Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have examined the long-term functional and structural stability of retroviral vectors in infected murine cells. We have used Moloney murine leukemia virus-based vectors expressing human HPRT, firefly luciferase (luc), and Escherichia coli beta-galactosidase (lacZ) as reporter genes, and the human HPRT and the transposon Tn5 neomycin resistance (neo) gene as selectable markers. All vectors, whether single or double gene, yielded both stable and unstable clones. Stability of the proviruses was dependent on a number of factors, including the nature of the infected cell, the reporter gene, the integration site of the provirus, the relative positions of the component genes in multigene vectors, and the presence or absence of selection pressure. Selection pressure was helpful, but not universally effective, in maintaining provirus structural and functional integrity. Reporter gene expression from an internal promoter was likely to be unstable with or without selection for an upstream, LTR-driven neo gene. In some clones, loss of proviral gene expression was accompanied by deletions, while other inactive clones retained an apparently intact provirus. In the latter clones, treatment with 5-azacytidine failed to reactivate the reporter genes, but superinfection with helper virus resulted in the reappearance of transmissible vector, indicating a reversible epigenetic mechanism for proviral shutdown. The design of effective retroviral vectors and their possible use in vivo will require further characterization of these determinants of provirus stability.
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PMID:Factors affecting long-term stability of Moloney murine leukemia virus-based vectors. 250 32

Transgenes in mice often exhibit different expression patterns in different transgenic lines. While the basis for this phenomenon is not understood, it is widely believed that the site at which the transgene becomes integrated into the mouse genome is a major factor in determining the pattern of expression. Most transgenic mice have been produced by microinjection of DNA into the male pronucleus, which results in integration of tandem arrays of the transgene at random chromosomal sites. In the experiments described in this report, electroporation of embryonic stem (ES) cells was used to place single copies of a lacZ transgene into either random sites or into the HPRT (hypoxanthine phosphoribosyl transferase) locus of the mouse genome. Expression of lacZ was assayed by histochemical staining for Escherichia coli beta-galactosidase activity in ES cells and in differentiated derivatives obtained by teratocarcinoma formation. Several of the randomly integrated cell lines expressed lacZ at high levels in a variety of cell types present in the tumours, but most notably in epithelial cells. Targeted cell lines with lacZ in opposite orientation to the direction of HPRT gene transcription also expressed well in epithelial cells, but the targeted cell lines did not express in a wider variety of cell types than some of the nontargeted cell lines. Targeted cell lines transcribing lacZ in the same orientation as HPRT transcription did not express high levels of lacZ in any differentiated cell type. Analysis of transcripts suggested that this orientation effect may have been the result of transcriptional interference perpetrated by the HPRT gene promoter.
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PMID:Expression of the lacZ gene targeted to the HPRT locus in embryonic stem cells and their derivatives. 851 34

To test the hypothesis that intact gap-junctional intercellular communication (GJIC) is necessary for genomic stability, we compared the spontaneous and chemically induced mutation frequencies in GJIC-proficient and -deficient HeLa cells. Thus, we determined microsatellite instability and mutation frequency in the HPRT gene in parental HeLa cells, which have no GJIC ability, and in HeLa cells in which GJIC was restored by transfection with the connexin 43 (Cx43) gene. When HeLa cells with (Cx43+) or without Cx43 gene (Cx43-) were treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or methylnitrosourea, the Cx43+ cells survived better than Cx43- cells. The mutation frequency at CA repeats was measured with a shuttle vector; in the vector, the coding region of the beta-galactosidase gene was rendered out of frame by insertion of CA repeats, and the frame could be restored by insertion or deletion mutations of the CA repeats. The mutation frequency at CA repeats was 2-fold lower in Cx43+ cells than in Cx43-, both before and after exposure to MNNG or methylnitrosourea (P < 0.05). The frequency of spontaneous HPRT gene mutations, selected by their resistance to 6-thioguanine, was 3-fold lower in Cx43+ cells than Cx43- cells. Similarly, the frequency of MNNG-induced HPRT mutations was significantly higher in Cx43- cells (P < 0.001). Similar results were obtained even when the mutant selection process was carried out in the presence of alpha-glycyrrhetinic acid, a long-term inhibitor of GJIC, suggesting that the observed effect is not due to unwanted killing of cells by GJIC-mediated metabolic cooperation. Thus, our data demonstrate that HeLa cells transfected with the Cx43 gene become more resistant to spontaneous as well as chemically induced genetic changes.
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PMID:Increased genetic stability of HeLa cells after connexin 43 gene transfection. 918 13

We studied the stability of a DNA triplex resulting from the binding of a 38 nt long purine motif triplex-forming oligonucleotide (TFO) to a covalently closed plasmid containing a target sequence from the human HPRT gene. Our in vitro experiments showed that the triplex formed at plasmid and TFO concentrations as low as 10(-9)M. Once formed, the triplex was remarkably stable and could withstand 10 min incubation at 65 degrees C. We next delivered these TFO-plasmid complexes into cultured human cells. To monitor the TFO-plasmid complexes inside cells we applied a new technique that we call 'radioprinting'. Because the TFO was(125)I labeled, we could quantitatively monitor the triplexes by measuring(125)I-induced DNA strand breaks in the target plasmid sequence. We found that the triplexes remain stable inside the cells for at least 48 h. Based on these findings we propose using TFO for indirect labeling of intact plasmid DNA. As a demonstration, we show that the intracellular distribution of a fluorescein-labeled TFO was different when it was liposome-delivered into cultured human cells alone or in a complex with the plasmid. In the latter case, the fluorescence was detected in nearly all the cells while detection of the plasmid by use of a marker gene (beta-galactosidase) revealed expression of the gene in only half of the cells.
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PMID:The stability of DNA triplexes inside cells as studied by iodine-125 radioprinting. 1048 Oct 23