Protein arginine methylation is an abundant post-translational modification catalyzed by protein arginine methyltransferases (PRMTs). Arginine methylation plays important roles in a variety of cellular pathways and human diseases. PRMT1, the predominant PRMT, catalyzes approximately 85% of all protein arginine methylation in vivo. While many details of how PRMT1 functions have been uncovered through the past two decades, there are many details which remain unclear, including how arginine methylation is regulated, how PRMT1 binds substrates, and what role PRMTs play in RNA surveillance. Our recent data presented in this thesis showed that reduction of the PRMT1 enzyme, following recombinant expression and purification, changes both enzymatic activity and oligomeric state. A cysteine residue(s) was found to be responsible for the observed redox chemistry in PRMT1 and at least one parameter in the kinetic mechanism, S-adenosylmethionine (AdoMet) binding, was faster with a reduced enzyme. This work suggests exciting potential for the regulation of PRMTs in vivo by oxidative stress. In addition to studying the effects of reduction/oxidation on PRMT1, a foundation for future experiments was laid. These experiments investigate substrate recognition by PRMTs and what the role arginine methylation may play in RNA processing and surveillance. To better understand how PRMTs selectively bind a wide variety of substrates, I have designed and preliminarily characterized several Hmt1 (the S. cerevisiae homologue of PRMT1) variants. These variants will be used for crystallization trials of a homogeneous complex, containing Hmt1, AdoMet, and a peptide substrate, capable of revealing specific chemical interactions between Hmt1 and the peptide substrate. To further our understanding of Hmt1's role in RNA processing and surveillance, particularly in RNA degradation pathways, I extracted yeast RNA from both wild type and Hmt1-null cells. The RNA was probed using a S. cerevisiae whole-genome microarray. This analysis revealed that Hmt1 exhibits statistically significant effects in several broad areas including molecular function, biological processes, cellular components, and some KEGG pathways. The presented studies have revealed the exciting potential for an in vivo regulatory mechanism of PRMT1 and each study is primed for further investigation both in vivo and in vitro.

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Call number: LD2668 .T4 1952 W5 / Master of Science

The main aim of this work is to study the bonding behaviour of Al alloys as a function of temperature, time and processing conditions from a perspective of oxidation so as to gain a comprehensive knowledge of the oxidation issues during processing and to design better bonding approaches for different alloy systems. Two major parts of work have been carried out during the study: (a) the use of a stacking approach and a double pouring approach to potentially join two Al alloys and their effectiveness are assessed; and (b) a precise investigation of the oxidation mechanisms for Al-Cu and Al-Mg alloys using a combination of theoretical analysis and experimental characterization. The project started with the use of a stacking approach to try to bond two stacked Al alloys. The stacked sample can be viewed as a bi-metal which has an oxide bi-film layer at the bond interface. It was found that the bi-film layer was a physical barrier preventing direct metallic bonding. How this bi-film layer evolves during the bonding process was then investigated. The work then moved on to investigate the oxidation mechanisms of Al-Cu alloys and Al-Mg alloys in greater detail. The thermodynamics, kinetics of oxidation, chemistry and morphology of the oxide scale were particularly studied. Briefly speaking, in the case of the Al-Cu-O₂ system, the oxidation proceeds in the order of amorphous γ-Al₂O₃ - to - crystalline γ-Al₂O₃ - to - α-Al₂O₃; in the case of the Al-Mg-O₂ system, the oxidation proceeds as amorphous γ-Al₂O₃ to MgO to MgAl₂O₄ and the morphology of the oxide scale develops from a protective layer to a porously structured composite layer. A double pouring approach was finally developed to bond Al and Al-5Cu but the method has still not been perfected due to the formation of bi-film defects along the bond interface. Induction melting, squeeze casting, and extrusion bonding were therefore studied as an attempt to reduce the harmful effect of bi-film defects. Although all of the approaches exhibit some limitations, they have potential for future development.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Pharmacology / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Science