摘要:

SummaryFilamentous haemagglutinin (FHA) is the major attachment factor produced by virulentBordetellaspp. Similar to the other virulence factors, its production is tightly regulated by a two‐component system in response to environmental changes. Although of impressive size (c. 220 kDa), it is very efficiently released into the culture supernatant ofBordetella pertussis.Its biogenesis involves complex processing of a larger precursor with a calculated molecular mass of 370 kDa. Export of FHA into the culture medium depends on an outer membrane protein homologous to haemolysin accessory proteins. Purified extracellular FHA is able to increase the adherence of other pathogens to the host, which may contribute to super‐infection in whooping cough. Although FHA‐mutants colonize lungs as efficiently as the wild‐type parent strains, immune responses against FHA appear to protect against colonization. Unlike many other adhesins, FHA expresses at least three different attachment activities, one specific for the CR3 integrins of macrophages, one involving a carbohydrate‐binding site, specific for interactions with cilia, and a heparin‐binding activity that may be important for interaction ofB. pertussiswith epithelial cells or extracellul

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01725.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThree tRNA binding sites, the A, P and E sites, have been demonstrated on ribosomes of bacterial, archaebacterial and eukaryotic origin. In all these cases the first and the third site, the A and the E site, are allosterically coupled in the sense of a negative co‐operativity. Therefore, the allosteric three‐site model seems to be a generally valid description of the ribosomal elongation phase, where in a cycle of reactions the nascent peptide chain is prolonged by one amino acid. The molecular concept of the allosteric three‐site model explains the astonishing ability of the ribosome to select the correct substrate out of a large number of very similar substrates, and it provides a framework within which the mechanisms of the elongation factors could be understood.Molecular recognition: the special case of the ribosomal selection of the correct aminoacy

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01726.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummarySteady‐state‐ and stress‐induced expression ofEscherichia coliheat‐shock genes is regulated at the transcriptional level through controls of concentration and activity of the positive regulator, the heat‐shock promoter‐specific subunit of RNA polymerase, σ;32. Central to these controls are functions of the DnaK, DnaJ, GrpE heat‐shock proteins as negative modulators that mediate degradation as well as repression of activity and, in some conditions, of synthesis of σ32. DnaJ has a key role in modulation since it binds σ32and, jointly with DnaK and GrpE, represses its activity. Furthermore, DnaJ is capable of binding heat‐damaged proteins, targeting DnaK and GrpE to these substrates, and thereby mediating DnaK‐, DnaJ‐, GrpE‐dependent repair. It is proposed that one important signal transduction pathway that converts stress to a heat‐shock response relies on the sequestering of DnaJ through binding to damaged proteins which derepresses and stabilizes σ32. Damage repair ameliorates the inducing signal and frees DnaJ, DnaK, GrpE to shut

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01727.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe coumarin group of antibiotics have as their target the bacterial enzyme DNA gyrase. The drugs bind to the B subunit of gyrase and inhibit DNA supercoiling by blocking the ATPase activity. Recent data show that the binding site for the drugs lies within theN‐terminal part of the B protein, and individual amino acids involved in coumarin interaction are being identified. The mode of inhibition of the gyrase ATPase reaction by coumarins is unlikely to be simple competitive inhibition, and the drugs may act by stabilizing a conformation of the enzyme with low affinity for AT

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01728.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryPathogenic bacteria frequently express surface proteins with affinity for components of the mammalian extracellular matrix, i.e. collagens, laminin, fibronectin or proteoglycans. This review summarizes our current knowledge on the mechanisms of bacterial adherence to extracellular matrices and on the biological significance of these interactions. The best‐characterized bacterial proteins active in these interactions are the mycobacterial fibronectin‐binding proteins, the fibronectin‐ and the collagen‐binding proteins of staphylococci and streptococci, specific enterobacterial fimbrial types, as well as the polymeric surface proteins YadA of yersinias and the A‐protein ofAeromonas.Some of these bacterial proteins are highly specific for an extracellular matrix protein, some are multifunctional and express binding activities towards a number of target proteins. The interactions can be based on a protein‐protein or on a protein‐carbohydrate interaction, or on a bridging mechanism mediated by a bivalent soluble target protein. Many of the interactions have also been demonstrated on tissue sections orin vivo, and adherence to the extracellular matrix has been shown to promote bacterial colonization of da

