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

---

Query: EC:3.2.1.23 (beta-galactosidase)
14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The transcriptional activator LAC9, a GAL4 homolog of Kluyveromyces lactis which mediates lactose and galactose-dependent activation of genes involved in the utilization of these sugars can also confer glucose repression to those genes. Here we report on the isolation and characterization of LAC9-2, an allele which encodes a glucose-sensitive activator in contrast to the one previously cloned. A single amino acid exchange of leu-104 to tryptophan is responsible for the glucose-insensitive phenotype. The mutation is located within the Zn-finger-like DNA binding domain which is highly conserved between LAC9 and GAL4. Glucose repression is also eliminated by duplication of the LAC9-2 allele. The data indicate that LAC9 is a limiting factor for beta-galactosidase gene expression under all growth conditions and that glucose reduces the activity of the activator.
...
PMID:A mutation in the Zn-finger of the GAL4 homolog LAC9 results in glucose repression of its target genes. 210 31

In Rhizobium meliloti, the genes involved in biosynthesis of the amino acid tryptophan are found at three separate chromosomal locations. Of the three gene clusters, trpE(G), trpDC, and trpFBA, only the trpE(G) gene is regulated by the end product of the pathway, tryptophan. We found that trpE(G) mRNA contains a leader transcript that terminates at a stem-loop structure in a putative transcription attenuator. The level of this leader transcript was constant regardless of the amount of tryptophan in the growth medium. However, the level of full-length trpE(G) mRNA decreased as the amount of tryptophan increased. The beta-galactosidase activity of an R. meliloti strain carrying a trpL'-'lacZ fusion remained constant at different tryptophan concentrations, but the beta-galactosidase activity of the same strain carrying a trpE(G)'-'lacZ fusion decreased as the tryptophan concentration increased. These data indicate that transcription of the R. meliloti trpE(G) gene is regulated only by attenuation. We also found that the product of the trpE(G) gene, anthranilate synthase, is feedback inhibited by tryptophan.
...
PMID:The Rhizobium meliloti trpE(G) gene is regulated by attenuation, and its product, anthranilate synthase, is regulated by feedback inhibition. 211 7

Retrovirus vectors only integrate into the genome of dividing cells and can thus be used to selectively infect tumor cells in the adult rat brain. Gene delivery was assessed by using the retrovirus BAG vector, which bears the Escherichia coli lacZ gene under the MoMLV LTR promoter-enhancer element, and by histochemical staining for bacterial beta-galactosidase activity. Direct injection of this vector (90-900 cfu) into the adult rat brain, with or without prior inoculation of C6 glioma cells (2 x 10(5) cells) resulted in labeling of only a few cells as assessed 1 week later. When the psi 2-BAG packaging line was grafted into the brain, labeled psi 2-BAG cells could be found after 1 day, but not after 5 days, following grafting, suggesting that the grafted cells had been rejected and that no endogenous cells had integrated released vector, or that expression of lacZ had been turned off. In contrast, when the psi 2-BAG packaging line was grafted into a brain region, which had been inoculated previously with rat C6 glioma cells (2 x 10(5) cells), beta-galactosidase labeling of these tumor cells, identified by immunocytochemistry for glial fibrillary acidic protein and S100, could be demonstrated 10 days later. Thus, grafting of retrovirus packaging lines into adult brain provides a mean to infect tumor cells in situ. The grafted packaging cells may continue to release retrovirus particles for an extended period, thus infecting more cells at the stage of division appropriate for viral integration, as compared to inoculation of the virus alone. Grafting of retrovirus packaging cell lines could be used to selectively deliver "killer" or "suppressor" genes to tumor cells in the brain to curtail their growth.
...
PMID:Gene delivery to glioma cells in rat brain by grafting of a retrovirus packaging cell line. 212 47

