Human DNA topoisomerase I is encoded by a single-copy gene that maps to chromosome region 20q12-13.2

cDNA clones of the human TOP1 gene encoding DNA topoisomerase I (EC 5.99.1.2) have been obtained by immunochemical screening of phage lambda libraries expressing human cDNA segments, using rabbit antibodies raised against purified HeLa DNA topoisomerase I. Hybridization patterns between the cloned cDNA sequences and human cellular DNA and cytoplasmic mRNAs indicate that human TOP1 is a single-copy gene. The chromosomal location of the gene has been mapped to the long arm of chromosome 20, in the region q12-13.2, by hybridization of a radioactively labeled TOP1 cDNA probe to human metaphase chromosomes and to a panel of rodent-human somatic hybrids retaining overlapping subsets of human chromosomes.

The primary structure of chicken liver cytochrome b5 deduced from the DNA sequence of a cDNA clone

A cDNA clone encoding the chicken liver cytochrome b5 was isolated by probing a library with synthetic oligonucleotides based on a partial amino acid sequence of the protein. Determination of the DNA sequence indicated a 414-nucleotide open reading frame which encodes a 138-amino acid residue polypeptide. The open reading frame contains 6 amino acids at the amino terminus which were not present on any of the cytochrome b5 polypeptides for which the amino acid sequence has been determined directly, suggesting that the protein is proteolytically processed to the mature form. The results of genomic Southern analysis were consistent with the presence of two structurally different genes in the chicken genome, raising the possibility that the soluble and membrane-bound forms of the protein are the products of separate genes.

pK shift of functional group in mechanochemical coupling due to hydrophobic effect: evidence for an apolar-polar repulsion free energy in water

In the sequential polypeptide poly[4(VPGVG),(VPGEG)] and its more hydrophobic analog poly[4(IPGVG),(IPGEG)] when the material is gamma-irradiation cross-linked to form an elastomeric matrix, mechanochemical coupling occurs on changing the pH, that is, motion and mechanical work are achieved by a change in proton chemical potential. The temperature dependence of aggregation at different pH values in phosphate buffered saline demonstrates the pK to be shifted approximately one pH unit higher for the more hydrophobic sequential polypeptide. The pH dependence of contraction or relaxation for each elastomer shows a similar shift. Data are reviewed and 2D-NMR data are presented which argue that the pK shift is not due to different conformations of the polypentapeptides. Specifically it is proposed that there exist a competition between carboxylates and hydrophobic side chains for mutually incompatible water structures; this results in an apolar-polar repulsion free energy in water with the difference in free energy reflecting the difference in the lle and Val hydrophobicities.

Mechanochemical coupling in synthetic polypeptides by modulation of an inverse temperature transition

For the polypentapeptide of elastin, (L-Val-L-Pro-Gly-L-Val-Gly)n, and appropriate analogs when suitably cross-linked, it has been previously demonstrated that development of elastomeric force at fixed length and length changes at fixed load occur as the result of an inverse temperature transition, with the temperature of the transition being inversely dependent on the hydrophobicity of the polypeptide. This suggests that at fixed temperature a chemical means of reversibly changing the hydrophobicity could be used for mechanochemical coupling. Evidence for this mechanism of mechanochemical coupling is given here with a 4%-Glu-polypentapeptide, in which the valine in position 4 is replaced in 1 out of 5 pentamers by a glutamic acid residue. Before cross-linking, the temperature for aggregation of 4%-Glu-polypentapeptide is remarkably sensitive to pH, shifting from 25 degrees C at pH 2 to 70 degrees C at pH 7.4 in phosphate-buffered saline (PBS). At 37 degrees C, the cross-linked 4%-Glu-polypentapeptide matrix in PBS undergoes a pH-modulated contraction and relaxation with a change from pH 4.3 to 3.3 and back. The mean distance between carboxylates at pH 4.3 in the elastomeric matrix is greater than 40 A, twice the mean distance between negatively charged species in PBS. Accordingly, charge-charge repulsion is expected to make little or no contribution to the coupling. Mechanochemical coupling is demonstrated at fixed load by monitoring pH dependence of length and at constant length by monitoring pH dependence of force. To our knowledge, this is the first demonstration of mechanochemical coupling in a synthetic polypeptide and the first system to provide a test of the recent proposal that chemical modulation of an inverse temperature transition can be a mechanism for mechanochemical coupling. It is suggested that phosphorylation and dephosphorylation may modulate structure and forces in proteins by locally shifting the temperatures of inverse temperature transitions.

