Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The LPD1 gene of Saccharomyces cerevisiae, encoding lipoamide dehydrogenase (LPDH), is subject to catabolite repression. The promoter of this gene contains a number of motifs for DNA-binding transcriptional activators, including three which show strong sequence homology to the core HAP2/HAP3/HAP4 binding motif. Here we report that transcription of LPD1 requires HAP2, HAP3 and HAP4 for release from glucose repression. In the wild-type strain, specific activity of LPDH was increased 12-fold by growth on lactate, 10-fold on glycerol and four- to five-fold on galactose or raffinose, compared to growth on glucose. In hap2, hap3 and hap4 null mutants, the specific activities of LPDH in cultures grown on galactose and raffinose showed only slight induction above the basal level on glucose medium. Similar results were obtained upon assaying for beta-galactosidase production in wild-type, or hap2, hap3 or hap4 mutant strains carrying a single copy of the LPD1 promoter fused in frame to the lacZ gene of Escherichia coli and integrated at the URA3 locus. Transcript analysis in wild-type and hap2 mutants confirmed that the HAP2 protein regulates LPD1 expression at the level of transcription in the same way as it does for the CYC1 gene. Site-directed mutagenesis of the putative HAP2/HAP3/HAP4 binding site at -204 relative to the ATG start codon showed that this element was required for full derepression of the LPD1 gene on non-fermentable substrates.
Mol Gen Genet 1992 Jan
PMID:Positive regulation of the LPD1 gene of Saccharomyces cerevisiae by the HAP2/HAP3/HAP4 activation system. 131 May 23

Mammalian liver contains two types of galactose receptors, specific for Kupffer or parenchymal cells. Because galactose-specific receptors are largely confined to the liver, galactose-bearing carriers are promising vehicles for the specific delivery of drugs to liver cells. In the present study, high density lipoprotein (HDL), a spherical particle with a diameter of 10 nm, in which a variety of lipophilic drugs can be incorporated, was provided with galactose residues by reductive lactosamination. After injection into rats, lactosylated 125I-HDL was rapidly cleared from the plasma (half-life, less than 1 min). Ten minutes after injection, the liver contained about 95% of the dose, whereas only small amounts of radioactivity were found in other tissues. The hepatic uptake was inhibited by preinjection with N-acetylgalactosamine, which indicates that the hepatic recognition sites are galactose specific. Subcellular fractionation of the liver indicated that recognition of lactosylated HDL is followed by internalization and degradation of the apoprotein in the lysosomes. Liver cells were isolated at 10 min after injection of lactosylated 125I-HDL, and it was found that uptake occurs almost exclusively by parenchymal cells. These cells contained about 98% of the hepatic radioactivity. The liver uptake of the lipid moiety of lactosylated HDL, labeled with [3H]cholesteryl oleate, was identical to that of the 125I-labeled apoproteins, which indicates that the particle is taken up as a unit. Thus, lactosylated HDL is taken up rapidly and selectively by parenchymal liver cells, and it appears that it might be a very effective vehicle for the specific delivery of lipophilic drugs to these cells.
Mol Pharmacol 1992 Feb
PMID:Lactosylated high density lipoprotein: a potential carrier for the site-specific delivery of drugs to parenchymal liver cells. 131 13

