Genome stability has great importance in maintaining cell viability and optimal functionality of cellular processes. Loss of genome stability can lead to cell death in the simplest organisms and to deregulation of the cell proliferation machinery in higher organisms, potentially causing cancer or morbid states. The Single Stranded DNA Binding (SSB) protein of Escherichia coli is an essential protein that binds and stabilises ssDNA stretches. Its role is particularly crucial during DNA replication, recombination and repair processes and it has therefore been predicted to play a prominent role in the maintenance of genome stability. The role of SSB in genome instability was investigated using an E. coli strain in which, the expression of the ssb gene was placed under the control of the arabinose promoter. The level of SSB protein present in the cell could therefore be tuned by varying the arabinose concentration in the medium. A wide characterisation of the behaviour of the strain at low SSB level was carried out. Viability and growth tests showed that a threshold level of protein is required to allow normal growth. Microscopy analyses were carried out to follow cell division, nucleoid morphology and SOS response activation. Cells grown at low SSB level, showed a phenotype consistent with impaired cell division and altered nucleoid morphology. The SOS response was activated at low SSB levels and cell elongation was detected. Lowering the arabinose concentration in solid medium allowed the selection of suppressor strains that could form colonies under the new conditions. Sequencing of the entire genome of one such suppressor strain was carried out revealing a possible candidate for the phenotype change. The stability of a 105bp and of a 246bp DNA imperfect palindromes and the stability of CAG·CTG trinucleotide repeat arrays, inserted in the E. coli chromosome, were investigated in correlation to the SSB cellular level. Lowering the SSB level in cells grown on solid medium, increased the instability of the 105bp palindrome presumably by increasing the number of slippage events. On the other hand, SSB overexpression did not have an effect on the stability of the 246bp palindrome. The stability of a leading strand (CAG)75 repeat array was highly increased by overexpressing SSB, while the same effect was not observed for a leading strand (CTG)137 repeat array. Furthermore, excess SSB caused a change in the deletion size distribution profile for the leading strand (CAG)75 strain, lowering the bias towards big deletions. This is consistent with SSB being able to preferentially impede the formation of big DNA hairpins. Also, SbcCD nuclease was shown to have an effect on the deletion size distribution profile of the leading strand (CTG)137 strain. The lack of SbcCD led to a slight reduction of the number of big deletions.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-05-02T17:32:14Z No. of bitstreams: 1 taisarthurcorrea.pdf: 3468557 bytes, checksum: 7986eaf836ba646f1ea15e0219b133b9 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-05-13T13:11:09Z (GMT) No. of bitstreams: 1 taisarthurcorrea.pdf: 3468557 bytes, checksum: 7986eaf836ba646f1ea15e0219b133b9 (MD5) / Made available in DSpace on 2017-05-13T13:11:09Z (GMT). No. of bitstreams: 1 taisarthurcorrea.pdf: 3468557 bytes, checksum: 7986eaf836ba646f1ea15e0219b133b9 (MD5) Previous issue date: 2009-02-09 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / O amino-álcool etambutol é um dos poucos e confiáveis agentes quimioterapêuticos antitubercular seguro de primeira escolha. Aminas e amino-álcoois glicosilados são conhecidos pelas suas atividades antimicobacterianas. Este trabalho trata da síntese de derivados de amino-álcoois das séries Dgalactose, D-arabinose e D-glicose, resultando na obtenção de dezoito novos compostos. Em um primeiro momento foram preparados vários amino-álcoois Nalquilados com cadeias carbônicas de diferentes tamanhos. Os amino-álcoois obtidos foram acoplados com derivados iodados ou tosilados da D-arabinose, D-galactose ou Dglicose. Para a preparação do derivado tosilado da D-arabinose, este foi tratado inicialmente com o metanol em meio ácido (Amberlite IR-120) fornecendo o composto α-D-arabinofuranosídeo de metila, que foi tosilado posteriormente na posição C-5, gerando o precursor 6-O-tosil-α-D-arabinofuranosídeo de metila. Os derivados iodados ou tosilados da D-galactose e da D-glicose foram previamente preparados por meio de reações clássicas da química de carboidratos. Os compostos finais foram obtidos através da substituição do grupo tosila ou do átomo de iodo desses derivados pelos aminoálcoois comerciais (2-amino-etanol, 3-amino-propanol, dietanolamina ou 2 amino-2metil-propanol) ou pelos amino-álcoois lipofílicos previamente preparados. Diversos destes compostos estão sendo submetidos a avaliação de suas atividades antiturbeculose e imunossupressora. Os compostos obtidos foram caracterizados por espectroscopia de absorção na região do infravermelho, RMN de 1H, RMN de 13C, espectrometria de massas e αD. / Ethambutol (amino-alcohol) is one of the few long-known and reliable first-line antitubercular chemotherapeutic agents. Glycosylated amino-alcohol and amines are known for their antimycobacterial activity. This work describes the synthesis of amino-alcohols derived from D-galactose, D-arabinose and D-glucose which resulted in eighteen new compounds. Initially we report the preparation of several N-alkyl amino-alcohols with alkyl chains of different lengths. The amino-alcohols obtained were condensed with iodo or tosyl derivatives of D-arabinose, D-galactose or D-glucose. For the preparation of the tosyl derivative of D-arabinose, the lates was initially treated with methanol under acidic conditions (Amberlite IR-120) leading to methyl-α-D-arabinofuranoside, wich was subsequently tosylated at the C-5 position, furnishing 6-O-tosyl-methyl-α-Darabinofuranoside. The iodo or tosyl derivatives of D-galactose and D-glucose had previously been prepared by classical sugar reactions. The final compounds were obtained via substitution of the tosyl group or iodine atom of these derivatives by commercial amino-alcohols (ethanolamine, 3-amino-propanol, 2-amino-2-methyl-propanol and diethanolamine) or by the previously prepared lipophilic amino-alcohols. Several of these compounds have been submitted for biological assays in order to evaluate their imunosuppressive and antitubercular activities. These compounds were characterized by infrared spectroscopy, 1H and 13C NMR, mass spectroscopy and αD.

