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H Yoon

Publications and source records attributed to H Yoon.

At least 55 records · Page 3Linked to original sources
PubMed1995

Cloning of salicylate hydroxylase gene and catechol 2,3-dioxygenase gene and sequencing of an intergenic sequence between the two genes of Pseudomonas putida KF715.

The salicylate hydroxylase can convert the salicylate to catechol, and catechol 2,3-dioxygenase catalizes the conversion of catechol to 2-hydroxymuconic semialdehyde. A salicylate hydroxylase gene and a catechol 2,3-dioxygenase have been cloned from chromosomal DNA of P. putida KF715. The two genes have different promoters. An open reading frame with 339 nucleotides preceded by a putative ribosome-binding sequence (GGAGG) was identified in the intergenic sequence between salicylate hydroxylase gene and catechol 2,3-dioxygenase gene of P. putida KF715 and its sequence analyzed. This open reading frame can encode a polypeptide of molecular weight 13 kDa containing 112 amino acids, whose sequence exhibited 87% homology with that of ferredoxin encoded in NAH7 of P. putida PpG7 and significant homology with those of redox components in phenol hydroxylase, benzoate 1,2-dioxygenase, toluate 1,2-dioxygenase, xylene monooxygenase, and toluene 4-monooxygenase.

Amino Acid Sequence↗
PubMed1995

Developmental expression and molecular cloning of REMP, a novel retinal epithelial membrane protein.

The retinal pigment epithelium (RPE), like other transport epithelia, has a polarized distribution of membrane and cytoskeletal proteins. The establishment of a polarized phenotype is an essential step in the differentiation of the RPE and the development and maintenance of visual function. Using a monoclonal antibody (MAb 3C4) we have identified a novel membrane protein that is uniquely expressed in chick RPE. We have referred to this protein as REMP for retinal epithelial membrane protein. In these studies we characterized the expression and distribution of this protein during embryonic development and determined its primary structure by cDNA cloning. The developmental expression of REMP was examined by immunocytochemical localization. REMP was first detected in the chick RPE at Embryonic Day 5 (E5) in both apical and basolateral membranes. By E14 the distribution of REMP was restricted to the basolateral surface of the RPE cells. Biochemical fractionation and surface labeling of RPE cells suggested that REMP was an integral protein. The gene encoding REMP was isolated from an E15 chick RPE cDNA library, cloned into lambda gt11, and screened with MAb 3C4. The cDNA was sequenced and found to contain one 1350-bp open reading frame encoding for a 450-amino-acid protein. The deduced amino-acid sequence of REMP shares 32.9% identity with MCT1, a monocarboxylate transporter (Garcia, Goldstein, Pathak, Anderson, and Brown, Cell, 76, 865-873, 1994). By Northern blot analysis, REMP mRNA was detected only in RPE cells. There was an increase in the expression REMP transcript during development but when RPE cells were grown in primary culture the expression of REMP was turned off. The unique expression of REMP in the RPE in vivo would suggest a role for this protein in development and maintenance of normal retinal function.

Amino Acid Sequence↗
PubMed1994

The transcription factor TFIIS zinc ribbon dipeptide Asp-Glu is critical for stimulation of elongation and RNA cleavage by RNA polymerase II.

The eukaryotic transcription factor TFIIS enhances elongation and nascent transcript cleavage activities of RNA polymerase II in a stalled elongation complex. By site-directed mutagenesis, we have demonstrated that invariant residues Asp-261 and Glu-262 of the nucleic acid-binding TFIIS Zn ribbon are critical for stimulation of both elongation and RNA cleavage activities of RNA polymerase II. Substitution of either of these residues inactivates both TFIIS functions, suggesting a related role in both activities. These acidic residues may participate in phosphoryl transfer reactions by a two-metal-ion mechanism in a manner analogous to Klenow fragment. The RNA polymerase II itself may contain a Zn ribbon, in as much as the polymerase's 15-kDa subunit contains a sequence that aligns well with the TFIIS Zn ribbon sequence, including a similarly placed pair of acidic residues.

Amino Acid Sequence↗
PubMed1994

Casein kinase II mediates multiple phosphorylation of Saccharomyces cerevisiae eIF-2 alpha (encoded by SUI2), which is required for optimal eIF-2 function in S. cerevisiae.

