroid include polyclonal and monoclonal patterns with encapsulated follicular adenomas most frequently monoclonal, and other nodules generally polyclonal. However, examples of polyclonal carcinomas or adenomas raise the possibility that histologically similar lesions may arise through different pathogenetic mechanisms. The authors have performed a clonal analysis of histologically benign and malignant thyroid nodules in seven women using HPRT (hypoxanthine phosphoribosyl transferase) and PGK (phosphoglycerate kinase) restriction fragment length polymorphisms (RFLPs) on the X chromosome. These RFLPs used in concert with methylation-sensitive restriction endonucleases HpaII and HhaI permit distinction of active and inactive X chromosomes. DNA from a multinodular goiter showed equal sensitivity of both X chromosome RFLP alleles to a methylation-sensitive restriction endonuclease, consistent with a polyclonal origin. In contrast, three solitary follicular nodules and three carcinomas displayed predominant sensitivity of a single RFLP allele, consistent with a monoclonal origin. Although further detailed studies will be necessary to understand polyclonal origins reported for some adenomas, our data from a limited number of samples supports a predominantly monoclonal origin, and possible neoplastic pathogenesis, for many solitary adenomatous nodules in the thyroid.
Am J Pathol 1990 Sep
PMID:Clonal analysis of solitary follicular nodules in the thyroid. 197 86

The Lowe oculocerebrorenal syndrome (OCRL) is characterized by congenital cataract, mental retardation, and renal tubular dysfunction. We are using the approaches of linkage analysis, mapping with somatic cell hybrids, and long-range restriction mapping to determine the order of Xq24-q26 markers with respect to each other and to the OCRL locus. DXS42 and DXS100 are proximal to the translocation breakpoint in a female patient with OCRL and a de novo translocation t(X;3)(q25;q27). DXS10, DXS86, HPRT, and DXS177 are distal to the breakpoint. These flanking markers show tight linkage to the disease locus in 11 families segregating for OCRL. Results from field inversion gel analysis show that DXS86 and DXS10 share a 460-kb BssHII fragment. Multipoint analysis to determine the position of HPRT with respect to (DXS10,DXS86) suggests that HPRT is proximal to (DXS10,DXS86). We propose the following order for markers in Xq24-q26: Xcen-(DXS42,DXS37,DXS100)-OCRL-DXS53 -HPRT-[(DXS10,DXS86),DXS177]-Xqter. The identification of additional tightly linked flanking markers extends the number of markers available for use in genetic counseling and begins to define the physical map of the region containing the gene for OCRL.
Genomics 1990 Sep
PMID:Genetic and physical mapping of Xq24-q26 markers flanking the Lowe oculocerebrorenal syndrome. 208 1

The effect of ionizing radiation on methotrexate (MTX) resistance and gene amplification in cultured mammalian cells was investigated. X-irradiation of mouse EMT-6 cells induced cell killing and MTX resistance due to amplification of dihydrofolate reductase (dhfr) gene in a dose-dependent manner. The highest yields of mutant cells were obtained at approximately D37 (the dose at which 37% of the cells survive), where the frequency of MTX-resistant cells was four- to eightfold over that of the unirradiated population. The proportion of MTX-resistant cells among the survivors increased logarithmically with dose, up to a 1000-fold increase over unirradiated cells at 1000 cGy, the highest dose tested. The induced frequency of MTX resistance after X-irradiation was greater than the induced frequency of 8-azaguanine resistance, which indicates deletion of the hypoxanthine phosphoribosyltransferase gene. Inhibition of poly(ADP-ribose) polymerase by the addition of 3-aminobenzamide before irradiation increased both cell killing and MTX resistance. Metaphase spreads of chromosomes from EMT-6 cells that had been irradiated and subjected to stepwise increases in MTX concentration showed numerous double minutes. Pulsed-field gel electrophoresis of the DNA from cells containing radiation-induced double minutes showed that many copies of the dhfr gene were present on circular DNA molecules of 10(6), 2 x 10(6), and 3 x 10(6) base pairs. These results suggest a relationship between the induction of chromosome aberrations and the induction of gene amplification.
Somat Cell Mol Genet 1990 Sep
PMID:X-ray induction of methotrexate resistance due to dhfr gene amplification. 212 27

The L1 gene of human papillomavirus type 16 (HPV-16) driven by the vaccinia virus major late 4b gene promoter has been inserted into three different sites of the vaccinia virus genome. Insertion into the thymidine kinase (TK) gene was achieved by selection of TK- mutants in BUdR on TK- cells. Insertion into two vaccinia virus serine protease inhibitor (serpin) genes was achieved by co-insertion of the Escherichia coli xanthine guanine phosphoribosyltransferase gene linked to the vaccinia virus 7.5K promoter and selection of mycophenolic acid-resistant recombinant viruses. Each recombinant virus expressed a 57K L1 protein at similar levels and with similar kinetics. However, immunization of mice with these recombinant viruses induced different levels of antibody to the L1 protein. Viruses lacking serpin genes B13R and B24R induced significantly higher antibody levels than did viruses lacking the TK gene. The presence of functional B13R and B24R gene products is therefore somehow immunosuppressive at least for antibody responses to the L1 protein of HPV-16.
J Gen Virol 1990 Sep
PMID:Increased antibody responses to human papillomavirus type 16 L1 protein expressed by recombinant vaccinia virus lacking serine protease inhibitor genes. 217 May 78


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