Comparative studies were conducted through more than six months into quantitative of bovine leukaemia virus (BLV) antigen of FLC/BLV 44 and its FLC/BLV 44-4 subline by means of an enzyme immuno-assay (EIA), using monoclonal antibodies against gp51 and p24. Synthesis of gp51 (factors of two to six) and of p24 (factor of two) by FLC/BLV 44 was clearly higher than that by FLC/BLV 44-4. The transactivation status in either line was determined by transfer of the beta-galactosidase indicator organ under transcription control of BLV-LTR (in pBLV beta Gal plasmid). Transient experiments showed beta-galactosidase activity in the FLC/BLV 44 to be clearly higher than that in subline FLC/BLV 44-4. There is obviously in both cell lines a close correlation between intensity of BLV antigen synthesis and transactivation processes.
...
PMID:[Different transactivation processes in two bovine leukemia virus producing cell lines]. 216 53

The tat gene of HIV is a strong activator of the viral LTR. The Tat protein contains a highly basic domain that is important for its transport to the nuclear/nucleolar locations. The Tat basic domain when fused to Escherichia coli beta-galactosidase directed the chimeric protein to the nucleus and nucleolus. Tat mutants lacking the entire basic domain were severely defective in trans-activation. Substitution of the basic domain of Tat with that of the functionally unrelated HIV-1 Rev protein targeted the chimeric protein to the nucleolus and restored the function of Tat. In contrast, substitution with the nuclear targeting signal (NLS) of SV40 T antigen targeted the chimeric protein to the nucleus and accumulation in the nucleolar region was excluded. The Tat-NLS chimeric protein did not restore the trans-activation function of Tat efficiently. These results indicate that the arginine-rich basic domain of the trans-activator, Tat, and post-transcriptional trans-regulator, Rev, are functionally similar with regard to trans-activation of HIV-1 LTR.
...
PMID:Functional substitution of the basic domain of the HIV-1 trans-activator, Tat, with the basic domain of the functionally heterologous Rev. 218 74

A convenient and sensitive enzyme-linked immunosorbent assay (ELISA) for the STb heat-stable enterotoxin of Escherichia coli was developed and used to quantify STb production by strains with a high level of expression. Based on an antigenic profile of the secreted form of STb, a synthetic peptide (STb3-27) spanning the major predicted epitope was synthesized, coupled to keyhole limpet hemocyanin, and used to immunize rabbits. Anti-STb3-27 antibodies were affinity purified on a synthetic peptide-Sepharose 4B column and used in a direct-binding STb ELISA. Based on a highly purified form of toxin as a standard, the ELISA detected as little as 1 to 2 ng of STb from crude culture filtrates. ELISA data revealed that natural STb-producing strains elaborate little STb in defined-medium cultures relative to that elaborated by a recombinant strain harboring a cloned copy of the estB gene. Replacement of the endogenous STb promoter with any of several highly active promoters, including a bacteriophage T7 promoter, a beta-galactosidase promoter, and a tryptophan-beta-galactosidase hybrid (tac) promoter, increased the yield of STb 10- to 20-fold over levels obtained by an E. coli strain harboring the recombinant estB gene. The high level of STb antigen detected by the ELISA correlated with intestinal secretory activity. The combination of a convenient assay and effective hyperproduction of STb will serve as a basis for a large-scale toxin purification strategy.
...
PMID:High-level production of Escherichia coli STb heat-stable enterotoxin and quantification by a direct enzyme-linked immunosorbent assay. 225 13

Permissiveness to Moloney Murine Leukemia Virus (MoMuLV) expression was examined during preimplantation and early postimplantation development of the mouse embryo. Blastocysts and 8th, 9th and 10th day postimplantation embryos were infected in vitro with a MoMuLV-based retroviral vector expressing the lacZ gene driven off an internal rat beta-actin promoter. Beta-galactosidase-positive cells were identified in all embryonic tissues including inner cell mass, epiblast, mesoderm, endoderm and definitive ectoderm. In contrast, embryos infected with a MoMuLV-based vector expressing the lacZ gene driven off the viral LTR showed beta-galactosidase-positive cells only in mesoderm and definitive ectoderm. We conclude that permissiveness to transcriptional activity of the LTR is acquired immediately upon differentiation of epiblast during gastrulation of the mouse embryo.
...
PMID:Permissiveness to murine leukemia, virus expression during preimplantation and early postimplantation mouse development. 240 Dec 17

