摘要:

SummaryThe toxin‐like and bactericidal colicin E1 molecule is of interest for problems of toxin action, polypeptide translocation across membranes, voltage‐gated channels, and receptor function. Colicin E1 binds to a receptor in the outer membrane and is translocated across the cell envelope to the inner membrane. Import of the colicin channel‐forming domain into the inner membrane involves a translocation‐competent intermediate state and a membrane potential‐dependent movement of one third to one half of the channel peptide into the membrane bilayer. The voltage‐gated channel has a conductance sufficiently large to depolarize theEscherichia colicytoplasmic membrane. Amino acid residues that affect the channel ion selectivity have been identified by site‐directed mutagenesis. The colicin E1 channel is one of a few membrane proteins whose secondary structures in the membrane, predominantly α‐helix, have been determined by physico‐chemical techniques. Hypotheses for the identity of thetrans‐membrane helices, and the mechanism of binding to the membrane, are influenced by the solved crystal structure of the soluble colicin A channel peptide. The protective action of immunity protein is a unique aspect of the colicin problem, and information has been obtained, by genetic techniques, about the probable membrane topography o

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00619.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryBiochemical and genetic techniques have provided considerable insight into the structure‐function relationship of one of the ADP‐ribosyl transferases produced byPseudomonas aeruginosa, exotoxin A. Exotoxin A contains a typical prokaryotic signal sequence which, in combination with the first 30 amino‐terminal amino acids of the mature protein, is sufficient for exotoxin A secretion fromP. aeruginosa.Determination of the nucleotide sequence andcrystallinestructure of thisprokaryotic toxinallowed a molecular model to be constructed. The model reveals three structural domains of exotoxin A. Analysis of the identified domains shows that the amino‐terminal domain (domain I) is involved in recognition of eukaryotic target cells. Furthermore, the central domain (domain II) is involved in secretion of exotoxin A into the periplasm ofEscherichia coli.Evidence also implicates the role of domain II in translocation of exotoxin A from the eukaryotic vesicle which contains the toxin after it becomes internalized into susceptible eukaryotic cells via receptor‐mediated endocytosis. The carboxy‐terminal portion of exotoxin A (domain III) encodes the enzymatic activity of the molecule. The structure of this domain includes a cleft which is hypothesized to be the catalytic site of the enzyme. Several residues within domain III have been identified as having a direct role in catalysis, while others are hypothesized to play an important stru

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00620.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryRegions close to the replication terminus of theEscherichia colichromosome are strongly refractory to genomic inversions (Rebolloet al., 1988). Since these regions also harbour polar replication terminator‐like sequences or pause sites (Françoiset al., 1989), we have investigated the possibility that slowing of replication as a result of pausing at inverted pause sites is responsible for inability to isolate stable inversions affecting these regions. A mutation in thetusgene is known to abolish replication pausing at terminators (Hillet al., 1988). We show here that the distribution of invertible and noninvertible segments along the chromosome is not affected bytusmutations. This observation eliminates replication pausing as a cause for the reduced fitness of bacteria harbouring certain chromosomal inversio

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00621.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe genespoIIID, which is essential for spore formation inBacillus subtilis, was cloned and sequenced. It consists of one open reading frame which would encode a 93‐amino‐acid protein with a classic helix‐turn‐helix motif, characteristic of sequence‐specific DNA‐binding proteins. SpoIIID protein is a previously identified transcription factor, capable of altering the specificity of RNA polymerase containing sigma Kin vitro(Krooset al., 1989). ThespoIIID83mutation (by which the locus was originally identified), was sequenced and found to be a single base substitution in the ribosome binding site upstream of thespoIIIDopen reading frame. A transcriptional fusion tolacZwas constructed and used to examine the regulation ofspoIIID.Expression ofspoIIIDoccurred only during sporulation, beginning 1.5 to 2 hours after the initiation of sporulation. The dependence ofspoIIIDexpression on otherspoloci suggests that it is mother‐cell‐specific, and that it is transcribed by sigma E‐containi

