摘要:

Pseudomonads have several siderophore‐mediated iron‐acquisition systems. These can be classified into two groups: (i) the biosynthesis of a siderophore (iron‐transport agent) followed by its uptake; and (ii) uptake of heterologous ferric‐siderophores in which the siderophore is produced by other microbial species. The regulation of these mechanisms employs both positive and negative elements ensuring expression of the relevant genes only when they are absolutely required. Siderophore biosynthesis is induced in response to iron limitation. In contrast, activation of the heterologous transport systems is not only regulated by iron availability but also requires the presence of their cognate ferric‐siderophores. The investigation of these regulation systems in three differentPseudomonasspecies gave similar results consisting of regulatory elements new to the field of iron regulation. These elements are superimposed upon the regulation by the Fur repressor, which in other bacteria directly regulate the expression of the iron‐assimilation genes in response to iron a

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040603.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

The nucleotide sequence of region 2 of theEscherichia coliK5 capsule gene cluster has been determined. This region, essential for the biosynthesis of the K5 poly‐saccharide, contained four genes, termedkfiA‐D. The G+C ratio was 33.4%, which was lower than the typical G+C ratio forE. coliand that of the flanking regions 1 and 3 in the K5 capsule gene cluster. Three major RNA transcripts were detected within region 2 by Northern blotting and three promoters located by transcript mapping. Promoter activity was confirmed by promoter‐probe analysis. The predicted amino acid sequence of KfiC had homology to a number of glycosyl transferase enzymes and overexpression of thekfiCgene resulted in increased K5 transferase activity. The predicted amino acid sequence of KfiD had homology to a number of NAD‐dependent dehydrogenase enzymes and was demonstrated to be a UDP‐glucose dehydrogenase that catalyses the formation of UDP‐glucuronic acid from

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040611.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

Various strains ofBacillus subtilis(natto) contain small cryptic plasmids that replicate via the rolling‐circle mechanism. Like plasmids from other Gram‐positive bacteria, these plasmids are composed of several distinct structural modules. A new structural module was identified on theB. subtilisplasmids pTA1015 and pTA1040. It is composed of two genes: one specifies an unidentified protein with a putative signal peptide; and the other (sipP) specifies a functional type I signal peptidase (SPase). The homologous, but non‐identical,sipPgenes of the two plasmids are the first identified plasmid‐specific SPase‐encoding genes. With respect to structure and activity, the corresponding enzymes (denoted SipP) are highly similar to the chromosomally encoded SPase, SipS, ofB. subtilisand several newly identified SPases of other bacilli. Our findings suggest that plasmid‐encoded SPases have evolved because, under certain conditions, SPase can be a limiting factor for protein secretion in

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040621.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

TheEscherichia coliNusG protein binds Rhoin vitroand is required for efficient Rho‐dependent transcription terminationin vivo. In this work we examine transcription termination in cells that overexpress NusG. Termination at the Rho‐dependent λtL1 and λtR1 sites was significantly inhibited by excess NusG, whereas the Rho‐independent λtl site was fully functional. Although Western analysis showed no reduction in the levels of soluble Rho, termination was restored when Rho was also overexpressed. Our data indicate that the ratio of NusG and Rho proteins affects the efficiency of transcription ter

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040633.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

InEscherichia colithe histidine kinase sensor protein, EnvZ, undergoes autophosphorylation and subsequently phosphorylates the regulatory protein, OmpR. Modulation of the levels of OmpR‐phosphate controls the differential expression ofompFandompC. While the phosphotransfer reaction between EnvZ and OmpR has been extensively studied, the domains involved in the sensing function of EnvZ are not well understood. We have used a comparative approach to study the sensing function of EnvZ. During our search of numerous bacteria we found that the symbiotic/pathogenic bacteriumXenorhabdus nematophiluscontained the operon encoding bothompRandenvZ. Nucleotide sequence analysis revealed that EnvZ ofX. nematophilus(EnvZX.n.) is composed of 342 amino acid residues, which is 108 residues shorter than EnvZ ofE. coli(EnvZE.c.). Amino acid sequence comparison showed that the cytoplasmic domains of the EnvZ moleculsshared 57% sequence identity. In contrast, the large hydrophilic periplasmic domain of EnvZE.c.was absent in EnvZX.n., and was replaced by a shorter hydrophobic region. Although the periplasmic domains had diverged extensively, envZX.n.was able to complement a ΔenvZstrain ofE. coli. OmpF and OmpC were differentially produced in response to changes in medium osmolarity in this strain. Further genetic analysis established that heterologous phosphorylation between EnvZX.n.and OmpR ofE. coli(OmpRE.c.) accounted for the complementation of the ΔenvZstrain. In addition we show that the OmpR molecules ofX. nematophilusandE. colishare 78% amino acid sequence identity. These results indicate that the EnvZ protein ofX. nematophiluswas able to sense changes in the osmolarity of the growth environment and properly regulate the levels of OmpR‐phosphate inE.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040643.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

A locus within chromosome XIII ofSaccharomyces cerevisiaecontaining four genes upregulated by osmotic stress has been characterized. Two of the genes, but not their osmotic induction, were already described: the DNA damage‐inducible geneDDR48and the protease inhibitor genePAI3. The two novel genes encode a cytoplasmic aldehyde dehydrogenase (ALD2) and a peptide of unknown function (SIP18). These genes form a cluster of two pairs of divergent promoters regulated by osmotic stress. The regulation of the divergentALD2andDDR48genes, however, occurs by different mechanisms.ALD2exhibits maximum induction with 0.3 M NaCl, negative regulation by protein kinase A and dependence onPBS2andHOG1protein kinases for osmotic induction.DDR48requires 1 M NaCl for maximum induction and its expression is independent ofPBS2andHOG1protein kinases and less sensitive to protein kinase A.PAI3andSIP18are as dependent on the above protein kinases asALD2. Deletion analysis indicates that most of the regulation of theALD2promoter is mediated by a negative element counteracted by osmotic stres

