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Biomedical subjects

T Hsieh

Publications and source records attributed to T Hsieh.

At least 55 records · Page 3Linked to original sources
PubMed1984

A protein kinase activity tightly associated with Drosophila type II DNA topoisomerase.

A protein kinase activity has been identified that is tightly associated with the purified Drosophila type II DNA topoisomerase. The kinase and topoisomerase activities are not separated when the enzyme is subjected to analytical chromatography (phosphocellulose, single-strand DNA agarose, and Sephacryl S-300) and analytical glycerol gradient sedimentation. These two activities are also inactivated to the same extent by either heat or N-ethylmaleimide treatment. The evidence, however, does not rule out the possibility that the kinase activity resides in a polypeptide other than the topoisomerase polypeptide. The topoisomerase-associated protein kinase activity is not stimulated by Ca2+ or cyclic nucleotides. It shows a broad substrate range, including the DNA topoisomerase itself, casein, phosvitin, and histones. Phosphoamino acid analysis identified phosphoserine and phosphothreonine in polypeptides modified by the topoisomerase-associated protein kinase. No similar activity has been identified previously in Drosophila melanogaster.

Animals↗
PubMed1984

Epstein-Barr virus-associated antibodies and serum biochemistry in nasopharyngeal carcinoma.

Nasopharyngeal carcinoma is difficult to diagnose in its early stages. It also has frequent recurrences and/or distant metastases after radiotherapy. Extensive clinical, serological and biochemical studies were done during 1980-1982 on 351 patients to aid in the diagnosis of the disease, especially with recurrence or metastasis. Seropositive rates of the antibody titers against viral capsid antigens (VCA) and early antigens (EA) of Epstein-Barr virus (EBV) in IgG and IgA classes were 41.7%-100%. They ranked, in order of frequency: anti-VCA/IgA, anti-VCA/IgG, anti-EA/IgG, and anti-EA/IgA. Mean total serum IgG and IgA levels were moderately increased in all patients. Serum GOT, GPT, alkaline phosphatase, lactate dehydrogenase and mucoprotein were elevated either alone or in combination in a few patients before treatment, in many patients with recurrence or metastases, and in all patients with liver metastasis.

Antibodies, Neoplasm↗
PubMed1983

Knotting of the circular duplex DNA by type II DNA topoisomerase from Drosophila melanogaster.

DNA molecules with topological knots can be detected in a reaction mixture of circular DNA and type II DNA topoisomerase purified from the embryos of Drosophila melanogaster. Similar to the DNA knotting reaction by bacteriophage T4-induced topoisomerase (Liu, L. F., Liu, C. C., and Alberts, B. M. (1980) Cell 19, 697-707), the knotting reaction by the Drosophila topoisomerase II requires a high ratio of enzyme/DNA. However, they differ in the following aspects: 1) the knotting reaction by the Drosophila enzyme is greatly stimulated by the presence of ATP; 2) the knotted DNA is a stable product in the reaction mixture over prolonged incubation; and 3) both the covalently closed circular DNA and its nicked form, which is devoid of any superhelical structure, can be knotted. The knotted DNA generated by the Drosophila topoisomerase II can be efficiently unknotted by a catalytic amount of Drosophila topoisomerase II, but not by topoisomerase I. The ionic strength optimum for the knotting reaction is close, but not identical, to the optimal condition for the unknotting and supercoil relaxation reactions. Aspects of DNA knotting are discussed.

Animals↗
PubMed1983

Double strand DNA cleavage by type II DNA topoisomerase from Drosophila melanogaster.

The purified type II DNA topoisomerase from the embryos of Drosophila melanogaster exists in its native form as a dimer of 170,000-dalton polypeptides. In addition to the 170,000-dalton polypeptides, 3 polypeptides with molecular weights of 151,000, 141,000, and 132,000 were resolved when the enzyme was analyzed by electrophoresis under denaturing conditions. All four polypeptides can participate in the topoisomerase cleavage reaction and form covalent complexes with the cleaved DNA. Furthermore, immunochemical and biochemical data showed that they are structurally related and, therefore, the smaller polypeptides are likely generated from the 170,000-dalton polypeptide by proteolysis. The double strand DNA cleavage reaction of Drosophila topoisomerase has different site specificity from the Escherichia coli DNA gyrase-effected reaction. However, they result in an identical DNA structure at the cleavage site, which is a staggered double strand break with 4-nucleotide long 5'-protruding ends. The 3'-ends at the site of cleavage by Drosophila topoisomerase II have free hydroxyl groups and can be extended by exactly 4 nucleotides with T4 DNA polymerase, while the 5'-ends are covalently linked to the topoisomerase molecules. This similarity in cleavage site structure for Drosophila topoisomerase II and E. coli DNA gyrase suggests that they share some fundamental features in their mechanism of action.

Animals↗
PubMed1983

[Serological and biochemical studies in late stage of nasopharyngeal carcinoma].

