Transcription of the Escherichia coli osmB gene is induced by several stress conditions. osmB is expressed from two promoters, osmBp1 and osmBp2. The downstream promoter, osmBp2, is induced after osmotic shock or upon entry into stationary phase in a sigma(s)-dependent manner. The upstream promoter, osmBp1, is independent of sigma(s) and is activated by RcsB, the response regulator of the His-Asp phosphorelay signal transduction system RcsCDB. RcsB is responsible for the induction of osmBp1 following treatment with chlorpromazine. Activation of osmBp1 by RcsB requires a sequence upstream of its -35 element similar to the RcsB binding site consensus, suggesting a direct regulatory role. osmB appears as another example of a multistress-responsive gene whose transcription involves both a sigma(s)-dependent promoter and a second one independent of sigma(s) but controlled by stress-specific transcription factors.

ABSTRACT The relationship between the survival of Escherichia coli during long-term starvation in rich medium and the supercoiling of a reporter plasmid (pBR322) has been studied. In aerated continuously shaken cultures, E. coli lost the ability to form colonies earlier in rich NaCl-free Luria-Bertani medium than in NaCl-containing medium, and the negative supercoiling of plasmid pBR322 declined more rapidly in the absence of NaCl. Addition of NaCl at the 24th hour restored both viability and negative supercoiling in proportion to the concentration of added NaCl. Addition of ofloxacin, a quinolone inhibitor of gyrase, abolished rescue by added NaCl in proportion to the ofloxacin added. This observation raises the possibility that cells had the ability to recover plasmid supercoiling even if nutrients were not available and could survive during long-term starvation in a manner linked, at least in part, to the topological state of DNA and gyrase activity.

ABSTRACT Transcription of the Escherichia coli osmC gene is induced by several stress conditions. osmC is expressed from two overlapping promoters, osmCp1 and osmCp2. The proximal promoter, osmCp2, is transcribed at the entry into the stationary phase by the σs sigma factor. The distal promoter, osmCp1, is activated by NhaR and RcsB. NhaR is a positive regulator of the LysR family and is known to be an activator of the nhaA gene encoding an Na+/H+ antiporter. RcsB is the response regulator of the RcsCDB His-Asp phosphorelay signal transduction system. Genetic data indicated that activation of osmCp1 by both NhaR and RcsB requires the same short sequences upstream of the −35 region of the promoter. Accordingly, DNase I footprint analysis indicated that both activators protect an overlapping region close to the −35 box of the promoter and suggested that the regulatory effect is direct. Despite the overlap of the binding sites, each activator acts independent of the other and is specific for a particular stress. NhaR can stimulate osmCp1 in response to an osmotic signal even in the absence of RcsB. RcsB is responsible for the induction of osmCp1 by alteration of the cell envelope, even in the absence of NhaR. osmCp1 as an example of multiple-stress-responsive promoter is discussed in light of a comparison of the NhaR and RcsB target regions in the Enterobacteriaceae.

The sigma(S) subunit of RNA polymerase is a key regulator of Escherichia coli transcription in stress conditions. sigma(S) accumulates in cells subjected to stresses such as an osmotic upshift or the entry into stationary phase. We show here that, at elevated osmolarity, sigma(S) accumulates long before the beginning of the sigma(S) -dependent induction of osmE (p) , one of its target promoters. A combination of in vivo and in vitro evidence indicates that a high level of DNA negative supercoiling inhibits transcription by Esigma(S). The variations in superhelical densities occurring as a function of growth conditions can modulate transcription of a subset of sigma(S) targets and thereby contribute to the temporal disconnection between the accumulation of sigma(S) and sigma(S)-driven transcription. We propose that, in stress conditions leading to the accumulation of sigma(S) without lowering the growth rate, the level of DNA supercoiling acts as a checkpoint that delays the shift from the major (Esigma(70)) to the general stress (Esigma(S)) transcriptional machinery, retarding the induction of a subset of the sigma(S) regulon until the conditions become unfavourable enough to cause entry into stationary phase.