The regulation of open complex formation at the Escherichia coli galactose operon promoters by galactose repressor and catabolite activator protein/cyclic AMP (CAP/cAMP) was investigated in DNA-binding and kinetic experiments performed in vitro. We found that gal repressor and CAP/cAMP bind to the gal regulatory region independently, resulting in simultaneous occupancy of the two gal operators and the CAP/cAMP binding site. Both CAP/cAMP and gal repressor altered the partitioning of RNA polymerase between the two overlapping gal promoters. Open complexes formed in the absence of added regulatory proteins were partitioned between gal P1 and P2 with occupancies of 25% and 75%, respectively. CAP/cAMP caused open complexes to be formed nearly exclusively at P1 (98% occupancy). gal repressor caused a co-ordinated, but incomplete, switch in promoter partitioning from P1 to P2 in both the absence and presence of CAP/cAMP. We measured the kinetic constants governing open complex formation and decay at the gal promoters in the absence and presence of gal repressor and CAP/cAMP. CAP/cAMP had the largest effect on the kinetics of open complex formation, resulting in a 30-fold increase in the apparent binding constant. We conclude that the regulation of open complex formation at the gal promoters does not result from competition between gal repressor, CAP/cAMP and RNA polymerase for binding at the gal operon regulatory region, but instead results from the interactions of the three proteins during the formation of a nucleoprotein complex on the gal DNA fragment. Finally, we present a kinetic model for the regulation of open complex formation at the gal operon.
J Mol Biol 1992 Mar 05
PMID:Regulation of open complex formation at the Escherichia coli galactose operon promoters. Simultaneous interaction of RNA polymerase, gal repressor and CAP/cAMP. 131 5

The two overlapping promoters that control mRNA synthesis at the galactose operon contain three phased stretches of adenine residues, located around positions -84.5, -74 and -63, with respect ot the start of the P1 promoter. As a result, the corresponding DNA sequence is bent, an anomaly that is relieved by the addition of small concentrations of drugs like distamycin A or netropsin. By abortive initiation assays performed on several DNA fragments derived from the wild-type promoter or from various mutants we show that the curved sequence increases the strength of the P1 promoter. In the absence of cyclic AMP (cAMP) and of the corresponding receptor protein (CRP), the upstream curved sequences enhance the rate of isomerization from the closed to the open complex at P1. This effect is abolished when distamycin A is bound in the bent region. In the presence of cAMP-CRP, a more drastic change is observed: activation of the gal P1 promoter takes place at a different formal step, depending whether the upstream curved sequence is present or not (enhancement of the rate of conversion from a closed to an open complex instead of an increase in the affinity of the enzyme during closed complex formation). These data, together with previous results obtained with other mutants of the gal control region, suggest that several closed complexes corresponding to different nucleoprotein arrangements are formed during open complex formation at gal P1, in the presence of CRP.
J Mol Biol 1992 Mar 20
PMID:Upstream curved sequences influence the initiation of transcription at the Escherichia coli galactose operon. 131 83

The transcriptional activation function of the Saccharomyces cerevisiae GAL4 protein is modulated by the GAL80 and GAL3 proteins. In the absence of galactose, GAL80 inhibits the function of GAL4, presumably by direct binding to the GAL4 protein. The presence of galactose triggers the relief of the GAL80 block. The key to this relief is the GAL3 protein. How GAL3 and galactose activate GAL4 is not understood, but the long-standing notion has been that a galactose derivative formed by catalytic activity of GAL3 is the inducer that interacts with GAL80 or the GAL80-GAL4 complex. Here we report that overproduction of the GAL3 protein causes constitutive expression of GAL/MEL genes in the absence of exogenous galactose. Overproduction of the GAL1 protein (galactokinase) also causes constitutivity, consistent with the observations that GAL1 is strikingly similar in amino acid sequence to GAL3 and has GAL3-like induction activity. Cells lacking the GAL10-encoded UDP-galactose-UDP-glucose epimerase retained the constitutivity response to overproduction of GAL3, making it unlikely that constitutivity is due to endogenously produced galactose. A galactose-independent mechanism of constitutivity is further indicated by the inducing properties of two newly created galactokinaseless alleles of GAL1. On the basis of these data, we propose a new model for galactose-induced activation of the GAL4 protein. This model invokes galactose-activation of the GAL3 and GAL1 proteins which in turn elicit an alteration of the GAL80-GAL4 complex to activate GAL4. This model is consistent with all the known features of the system and has important implications for manipulating GAL4-dependent transcriptional activation in vitro.
Mol Cell Biol 1992 Jun
PMID:Overproduction of the GAL1 or GAL3 protein causes galactose-independent activation of the GAL4 protein: evidence for a new model of induction for the yeast GAL/MEL regulon. 131 7

