Ribonuclease II (RNase II) is a bacterial enzyme responsible for 90% of the exonucleolytic degradation of mRNA in bacteria, and has bacterial homologues known to be involved in virulence. The goal of this project was to examine the structural dynamics of RNase II using fluorescence. Prior to the beginning of this project, little was known regarding the structural composition of RNase II – required information in the study of structural dynamics. Consequently, the structure of RNase II was studied by constructing a series of deletion mutants in order to map the domains. The publication of an atomic resolution structure of RNase II allowed the project to move directly into the study of RNase II structural dynamics as it degrades mRNA. As a step towards this, RNase II was fluorescently labeled, and preliminary binding studies of DNA – a competitive inhibitor – to RNase II using fluorescence were conducted. / xii, 90 leaves : ill. (some col.) ; 29 cm

Using the Gillespie algorithm, the export of the mRNA molecules from their transcription site to the nuclear pore complex is simulated. The effect of various structures in the nu- cleus on the efficiency of export is discussed. The results show that having some of the space filled by chromatin near the mRNA synthesis site shortens the transport time. Next, the complete eukaryotic gene expression including transcription, splicing, mRNA export, translation, and mRNA degradation is modeled using delay stochastic simulation. This allows for the study of stochastic effects during the process and on the protein production rate patterns. Various protein production patterns can be produced by adjusting the poly-A tail length of the mRNA and the promoter efficiency of the gene. After that, the opposing effects of the chromatin density on the seeking time of the transcription factors for the promoter and the exit time of the mRNA product are discussed. / xi, 102 leaves ; 28 cm

Indiana University-Purdue University Indianapolis (IUPUI) / The Lyme disease agent, Borrelia burgdorferi, has a complex system that allows it to thrive in the harsh and distinct environments of its tick vector and mammalian host. Although it has been known for some time that the Borrelia oxidative stress regulator protein (BosR) plays a necessary role in mammalian infectivity and functions as a transcriptional regulator of alternative sigma factor RpoS, very little is known about its mechanism of action, other than the suggestion that BosR activates rpoS transcription by binding to certain upstream regions of the gene. In our studies, we performed protein degradation assays and luciferase reporter assays for further understanding of BosR function. Our preliminary findings suggest that BosR is post-transcriptionally regulated by an unknown protease and may not need to bind to any rpoS upstream regions in order to activate transcription. We also describe the construction of luciferase reporter systems that will shed light on BosR’s mechanism of action. We postulate the provocative possibility that unlike its homologs Fur and PerR in other bacterial systems, BosR may not utilize a DNA-binding mechanism in order to fulfill its role as a transcriptional regulator to modulate virulence gene expression.

Indiana University-Purdue University Indianapolis (IUPUI) / Mammalian target of rapamycin (mTOR) is a key regulator of protein synthesis. Dysregulation of mTOR signaling occurs in many human cancers and its inhibition causes arrest at the G1 cell cycle stage. However, mTOR’s impact on mitosis (M-phase) is less clear. Here, suppressing mTOR activity impacted the G2-M transition and reduced levels of M-phase kinase, Aurora A. mTOR inhibitors did not affect Aurora A mRNA levels. However, translational reporter constructs showed that mRNA containing a short, simple 5’-untranslated region (UTR), rather than a complex structure, is more responsive to mTOR inhibition. mTOR inhibitors decreased Aurora A protein amount whereas blocking proteasomal degradation rescues this phenomenon, revealing that mTOR affects Aurora A protein stability. Inhibition of protein phosphatase, PP2A, a known mTOR substrate and Aurora A partner, restored mTOR-mediated Aurora A abundance. Finally, a non-phosphorylatable Aurora A mutant was more sensitive to destruction in the presence of mTOR inhibitor. These data strongly support the notion that mTOR controls Aurora A destruction by inactivating PP2A and elevating the phosphorylation level of Ser51 in the “activation-box” of Aurora A, which dictates its sensitivity to proteasomal degradation. In summary, this study is the first to demonstrate that mTOR signaling regulates Aurora-A protein expression and stability and provides a better understanding of how mTOR regulates mitotic kinase expression and coordinates cell cycle progression. The involvement of mTOR signaling in the regulation of cell migration by its upstream activator, Rheb, was also examined. Knockdown of Rheb was found to promote F-actin reorganization and was associated with Rac1 activation and increased migration of glioma cells. Suppression of Rheb promoted platelet-derived growth factor receptor (PDGFR) expression. Pharmacological inhibition of PDGFR blocked these events. Therefore, Rheb appears to suppress tumor cell migration by inhibiting expression of growth factor receptors that in turn drive Rac1-mediate actin polymerization.