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01729.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe incompatibitity that pSC101‐derived plasmids express toward each other is mediated by directly repeated sequences (iterons) located near the plasmid's replication origin. We report here that the pSC101parlocus, which stabilizes plasmid inheritance in dividing cell populations and alters DNA superheliclty, can function as a cis‐acting enhancer of incompatibility, which we show is determined jointly by the copy number of the plasmid and the number of iterons per copy. A single synthetic 32 bp iteron sequence carried by the pUC19 plasmid confers strong pSC101‐specific incompatibility in the absence of any other pSC101 sites but requires theparlocus to express strong incompatibility when carried by a lower‐copy‐number plasmid. We propose a model by which theparlocus can enchance the apparently antagonistic processes of incompatibility and pSC101 DNA replication while concurrently facilitating plasmid distribution during cell

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01730.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe chromosomalampCβ‐lactamase inCitrobacter freundiiandEnterobacter cloacaeis inducible by β‐lactam antibiotics. When an inducibleampCgene is introduced on a plasmid intoEscherichia colitogether with its transcriptional regulatorampR, the plasmid‐borne β‐lactamase is still inducible. We have isolated mutants, containing alterations in a novelE. coligene,ampG, in which a clonedC. freundii ampCgene is unable to respond to β‐lactam inducers. TheampGgene was cloned, sequenced and mapped to minute 9.6 on theE. colichromosome. The deduced amino acid sequence predicted AmpG to be a 53kDa, trans‐membrane protein, which we propose acts as a signal transducer or permease in the β‐lactamase induction system. Immediately upstream ofampGthere is another 579‐base‐pair‐long open reading frame (ORF) encoding a putative lipoprotein shown to be non‐essential for β‐lactamase induction. We have found thatampGand this ORF form an operon, whose promoter is located in front of the ORF. Located closely upstream of the putative promoter is the morphogenebolA, which is transcribed in the opposite orientation. However, using transcription fusions, we have found that theampGtranscription is not regulated bybolA.In addition, we show that transcription is probably not regulated by either the starvation specific sigma factor RpoS, which controlsbolA, or by AmpD the negative r

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01731.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummarySpecific cleavage of mRNAs by RNase III has been shown to control the expression of severalEscherichia coligenes. We show here that the expression of gene19of the conjugative resistance plasmid R1 is controlled in its expression by the same endoribonuclease.In vivostudies revealed that a DNA fragment of 150 nucleotides including a perfect 22 nucleotide inverted repeat in the gene19coding region is responsible for the low expression of the gene both at the protein and the RNA levels. By using a translational gene19‐lacZfusion in isogenic RNase III+and RNase III‐strains we could identify RNase III as the key element in the down‐regulation of gene19expression. The sequencing ofin vitrogenerated and RNase Ill‐digested transcripts confirmed thein vivostudies and revealed the exact positions of the RNase III cleavage sites within the coding part of the gene19transcript. Thein vitrodetermined RNase III cleavage of gene19mRNA was confirmed byin vivoprimer extension analysis. Finally, we could show that an exchange of three nucleotides within the RNase III recognition site abolished RNase III cleavagei

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01732.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryWe report here the discovery of a novel bacterial gene (cycH) whose product is involved in the biogenesis of most of the cellular cytochromesc.ThecycHgene was detected in the course of characterizing a cytochrome oxidase‐deficientBradyrhizobium japonicumTn5mutant (strain CO×3) in which the transposon insertion disruptedcycH.Ali of the c‐type cytochromes detectable in aerobically grownB. Japonicumwild‐type cells were absent in the C0X3 mutant, with the exception of cytochrome c1. A secondary phenotypic effect was the spectroscopic absence of the aa3‐type cytochromecoxidase. The nucleotide sequence of the cloned wild‐typecycHgene predicted a membrane‐bound 369‐amino‐acid protein with an Mrof 39727. Results from studies on its membrane topology suggested that approximately 110N‐terminal amino acids are involved in anchoring the protein in the membrane, whereas the remaining two‐thirds of the protein are exposed to the periplasm. We postulate that the CycH protein plays an essential role in an as yet unidentified periplasmic step in the biogenesis of holocytochromesc, except t

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01733.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThespollGoperon ofBacillus subtiliscodes for a sporulation‐specjfic sigma factor, σ;E,In vivoexpression of thespollGpromoter is activated shortly after the onset of sporulation and is dependent onkinA, spo0F, spo0Bandspo0Agenes. The products of these genes have been shown to participate in a phosphorelay reactionin vitro, culminating in phosphorylation of the transcription factor, Spo0A. The effect of Spo0A phosphorylation onin vitrotranscription from thespollGpromoter was determined. Aliquots from phos‐phorelay reactions enhancedspollGpromoter activity 10‐fold in transcription assays and stimulation of transcription was dependent on Spo0A phosphorylation. Our results provide biochemical evidence that Spo0A and the phosphoreiay form a signal transduction pathway which activatesspoilgene expression in devel

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01734.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY