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Differential Expression of the Components of the Two Alkane Hydroxylases from Pseudomonas aeruginosa. Mercedes M. Marín, 2003.Oxidation of n-alkanes in bacteria is normally initiated by an enzyme system formed by a membrane-bound alkane hydroxylase and two soluble proteins, rubredoxin and rubredoxin reductase . Pseudomonas aeruginosa strains PAO1 and RR1 contain genes encoding two alkane hydroxylases (alkB1 and alkB2), two rubredoxins (alkG1 and alkG2), and a rubredoxin reductase (alkT) . We have localized the promoters for these genes and analyzed their expression under different conditions . The alkB1 and alkB2 genes were preferentially expressed at different moments of the growth phase; expression of alkB2 was highest during the early exponential phase, while alkB1 was induced at the late exponential phase, when the growth rate decreased . Both genes were induced by C10 to C22/C24 alkanes but not by their oxidation derivatives . However, the alkG1, alkG2, and alkT genes were expressed at constant levels in both the absence and presence of alkanes . Mutations in the Bacillus subtilis glnRA Operon That Cause Nitrogen Source-Dependent Defects in Regulation of TnrA Activity. Susan H. Fisher, 2002.The Bacillus subtilis nitrogen transcriptional factor TnrA is inactive in cells grown with excess nitrogen, e.g., glutamine or glutamate plus ammonium, because feedback-inhibited glutamine synthetase (product of glnA) binds to TnrA and blocks its DNA-binding activity . Two conditional mutations that allow TnrA-dependent gene expression in cells grown with glutamate plus ammonium, but not in glutamine-grown cells, were characterized . One mutant contained a mutation in the glnA ribosome binding site, while the other mutant synthesized a truncated GlnR protein that constitutively repressed glnRA expression . The levels of glutamine synthetase were reduced in both mutants . As a result, when these mutants are grown with excess nitrogen in the absence of glutamine, there is insufficient production of the feedback inhibitors necessary to convert glutamine synthetase into its feedback-inhibited form and TnrA-activated genes are expressed at high levels . The Product of the fimI Gene Is Necessary for Escherichia coli Type 1 Pilus Biosynthesis. Mary L. Valenski, 2003.Site-directed mutagenesis was employed to create lesions in fimI, a gene of uncertain function located in the chromosomal gene cluster (fim) involved in Escherichia coli type 1 pilus biosynthesis . Chromosomal fimI mutations produced a piliation-negative phenotype . Complementation analysis indicated that a fimI'-kan insertion mutation and a fimI frameshift mutation produced polarity-like effects not seen with an in-frame fimI deletion mutation . Minicell analysis associated fimI with a 16.4-kDa noncytoplasmic protein product (FimI) . We conclude that FimI has a required role in normal pilus biosynthesis . Growth Phase-Coupled Alterations in Cell Structure and Function of Escherichia coli. Hideki Makinoshima, 2003.Escherichia coli cultures can be fractionated into more than 20 cell populations, each having a different bouyant density and apparently representing a specific stage of cell differentiation from exponential growth to stationary phase (H . Makinoshima, A . Nishimura, and A . Ishihama, Mol . Microbiol . 43:269-279, 2002) . The density increase was found to be impaired at an early step for a mutant E . coli with the disrupted rpoS gene, which encodes the RNA polymerase RpoS (sigma-S) for stationary-phase gene transcription . This finding suggests that RpoS is need for the entire process of cell density increase . In the absence of RpoF sigma factor, the flagella are not formed as observed by electron microscopy, but the growth phase-coupled density increase takes place as in wild-type E . coli, confirming that the alteration in cell density is not directly correlated with the presence or absence of flagella . In the stationary-phase cells, accumulation of electron-dense areas was observed by electron microscopic observation of bacterial thin sections . By chemical determination, the increase in glycogen (or polysaccharides) was suggested to be one component, which contributes to the increase in weight-to-volume ratio of stationary-phase E . coli cells . Aminopeptidase C of Aspergillus niger Is a Novel Phenylalanine Aminopeptidase. Daniëlle E. J. W. Basten, 2003.A novel enzyme with a specific phenylalanine aminopeptidase activity (ApsC) from Aspergillus niger (CBS 120.49) has been characterized . The derived amino acid sequence is not similar to any previously characterized aminopeptidase sequence but does share similarity with some mammalian acyl-peptide hydrolase sequences . ApsC was found to be most active towards phenylalanine ß-naphthylamide (F-ßNA) and phenylalanine para-nitroanilide (F-pNA), but it also displayed activity towards other amino acids with aromatic side chains coupled to ßNA; other amino acids with nonaromatic side chains coupled to either pNA or ßNA were not hydrolyzed or were poorly hydrolyzed . ApsC was not able to hydrolyze N-acetylalanine-pNA, a substrate for acyl-peptide hydrolases .
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