Previous studies have demonstrated that the alpha subunit of eukaryotic initiation factor 2 (eIF-2 alpha), encoded by the SUI2 gene in the yeast Saccharomyces cerevisiae, is phosphorylated at Ser-51 by the GCN2 kinase in response to general amino acid control. Here we describe that yeast eIF-2 alpha is a constitutively phosphorylated protein species that is multiply phosphorylated by a GCN2-independent mechanism. 32Pi labeling and isoelectric focusing analysis of a SUI2+ delta gcn2 strain identifies eIF-2 alpha as radiolabeled and a single isoelectric protein species. Treatment of SUI2+ delta gcn2 strain extracts with phosphatase results in the identification of three additional isoelectric forms of eIF-2 alpha that correspond to the stepwise removal of three phosphates from the protein. Mutational analysis of SUI2 coupled with biochemical analysis of eIF-2 alpha maps the sites to the carboxyl region of SUI2 that correspond to Ser residues at amino acid positions 292, 294, and 301 that compose consensus casein kinase II sequences. 32Pi labeling or isoelectric focusing analysis of eIF-2 alpha from conditional casein kinase II mutants indicated that phosphorylation of eIF-2 alpha is abolished or dephosphorylated forms of eIF-2 alpha are detected when these strains are grown at the restrictive growth conditions. Furthermore, yeast casein kinase II phosphorylates recombinant wild-type eIF-2 alpha protein in vitro but does not phosphorylate recombinant eIF-2 alpha that contains Ser-to-Ala mutations at all three consensus casein kinase II sequences. These data strongly support the conclusion that casein kinase II directly phosphorylates eIF-2 alpha at one or all of these Ser amino acids in vivo. Although substitution of SUI2 genes mutated at these sites for the wild-type gene have no obvious effect on cell growth, one test that we have used appears to demonstrate that the inability to phosphorylate these sites has a physiological consequence on eIF-2 function in S. cerevisiae. Haploid strains constructed to contain Ser-to-Ala mutations at the consensus casein kinase II sequences in SUI2 in combination with a mutated allele of either the GCN2, GCN3, or GCD7 gene have synthetic growth defects. These genetic data appear to indicate that the modifications that we describe at the carboxyl end of the eIF-2 alpha protein are required for optimal eIF-2 function in S. cerevisiae.

Amino Acid Sequence↗
PubMed1994

Expression of v-src alters the expression of myogenic regulatory factor genes.

Inactivation of v-src in transformed chicken myoblasts induced changes in expression of the myogenic regulatory factors (MRF's), MyoD, myogenin and Myf5. Both MyoD and Myf5 were expressed in the transformed cells. The inactivation of v-src by a temperature up-shift resulted in the loss of Myf5 expression, a transient increase in MyoD, followed by a rise in myogenin mRNA levels. The increase in transcripts for the later muscle proteins, myosin heavy and light chains, alpha-actin and troponin T followed the sequence of changes in MRF expression suggesting that their induction was the result of altered MRF expression. Thus, v-src appears to operate through effects on MRF's and not directly on the expression of the late muscle-specific proteins. When v-src was reactivated in mature myotubes by a temperature down-shift, the pattern of expression was quite different, the late muscle-specific transcripts decreased before the loss of myogenin transcripts and before the rise of Myf5 transcripts.

Animals↗
PubMed1993

Novel zinc finger motif in the basal transcriptional machinery: three-dimensional NMR studies of the nucleic acid binding domain of transcriptional elongation factor TFIIS.

Transcriptional elongation provides a key control point in the regulation of eukaryotic gene expression. Here we describe homonuclear and 15N-heteronuclear 3D NMR studies of the nucleic acid binding domain of human transcriptional elongation factor TFIIS. This domain contains a Cys4 Zn(2+)-binding site with no homology to previously characterized Cys4, Cys6, or Cys2-His2 Zn fingers. Complete 1H and 15N NMR resonance assignment of a 50-residue TFIIS peptide-Zn2+ complex is obtained. Its solution structure, as determined by distance geometry/simulated annealing (DG/SA) calculations, exhibits a novel three-stranded antiparallel beta-sheet (designated the Zn ribbon). Analogous sequence motifs occur in a wide class of proteins involved in RNA or DNA transactions, including human basal transcriptional initiation factor TFIIE. A three-dimensional model of the TFIIE Cys4 domain is obtained by DG-based homology modeling. The role of the TFIIS Zn ribbon in the control of eukaryotic transcriptional elongation is discussed.

Amino Acid Sequence↗
PubMed1993

Structure of a new nucleic-acid-binding motif in eukaryotic transcriptional elongation factor TFIIS.

Transcriptional elongation involves dynamic interactions among RNA polymerase and single-stranded and double-stranded nucleic acids in the ternary complex. In prokaryotes its regulation provides an important mechanism of genetic control. Analogous eukaryotic mechanisms are not well understood, but may control expression of proto-oncogenes and viruses, including the human immunodeficiency virus HIV-1 (ref. 8). The highly conserved eukaryotic transcriptional elongation factor TFIIS enables RNA polymerase II (RNAPII) to read though pause or termination sites, nucleosomes and sequence-specific DNA-binding proteins. Two distinct domains of human TFIIS, which bind RNAPII and nucleic acids, regulate read-through and possibly nascent transcript cleavage. Here we describe the three-dimensional NMR structure of a Cys4 nucleic-acid-binding domain from human TFIIS. Unlike previously characterized zinc modules, which contain an alpha-helix, this structure consists of a three-stranded beta-sheet. Analogous Cys4 structural motifs may occur in other proteins involved in DNA or RNA transactions, including RNAPII itself. This new structure, designated the Zn ribbon, extends the repertoire of Zn-mediated peptide architectures and highlights the growing recognition of the beta-sheet as a motif of nucleic-acid recognition.

Amino Acid Sequence↗
PubMed1992

SSL1, a suppressor of a HIS4 5'-UTR stem-loop mutation, is essential for translation initiation and affects UV resistance in yeast.

The SSL1 locus was identified as a trans-acting suppressor that restores HIS4 expression despite a stem-loop structure in the 5'-UTR. SSL1 encodes an essential protein of 52 kD with features characteristic of a protein with multiple zinc fingers. The mechanism of SSL1 suppression is not related to altering his4 transcription or removing the stem-loop sequence from the 5'-UTR; rather, 3- to 5-fold increases in His4 translational expression are observed indicating a post-transcriptional mechanism for SSL1 suppression. SSL1 suppressor mutants that are conditional for growth have altered polysome profiles at the restrictive temperature, and their cell-free extracts are thermolabile in their ability to translate exogenously added mRNA. In addition, the mechanism of suppression appears to be specific for stem-loop structures placed near the 5' end of the message as opposed to a stem-loop located at a downstream position in the 5'-UTR. These observations suggest a role for this protein in promoting translation initiation presumably at the level of ribosomal binding to mRNA. Surprisingly, SSL1 suppressor mutations that are shown to confer an in vivo and in vitro defect in translation initiation also rendered yeast hypersensitive to UV irradiation. This latter phenotype was observed previously with a mutation in the SSL2 suppressor gene, which encodes the yeast homolog of the human gene ERCC-3, for which a defective form causes xeroderma pigmentosum. In light of the related effects of mutations in the SSL1 and SSL2 genes, the encoded proteins may functionally interact both to promote DNA repair and perform an essential function during translation initiation.

Amino Acid Sequence↗
PubMed1992

Control of translation initiation in Saccharomyces cerevisiae.

The first observations regarding the control of translation initiation in the yeast Saccharomyces cerevisiae were made by Fred Sherman and his colleagues in 1971. Elegant genetic studies of the CYC1 gene resulted in the formulation of 'Sherman's Rules' for translation initiation as follows: (i) AUG is the only initiator codon. (ii) the most proximal AUG from the 5' end of a message will serve as the start site of translation; and (iii) if the upstream AUG codon is mutated then initiation begins at the next available AUG in the message. Hidden within these rules is the mechanism of eukaryotic translation initiation, as these very same rules were later shown to apply to higher eukaryotic organisms and were formulated into the scanning model. However, only in the past five years has yeast been taken seriously as an organism for studying the mechanism of eukaryotic translation initiation. The basis for this is that the yeast genes for at least four mammalian translation initiation factor homologues have been identified and the number is growing. Similar factors suggest similar mechanisms for translation initiation between yeast and mammals. For some translation initiation factors, the genetics of yeast has provided new insights into their function. A mechanism for regulating translation initiation in mammalian cells is now evident in yeast. It seems clear that the molecular genetics of yeast coupled with the available in vitro translation system will provide a wealth of information in the future regarding translational control and regulatory mechanisms. The purpose of this review is to summarize what is known about translational control in S. cerevisiae.