Serological and biochemical studies were done at the National Taiwan University Hospital, on 243 patients with biopsy-proved anaplastic nasopharyngeal carcinoma (NPC) in various clinical conditions. The remarkable elevation of both IgG and IgA antibody titers against EB virus was specific for NPC patients. The seropositive rates ranged from 75% to 100% in various stages of NPC patients. Serum IgG and IgA levels were also increased moderately and nonspecifically in stages II-IV and recurrent patients. Peripheral white blood cell count was also slightly increased in these patients. Peripheral lymphocyte counts were slightly decreased in patients with neck recurrence or distant metastasis. Serum IgM, C3, C4 and Acid phosphatase levels were within normal range in all the patients. Serum GOT, GPT, alkaline phosphatase, and lactate dehydrogenase were elevated in some of patients with distant metastasis and in most of those with liver metastasis. Mucoprotein was elevated in about 10% of stage II-IV patients but in about 50% of patients with recurrent neck metastasis or distant metastasis. in conclusion, serological and biochemical examinations are important in the diagnosis of late stages and recurrence or metastasis of NPC.

Antibodies, Viral↗
PubMed1980

ATP-dependent DNA topoisonmerase from D. melanogaster reversibly catenates duplex DNA rings.

Extracts of Drosophila embryos contain an enzymatic activity that converts circular DNAs into huge networks of catenated rings in an ATP-dependent fashion. The catenated activity is resolved into two protein components during purification. One component is a novel DNA topoisomerase that requires the presence of ATP in order to relax supercoiled DNA. We have shown that the ATP-dependent DNA topoisomerase relaxes DNA by a mechanism distinct from that of nicking-closing enzymes. The Drosophila ATP-dependent topoisomerase allows one segment of a circular DNA to pass through transient breaks in both strands at another site on the DNA circle without any relative rotation between the ends at the transient break. This mechanism can convert negative supertwists to positive twists and vice versa until a relaxed equilibrium state is reached. The formation of catenated rings is mediated by an analogous bimolecular reaction which can occur between two nonhomologous DNA circles. The catenation reaction is fully reversible: in the presence of the second protein component, circular DNA is converted quantitatively into catenated forms; in its absence, the ATP-dependent topoisomerase resolves catenated networks back into monomer circles. The Drosophila ATP-dependent topoisomerase appears to be closely related to E. coli DNA gyrase in that both use a similar mechanism to change the topology of DNA, both require ATP and both are inhibited by the antibiotic novobiocin. The presence of an enzyme that allows one DNA helix to pass freely through another could not only be useful in relaxation of topological constraints, but also may be involved in the folding and unfolding of eucaryotic chromosomes.

Adenosine Triphosphate↗
PubMed1979

A protein that preferentially binds Drosophila satellite DNA.

Using a nitrocellulose filter binding assay, we have detected and partially purified a protein from embryos of Drosophila melanogaster that preferentially binds to a highly repeated satellite DNA of the same species. Formation of the satellite DNA-protein complex requires physiological conditions of salt and temperature, but once formed, the complex is stable in high salt (1 M NaCl) or at low temperature. Optimal formation of the specific complex also requires the satellite DNA to be in a supertwisted conformation. The protein interacts with a limited region within the 359-base-pair repeated sequence of the satellite DNA.

Animals↗
PubMed1978

Physiochemical studies on interactions between DNA and RNA polymerase. Ultraviolet absorption measurements.

The interaction between Escherichia coli RNA polymerase and a restriction fragment of coliphage T7 DNA containing four promoter sites for the coli enzyme has been studied by difference uv absorption spectroscopy in a low ionic strength buffer containing 10 mm MgCl2 and 50 mM KCl. The binding of the enzyme to the DNA is accompanied by a hyperchromic shift which shows a maximum around 260 nm, and increases with increasing temperature in the temperature range studied (4-40 degrees C). Measurements were also carried out with whole T7 DNA and a restriction fragment containing no promoter site. A comparison of the results obtained with the various DNAs suggests that the binding of an RNA polymerase to a promoter site in the low ionic strength medium causes the disruption of a short segment of the DNA helix, of the order of ten pairs; the binding of an enzyme molecule to a promotor site appears to have a cooperative effect on the binding of the enzyme molecules to adjacent non-promoter sites with concomitant disruption of DNA base pairs.

Binding Sites↗
PubMed1977

Prognosis of nasopharyngeal carcinoma by Epstein-Barr virus antibody titer.

A total of 433 samples of serum were collected from 305 patients with histopathologically proved anaplastic nasopharyngeal carcinoma (NPC). Antibodies against viral capsid antigens (VCA) of Epstein-Barr (EB) virus were titrated by means of indirect fluorescent antibody technique, using P3HR-1 cells as the target. High anti-VCA antibody titer in patients with NPC was found beginning to decline at the end of radiotherapy. Most (66.7%) of the patients were found to have a detectable reduction in antibody titer within six months after radiotherapy. Persistent high antibody titer after treatment correlates to high risk of the recurrence of the disease. This prognostic importance of anti-VCA titer becomes apparent at the end of radiotherapy, significant (P less than .05) within one year after treatment, and highly significant (P less than .0005) over one year after treatment.

Antibodies, Viral↗