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Thesis (Ph. D.)--Institute of Paper Chemistry, 1959. / Includes bibliographical references (p. 64-66).

Escherichia coli has a proven track record for successful production of anything from small molecules like organic acids to large therapeutic proteins, and has thus important applications in both R&amp;D and commercial production. The versatility of this organism in combination with the accumulated knowledge of its genome, metabolism and physiology, has allowed for development of specialty strains capable of performing very specific tasks, opening up opportunities within new areas. The work of this thesis has been devoted to alter membrane transport proteins and the regulation of these, in order for E. coli to find further application within two such important areas. The first area was vaccine development, where it was investigated if E. coli could be a natural vehicle for live vaccine production. The hypothesis was that the introduction and manipulation of a protein surface translocation system from pathogenic E. coli would result in stable expression levels of Salmonella subunit antigens on the surface of laboratory E. coli. While different antigen combinations were successfully expressed on the surface of E. coli, larger proteins were affected by proteolysis, which manipulation of cultivation conditions could reduce, but not eliminate completely. The surface expressed antigens were further capable of inducing proinflammatory responses in epithelial cells. The second area was biorefining. By altering the regulation of sugar assimilation, it was hypothesized that simultaneous uptake of the sugars present in lignocellulose hydrolyzates could be achieved, thereby improving the yield and productivity of important bio-based chemicals. The dual-layered catabolite repression was identified and successfully removed in the engineered E. coli, and the compound (R)-3-hydroxybutyric acid was produced from simultaneous assimilation of glucose, xylose and arabinose. / <p>QC 20150508</p>

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21837号 / 農博第2350号 / 新制||農||1069(附属図書館) / 学位論文||H31||N5209(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 田中 千尋, 教授 本田 与一, 准教授 刑部 正博 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

The opportunistic bacterial pathogen Pseudomonas aeruginosa uses type IV pili (T4P) for adherence to, and rapid colonization of, surfaces via twitching motility. T4P are formed from thousands of pilin (PilA) subunits. Two groups of P. aeruginosa pilins were described previously (I and II), distinguished by protein length and sequence. PilA_I was glycosylated with an O-antigen subunit through the action of PilO/TfpO, encoded downstream of pilA_I. To determine if additional pilin variants existed, analysis of the pilin locus of >300 P. aeruginosa strains from a variety of environments was conducted. Three additional pilin alleles were discovered, each of which was invariantly associated with a unique, previously unidentified, downstream gene(s): pilA_III+tfpY, pilAIV+tfpW+tfpX, pilA_V+tfpZ. This survey also revealed that strains with group I T4P were more commonly associated with respiratory infections than strains with other pilins, suggesting that glycosylated T4P may confer a colonization advantage in this environment. The newly identified group IV pilin, represented by strain Pa5196, migrated aberrantly through SDS-PA gels, suggesting it was also glycosylated, a hypothesis confirmed by periodic acid-Schiff staining and mass spectrometry (MS) analyses. Disruption of Pa5196 O-antigen biosynthesis did not prevent the production of glycosylated pilins, demonstrating that these pilins were modified in a novel manner, unlike group I pilins. Using MS, nuclear magnetic resonance spectroscopy and site-directed mutagenesis, the Pa5196 pilins were shown to be uniquely modified with homo-oligosaccharides of mycobacterial-like α-1,5-D-arabinofuranose at multiple locations. Residues Thr64 and Thr66, located on the αβ-loop region of the protein, appear to be the preferred, but not exclusive sites of modification, each being modified with up to four D-Araf sugars. This region of the pilin is partially surface-exposed in the pilus, therefore modification of these sites may influence the surface chemistry of the fibre. Residues Ser81, Ser82, Ser85 and Ser89, located in the β-strand region, were also modified, mainly with mono- and disaccharides. Bioinformatic analyses and mutagenesis of TfpW suggest that this novel protein is an arabinosyltransferase necessary for PilA_IV modification. This research has increased our understanding of the complexity of this virulence factor, and may aid in development of new therapeutics for P. aeruginosa and mycobacterial infections.