Thesis (M.Sc.). / Written for the Dept. of Biochemistry. Title from title page of PDF (viewed 2009/06/23). Includes bibliographical references.

Thesis (M.S.)--Duquesne University, 2004. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 76-88) and abstract.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 141-154).

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009. / Submitted to the African Centre for Crop Improvement. Full text also available online. Scroll down for electronic link.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 81-83). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Florida, 2004. / Typescript. Title from title page of source document. Document formatted into pages; contains 258 pages. Includes vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on September 24, 2007) Vita. Includes bibliographical references.

<p>Topoisomerase 1 (Top1) resolves transcription-associated supercoils by generating transient single-strand breaks in DNA and is a major source of transcription-associated mutagenesis in Saccharomyces cerevisiae. Top1 generates a distinctive mutation signature characterized by deletions in short, tandem repeats, and a similar signature is associated with ribonucleoside monophosphates (rNMPs) in DNA. DNA polymerases incorporate rNMPs into genomic DNA, and such rNMPs are efficiently removed in an error-free manner by ribonuclease (RNase) H2. In the absence of RNase H2, persistent rNMPs give rise to short deletions via a mutagenic process initiated by a Top1 incision at an rNMP. There is only partial overlap, however, between Top1-dependent deletion hotspots identified in highly transcribed DNA and those associated with rNMPs, suggesting the existence of both rNMP-dependent and rNMP-independent events. Here I present evidence that rNMP-independent hotspots reflect processing of a trapped Top1 cleavage complex (Top1cc), and that rNMP-dependent hotspots reflect sequential Top1 reactions. A sequential-cleavage model for rNMP-dependent deletions is tested in vivo and in vitro, employing Top1 cleavage and ligation assays. In addition, I report that rNMP-dependent hotspot activity is significantly enhanced when Top1 incises the non-transcribed strand of an actively transcribing reporter gene. Finally, I describe a novel type of mutagenesis that reflects repair of multiple Top1ccs. Specifically, expression of a mutant Top1 with reduced ligation activity (Top1-T722A) caused large deletion mutations that are distinct from Top1-dependent short deletions. Genetic data indicates that Top1-T722A-dependent large deletions are non-homologous end joining events.</p> / Dissertation

Resumo: Mutantes foram obtidos através de tratamento mutagênico dos esporos de S. clavuligerus ATCC 27064 com metil-metanosulfonato. Um total de 822 colônias, obtidas por repiques sucessivos, foram selecionadas em testes qualitativos e/ou quantitativos. O melhor mutante S. clavuligerus 45.41, mostrou-se de duas a quatro vezes mais produtivo que a linhagem selvagem, e manteve-se estável após 35 repiques sucessivos ao longo deste estudo. O comportamento das linhagens foi investigado pela adição de diferentes diaminas ao meio de cultivo, uma a uma, na ausência de lisina. Também se investigou duas fontes distintas de C, além de compostos como o ácido 2,6- diaminopimélico. Um planejamento de dois fatores (cadaverina e lisina), três níveis, baseado no ponto central, faces centradas, indicou que a adição de lisina aumenta a produção de CefC para ambas as linhagens. O efeito positivo da cadaverina foi observado principalmente na linhagem mutante 45.41. Resultados obtidos em processo de batelada, em biorreator de bancada confirmaram as diferenças observadas entre as linhagens nos cultivos em frascos agitados. Procedimento de mutagênese clássica foi utilizado em conjunto com critérios bem definidos para se estabelecer um meio de cultura apropriado, com o objetivo de alcançar um aumento significativo da produção de CefC. Este é o primeiro estudo utilizando um mutante de S. clavuligerus obtido por mutagênese clássica, cuja produção de CefC é de três vezes maior que a da linhagem selvagem, em meios contendo diaminas / Abstract: Mutants were obtained by treating S. clavuligerus ATCC 27064 spores with methyl-methanesulfonate. A total of 822 colonies, obtained by successive sampling, were selected by qualitative and/or quantitative tests. The best mutant, S. clavuligerus 45.41, was two to four times more productive than the wild-type strain, and remained stable even after 35 successive samplings throughout the study. Strains behavior was investigated by adding different diamines in media, one by one, in the absence of lysine. Also investigated two different sources of C, and compounds such as 2,6-diaminopimelic acid. The two-factor (cadaverine and lysine), three-level, central composite-based, face-centered experimental design indicates that adding lysine increases CephC production for both strains alike. The positive effect of cadaverine was observed mainly in the Mutant 45.41 strain. Results obtained in batch-processes in a bench-scale bioreactor confirmed differences among strains observed in shaken flasks cultures. Classical mutagenesis procedures in conjunction with the adoption of well-defined criteria to establish an appropriate culture medium promoted a significant improvement in CephC production. It is the first study indicating an increase in CephC production in media containing diamines employing a mutant of S. clavuligerus obtained by classical mutagenesis / Orientador: Maria Lucia Gonsales da Costa Araujo / Banca: Pedro de Oliva Neto / Banca: Cecilia Laluce / Banca: José Gregório Cabrera Gomez / Banca: Cristina Paiva de Sousa / Doutor

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is the most devastating pathogen of soybeans, Glycine max (L.) Merr., causing over $1 billion in yield losses annually in the United States alone. Currently, planting of genetically resistant cultivars is the most commonly employed management strategy. Due to an overuse of genetic resistance derived from the soybean variety ‘PI 88788’, many populations of soybean cyst nematodes are becoming virulent on previously resistant cultivars, urging the understanding and discovery of alternative mechanisms of SCN resistance. In this study, we will delve into the history and epidemiology of Heterodera glycines, learn about the molecular etiology underlying SCN pathogenesis, begin to understand the mechanism of resistance by Peking-type soybeans, and look to discover a novel mechanism of resistance by establishment of a mutagenized population of the soybean variety ‘PI 567516C’.