Cloning, heterologous expression, and sequencing of the Proteus vulgaris glnAntrBC operon and implications of nitrogen control on heterologous urease expression

Compilation and analysis of sigma(54)-dependent promoter sequences

Promoters recognized by the RNA-polymerase with the alternative sigma factor sigma(54) (Esigma54) are unique in having conserved positions around -24 and -12 nucleotides upstream from the transcriptional start site, instead of the typical -35 and -10 boxes. Here we compile 186 -24/-12 promoter sequences reported in the literature and generate an updated and extended consensus sequence. The use of the extended consensus increases the probability of identifying genuine -24/-12 promoters. The effect of several reported mutations at the -24/-12 elements on RNA-polymerase binding and promoter strength is discussed in the light of the updated consensus.

The histidine protein kinase superfamily

Signal transduction in microorganisms and plants is often mediated by His-Asp phosphorelay systems. Two conserved families of proteins are centrally involved: histidine protein kinases and phospho-aspartyl response regulators. The kinases generally function in association with sensory elements that regulate their activities in response to environmental signals. A sequence analysis with 348 histidine kinase domains reveals that this family consists of distinct subgroups. A comparative sequence analysis with 298 available receiver domain sequences of cognate response regulators demonstrates a significant correlation between kinase and regulator subfamilies. These findings suggest that different subclasses of His-Asp phosphorelay systems have evolved independently of one another.

Molecular cloning and overexpression of a glutathione transferase gene from Proteus mirabilis

The structural gene of the Proteus mirabilis glutathione transferase GSTB1-1 (gstB) has been isolated from genomic DNA. A nucleotide sequence determination of gstB predicted a translational product of 203 amino acid residues, perfectly matching the sequence of the previously purified protein [Mignogna, Allocati, Aceto, Piccolomini, Di Ilio, Barra and Martini (1993) Eur. J. Biochem. 211, 421-425]. The P. mirabilis GST sequence revealed 56% identity with the Escherichia coli GST at DNA level and 54% amino acid identity. Similarity has been revealed also with the translation products of the recently cloned gene bphH from Haemophilus influenzae (28% identity) and ORF3 of Burkholderia cepacia (27% identity). Putative promoter sequences with high similarity to the E. coli sigma 70 consensus promoter and to promoters of P. mirabilis cat and glnA genes preceded the ATG of the gstB open reading frame (ORF). gstB was brought under control of the tac promoter and overexpressed in E. coli by induction with isopropyl-beta-D-thiogalactopyranoside and growth at 37 degrees C. The physicochemical and catalytic properties of overexpressed protein were indistinguishable from those of the enzyme purified from P. mirabilis extract. Unlike the GST belonging to Mu and Theta classes, GSTB1-1 was unable to metabolize dichloromethane. The study of the interaction of cloned GSTB1-1 with a number of antibiotics indicates that this enzyme actively participates in the binding of tetracyclines and rifamycin.

Nitrogen control in bacteria

Nitrogen metabolism in prokaryotes involves the coordinated expression of a large number of enzymes concerned with both utilization of extracellular nitrogen sources and intracellular biosynthesis of nitrogen-containing compounds. The control of this expression is determined by the availability of fixed nitrogen to the cell and is effected by complex regulatory networks involving regulation at both the transcriptional and posttranslational levels. While the most detailed studies to date have been carried out with enteric bacteria, there is a considerable body of evidence to show that the nitrogen regulation (ntr) systems described in the enterics extend to many other genera. Furthermore, as the range of bacteria in which the phenomenon of nitrogen control is examined is being extended, new regulatory mechanisms are also being discovered. In this review, we have attempted to summarize recent research in prokaryotic nitrogen control; to show the ubiquity of the ntr system, at least in gram-negative organisms; and to identify those areas and groups of organisms about which there is much still to learn.