Codon↗
PubMed1990

Tyrosine hydroxylase in secretory granules from bovine adrenal medulla. Evidence for an integral membrane form.

Intact secretory granules isolated from bovine adrenal medulla express tyrosine hydroxylase (TH) activity. Granule-associated TH sediments on continuous sucrose gradients with dopamine beta-hydroxylase, a marker for granule membranes, indicating that TH is associated with chromaffin granules. Membranes prepared from lysed granules retain TH, whereas granule contents are free of the enzyme. TH immunoreactivity was detected in granule membranes by immunoblot analysis using a polyclonal antiserum against TH. TH immunoreactivity cannot be removed from membranes by washes in high ionic strength buffers and is only partially removed from membranes by treatment with either urea or Na2CO3. TH can be removed from granule membranes by the detergents Nonidet P-40, Triton X-100, and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate. Treatment of membranes with a phosphatidylinositol-specific phospholipase C did not remove TH, ruling out the possibility of a glycosyl phosphatidyl anchor. Fractionation of granule membranes by temperature-induced phase separation in Triton X-114 revealed that TH is recovered in phases in which integral (detergent phase) and hydrophobic (phospholipid phase) membrane proteins are typically found. By contrast, TH from adrenal cytosol fractionated exclusively into the aqueous phase along with other soluble proteins. Digestion of granules with various protease enzymes revealed that TH is resistant to degradation, suggesting that the enzyme is embedded within membranes. TH becomes phosphorylated when intact granules are exposed to the catalytic subunit of the cAMP-dependent protein kinase, indicating that at least the N-terminal region of TH is exposed on the cytoplasmic surface of granules. These results establish that a fraction of TH is an integral component of bovine granule membranes. The association of TH with granule membranes may play a role in coordinating TH activity and catecholamine release.

Adrenal Medulla↗
PubMed1990

Genetic characterization of the Saccharomyces cerevisiae translational initiation suppressors sui1, sui2 and SUI3 and their effects on HIS4 expression.

Saccharomyces cerevisiae strains containing mutations of the HIS4 translation initiation AUG codon were studied by reversion analysis in an attempt to identify components of the translation initiation complex that might participate in initiation site selection during the scanning process. The genetic characterization of these revertants identified three unlinked suppressor loci: SUI1, SUI2 and sui3, which when mutated restored the expression of the HIS4 allele despite the absence of the AUG initiator codon. Both sui1 and sui2 are recessive and cause temperature-sensitive growth on enriched medium. The temperature-sensitive phenotype and the ability to restore HIS4 expression associated with either sui1 or sui2 mutations cosegregate in crosses. SUI3 mutations are dominant and do not alter the thermal profile for growth. None of the mutations at the three loci suppresses known frameshift, missense or nonsense mutations. Each is capable of suppressing the nine different point mutations of the initiator codon at HIS4 or HIS4-lacZ as well as a two base change (ACC) and a three base deletion of the AUG codon, suggesting that the site of suppression resides outside the normal initiator region. sui1 and sui2 suppressor mutations were mapped to chromosomes XIV and X, respectively. Suppression by sui1, sui2 and SUI3 mutations results in 14-, 11- and 47-fold increases, respectively, relative to isogenic parent strains, in the expression of a HIS4 allele lacking the initiator AUG codon. Part of this increase in the HIS4 expression by sui2 and SUI3 can be attributed to increases of HIS4 mRNA levels, presumably mediated by perturbation of the general amino acid control system of yeast.

Chromosome Mapping↗
PubMed1989

Kinetic studies of Haemophilus influenzae 6-phosphogluconate dehydrogenase.

Haemophilus influenzae 6-phosphogluconate dehydrogenase (6-phospho-D-gluconate:NADP+ 2-oxidoreductase (decarboxylating), EC 1.1.1.44) was purified 308-fold to electrophoretic homogeneity with a 16% recovery through a five-step procedure involving salt fractionation and hydrophobic and affinity chromatography. The purified enzyme was demonstrated to be a dimer of Mr 70,000, and to catalyze a sequential reaction process. The enzyme was NADP-specific and kinetic parameters for the oxidation of 6-phosphogluconate were determined for NADP and four structural analogs of NADP. Coenzyme-competitive inhibition by adenosine derivatives was significantly enhanced by the presence of a 2'-phosphoryl group consistent with the observed coenzyme specificity of the enzyme. The purified enzyme was effectively inhibited by 3-aminopyridine adenine dinucleotide phosphate, but at concentrations higher than that observed to inhibit growth of the organism. Rates of inactivation of the enzyme by N-ethylmaleimide were suggestive of sulfhydryl involvement in the reaction catalyzed.