High-level expression of a transpositionally competent Ty1 element fused to the inducible GAL1 promoter on a 2 microns plasmid (pGTy1) overcomes transpositional dormancy in Saccharomyces cerevisiae. To investigate the mechanisms controlling the rate of Ty1 retrotransposition, we quantitated transposition and Ty1 gene products in cells induced and uninduced for expression of pGTy1. The increase in Ty1 transposition was 45- to 125-fold greater than the increase in Ty1 RNA effected by pGTy1 induction. Translational efficiency of Ty1 RNA was not altered in transposition-induced cells, since p190TYA1-TYB1 protein synthesis increased in proportion to steady-state Ty1 RNA levels. Therefore, expression of a pGTy1 element increases the efficiency of Ty1 transposition at a posttranslational level. Galactose induction of pGTy1 enhanced TYA1 protein processing and allowed detection of processed TYB1 proteins, which are normally present at very low levels in uninduced cells. When the ability of genomic Ty1 elements to complement defined mutations in HIS3-marked pGTy1 elements was examined, mutations in the protease domain or certain mutations in the integrase domain failed to be complemented, but mutations in the reverse transcriptase domain were partially complemented by genomic Ty1 elements. Therefore, the activity of Ty1 elements in yeast cells may be limited by the availability of Ty1 protease and possibly integrase. These results suggest that Ty1 transposition is regulated at the level of protein processing and that this regulation is overcome by expression of a pGTy1 element.
Mol Cell Biol 1992 Jun
PMID:Posttranslational control of Ty1 retrotransposition occurs at the level of protein processing. 131 8

The periplasmic ribose and glucose-galactose receptors (binding proteins) of Gram-negative bacteria compete for a common inner membrane receptor in bacterial chemotaxis, as well as being the essential primary receptors for their respective membrane transport systems. The high-resolution structures of the periplasmic receptors for ribose (from Escherichia coli) and glucose or galactose (from both Salmonella typhimurium and E. coli) are compared here to outline some features that may be important in their dual functions. The overall structure of each protein consists of two similar domains, both of which are made up of two non-contiguous segments of amino acid chain. Each domain is composed of a core of beta-sheet flanked on both sides with alpha-helices. The two domains are related to each other by an almost perfect intramolecular axis of symmetry. The ribose receptor is smaller as a result of a number of deletions in its sequence relative to the glucose-galactose receptor, mostly occurring in the loop regions; as a result, this protein is also more symmetrical. Many structural features, including some hydrophobic core interactions, a buried aspartate residue and several unusual turns, are conserved between the two proteins. The binding sites for ligand are in similar locations, and built along similar principles, although none of the specific interactions with the sugars is conserved. A comparison shows further that slightly different rotations relate the domains to each other in the three proteins, with the ribose receptor being the most closed, and the Salmonella glucose-galactose receptor the most open. The primary axis of relative rotation is almost perpendicular to that which describes the intramolecular symmetry in each case. These relative rotations of the domains are accompanied by the sliding of some helices as the structures adjust themselves to relieve strain. The hinges which are responsible for most of these relative domain rotations are very similar in the three proteins, consisting of a symmetrical arrangement of beta-strands and alpha-helices and two conserved water molecules that are critical to the hydrogen bonding in the important interdomain region. A region of high sequence and structural similarity between the ribose and glucose-galactose receptors is also located around the intramolecular symmetry axis, on the opposite side of the proteins from the hinge region. This region is that which is altered most by the relative rotations, and is the location of most of the known mutations which affect chemotaxis and transport in the ribose receptor.
J Mol Biol 1992 Sep 20
PMID:Ribose and glucose-galactose receptors. Competitors in bacterial chemotaxis. 132 50