. Transcription of the gene osmE of Escherichia coli is osmotically inducible and regulated by the growth phase. Expression of osmE is directed by a single promoter, osmE p , which is recognized by Eσ 70 and Eσ s , two forms of RNA polymerase using, respectively, the sigma factors σ 70 and σ s . Eσ s transcribes osmE p during entry into stationary phase. Eσ 70 is responsible for osmotic induction of osmE p during the exponential growth phase. In a search for proteins that can modulate osmE p expression in trans , we performed electrophoretic mobility shift experiments using a DNA fragment carrying osmE p and crude extracts from E. coli . One major retarded band was observed in these experiments. The Fis protein is responsible for this retarded band, and binds to several sites upstream and downstream of, and overlapping, the promoter region of osmE . In a fis mutant background, the kinetics of in vivo transcription of osmE p during growth demonstrated that Fis is not responsible for the repression of the promoter seen during early exponential phase. In contrast, expression of osmE p at elevated osmolarity during the mid-exponential growth phase is increased in the absence of Fis, demonstrating that Fis is able to act as a repressor in vivo at a particular stage of growth.

ABSTRACT The RcsCB His-Asp phosphorelay system regulates the expression of several genes of Escherichia coli , but the molecular nature of the inducing signal is still unknown. We show here that treatment of an exponentially growing culture of E. coli with the cationic amphipathic compound chlorpromazine (CPZ) stimulates expression of a set of genes positively regulated by the RcsCB system. This induction is abolished in rcsB or rcsC mutant strains. In addition, treatment with CPZ inhibits growth. The wild-type strain is able to recover from this inhibition and resume growth after a period of adaptation. In contrast, strains deficient in the RcsCB His-Asp phosphorelay system are hypersensitive to CPZ. These results suggest that cells must express specific RcsCB-regulated genes in order to cope with the CPZ-induced stress. This is the first report of the essential role of the RcsCB system in a stress situation. These results also strengthen the notion that alterations of the cell envelope induce a signal recognized by the RcsC sensor.

ABSTRACT The Escherichia coli osmC gene encodes an envelope protein of unknown function whose expression depends on osmotic pressure and growth phase. The gene is transcribed from two overlapping promoters, osmCp 1 and osmCp 2 . Several factors regulating these promoters have been reported. The leucine-responsive protein Lrp represses osmCp 1 and activates osmCp 2 , the nucleoid-associated protein H-NS represses both promoters, and the stationary-phase sigma factor ς s specifically recognizes osmCp 2 . This work reports the identification of an additional regulatory element, the two-component system rcsB - rcsC , affecting positively the distal promoter osmCp 1 . The response regulator of the system, RcsB, does not affect expression of the proximal promoter osmCp 2 . Deletion analysis located the site necessary for RcsB activation just upstream of osmCp 1 . In vitro transcription experiments and gel mobility shift assays demonstrated that RcsB stimulates RNA polymerase binding at osmCp 1 .

Two overlapping promoters, osmC(p1) and osmC(p2), direct the transcription of the osmC gene of Escherichia coli. The proximal promoter, osmC(p2), is induced upon entry into stationary phase under the control of Esigma(s), the RNA polymerase that uses the sigma(s) (RpoS) sigma factor. Transcription from the distal promoter, osmC(p1), is independent of sigma(s). Previous analysis demonstrated that the osmolarity of the growth medium modulates expression of both promoters. The use of an E. coli genomic library showed that the cloned nhaR gene was able to stimulate transcription of an osmC-lac reporter fusion. NhaR is a positive regulator of the LysR family, previously identified as an activator of nhaA, a gene encoding a Na+/H+ antiporter involved in adaptation to Na+ and alkaline pH in E. coli and other enteric bacteria. NhaR was shown to activate only the expression of osmC(p1) and to be necessary for the induction of this promoter by LiCl, NaCl and sucrose. Therefore, activation by NhaR is responsible for the osmotic induction of osmC(p1). In contrast to its action on nhaA, NhaR activation of osmC(p1) is independent of H-NS. Activation of osmC(p1) by NhaR requires a site located just upstream of the atypical -35 region of the promoter.

