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Transcription Regulation Coupling of the Divergent argG and metY Promoters in Escherichia coli K-12. Evelyne Krin, 2003.The cAMP-catabolite activator protein (CAP) complex is a pleiotropic regulator that regulates a vast number of Escherichia coli genes, including those involved in carbon metabolism . We identified two new targets of this complex: argG, which encodes the arginosuccinate synthase involved in the arginine biosynthetic pathway, and metY, which encodes one of the two methionine tRNA initiators, tRNAf2Met . The cAMP-CAP complex activates argG transcription and inhibits metY transcription from the same DNA position . We also show that ArgR, the specific repressor of the arginine biosynthetic pathway, together with its arginine cofactor, acts on the regulation of metY mediated by CAP . The regulation of the two divergent promoters is thus simultaneously controlled not only by the cAMP-CAP complex, a global regulator, but also by a specific regulator of arginine metabolism, suggesting a previously unsuspected link between carbon metabolism and translation initiation . Genetic and Molecular Characterization of ß-Lactamase-Negative Ampicillin-Resistant Haemophilus influenzae with Unusually High Resistance to Ampicillin. Frank S. Kaczmarek, 2004.Previous studies with beta-lactamase-negative, ampicillin-resistant (BLNAR) Haemophilus influenzae from Japan, France, and North America indicate that mutations in ftsI encoding PBP3 confer ampicillin MICs of 1 to 4 µg/ml . Several BLNAR strains with ampicillin MICs of 4 to 16 µg/ml recently isolated from North America were studied . Pulsed-field gel electrophoresis identified 12 unique BLNAR strains; sequencing of their ftsI transpeptidase domains identified 1 group I and 11 group II mutants, as designated previously (K . Ubukata, Y . Shibasaki, K . Yamamoto, N . Chiba, K . Hasegawa, Y . Takeuchi, K . Sunakawa, M . Inoue, and M . Konno, Antimicrob . Agents Chemother . 45:1693-1699, 2001) . Geometric mean ampicillin MICs for several clinical isolates were 8 to 10.56 µg/ml . Replacement of the ftsI gene in H . influenzae Rd with the intact ftsI from several clinical isolates resulted in integrants with typical BLNAR geometric mean ampicillin MICs of 1.7 to 2.2 µg/ml . Cloning and purification of His-tagged PBP3 from three clinical BLNAR strains showed significantly reduced Bocillin binding compared to that of PBP3 from strain Rd . Based on these data, changes in PBP3 alone could not account for the high ampicillin MICs observed for these BLNAR isolates . In an effort to determine the presence of additional mechanism(s) of ampicillin resistance, sequencing of the transpeptidase regions of pbp1a, -1b, and -2 was performed . While numerous changes were observed compared to the sequences from Rd, no consistent pattern correlating with high-level ampicillin resistance was apparent . Additional analysis of the resistant BLNAR strains revealed frame shift insertions in acrR for all four high-level, ampicillin-resistant isolates . acrR was intact for all eight low-level ampicillin-resistant and four ampicillin-susceptible strains tested . A knockout of acrB made in one clinical isolate (initial mean ampicillin MIC of 10.3 µg/ml) lowered the ampicillin MIC to 3.67 µg/ml, typical for BLNAR strains . These studies illustrate that BLNAR strains with high ampicillin MICs exist that have combined resistance mechanisms in PBP3 and in the AcrAB efflux pump . Studies on the Mode of Action of Reutericyclin. Michael G. Gänzle, 2003.The mode of action of reutericyclin was determined with fluorescent dyes that probed the permeability of the cytoplasmic membrane by large molecules, protons, and potassium . A comparison of reutericyclin activity with those of nisin, nigericin, and valinomycin demonstrated that reutericyclin does not form pores but selectively dissipates the transmembrane proton potential .
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