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040653.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

Transcriptional studies have demonstrated that thednaKgene ofStreptomyces coelicolorA3(2) is contained within a 4.3 kb operon. The operon is transcribed from a single (transiently) heat‐inducible promoter,dnaKp, that resembles the typical vegetative (σ70‐recognized) eubacterial consensus promoter sequence.dnaKtranscription was found to be heat‐inducible at all stages of development in surface‐grown cultures. In addition, at the normal growth temperature of 30°C,dnaKtranscript levels were shown to vary at different stages of development, being more abundant in young germinating cultures and in mycelium undergoing sporogenesis. The nucleotide sequence of thednaKoperon has been completed, revealing the gene organization 5′‐dnaK‐grpE‐dnaJ‐orfX.orfXrepresents a novel heat‐shock gene. Its predicted product displays high similarity to the GlnR repressor proteins ofBacillusspp. and to the MerR family of eubacterial transcriptional regulators. TheS. coelicolorOrfX protein has been over‐produced inEscherichia coli, and DNA‐binding experiments indicate that it interacts specifically with thednaKpregion, binding to three partially related inverted repeat sequences; they are centred at −75, −49 and +4, respectively, relative to the transcription start site of the operon. These results suggest that OrfX plays a direct role in th

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040663.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

A new binding‐protein‐dependent transport system ofEscherichia colispecific forl‐arginine was characterized by genetic and biochemical means. The system is encoded by five adjacent genes,artPIQMJ(art standing forargininetransport), which are organized in two transcriptional units (artPIQMandartJ). TheartlandartJgene products (Artl and ArtJ) are periplasmic binding proteins with sequence similarity to binding proteins for polar (basic) amino acids. TheartQ, artMandartPproducts are similar to the transmembraneous proteins and the ATPase of binding‐protein‐dependent carriers. The mature Artl and J proteins were localized in the periplasm and lacked signal peptides of 19 amino acid residues. Artl and ArtJ were isolated from overproducing strains. ArtJ specifically bindsl‐arginine with high affinity and overproduction of ArtJ stimulatedl‐arginine uptake by the bacteria. The substrate for Artl is not known, and isolated Artl did not bind common amino acids, various basic uncommon amino acids or amines. It is concluded that theartPIQM artJgenes encode a third arginine‐uptake system in addition to the knownargT hisJQMPsystem ofSalmonella typhimuriumandE. coliand the arginine (‐ornithine) carri

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040675.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

InRhizobium meliloti, the genes required for nodulation of legume hosts are under the control of DNA regulatory sequences callednodboxes. In this paper, we have characterized three host‐specific nodulation genes, which form a flavonoid‐inducible operon down‐stream of thenodbox n5. The first gene of this operon is identical to thenodLgene identified by Baev and Kondorosi (1992) inR. melilotistrain AK631. The product of the second gene, NoeA, presents some homology with a methyl transferase.nodLmutants synthesize Nod factors lacking theO‐acetate substituent. In contrast, in strains carrying a mutation in eithernoeAornoeB, no modification in Nod‐factor structure or production could be detected. On particular hosts, such asMedicago littoralis, mutants of the n5 operon showed a very weak nodule‐forming ability, associated with a drastic decrease in the number of infection threads, while nodulation ofMedicago truncatulaorMelilotus albawas not affected. Thus,nodL,noeAandnoeBare host‐specific nodulation genes. By using a gain‐of‐function approach, we showed that the presence ofnodL, and hence ofO‐acetylated Nod factors, is a major prerequisite for confering the ability to nodulate alfalfa upon the heterologous bacteri

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040687.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY

摘要:

The ability ofSalmonellato invade tissue culture cells is correlated with virulence. Therefore, the tissue culture invasion model has been used extensively to study this process and to identify the bacterial genes involved and their products. Described here is the further characterization of aSalmonella enteritidismutant (SM6T) originally identified as non‐invasive for tissue culture cells. A chromosomal DNA fragment complementing this defect was cloned and sequenced. The derived protein sequence is 89% identical to TolC fromEscherichia coli, an outer membrane protein required for the signal peptide‐independent transport of α‐haemolysin and colicin V. Therefore,sinAwas renamedtolCand is referred to in this text astolCsto distinguish it fromtolCofE. coliTolCsand TolC are functionally similar sincetolCcan complement the invasion‐defective phenotype of atolCsmutant, andtolCsis required for export of α‐haemolysin bySalmonella. ThetolCsmutant is avirulent for mice when administered by the oral route, suggesting that the gene is important for virulence. Further characterization of thetolCsmutant indicated that liketolCmutants it is more sensitive than the wild‐type strain to various detergents, antibiotics and dyes. This mutant is more sensitive to Triton X‐100 only when associated with the monolayer, and the invasion‐defective phenotype appears to be an artifact of this sensitivity. In addition, thetolCsmutant is more sensitive to the bactericidal activity of human serum. Therefore, the avirulent phenotype could be the result of an inability to secrete a necessary virulence factor, or an increased sensitivity to complement and detergents as a result of a subtle alteration in the lipopolysaccharide (LPS) associated

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_17040701.x

出版商:Blackwell Scientific Publication    

年代:1995

数据来源: WILEY