The survival of Escherichia coli was investigated during long-term starvation in rich media. In aerated cultures, E. coli lost the ability to form colonies earlier in NaCl-free Luria broth than in LB medium containing NaCl. Improved survival at low aeration and the sensitivity to hydrogen peroxide in aging cultures indicated a major role for oxidative stress in cell mortality. Mutants in rpoS, lacking the sigma (s) subunit of RNA polymerase, showed altered survival in salt-containing media. However, in the absence of NaCl, although these mutants exhibited a massive loss of viability during the first 2 days, this was followed by a stabilization of the number of survivors. The starved culture contained survivors until at least day 9, long after a wild-type strain had completely lost viability. This peculiar behavior suggests that, in rich media of low osmotic pressure, sigma (s) helps in short-term survival but hampers long-term survival. Mutants in osmC, a member of the rpoS regulon, also exhibited reduced survival and increased sensitivity to oxidative stress. The biochemical function of the envelope protein OsmC remains unknown, but present data indicated that it participates, directly or indirectly, in the defense against oxidative compounds. (C) 2001 Editions scientifiques et medicales Elsevier SAS.

Transcription of the gene osmE of Escherichia coli is osmotically inducible and regulated by the growth phase. In a medium of low osmotic pressure, expression of osmE is induced at the onset of stationary phase. At elevated osmotic pressure, a biphasic induction pattern is observed. The first step occurs during exponential phase, and this is followed by a strong induction at the onset of stationary phase. Both steps appear to result from stimulation of transcription at the same promoter, osmEp. In the absence of sigma s, the stationary phase sigma factor encoded by rpoS, osmEp stationary phase induction is abolished, while the osmotic effect is still observed. Mutations that compensate for the absence of sigma s mapped to the gene topA. The effect of such mutation and of novobiocin, an inhibitor of DNA gyrase, suggest that changes in DNA supercoiling are involved in the osmotic induction of osmEp. In addition, modulation of the supercoiling level of a reporter plasmid was observed during growth in rich media. The kinetics of osmEp transcription are discussed in light of the variations of DNA supercoiling.

A gene function carried by a plasmid, causing arrest of cell division in Escherichia coli, has been identified as the product of a short open reading frame of the prophage Rac, previously designated orfE, expressed only under conditions of prophage induction. Because Rac carries a killing function expressed under conditions of zygotic induction, an orfE-defective Rac+ strain was constructed. This strain had lost the killing function, indicating that orfE is kil. Division inhibition by kil was specifically relieved by overexpression of essential division gene ftsZ. The kil gene product acts independently of the min operon, and its effects are increased in conditions of high cyclic AMP (cAMP) receptor protein-cAMP complex levels in the cell. Furthermore, at high levels of expression, kil product distorts the rod shape of the cells. These features distinguish kil-encoded protein from the inhibitory product of gene dicB, which occupies a similar genetic location in Kim (Qin), another defective prophage of Escherichia coli.

The cell-cycle parameters of an Escherichia coli strain expressing essential division gene ftsZ at one-fifth of its normal level, because of antisense regulation by DicF RNA, have been analysed. Inhibition of FtsZ expression affects neither the generation time nor the replication initiation mass, the C period, or the constriction period, but it does dramatically retard the initiation of constriction relative to replication termination. Separation of the nucleoids is equally postponed, indicating that division is not coupled to termination of replication, but to partitioning. The severe inhibition of nucleoid separation by DicF RNA, and its suppression by overproduction of FtsZ, suggest a role for FtsZ in the control of separation, and consequently in the coupling of separation and division. We suggest that the normal pattern of nucleoid separation previously found in cells deficient in ftsZ function was a consequence of the loss of a negative effect exerted by FtsZ on separation. In agreement with this view, we find that nucleoid separation is temporarily inhibited after arrest of FtsZ synthesis, but is later resumed as FtsZ is further diluted into the elongating filaments.

