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)

A panel of five hybrid cell lines containing mouse X chromosomes with various deletions has been obtained by fusing splenocytes from male mice carrying one of a series of reciprocal X-autosome translocations with the azaguanine-resistant Chinese hamster cell line CH3g. These hybrids have been extensively characterized by using the allozymes hypoxanthine/guanine phosphoribosyltransferase (encoded by the Hprt locus) and alpha-galactosidase (Ags) and a series of 11 X-chromosome-specific DNA probes whose localization had been previously established by linkage studies. Such studies have established the genetic breakpoints of the T(X;12)13Rl and T(X;2)14Rl X-autosome translocations on the X chromosome and provided additional information as to the X-chromosome genetic breakpoints of the T(X;16)16H, T(X;4)7Rl, and T(X;7)6Rl translocations. The data establish clearly that both the T(X;4)7Rl and T(X;12)13Rl X-chromosome breakpoints are proximal to Hprt, the breakpoint of the former being more centromeric, lying as it does in the 9-centimorgan interval between the ornithine transcarbamoylase (Otc) and DXPas7 (M2C) loci. Similarly, it is now clear that the T(X;16)16H X-autosome translocation breakpoint lies distal to the DXPas8 (St14-1) locus, narrowing the X-chromosome breakpoint down to a region flanked proximally by this marker and representing, as expected from previous data, the distal quarter of the Hprt-Ta subchromosomal span. These five hybrid cell lines provide, with the previously characterized EBS4 hybrid cell line, a nested series of seven mapping intervals distributed along the length of the mouse X chromosome. Their characterization not only allows further correlation of the genetic and cytological X-chromosome maps but also should permit the rapid identification of DNA probes specific for particular regions of the mouse X chromosome.
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PMID:Characterization of a panel of somatic cell hybrids for regional mapping of the mouse X chromosome. 303 43

A panel of over 50 hybrid cells containing varying portions of the long arm of the human X chromosome have been obtained by chromosome-mediated gene transfer (CMGT) of human chromosomes to mouse cells deficient in HPRT. This panel is used to investigate the size and integrity of transfected human chromosome fragments and also to examine the effect of including a selectable DNA plasmid in the transfection mix. Chromosomal rearrangements are found to be generated in the chromosome transfer process, and the human X centromeric region is detected in the transfected cells at an unusually high frequency. Extensive lengths of X chromosome DNA are transferred intact, suggesting potential uses of CMGT in cloning large genes and loci for which only the chromosomal map position is known.
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PMID:Investigation of chromosome-mediated gene transfer using the HPRT region of the human X chromosome as a model. 367 22

Mutations caused by exposure to X-radiation and to radon and its decay products were compared in the hprt gene of a human lymphoblastoid cell line. Thirty-one X-radiation-induced, 29 radon-induced, and 24 spontaneous mutants were recovered from cell cultures under identical conditions except for the exposure to radiation. Seven spontaneous point mutations were recovered and DNA sequenced. These mutations included three C:G-->T:A transitions. These spontaneous point mutations were located in the exon or splice donor regions of five of the nine hprt exons. Four X-radiation-induced and three radon-induced point mutations were also analyzed by DNA sequencing. The frequency of induced mutants at the D0 doses for radon and X-radiation respectively were 5 x 10(-6) and 4.5 x 10(-6). Deletions were the predominant mutations recovered from both radon- and X-irradiated cells. Eighty-one percent of the mutants from X-radiation-treated cultures, 86% of the radon-treated cultures, and 63% of the spontaneous mutants involved deletions. Deletions involving exon and intron DNA, as well as intron DNA alone, were found to inactivate the hprt gene and result in a selectable HPRT- phenotype. Among the deletion mutants, however, only 21% of the spontaneous mutants versus 55% of both the X-radiation- and radon-induced mutants exhibited loss of the entire hprt gene. More X-radiation-induced deletions than radon-induced deletions extended further than 800 bp in the telomeric direction from the hprt gene (six of 17 versus two of 17). The results show that at the human hprt locus of TK-6 cells the predominant kind of mutation indicative of exposure to both high LET alpha-radiation and low LET X-radiation is a large deletion, spanning the entire hemizygous hprt gene and extending into flanking sequences.
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PMID:Molecular analysis of hypoxanthine phosphoribosyltransferase gene deletions induced by alpha- and X-radiation in human lymphoblastoid cells. 752 77

