Flavocytochrome b2 catalyzes the oxidation of lactate to pyruvate. Primary deuterium and solvent kinetic isotope effects have been used to determine the relative timing of cleavage of the lactate OH and CH bonds by the wild type enzyme, a mutant protein lacking the heme domain, and the D282N enzyme. The DVmax and D(V/Klactate) values are both 3.0, 3.6 and 4.5 for the wild type enzyme, flavin domain and D282N enzymes, respectively. The D20Vmax values are 1.38, 1.18, and 0.98 for the wild type enzyme, the flavin domain, and the D282N enzyme; the respective D20(V/Klactate) values are 0.9, 0.44, and 1.0. The Dkred value is 5.4 for the wild type enzyme and 3.5 for the flavin domain, whereas the D2Okred is 1.0 for both enzymes. The V/Klactate value for the flavin domain increases 2-fold at moderate concentrations of glycerol. The data are consistent with the lactate hydroxyl proton not being in flight in the transition state for CH bond cleavage and there being an internal equilibrium prior to CH bond cleavage which is sensitive to solution conditions. Removal of the hydroxyl proton may occur in this pre-equilibrium. Tryptophan 2-monooxygenase catalyzes the oxidative decarboxylation of tryptophan to indoleacetamide, carbon dioxide and water. Sequence alignments identified this enzyme as a member of the L-amino acid oxidase family. The tyrosine and arginine residues in L-amino acid oxidase that bind the carboxylate of o-aminobenzoate are conserved and correspond to Tyr413 and Arg98 in tryptophan 2-monooxygenase. Mutation and characterization of the Y413A, Y413F, R98K and R98A enzymes indicate that these residues are in the active site and interact with the substrate. Deletion of the OH group of Tyr413 increases the Kd for the substrate and makes CH bond cleavage totally rate limiting. The pH V/Ktrp rate profile for the Tyr413 mutant enzymes shows that this residue must be protonated for activity. For both the R98A and R98K enzymes flavin reduction is rate limiting. The Vmax and V/Ktrp pH profiles indicate that the unprotonated form of the substrate is the active form for activity.

Breast cancer is the most frequently diagnosed form of cancer in women and the second leading cause of cancer-related deaths. Breast cancer is a heterogeneous disease consisting of many types of tissue neoplasia, and there appears to be no model of how a particular lesion develops into an aggressive, malignant, invasive carcinoma. Genetic mutation and aberrant epigenetic regulation are among the most common events that lead to neoplasia. In breast cancer, p53 mutation is the most common genetic defect related to a single gene. Therefore, this dissertation focuses on the mechanisms and consequences of p53 mutation during breast tumorigenesis. Genome-wide analysis of gene expression and epigenetic modifications in a panel of breast cancer cell lines suggested that p53 mutation and aberrant epigenetic silencing were cooperating mechanisms in the silencing of wild-type p53 target genes during cancer progression. Therefore, models of p53 inactivation were created in non-malignant human mammary epithelial cells to determine the role of p53 mutation on the epigenetic status of its target genes and the acquisition of malignant phenotypes. Comparisons of each model demonstrated that differing modes of p53 inactivation produced different functional consequences. Loss of wild-type p53 function alone ablated the normal cellular response to external stress stimuli, but had no affect on the expression of genes or epigenetic status in untreated cells. Introduction of missense mutant p53 protein caused very few changes when the protein was expressed at low levels. However, accumulation of mutant p53 caused a variety of gene expression changes and interfered with endogenous wild-type p53. The accumulation of mutant p53 also caused an increase in migration and invasion of the cells that expressed it. Interestingly, epigenetic aberrations were not detected in response to any of the p53 manipulations. These data suggest that accumulation of missense mutation is particularly dangerous to normal cells. They also suggest that p53 mutation and epigenetic aberration are two distinct mechanisms, which overlap and cooperate during tumorigenesis. These data suggest that treatment strategies for human breast cancer should include modalities to target both defects for increased efficacy.

APLF (Aprataxin and Polynucleotide kinase/phosphatase-Like Factor) is an FHA (forkhead-associated)-domain-containing nuclear protein that facilitates the repair of single-strand and double-strand breaks (SSBs and DSBs). Specifically, the APLF-FHA domain mediates interactions with XRCC1 and XRCC4, factors involved in SSB and DSB repair, respectively. A novel substitution was identified in pancreatic cancer patients, where a conserved histidine was substituted to leucine (H42L) in the APLF-FHA domain. The functional and biological characterization of this “variant of unknown significance” was investigated. This thesis shows that the H42L substitution affects APLF phosphorylation, impairs APLF retention at laser-induced DNA breaks, disrupts protein-binding to XRCC1 but not to XRCC4, and reduces cell survival following irradiation and etoposide exposure. Collectively, these data suggest that the H42L substitution impacts APLF participation in global DNA damage repair. The findings from this work could provide insight into the role of APLF in genomic integrity and, moreover, in cancer predisposition.