Lethality of a dut (deoxyuridine triphosphatase) mutation in Escherichia coli

A chloramphenicol resistance gene was cloned into a plasmid-borne dut gene, producing an insertion mutation that was then transferred to the chromosome by allelic exchange. The mutation could not be acquired by haploid strains through substitutive recombination, even when two flanking markers were simultaneously transduced. The insertion was easily transferred, via generalized transduction, into the chromosomal dut region of strains harboring a lambda dut + transducing phage; however, the resulting dut mutant/lambda dut + merodiploid could not then be cured of the prophage. This apparent lethality of the mutation could not be explained by effects on adjacent genes; the dfp gene retained complementing activity, and a ttk insertion mutant was viable. The dut gene product, deoxyuridine triphosphatase, is known to reduce incorporation of uracil into DNA and to be required in the de novo synthesis of thymidylate. Therefore, an attempt was made to determine whether the dut insertion would be tolerated in strains carrying the following compensatory mutations: dcd (dCTP deaminase) and cdd (deoxycytidine deaminase), which should reduce dUTP formation; ung (uracil-DNA glycosylase), which should reduce fatally excessive excision repair; deoA (thymidine phosphorylase), which should enhance the utilization of exogenous thymidine; and sulA, which should reduce the lethal side effects of SOS regulon induction. These mutations, either alone or in various combinations, did not permit the survival of a haploid dut insertion mutant, suggesting that the dut gene product might have an essential function apart from its deoxyuridine triphosphatase activity.

Double stranded DNA sequencing as a choice for DNA sequencing

Images

Spatial heterogeneity of local blood flow and metabolite content in dog hearts

Spatial variation (heterogeneity) of myocardial blood flow was studied under basal conditions in relation to four biochemical markers: creatine kinase (CK), lactate dehydrogenase (LDH), ATP, and glycogen. A total of 508 individual 0.5-g samples from the left ventricular free wall was studied in 12 dogs. Myocardial blood flow was measured by radioactive microspheres (15 micron diam) injected via a pigtail catheter into the left ventricle during light sedation (closed-chest flow measurements); following thoracotomy, a second set of microspheres was injected via a catheter into the left atrium (open-chest flow measurements, n = 5). In 27-54 samples/heart, myocardial blood flow, CK, LDH, protein, ATP, and glycogen were determined, permitting a direct correspondence between local blood flow and metabolic markers in each sample and an assessment of the spatial heterogeneity of flow and metabolite content. Correlations between myocardial blood flow per gram tissue and metabolite concentration per gram tissue in pooled data were weak but significant: partial correlation coefficients were 0.137 for CK (P = 0.024), 0.167 for LDH (P = 0.006), 0.341 for ATP (P less than 0.001), 0.123 for glycogen (P = 0.053), but not significant for protein vs. myocardial blood flow. The coefficient of variation, which defines the extent of spatial heterogeneity, averaged 20% for closed-chest flow measurements, 19% for open-chest flow measurements, 22% for CK, 17% for LDH, 15% for protein, 8% for ATP, and 18% for glycogen; these values are over and above the variability due to the technique error, indicating a definite physiological spatial variability. The correlation between local blood flow and the studied metabolites can only explain a minor portion of the spatial heterogeneity of myocardial blood flow. Although a physiological link between blood flow and metabolite content for small regions of the heart is demonstrated, the true local variability of blood flow may be modulated predominantly by other factors.

Involvement of DNA topoisomerase I in transcription of human ribosomal RNA genes

Treatment of HeLa cells with a DNA topoisomerase I-specific inhibitor, camptothecin, results in rapid cessation of the synthesis of the 45S rRNA precursor. The inhibition of rRNA synthesis is reversible following drug removal and correlates with the presence of camptothecin-trapped topoisomerase I-DNA abortive complexes, which can be detected as topoisomerase I-linked DNA breaks upon lysis with sodium dodecyl sulfate. These breaks were found to be concentrated within the transcribed region of human rRNA genes. No such sites can be detected in the inactive human rRNA genes in mouse-human hybrid cells, suggesting a preferential association of topoisomerase I with actively transcribed genes. The distribution of RNA polymerase molecules along the transcription unit of human rRNA genes in camptothecin-treated HeLa cells, as assayed by nuclear run-on transcription, shows a graded decrease of the RNA polymerase density toward the 3' end of the transcription unit; the density is minimally affected near the 5' start of the transcription unit. These results suggest that DNA topoisomerase I is normally involved in the elongation step of transcription, especially when the transcripts are long, and that camptothecin interferes with this role.

