Schlüsselseiten aus dem Exemplar der ULB Halle: Strassburg, Diss., 1623-26 (9).

Würzburg, Univ., Diss., 2009

Reproduction de : Thèse de doctorat : Astrophysique : Cergy : 2007. / Titre provenant de l'écran titre. Bibliogr. p. 197-208.

High nutrient, low chlorophyll (HNLC) regions, where the availability of iron (Fe) limits primary production, comprise approximately 40% of the global ocean. Variability in Fe supply to these regions has the potential to impact Earth's climate by affecting the efficiency of the biological carbon pump, and thereby carbon dioxide uptake by the oceans. Characterizing Fe sources to HNLC regions is thus crucial for a better understanding of the connections and feedbacks between the ocean and climate change. This work addresses the question of Fe supply to two HNLC regions: the Southern Ocean and the subarctic northeast (NE) Pacific Ocean. In both regions, dissolved Fe (dFe) and the reduced form of iron, Fe(II), were measured in the water column. In the Southern Ocean, measurements were undertaken under the seasonal pack ice in the East Antarctic south of Australia. The results indicate that the sea ice represents a significant dFe source for the under-ice water column in spring, and that the Fe delivered from brine drainage and sea ice-melt likely contributes to the formation of the spring bloom at the ice edge. Shelf sediments were also found to supply dFe to the water column. Their effect was most pronounced near the shelf break and at depth, but offshore transport of Fe-enriched waters was also implicated. Fe(II) concentrations in spring were very low, most likely due to a lack of electron donors in the water column and limited solar radiation underneath the sea ice. Repeat measurements along a transect in the subarctic NE Pacific indicate that shelf sediments supply dFe and Fe(II) at depth, but their influence does not appear to extend offshore beyond several hundred kilometres. Episodic events such as the passage of sub-mesoscale eddies may transport subsurface waters a limited distance from the shelf break, supplying Fe(II) in a depth range where upwelling and deep mixing could bring it to the surface. Offshore, dFe shows little variability except in June 2012, where an aerosol deposition event is suspected to have increased dFe concentrations at depth. Fe(II) concentrations offshore are generally low, but show transient maxima at depth that likely result from remineralization processes in the oxygen deficient zone that stretches from ~600 to 1400 m depth in the subarctic NE Pacific. Elevated Fe(II) concentrations at depth were also observed in conjunction with the aerosol deposition event, which might indicate Fe(II) production associated with settling particles. However, the aerosol deposition event, which most likely stemmed from forest fires in Siberia, did not appear to trigger a phytoplankton bloom in surface waters, possibly due to a lack of Fe fertilization from the deposited material, or due to toxic effects on the resident phytoplankton community. Dust deposition from the atmosphere is considered a major Fe supply mechanism to remote HNLC regions, but the factors affecting Fe solubility of dust are poorly constrained. A laboratory experiment was conducted to test whether the presence of superoxide, a reactive oxygen species, enhances the dissolution of dust from different geographic source regions. The results indicate that superoxide may promote Fe solubilization from the dust sources tested, and that the effect of exposure to superoxide is on par with the Fe solubilizing effect of photochemical reactions. Given the possibility of widespread superoxide production by heterotrophic bacteria at all depths of the ocean, this finding suggests that significant Fe dissolution of dust particles could occur throughout the water column, not only in the well-lit surface layer. / Graduate / 0425 / 0996 / cschalle@uvic.ca

This report describes the MileageAIDE system for recording the business mileage of a vehicle. The system consists of a mobile application for an Android phone and a hardware device connected to the vehicle’s On-Board Diagnostic port (OBD-II). The two interact via Bluetooth to record the time and odometer value for every trip in the vehicle and remind the user to classify the trip as business or personal. The result is a system that is easy to install, easy to use, inexpensive and keeps detailed and accurate records that are acceptable for reporting to an employer for reimbursement or as business expenses on a tax return. / text

Group II introns are highly structured RNAs that carry out self-splicing reactions. The multiple turnover version of one of these introns, termed the D135 ribozyme, is derived from the mitochondrial aI5γ intron of Saccharomyces cerevisiae and is widely studied as a model RNA for group II intron folding. An important current goal is to probe global changes during its folding with or without DEAD-box chaperone proteins. My initial experiments to study global compaction using small angle X-ray scattering (SAXS) of D135 reveal rapid initial compaction. Unexpectedly, slower increases in Rg value and forward scattering were observed and shown to result from dimerization of the ribozyme. Dimerization was also observed with native electrophoretic mobility shift assays. Here, I have characterized the dimerization process at various conditions. Dimerization requires Mg2+, with similar concentration dependence as tertiary folding, and the dimer is efficiently disrupted by the ATP-dependent activity of DEAD-box proteins. Dimerization does not affect ribozyme catalysis, as both the monomer and the dimer are shown to be fully active. Further experiments showed that dimerization results from duplex formation by an artificial 3’ tail that has extensive self-complementarity, as the deletion of this tail ablates dimerization. Constructs lacking this artificial 3’ tail are likely to simplify further study of the folding process of this ribozyme. / text

Group II introns insert site-specifically into DNA target sites through a process termed retrohoming. They consist of a structured, catalytically active intron RNA and its encoded protein. The protein contains several domains, including a reverse transcriptase domain and a DNA endonuclease domain used for bottom-strand cleavage. Recently, the thermophile Thermosynechococcus elongatus BP-1 was found to contain eight functional group II intron-encoded proteins. The proteins are thermostable and active at temperatures up to 65°C. The intron-encoded protein, TeI4c displays the greatest reverse transcriptase activity of these eight proteins, as well as high fidelity and processivity; ideal qualities for a commercial reverse transcriptase. This work explores the possibility of using TeI4c for biotechnology applications, and specifically examines the C-terminal endonuclease domain of TeI4c and its effect on reverse transcription. Additionally, this work investigates the retrohoming activity of a TeI4c truncation that deletes the endonuclease domain. / text

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Ethonafide is an anthracene-containing derivative of amonafide that belongs to the azonafide series of anticancer agents. The lack of cross-resistance in MDR-expressing cancer cell lines and the absence of a quinone and hydroquinone moiety make ethonafide a possible less-cardiotoxic replacement for existing anthracene-containing anticancer agents, such as mitoxantrone and doxorubicin. For this study, we investigated the anticancer activity and mechanism of action of ethonafide in human prostate cancer cell lines. Ethonafide was cytotoxic against three human prostate cancer cell lines at nanomolar concentrations. Ethonafide was also found to be better tolerated and more effective at inhibiting tumor growth compared to mitoxantrone in DU 145 prostate cancer-bearing mice. Mechanistically, we found that ethonafide inhibits topoisomerase II activity in human prostate cancer cell lines and equally inhibits purified topoisomerase IIα and recombinant topoisomerase IIβ. The inhibition of topoisomerase II activity was due to stabilization of the cleavable complex, involving both topoisomerase IIα and β. By creating stable DU 145 cell lines with decreased expression of either topoisomerase IIα or β, we found that topoisomerase IIα is necessary for ethonafide-induced cytotoxicity. The decrease in sensitivity to ethonafide was due to a decrease in DNA damage and an increase in DNA repair as measured by the neutral comet assay. Additionally, ethonafide induces potent G₂ cell cycle arrest in the DU 145 human prostate cancer cell line. Ethonafide also induces apoptosis as measured by procaspase and PARP cleavage. In conclusion, we have identified ethonafide as a topoisomerase II poison and determined that it is topoisomerase IIα-specific in the DU 145 human prostate cancer cell line. Due to ethonafide’s activity in vitro and in vivo, decreased toxicity in mice compared to mitoxantrone, and its activity in multi-drug resistant cancer cell lines, ethonafide may be a suitable replacement to mitoxantrone for the treatment of hormone-refractory prostate cancer.