Transcription of the trp operon of Bacillus subtilis is regulated in response to the availability of tryptophan. The first structural gene of the operon is preceded by a 204-base-pair transcribed leader region that contains a segment with the features of a procaryotic termination site. Transcription of the leader region was analyzed in vivo and in vitro to determine whether this putative termination site was used to regulate operon expression. When RNA was isolated from wild-type cells grown in the presence of excess tryptophan, transcripts of the operon ended at the putative termination site. In contrast, RNA isolated from cells grown in the absence of tryptophan or from a mutant strain which is constitutive for trp operon expression contained trp transcripts that extended beyond the termination site into the structural genes. To assess termination quantitatively in vivo, a trpE-lacZ fusion was constructed in which the trp promoter and leader region controls hybrid beta-galactosidase formation. The effects on hybrid beta-galactosidase levels of point mutations and deletions introduced into this leader region were determined. The results obtained establish that transcription of the trp operon structural genes is regulated in the leader region. This regulation appears to be mediated by the formation of alternative secondary structures of the leader transcript. In vitro transcription studies with wild-type and mutant templates provided additional evidence that the identified alternative RNA secondary structures regulate transcription termination. We hypothesize that binding of a tryptophan-activated regulatory protein to a specific segment of the nascent leader transcript prevents formation of one of the alternative secondary structures, thereby directing RNA polymerase to terminate transcription.
...
PMID:Novel form of transcription attenuation regulates expression the Bacillus subtilis tryptophan operon. 242 55

Hypertonic NaCl administered to rats or mice has been demonstrated to induce in the liver a rapid disaggregation of polyribosomes and inhibition of protein synthesis. This study was concerned with whether hypertonic NaCl would affect nucleocytoplasmic translocation of RNA in the livers of rats. The effect of tube-feeding a hypertonic (10.7%) NaCl solution (321 mg in 3 ml/100 g body wt) for 10 minutes on in vitro release of 14C-orotate-labeled nuclear RNA was assayed. Although the combination of nuclei and cytosols of livers of hypertonic NaCl-treated rats revealed diminished in vitro labeled nuclear RNA release in comparison with hepatic nuclei and cytosols of control (water-treated) rats, each of the two components varied in activity. Even though the overall effect was an inhibitory one, cytosols of livers of hypertonic NaCl-treated rats stimulated in vitro release of labeled nuclear RNA, whereas nuclei of livers of hypertonic NaCl-treated rats revealed diminished in vitro release of labeled nuclear RNA in comparison with cytosols and nuclei of livers of control rats. The stimulatory effect of the hepatic cytosols of the hypertonic NaCl-treated rats was essentially unaffected by pretreatment of the rats with puromycin or cycloheximide, but was abolished by pretreatment of the cytosols in vitro with alpha-mannosidase or beta-galactosidase. Passage of cytosols of control and experimental livers through concanavalin A-agarose columns concentrated the activities of the eluates in stimulating in vitro labeled nuclear RNA release. In vivo 14C-orotate labeling of hepatic nuclear RNA for 30 minutes was increased by hypertonic NaCl treatment in comparison with water treatment of control animals. In vivo 14C-glucosamine incorporation into hepatic proteins of nuclei and nuclear envelopes was increased in hypertonic NaCl-treated rats in comparison with controls. In vitro 3H-tryptophan binding to proteins (trichloracetic acid-precipitable) to cytosols of livers of hypertonic NaCl-treated rats was increased in comparison with binding of controls. The results suggest that the administration of hypertonic NaCl rapidly leads to a change in hepatic cytosol whereby the activity to stimulate in vitro labeled nuclear RNA release is enhanced. This occurs without new protein synthesis, and the effect is probably mediated through a glycoprotein. In contrast, the hepatic nuclei of the rats treated with hypertonic NaCl show a decreased ability to release in vitro labeled nuclear RNA, possibly because of the development of a nuclear lesion.
...
PMID:The influence of hypertonic NaCl on nucleocytoplasmic translocation of RNA in the rat liver. 242 14

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.
...
PMID:Factors affecting long-term stability of Moloney murine leukemia virus-based vectors. 250 32


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---