The StpA Protein Functions as a Molecular Adapter To Mediate Repression of the bgl Operon by Truncated H-NS in Escherichia coli

The mechanism of repression of the β-glucoside utilization (bgl) operon of Escherichia coli by a carboxy-terminally truncated derivative of the nucleoid-associated protein H-NS which is defective in DNA binding was investigated. The DNA-binding function of the H-NS-like protein StpA was found to be necessary for repression, which is consistent with a role for StpA as a DNA-binding adapter for mutant derivatives of H-NS.     

Differential spectrum of mutations that activate the Escherichia coli bgl operon in an rpoS genetic background

The bgl promoter is silent in wild-type Escherichia coli under standard laboratory conditions, and as a result, cells exhibit a beta-glucoside-negative (Bgl-) phenotype. Silencing is brought about by negative elements that flank the promoter and include DNA structural elements and sequences that interact with the nucleoid-associated protein H-NS. Mutations that confer a Bgl+ phenotype arise spontaneously at a detectable frequency. Transposition of DNA insertion elements within the regulatory locus, bglR, constitutes the major class of activating mutations identified in laboratory cultures. The rpoS-encoded sigmaS, the stationary-phase sigma factor, is involved in both physiological as well as genetic changes that occur in the cell under stationary-state conditions. In an attempt to see if the rpoS status of the cell influences the nature of the mutations that activate the bgl promoter, we analyzed spontaneously arising Bgl+ mutants in rpoS+ and rpoS genetic backgrounds. We show that the spectrum of activating mutations in rpoS cells is different from that in rpoS+ cells. Unlike rpoS+ cells, where insertions in bglR are the predominant activating mutations, mutations in hns make up the majority in rpoS cells. The physiological significance of these differences is discussed in the context of survival of natural populations of E. coli.     

The leuO Gene Product Has a Latent Ability To Relieve bgl Silencing in Escherichia coli

The Escherichia coli bgl operon is of interest, since its expression is silent (phenotypically Bgl⁻), at least under standard laboratory conditions. Here we attempted to identify a trans-acting factor(s) that is presumably relevant to the regulation of bgl by a random insertion mutagenesis with mini-Tn10. These collected mutations, conferring the phenotype of Bgl⁺, were localized in three loci on the genetic map, two of which appeared to be hns and bglJ, which were previously implicated as the factors affecting the Bgl phenotype. The other locus at 1 to 2 min on the genetic map appeared to be a new one. In this case, the insertion mutation was found to be just in front of the leuO gene encoding a putative LysR-like DNA-binding protein. Genetic analyses revealed that overproduction of LeuO in the wild-type cells causes the phenotype of Bgl⁺. A leuO deletion mutant was also characterized in terms of expression of bgl. From these results, the possible function of LeuO in bgl expression will be discussed from an evolutionary and/or ecological point of view.     

mraY Is an Essential Gene for Cell Growth in Escherichia coli

The synthesis of the murein precursor lipid I is performed by MraY. We have shown that mraY is an essential gene for cell growth. Cells depleted of MraY first swell and then lyse. The expression of mraY DNA in vitro produces a 40-kDa polypeptide detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.     

Polymorphism and selection of rpoS in pathogenic Escherichia coli

Background  

Though RpoS is important for survival of pathogenic Escherichia coli in natural environments, polymorphism in the rpoS gene is common. However, the causes of this polymorphism and consequential physiological effects on gene expression in pathogenic strains are not fully understood.     

Loss of an Essential Function of Escherichia coli by Deletions in the thyA Region

In an attempt to obtain deletions in the thyA gene, an abnormal lysogen of lambda having the prophage inserted between the thyA and lysA genes was induced, and the surviving cured cells were examined for Thy(-) and Lys(-) mutants. In nearly 10,000 cured cells, 184 Lys(-) but no Thy(-) mutants were found. At the same time, the induced lambda phage contained an approximately equivalent number of lambdathyA(+) and lambdalysA(+) transducing particles. By contrast, in a strain with the genotype F' thyA(-)lysA(+)/ thyA(+)lysA(+), induction of the abnormal lambda lysogen gave rise to many Thy(-) mutants in the cells cured of the prophage. In these Thy(-) mutants it was not possible to eliminate the episome with acridine orange, although the episome could be removed in control cultures with a thyA(+) allele in the resident gene. Therefore, it was suggested that deletion of a gene in the region of the chromosome from the position of the insertion of the lambda prophage through the thyA gene caused loss of an essential and diffusible function.