RESUMO
A transposon mutant of Rhodobacter sphaeroides WS8 was isolated that showed reduced swarming on soft agar plates. Liquid cultures of this mutant (M18) showed a low percentage of motile swimming cells in mid-exponential phase and a low level of extracellular flagellin protein by Western blotting. M18 was complemented by a clone from a library of R. sphaeroides WS8 DNA, and restriction mapping of the site of TnphoA insertion in the mutant, coupled with DNA sequencing, showed that it had a defect in the fliI gene. To determine if a partly functional fliI gene was giving the low-motility phenotype of M18, a drug resistance omega cartridge was inserted into the gene to give a complete null mutant. This null strain also produced a low percentage of motile cells. Possible reasons for this apparent fliI-independent flagellar formation are discussed.
Assuntos
Proteínas de Bactérias , Genes Bacterianos , Proteínas/genética , ATPases Translocadoras de Prótons , Rhodobacter sphaeroides/genética , Sequência de Aminoácidos , Elementos de DNA Transponíveis , Flagelos/fisiologia , Dados de Sequência Molecular , Mutação , Mapeamento por Restrição , Rhodobacter sphaeroides/fisiologia , Salmonella typhimurium/genética , Homologia de Sequência de Aminoácidos , Xanthomonas campestris/genéticaRESUMO
Recombinant human platelet-derived endothelial cell growth factor, expressed in the yeast Saccharomyces cerevisiae was purified to greater than 98% purity by anion-exchange and hydroxyapatite chromatography. It was shown to possess thymidine phosphorolytic activity in vitro (pH optimum, pH 5.3; Km, 0.11 mM; Vmax, 12.5 mmol min-1 mg-1; turnover number, 9.4 s-1). Covalent modification simultaneously inhibited the enzymatic and mitogenic properties of the protein, while interaction with a cell-surface receptor was not required to stimulate mitogenesis. Purified Escherichia coli thymidine phosphorylase was also mitogenic toward endothelial cells. It is proposed that platelet-derived endothelial cell growth factor is human thymidine phosphorylase which promotes endothelial cell proliferation by reducing thymidine levels that would otherwise be inhibitory to endothelial cell growth.
Assuntos
Endotélio Vascular/efeitos dos fármacos , Mitógenos/farmacologia , Timidina Fosforilase/farmacologia , Células Cultivadas , DNA/biossíntese , Endotélio Vascular/citologia , Escherichia coli/enzimologia , Humanos , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/farmacologia , Saccharomyces cerevisiae/metabolismo , Timidina Fosforilase/metabolismoRESUMO
The Erwinia amylovora rpoS gene, encoding the alternative sigma factor RpoS, has been cloned and characterized. Though highly sensitive to a number of environmental stresses, an E. amylovora rpoS mutant was not compromised in its ability to grow or cause disease symptoms within apple seedlings or in an overwintering model.