Profound structural alterations of the extracellular collagen matrix in postischemic dysfunctional ("stunned") but viable myocardium

Ultrastructural studies of the extracellular collagen matrix were made on the "stunned" myocardium using scanning, conventional and high voltage transmission electron microscopy and light microscopy. Regional myocardial dysfunction was produced by 12 sequential 5 minute occlusions of the left anterior descending coronary artery, separated by 10 minute intervals of reperfusion. A final 90 minute reperfusion period documented persistent myocardial dysfunction. At the end of the final reperfusion period, the percent systolic shortening, measured by sonomicrometers, was depressed significantly to 35 +/- 9% of baseline. The heart was then perfusion fixed, and samples were taken from both control and stunned areas. No changes associated with irreversible cellular damage were noted in the stunned region. However, scanning electron microscopy of the stunned area showed that the extracellular collagen matrix underwent profound structural changes. Collagen cables were roughened, uncoiled and discontinuous. Linear grooves on the surface of the myocytes were frequently seen, indicating complete loss of collagen cables. The usual dense collagen weave surrounding myocytes became patchy or absent. Myocyte to myocyte struts were sparse and frequently absent, with remnant nodular or nublike structures indicative of breakage. High voltage electron microscopy of the stunned area showed that the collagen struts were discontinuous and vacuolated with rounded tips. Light microscopy of silver-stained sections of the stunned tissue demonstrated large patchy areas that were devoid of silver, indicating absence of the collagen matrix. There was a progressive increase in percent systolic bulging during each sequential coronary occlusion, suggesting increasing myocardial compliance. These results indicate that the myocardial collagen matrix is severely damaged from reversible ischemic cell injury. The greater myocardial compliance and less effective contractile effort in the stunned myocardium might be explained on a structural basis: disruption of the mechanical coupling function provided by the extracellular collagen matrix.

Isolation and Characterization of a Fast-Growing, Thermophilic Methanobacterium Species

A thermophilic, autotrophic methanogen (strain CB12, DSM 3664) was isolated from a mesophilic biogas digestor. This bacterium used H 2 -CO 2 or formate as a substrate and grew as short rods, sometimes in pairs and in crooked filaments. Motility was not observed. Its optimum temperature (56°C) was lower than that of other thermophilic members of the genus Methanobacterium . The maximum observed specific growth rate was 0.564 h −1 (74-min doubling time).

[Value and factors of influence in the combined method of the urine-purple-heat tolerance test in the diagnosis of cancer]

A method combining the urine cancer reaction, purple reaction and heat tolerance test (combined method of urine-purple-heat tolerance) was used to examine 112 normal persons, 110 non-cancer patients and 93 cancer patients. It was found that the accuracy rate of the urine reaction was 82%, of the purple reaction 77.4%, and of the heat tolerance 79%. The combined method showed great diagnostic value for cancers in the digestive tract, such as stomach, biliary duct, colon, pancreas and liver, as well as other cancers, e.g., lung cancer, lymphosarcoma and brain tumor. This method may be best for screening the above tumors. Its positive rate was also high in malignant reticuloma, chronic granulocytic leukemia and reticulosarcoma. The mechanism of the combined method and the influential factors, such as the freshness of the specimen, reactive time, temperature and quality of the reagents are discussed.

Responses of recurrent laryngeal motoneurons to changes of pulmonary afferent inputs

In decerebrate, paralyzed cats ventilated with a cycle-triggered pump, the discharges of the recurrent laryngeal (whole nerve or single fibers) and phrenic nerves, and the changes produced by pulmonary afferent inputs (lung inflation), were compared. When lung inflation was in phase with neural inspiration, four types of laryngeal fiber activities were observed: (a) phasic-inspiratory; (b) tonic-inspiratory; (c) expiratory-inspiratory; (d) early-expiratory. The firing patterns during inspiration were plateau-like, whereas the phrenic pattern was augmenting. When inflation was withheld, the plateau patterns usually became augmenting, indicating inhibition of laryngeal inspiratory activity by pulmonary afferents. Secondary effects of withholding inflation were (a) increases of early-expiratory activity (both whole nerve and individual fiber), indicating increased post-inhibitory rebound excitation; (b) decreased activity of tonic-inspiratory and expiratory-inspiratory fibers during early neural expiration, indicating increased inhibition by early-expiratory neurons. The discharge patterns of different types of laryngeal motoneuron, as well as their changes with inflation, are interpreted in relation to the function of regulating airway resistance.