We have examined the extent of HPRT- total gene deletions in three mutant collections: spontaneous and X-ray-induced deletions in TK6 human B lymphoblasts, and HPRT- deletions arising in vivo in T cells. A set of 13 Xq26 STS markers surrounding hprt and spanning approximately 3.3 Mb was used. Each marker used was observed to be missing in at least one of the hprt deletion mutants analyzed. The largest deletion observed encompassed at least 3 Mb. Nine deletions extended outside of the mapped region in the centromeric direction (> 1.7 Mb). In contrast, only two telomeric deletions extended to marker 342R (1.26 Mb), and both exhibited slowed or limited cell growth. These data suggest the existence of a gene, within the vicinity of 342R, which establishes the telomeric limit of recoverable deletions. Most (25/41) X-ray-induced total gene deletion mutants exhibited marker loss, but only 1/8 of the spontaneous deletions encompassed any Xq26 markers (P = 0.0187). Furthermore, nearly half (3/8) of the spontaneous 3' total deletion breakpoints were within 14 kb of the hprt coding sequence. In contrast, 40/41 X-ray-induced HPRT- total deletions extended beyond this point (P = 0.011). Although the overall representation of total gene deletions in the in vivo spectrum is low, 4/5 encompass Xq26 markers flanking hprt. This pattern differs significantly from spontaneous HPRT- large deletions occurring in vitro (P = 0.032) but resembles the spectrum of X-ray-induced deletions.
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PMID:Mapping the end points of large deletions affecting the hprt locus in human peripheral blood cells and cell lines. 799 11

A human x Chinese hamster (CH) somatic cell hybrid subclone deficient in HPRT and containing only human chromosome 18 was irradiated with 7000 rad and fused to a thymidine kinase deficient CH cell line. Radiation-rescued hybrid cell lines, selected in HAT medium, were analyzed for human DNA with human interspersed-repeat sequence primers. Size and number of human chromosome fragments retained in a subset of hybrids were determined by FISH. A panel of 98 radiation hybrids (RH) was selected and analyzed for 90 chromosome 18-specific STSs by PCR, and for the D18Z1 centromeric marker by Southern blotting. STSs were developed from previously mapped RFLP loci and from published sequences. In addition, 32 novel STSs were generated from an 18-specific lambda library and from 18-specific YACs previously localized to chromosome bands by FISH. Marker retention frequency varied from 8-65% with an average of 24%. In selected RH the STS typing data were correlated with the chromosome 18 regions retained using 'reverse FISH' of IRS-PCR products from the RH to normal metaphase chromosomes. The order and intermarker distances of loci were determined using two-point and multipoint maximum likelihood methods. The resulting RH map covers most of chromosome 18 with four groups of tightly linked markers and three regions of loosely linked markers, one around the centromere and two on the long arm. More than a third of the markers are polymorphic and allow integration with the linkage map. This RH map provides a framework for establishing a clone contig of the entire chromosome 18.
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PMID:A radiation hybrid map of human chromosome 18. 812 19

Genetic alterations in gamma-ray- and alpha-particle-induced HPRT mutants were examined by multiplex polymerase chain reaction (PCR) analysis. A total of 39-63% of gamma-ray-induced and 31-57% of alpha-particle-induced mutants had partial or total deletions of the HPRT gene. The proportion of these deletion events was dependent on radiation dose, and at the resolution limits employed there were no significant differences between the spectra induced by equitoxic doses of alpha particles (0.2-0.4 Gy) and gamma rays (3 Gy). The molecular nature of the deletions was analyzed by the use of sequence tagged site (STS) primers and PCR amplification as a "probe" for specific regions of the human X chromosome within the Xq26 region. These STSs were closely linked and spanned regions approximately 1.7 Mbp from the telomeric side and 1.7 Mbp from the centromeric side of the HPRT gene. These markers include: DXS53, 299R, DXS79, yH3L, 3/19, PR1, PR25, H2, yH3R, 1/44, 1/67, 1/1, DXS86, D8C6, DXS10 and DXS144. STS analyses indicated that the maximum size of total deletions in radiation-induced HPRT mutants can be greater than 2.7 Mbp and deletion size appears to be dependent on radiation dose. There were no apparent differences in the sizes of the deletions induced by alpha particles or gamma rays. On the other hand, deletions containing portions of the HPRT gene were observed to be 800 kbp or less, and the pattern of the partial deletion induced by alpha particles appeared to be different from that induced by gamma rays.
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PMID:Molecular analysis and comparison of radiation-induced large deletions of the HPRT locus in primary human skin fibroblasts. 860 May 9

In an attempt to combine a cloned genomic copy of a selectable gene with different cloned centromeric sequences to develop mammalian artificial chromosomes (MAC) we used site specific recombination mediated by purified Cre recombinase acting on the loxP sequence in PAC vector DNA. A new method was required to purify highly concentrated, virtually 100% intact PAC DNA which could be stored for a long period. Here we show the efficient linking of linearized PACs containing alpha satellite DNA from chromosomes X and 17 with sizes of 125 and 140 kb, respectively, to a 95 kb restriction fragment derived from a 175 kb PAC containing the intact human HPRT gene locus.
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PMID:Efficient combination of large DNA in vitro: in gel site specific recombination (IGSSR) of PAC fragments containing alpha satellite DNA and the human HPRT gene locus. 915 31