beta-Hexosaminidases, potent mitogens in bovine tracheal myocytes (BTM), stimulate a rapid and transient increase in intracellular cyclic adenosine monophosphate (cAMP) accumulation. The objective of this study was to elucidate the contribution of cAMP in hexosaminidase-induced airway muscle proliferation. Rate of DNA synthesis was measured by 3H-thymidine incorporation in quiescent cells prepared by a low-serum treatment (0.4%) for 48 h after reaching confluency in microtiter wells. cAMP accumulation was measured in acetylated cell extracts in the presence of isobutyl methylxanthine (100 microM) by radioimmunoassay using 125I-cAMP as tracer. Exposure of quiescent cells to purified human placental hexosaminidase B (5 micrograms/ml, 50 nM) caused a significant transient increase in cAMP accumulation (49 to 107 fmol/micrograms protein, or a 20- to 70-fold increase from basal level). Maximum increase occurred at 15 min followed by a rapid decline in cAMP accumulation within 30 min after exposure to hexosaminidase. Similar results were obtained in cells treated with neoglycoprotein mannose bovine serum albumin (100 to 500 nM). The increase in cAMP accumulation was inhibited by mannan (mannose receptor blocker, 0.1 mg/ml), as well as phenylisopropyladenosine (PIA; A1 receptor agonist that inhibits adenylyl cyclase, 0.1 to 1.0 microM). The increase in 3H-thymidine incorporation induced by hexosaminidase B was also inhibited by mannan and PIA. Exposure to 8-(4-chlorophenylthio)-cAMP (cpt-cAMP; a cell-permeable analog of cAMP, 100 microM) or forskolin (a direct activator of catalytic subunit of adenylyl cyclase, 24 microM) up to 6 h enhanced 3H-thymidine incorporation. In contrast, a prolonged exposure (18 to 30 h) to these agents inhibited 3H-thymidine incorporation.(ABSTRACT TRUNCATED AT 250 WORDS)
Am J Respir Cell Mol Biol 1992 Dec
PMID:Dual regulation by cAMP of beta-hexosaminidase-induced mitogenesis in bovine tracheal myocytes. 133 45

We studied the receptor mediated endocytosis of a modified glycoprotein (N-acetylglucosamine-BSA) and mannan in cultured hepatocytes isolated from 19-days-old embryos. The binding sites for molecules exposing terminal N-acetylglucosamine (GlcNac) and mannose residues were localized and quantified at the ultrastructural level by means of protein-gold complexes. The binding sites were found to be randomly distributed as single gold particles on cultured hepatocyte cell surfaces not restricted to specialized areas of the plasma membrane. The gold ligands were internalized following a receptor mediated pathway, which was studied at different interval times (15, 30 and 60 min.) after incubating the cells with the electron dense markers.
Cell Mol Biol (Noisy-le-grand)
PMID:Receptor mediated endocytosis of N-acetylglucosamine and mannose exposing molecules by cultured chick embryo hepatocytes. 133 27

Up to 80% of faecal Escherichia coli strains are able to produce type 1 pili. These filamentous bacterial surface organelles, which mediate mannose-sensitive attachment to mammalian epithelial cells, are also conserved throughout the Enterobacteriaceae. As a potential explanation for their prevalence among intestinal isolates of enteric bacteria, it has been widely speculated that type 1 pili are important for adherence to the host's intestinal mucosa. However, conclusive evidence for this idea is lacking, and there are reasonable grounds for doubting such an effect. Permanent interruption of type 1 piliation in previously pil+ E. coli (by directed mutagenesis of pilA, the gene coding for the major structural subunit of type 1 pili) does not diminish the density of intestinal colonization in individual animals. Rather, as we demonstrate here, this lesion results in a dramatic decrease in transmission of E. coli K1 from experimentally colonized neonatal rats to their littermates. The enhanced communicability associated with type 1 piliation suggests a heretofore unrecognized explanation for the prevalence of type 1 pili among intestinal E. coli; one that does not necessarily require the direct action of these organelles at the intestinal mucosa.
Mol Microbiol 1992 Mar
PMID:A key role for type 1 pili in enterobacterial communicability. 134 17


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