APLF (Aprataxin and Polynucleotide kinase/phosphatase-Like Factor) is an FHA (forkhead-associated)-domain-containing nuclear protein that facilitates the repair of single-strand and double-strand breaks (SSBs and DSBs). Specifically, the APLF-FHA domain mediates interactions with XRCC1 and XRCC4, factors involved in SSB and DSB repair, respectively. A novel substitution was identified in pancreatic cancer patients, where a conserved histidine was substituted to leucine (H42L) in the APLF-FHA domain. The functional and biological characterization of this “variant of unknown significance” was investigated. This thesis shows that the H42L substitution affects APLF phosphorylation, impairs APLF retention at laser-induced DNA breaks, disrupts protein-binding to XRCC1 but not to XRCC4, and reduces cell survival following irradiation and etoposide exposure. Collectively, these data suggest that the H42L substitution impacts APLF participation in global DNA damage repair. The findings from this work could provide insight into the role of APLF in genomic integrity and, moreover, in cancer predisposition.

Q-Beta phage RNAs with inactivating insertion (8 base) or deletion (17 base) mutations within their replicase genes were transfected into Escherichia coli spheroplasts containing QB replicase provided in trans by a resident plasmid. Replicase-defective (Rep~) Q3 phage produced by these spheroplasts were unable to form plaques on cells lacking this plasmid. When individual Rep~ phage were isolated and grown to high titer in cells containing plasmid derived Q3 replicase, revertant Q3 phage (Rep'), with the original mutation (insertion or deletion) repaired, were obtained at a frequency of ca. 1 x 108. RNA recombination via a "template switching" mechanism involving Q3 replicase, the mutant phage genome, and the plasmid-derived replicase mRNA was shown to be the primary means by which these mutant phages reverted to wild type.

Indiana University-Purdue University Indianapolis (IUPUI) / Chlamydia is the most frequently reported bacterial sexually transmitted infection in the world. Most urogenital chlamydia infections in men and women are asymptomatic, but these infections can lead to irreparable damage in the reproductive system and other tissues. Apart from the urogenital chlamydial infections, we know that chlamydia infects the gastrointestinal tract (GIT) in humans and can colonize the GIT for extended intervals without eliciting pathology. We are interested in investigating tissue tropism determinants in Chlamydia spp. because these could be targeted to development live-attenuated vaccines. Recently, we generated mutagenized isolates of the mouse pathogen Chlamydia muridarum, a close relative of the human pathogen Chlamydia trachomatis which causes chlamydia. One mutant that we isolated is significantly attenuated in murine gastrointestinal tissues compared to wild type, but retains its pathogenicity in the murine urogenital tract. Using novel genetic techniques, whole-genome sequencing, and complementation using newly developed vector systems we identified a chromosomal factor, tc0600, that we believe mediates the altered tissue tropism phenotype of this mutant in mice. Notably, the Chlamydia trachomatis ortholog of tc0600 has been linked to chlamydial GIT tropism in humans.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

<p> Temperature-sensitive mutants of the bacteriophage PBS 2 were isolated from lysates treated with various mutagens. Complementation tests assigned the mutants to 10 cistrons. The mutants were mapped by two factor crosses and formed a linear map approximately 50 recombination percent in length. </p> <p> A method for phage transformation was developed. By the use of wild type DNA fragments fractionated according to their guanine + cytosine content in HgCs₂SO₄ gradients, it was possible to determine the base composition of certain regions of the chromosomes. </p> / Thesis / Doctor of Philosophy (PhD)

<p> Age-Related Resistance (ARR) has been observed in numerous plant species, resulting in increased disease resistance as the plant matures. The ARR defective mutant, iap1-1, (important in the ARR Pathway,) was discovered in an ARR mutant screen and EDS1, (enhanced disease susceptibility,) which is involved in other disease resistance pathways, was shown to be required for ARR. lntercellular accumulation of salicylic acid (SA) is required for ARR suggesting that SA may act as an anti-microbial agent. Mature (6 wpg) iap1-1 does not accumulate intercellular or intracellular SA in response to Pst inoculation. lntercellular and intracellular SA accumulation is also partially reduced in young (4 wpg) plants during R gene-mediated resistance to Pst(AvrRpt2) which is partially compromised suggesting that the two pathways share common elements. The novel discovery of the presence of intercellular SA during R gene-mediated resistance suggests that it may act as an antimicrobial agent during R gene-mediated resistance as it is hypothesized to during ARR. The iap1-1 mutation maps to chromosome four between 17,938,268bp and 18,133,423b. The semi-dominant, loss of function nature of the iap1-1 mutation suggests that IAP1 is a positive regulator in the ARR pathway.</p> / Thesis / Doctor of Philosophy (PhD)

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