Loss of heterozygosity (LOH) plays an important role in the expression of recessive mutations in mammalian cells. To gain insight into the rate and mechanisms of LOH the autosomal HLA-A gene was used as a model system. Spontaneous HLA-A2 mutants originated with a rate of respectively 4.1 x 10(-6) and 6.9 x 10(-6) per cell per generation in TK6 and WI-L2-NS, two isogenic lymphoblastoid cell lines which differ in TP53 status. The rate of loss of HLA-A2 is 10-50 times higher compared to the mutation rate of the X-linked HPRT gene. The homozygous TP53 mutation in WI-L2-NS had no effect on the rate of HLA-A2 loss or the spectrum of these mutations. Microsatellite analysis of most of the HLA-A2 mutants (84%) showed LOH for multiple markers on chromosome arm 6p telomeric of a recombination breakpoint, LOH for all 6p markers, or LOH for markers on both the 6p- and 6q-arms. Cytogenetic analysis showed that these mechanisms gave mutant cells which harbored two intact chromosomes 6 and which were indistinguishable from non-mutant cells. Therefore, loss of HLA-A2 is mainly caused by somatic recombination (33-50%) or chromosome loss with duplication of the remaining chromosome (34-40%). These findings correspond to the mechanisms behind loss of the wild-type RBI allele in retinoblastoma and suggest that both somatic recombination and chromosome loss followed by duplication contribute to tumorigenesis.
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PMID:Chromosome loss with concomitant duplication and recombination both contribute most to loss of heterozygosity in vitro. 944 39

The most common isochromosome found in humans involves the long arm of the X, i(Xq), and is associated with a subset of Turner syndrome cases. To study the formation and behavior of isochromosomes in a more tractable experimental system, we have developed a somatic cell hybrid model system that allows for the selection of mono- or dicentric isochromosomes involving the short arm of the X, i(Xp). Simultaneous positive and negative counterselection of a mouse/human somatic cell hybrid containing a human X chromosome, selecting for retention of the UBE1 locus in Xp but against the HPRT locus in Xq, results in a variety of abnormalities of the X chromosome involving deletions of Xq. We have generated 70 such "Pushmi-Pullyu" hybrids derived from seven independent X chromosomes. Cytogenetic analysis of these hybrids using fluorescence in situ hybridization showed i(Xp) chromosomes in approximately 19% of the hybrids. Southern blot and polymerase chain reaction analyses of the Pushmi-Pullyu hybrids revealed a distribution of breakpoints along Xq. The distance between the centromeres of the dicentric i(Xp)s generated ranged from approximately 2 Mb to approximately 20 Mb. To examine centromeric activity in these dicentric i(Xp)s, we used indirect immunofluorescence with antibodies to centromere protein E (CENP-E). CENP-E was detected at only one of the centromeres of a dicentric i(Xp) with approximately 2-3 Mb of Xq DNA. In contrast, CENP-E was detected at both centromeres of a dicentric i(Xp) with approximately 14 Mb of Xq DNA. Two other dicentric i(Xp) chromosomes were heterogeneous with respect to centromeric activity, suggesting that centromeric activity and chromosome stability of dicentric chromosomes may be more complicated than previously thought. The Pushmi-Pullyu model system presented in this study may provide a tool for examining the structure and function of mammalian centromeres.
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PMID:Chromosome engineering: generation of mono- and dicentric isochromosomes in a somatic cell hybrid system. 1046 Apr 14

A novel human X-linked gene shows placenta-specific expression and has been named PLAC1. The gene maps 65 kb telomeric to HPRT at Xq26 and has been completely sequenced at the cDNA and genomic levels. The mouse orthologue Plac1 maps to the syntenically equivalent region of the mouse X chromosome. In situ hybridization studies with the antisense mRNA during mouse embryogenesis detect Plac1 expression from 7.5 dpc (days postcoitum) to 14.5 dpc in ectoplacental cone, giant cells, and labyrinthine trophoblasts. The putative human and murine PLAC1 proteins are 60% identical and 77% homologous. Both include a signal peptide and a peptide sequence also found in an interaction domain of the ZP3 (zona pellucida 3) protein. These results make PLAC1 a marker for placental development, with a possible role in the establishment of the mother-fetus interface.
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PMID:PLAC1, an Xq26 gene with placenta-specific expression. 1099 72


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