Responses of early and late onset phrenic motoneurons to lung inflation

In anesthetized or decerebrate cats that were paralyzed and ventilated with a cycle-triggered pump, we produced changes in activity of the whole phrenic nerve and of individual phrenic motoneurons (fibers or cells in the spinal cord) by withholding lung inflation during the inspiratory (I) phase. The neurons were classified into early- and late-onset types (discharge onset less or greater than 80 msec, respectively, after whole phrenic onset). Both unit and whole phrenic activity exhibited a variety of responses to inflation (excitation, depression, or no effect); but there were no consistent differences between responses of early- and late-onset neurons. The distribution of responses was quite different from that of dorsal respiratory group (DRG) I neurons (Cohen and Feldman, 1984); in particular there was no group of phrenic neurons corresponding to the late-onset I-beta neurons (I neurons excited by inflation). We conclude that the inputs to late-onset phrenic neurons are not predominantly or exclusively from late-onset DRG neurons.

Hypoglossal motoneuron responses to pulmonary and superior laryngeal afferent inputs

In decerebrate, paralyzed cats ventilated with a cycle-triggered pump, the inspiratory discharges of the hypoglossal (whole nerve or single fibers), phrenic, and recurrent laryngeal nerves were compared, and the effects of pulmonary and superior laryngeal afferent inputs were observed. During lung inflations in phase with neural inspiration, hypoglossal and recurrent laryngeal activities differed from phrenic with respect to (a) burst onset times: both preceded the phrenic; (b) overall pattern: phrenic, augmenting; hypoglossal, decrementing; recurrent laryngeal, plateau-like. When inflation was withheld, the phrenic pattern was not markedly changed, but both hypoglossal and recurrent laryngeal became augmenting; the marked increase of hypoglossal activity (both whole nerve and single fiber) indicated strong inhibition by lung afferents. Superior laryngeal electrical stimulation evoked excitation of the contralateral phrenic (latency 4.1 msec) and the ipsilateral whole hypoglossal (latency 5.3 msec), followed by bilateral inhibitions (durations 20-30 msec); most hypoglossal fibers showed only inhibition. We conclude that, although both hypoglossal and phrenic outputs are driven by the inspiratory pattern generator(s), their promotor systems differ with respect to influences from central and peripheral inputs.

Fatty acid metabolism and cell proliferation. V. Evaluation of pathways for the generation of lipid peroxides

Primary cultures of smooth muscle cells were established from the medial layer of guinea pig aorta. Confluent cells at passage level 4-6 were challenged with arachidonic acid and treated with a number of antioxidants and inhibitors of specific lipid peroxidation pathways. Lipid peroxidation was measured by the thiobarbituric acid test for malondialdehyde (MDA) and the isolation of hydroperoxy fatty acids (HPETE) by high performance liquid chromatography (HPLC). Prostanoids were measured by radioimmunoassay and the separation of labeled compounds by HPLC. MDA, 6-keto-PGF1 alpha, and PGE2 were formed when cells were challenged with arachidonic acid and these cells synthesized small amounts of one HPETE isomer, 15-HPETE. The HPETE isomers characteristic of the lipoxygenase pathway, 12-HPETE and 5-HPETE, were not detected. Furthermore, the lipoxygenase inhibitors, eicosatetraynoic acid (ETYA) and 6,7-dihydroxycoumarin (Esculetin), did not block MDA formation. These data show that MDA is not generated in the cells by a lipoxygenase pathway. The cyclooxygenase inhibitors, indomethacin and ETYA, did not block MDA formation but these agents blocked the formation of 15-HPETE. These data show both that 15-HPETE is generated by a cooxidation pathway and that 15-HPETE and cooxidation are not involved in MDA formation. Three inhibitors of cytochrome P450 linked lipid peroxidation, 2-amino-3-ethoxycarbonyl-6-benzyl-4, 5,6,7-tetrahydrothieno-[2,3-C]-pyridine (Tinoridine), 3-methyl-1,2-di-3-pyridyl-1-propanone (Metyrapone) and phenobarbital, did not block MDA formation. These data support earlier studies that indicated that MDA is not generated by a P450 pathway. Cells contained a bound precursor that decomposed to MDA when cells were treated with Fe3+. The cells exhibited autofluorescence and concentric lamellae in lipid droplets that are characteristic of ceroid-lipofuscin. These observations are consistent with lipid peroxidation through increased peroxisomal activity leading to the generation of MDA and the accumulation of ceroid-lipofuscin. The natural antioxidants, vitamin E and vitamin E quinone (EQ), and the synthetic antioxidants, butylated hydroxytoluene and nordihydroguaiaretic acid (NDGA), alpha-naphthol (alpha-N) and propyl gallate (PrGa), all blocked MDA formation in confluent smooth muscle cells, showing that these antioxidants did not function solely as specific inhibitors of lipoxygenase, cooxidation or P450 pathways. Cell proliferation was measured in cells challenged with arachidonic acid and treated with antioxidants and other inhibitors. The least cytotoxic and most potent antioxidant, EQ, blocked MDA formation in confluent cells and promoted grow