Adenine Nucleotides↗
PubMed1989

Site-directed inhibition of Haemophilus influenzae malate dehydrogenase.

Previous studies of Haemophilus organisms documented the importance of an NAD+-dependent malate dehydrogenase in the incomplete tricarboxylic acid cycle present in these organisms. Selective interactions occurring at the coenzyme and substrate binding sites of a purified Haemophilus influenzae malate dehydrogenase were investigated. Coenzyme-competitive inhibition by adenosine derivatives demonstrated the presence of regions in the coenzyme binding site that interacted with the adenosine and pyrophosphate moieties of the coenzyme. Positive chainlength effects in the coenzyme-competitive inhibition by aliphatic carboxylic acids indicated the presence of a hydrophobic region at this site that was close to the pyrophosphate region. Seven analogues of NAD+ that were structurally altered in either the pyridine or purine ring were evaluated as selective inhibitors of the enzyme. The three most effective inhibitors of the purified malate dehydrogenase inhibited the growth of H. influenzae when the organism was grown on a limiting concentration of NAD+.

Adenosine Diphosphate↗
PubMed1989

Efficacy of intermittent epidural morphine following posterior spinal fusion in children and adolescents.

Postoperative pain is a distressing and disabling feature of scoliosis surgery. Epidural morphine has recently been advocated to reduce the frequency and severity of postoperative pain in adults. A retrospective study of 35 patients was conducted to determine whether epidural administration of morphine is useful in the management of postoperative pain in children and adolescents following posterior spinal fusion. The derived data included dose and frequency of narcotic administration on the day of surgery and during the subsequent three days. On the first postoperative day, the total morphine given averaged only 16.4 mg in patients receiving epidural morphine compared to 27 mg in those receiving only conventional parenteral morphine. Similar significant differences persisted through the second postoperative day. Intermittent epidural injection of small doses of morphine can give satisfactory and prolonged analgesia for early postoperative pain management.

Adolescent↗
PubMed1988

Kinetic studies of Haemophilus influenzae malate dehydrogenase.

Haemophilus influenzae malate dehydrogenase [S)-malate: NAD+ oxidoreductase EC 1.1.1.37) was purified 109-fold with a 26% recovery through a four-step procedure involving salt fractionation, hydrophobic and dye affinity chromatography. The purified enzyme was demonstrated to be a dimer of Mr 61,000. Initial velocity studies of all four substrates in the forward and reverse reactions indicated a sequential mechanism for the enzyme. Product and dead-end inhibition studies were consistent with an ordered bi-bi mechanism in which NAD is the first substrate bound to the enzyme and NADH, the second product released. Several analogs of NAD structurally altered in either the pyridine or purine moiety were observed to function as coenzymes in the reaction catalyzed by the purified malate dehydrogenase. Alterations in the purine portion of the dinucleotides had a more pronounced effect on the kinetic parameters observed in malate oxidation. The enzyme was inactivated by incubation with diethylpyrocarbonate, whereas no inactivation was observed with sulfhydryl reagents.

Haemophilus influenzae↗
PubMed1983

Failure of single-dose lecithin to alter aspects of central cholinergic activity in Alzheimer's disease.

The effect of a single dose (15 g/70 kg) of lecithin (95% phosphatidylcholine) on several measures of central cholinergic activity (memory, cortisol, prolactin, pulse, blood pressure) was assessed in individuals with Alzheimer's disease. In contrast to the reported effects of physostigmine, a cholinesterase inhibitor, lecithin had no effect on these parameters, despite significant increases in plasma and erythrocyte choline.

Aged↗
PubMed1977

Competition for mixed substrates by microbial populations.

A model for the growth of an organism on multiple substrates was developed, assuming that each substrate has a competitive inhibition effect on the uptake of other substrates. The model was extended to examine mixed substrates, showing that the coexistence of several species at steady state in continuous cultures is possible, even when all the organisms all strongly prefer the one substrate. The diversity of nutrient sources in a real system may be a key factor in supporting a heterogeneous microbial population.

Bacteria↗