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Resultados filtrados por Publicador: American Society for Microbiology

‣ Rifampin Resistance in Mycobacterium kansasii Is Associated with rpoB Mutations

Klein, John L.; Brown, Timothy J.; French, Gary L.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /11/2001 Português
Relevância na Pesquisa
387.70277%
Rifampin is the most potent drug used in the treatment of disease due to Mycobacterium kansasii. A 69-bp fragment of rpoB, the gene that encodes the β subunit of the bacterial RNA polymerase, was sequenced and found to be identical in five rifampin-susceptible clinical isolates of M. kansasii. This sequence showed 87% homology with the Mycobacterium tuberculosis gene, with an identical deduced amino acid sequence. In contrast, missense mutations were detected in the same fragment amplified from five rifampin-resistant isolates. A rifampin-resistant strain generated in vitro also harbored an rpoB gene missense mutation that was not present in the parent isolate. All mutations detected (in codons 513, 526, and 531) have previously been described in rifampin-resistant M. tuberculosis isolates. Rifampin MICs determined by E-test were <1 mg/liter for all rifampin-susceptible isolates and >256 mg/liter for all rifampin-resistant ones. In addition, four of the five rifampin-resistant isolates were also resistant to rifabutin. We have thus shown a strong association between rpoB gene missense mutations and rifampin resistance in M. kansasii. Although our results are derived from a small number of isolates and confirmation with larger numbers would be useful...

‣ Control of the Ferric Citrate Transport System of Escherichia coli: Mutations in Region 2.1 of the FecI Extracytoplasmic-Function Sigma Factor Suppress Mutations in the FecR Transmembrane Regulatory Protein

Stiefel, Alfred; Mahren, Susanne; Ochs, Martina; Schindler, Petra T.; Enz, Sabine; Braun, Volkmar
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /01/2001 Português
Relevância na Pesquisa
387.70277%
Transcription of the ferric citrate transport genes is initiated by binding of ferric citrate to the FecA protein in the outer membrane of Escherichia coli K-12. Bound ferric citrate does not have to be transported but initiates a signal that is transmitted by FecA across the outer membrane and by FecR across the cytoplasmic membrane into the cytoplasm, where the FecI extracytoplasmic-function (ECF) sigma factor becomes active. In this study, we isolated transcription initiation-negative missense mutants in the cytoplasmic region of FecR that were located at four sites, L13Q, W19R, W39R, and W50R, which are highly conserved in FecR-like open reading frames of the Pseudomonas aeruginosa, Pseudomonas putida, Bordetella pertussis, Bordetella bronchiseptica, and Caulobacter crescentus genomes. The cytoplasmic portion of the FecR mutant proteins, FecR1–85, did not interact with wild-type FecI, in contrast to wild-type FecR1–85, which induced FecI-mediated fecB transport gene transcription. Two missense mutations in region 2.1 of FecI, S15A and H20E, partially restored induction of ferric citrate transport gene induction of the fecR mutants by ferric citrate. Region 2.1 of ς70 is thought to bind RNA polymerase core enzyme; the residual activity of mutated FecI in the absence of FecR...