Biology of the CellVolume 76, Issue 2 p. 214-214 FTSZ COUPLES CELL DIVISION TO NUCLEOID PARTITIONING IN A PROKARYOTIC CELL Tetart Françoise, Tetart Françoise CNRS-Laboratoire de Microbiologie et Génétique Moléculaire, 118 Route de Narbonne, 31062 Toulouse Cédex, FranceSearch for more papers by this authorMulder Egberl, Mulder Egberl Department of Molecular Cell Biology, Plantage Muidergrachl, 1018 TV Amsterdam, N.L.Search for more papers by this authorConter Annie, Conter Annie CNRS-Laboratoire de Microbiologie et Génétique Moléculaire, 118 Route de Narbonne, 31062 Toulouse Cédex, FranceSearch for more papers by this authorBouche Jean-Pierre, Bouche Jean-Pierre CNRS-Laboratoire de Microbiologie et Génétique Moléculaire, 118 Route de Narbonne, 31062 Toulouse Cédex, FranceSearch for more papers by this author Tetart Françoise, Tetart Françoise CNRS-Laboratoire de Microbiologie et Génétique Moléculaire, 118 Route de Narbonne, 31062 Toulouse Cédex, FranceSearch for more papers by this authorMulder Egberl, Mulder Egberl Department of Molecular Cell Biology, Plantage Muidergrachl, 1018 TV Amsterdam, N.L.Search for more papers by this authorConter Annie, Conter Annie CNRS-Laboratoire de Microbiologie et Génétique Moléculaire, 118 Route de Narbonne, 31062 Toulouse Cédex, FranceSearch for more papers by this authorBouche Jean-Pierre, Bouche Jean-Pierre CNRS-Laboratoire de Microbiologie et Génétique Moléculaire, 118 Route de Narbonne, 31062 Toulouse Cédex, FranceSearch for more papers by this author First published: 1992 https://doi.org/10.1016/0248-4900(92)90227-RAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume76, Issue21992Pages 214-214 RelatedInformation

Conjugative temperature-sensitive plasmids were derived from pSC101. These plasmids are useful in genetic analysis for two reasons: (i) they render possible the construction of new Hfr lines by plasmid integration at predetermined chromosomal loci via Tn10 inverse transposition, and (ii) the Hfr characters are transducible via bacteriophage P1. We also showed that replication from pSC101 origin is deleterious for the plasmid-chromosome fusion.

A cytogenetic study has lead us to a stock of fertile heterozygotes for a triple translocation. The chromosomal rearrangement has first been detected in a female resulting from a cross between a normal female and a male submitted to X ray-irradiation. The aberration consists of rearrangements between a chromosome 3, a chromosome 6 and a chromosome 7. Abnormal chromosomes have the following constitution: 7q−: the terminal portion of the long arm is lost and replaced by the end of the short arm of the chromosome 3. 6 q+: the terminal portion of the long arm is lost and replaced by the end of the long arm of the chromosome 7. 3p+: the terminal portion of the short arm is lost and replaced by the end of the long arm of the chromosome 6. On the analogy of the human chromosome standardization, the formula of heterozygotes is 24, t (3p+, 6q+, 7q−). The first meiotic division shows both in the female and in the male 9 bivalents and one hexavalent. The formulae of the gametes are the same in both sexes. When a heterozygote is bred with a normal individual the offspring is composed of phenotypically normal or abnormal animals, depending on their karyotypes. The unbalanced karyotypes are lethal or semilethal. The importance of the malformations depends on the temperature of the water where the animals grow. The study of the meiotic slides brings a cytological confirmation of the results obtained from the study of the phenotypes and karyotypes which appear in the offspring.