http://digital.library.wisc.edu/1793/8139 Includes Bacteriology majors (2007) http://minds.wisconsin.edu:80/retrieve/8036 http://digital.library.wisc.edu/1793/8139 http://digital.library.wisc.edu/1793/37492 Second Sphere Effects of O2 Activation in Stearoyl-Acyl Carrier Protein Delta9 Desaturase Ng, Yi Han Stearoyl-acyl carrier protein Delta9 desaturase (Delta9D) from Ricinus communis converts stearic acid into monounsaturated oleic acid and functions to maintain the lipid composition of the cell membrane. While the desaturase active site glutamate and histidine residues are crucial to catalysis, there are a number of conserved "second sphere" residues. One such residue is Threonine 199 found ~5Angstroms from the diiron center and it has been hypothesized to stabilize the peroxo intermediate formed during catalysis. In this work, the role of this residue has been probed through studies of a series of mutants. These mutations show a lower kcat and an increase in the rate of decay of the peroxo intermediate, providing evidence of stabilization of the intermediate. 18 p. Mon, 29 Oct 2007 22:58:59 GMT http://digital.library.wisc.edu/1793/8142 Starvation responses of invasive and non-invasive Eurytemora affinis populations Chau, Fong Ching Within the past century, the copepod Eurytemora affinis have invaded freshwater from saline sources throughout the Northern Hemisphere. Two genetically divergent clades (Atlantic and North Atlantic) of E. affinis coexist in the St. Lawrence estuary, but only the Atlantic clade was able to invade into freshwater ecosystem. A common-garden reaction norm experiment was performed on populations from these two clades to determine their differences in survival and development time across three food levels (high, medium and low) in fresh water. The populations were fed with the freshwater alga Rhodomonas minuta. The developmental progress and survival of the populations were monitored throughout the experiment. The results indicated that the population from the invasive Atlantic clade is more starvation resistant and has faster development time to adulthood. The differences between the populations might be due to their different osmoregulatory mechanisms and energy usages. These different physiological responses to starvation are likely to have functional consequences for the populations' ability to expand their ranges into novel environments. 24 p. Sun, 29 Oct 2006 22:58:59 GMT http://digital.library.wisc.edu/1793/8140 Protein-DNA interactions involved in the initiation of DNA replication Chu, Chun Him (Bosco) DNA synthesis is a complex process that is regulated at the stage of initiation of DNA replication. In bacteria, replication initiation occurs at the origin of replication (ori), where multiple molecular interactions occur. Our model system to study replication initiation is the Escherichia coli plasmid, R6K. The initiation of R6K replication occurs at γ ori, where there is an A+T rich region followed by seven binding sites for the replication initiator protein, π. π has two functions: monomers of the protein activate γ ori while dimers inhibit replication. We hypothesize that variations in the DNA sequences of the seven π -binding sites (iterons) at γ ori and an eighth iteron downstream of γ ori are important for π monomer and/or dimer binding. To test this hypothesis, the affinity of each of the different iterons for π was studied both in vivo and in vitro. The in vivo assay monitored the relative affinity of each iteron for π in competition with the full γ ori. In the in vitro assay, electrophoretic mobility shift assay was used to quantify π binding affinity with or without a competitor iteron. Results suggested that π binds to different iterons with different affinities, with strongest binding to the iteron having the most consensus sequence, and weakest binding to the iteron with the least consensus sequence. 19 p. Sun, 29 Oct 2006 22:58:59 GMT