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00622.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryType 1 fimbriae are surface organelles onEscherichia coli, which mediate specific binding to D‐mannose‐containing structures. These fimbriae are hetero‐polymers composed of a major building element, the FimA protein, and small amounts of the FimF, FimG and FimH proteins. The FimH protein is uniquely responsible for the D‐mannose receptor binding. In this work data are presented which indicate that the major subunit of type 1 fimbriae is dispensable for D‐mannose‐specific binding. A recombinant strain was studied which harboured an insertional deletion in thefimAgene, and was thereby unable to produce type 1 fimbriae; however, it was still able to express a D‐mannose‐binding phenotype. However, the deletion resulted in a 25‐fold reduction of the adhesive potential, as measured by binding to D‐mannose‐coated Sepharose beads. Serological and specific receptor binding evidence is presented that suggests that the FimH adhesin is capable of being exposed on the bacterial surface without being an integral

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00623.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryWe have shown that a mini‐Mu can transpose into itselfin vivoto generate a circle containing only transposon sequences. This deletion‐inversion product, which has previously been observedin vitro, is formed by non‐replicative transposition and has directly repeated Mu ends. It therefore cannot undergo further rounds of transposition and retains the two copies of the target sequence duplicated in the event. Thus we have been able to confirm that a mini‐Mu can undergo non‐replicative reactionsin vivoand that these generate a 5bp target site duplication, as has been shown to occur following replicative transposition and lysogenizatio

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00624.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryA system which allows direct selection for curing of plasmids in Gram‐negative bacteria was used to generate derivatives ofRhizobium leguminosarumVF39 cured of each of six plasmids present in this strain. Phenotypes could be correlated with the absence of five of the six plasmids. The smallest plasmid, pRIeVF39a, carries genes for the production of a melanin‐like pigment as has been previously reported. Plasmid pRIeVF39d carries nodulation and nitrogen fixation genes. Curing of the plasmids pRleVF39c and pRleVF39e gave rise to strains which formed Fix−nodules on peas, lentils, and faba beans. The nodules formed by the strains cured of pRIeVF39c contained few, if any, bacteria. Analysis of washed cells by SDS‐PAGE showed that this strain is defective in lipopolysaccharide (LPS) production; the defect could be complemented by introducing plasmids from several otherR. leguminosarumstrains, and by theR. leguminosarumbiovarphaseoliLPS gene clones pCos126 and pDel27. The nodules formed by the strain cured of pRleVF39e had a reduced symbiotic zone, an enlarged senescence zone, and an abundance of starch granules. This strain grew at a much slower rate than the wild type, was unable to grow on minimal medium, and no longer produced melanin. These defects could be complemented by at least one otherRhizobiumplasmid, pRle336e, a plasmid of strain 336 which is distinct from the nodulation plasmid (pRle336c) and the plasmid (pRle336d) which could complement the LPS defect associated with the loss of pRleVF39c. This demonstrates that genes necessary for symbiosis can be carried on at least three different plasmids inR. legumi

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00625.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryTheftsYEXoperon inEscherichia coliencodes three proteins, two of which (FtsE and FtsX) are known to be required for cell division. Although FtsE and FtsX have been identified using SDS‐PAGE, the FtsY protein has not. We have usedin vitroinsertion mutagenesis to identify FtsY as a 92kD polypeptide in maxicell experiments, although predictions from the DNA sequence estimated FtsY to be 54kD. Results suggest that this disparity could be due to the unusually high percentage of acidic residues within the protein. Complementation tests indicated the presence of a promoter withinftsYrequired for expression offtsEandftsX.The FtsY protein exhibits sequence homology with the SRα protein of eukaryotes which is involved in protein secretion. The essential nature of theftsYgene was also demonstrat

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00626.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryA 2.1 kb DNA segment carrying the purine‐cytosine permease gene (FCY2) ofSaccharomyces cerevisiaewas sequenced, the primary structure of the protein (533 amino acids) deduced and a folding pattern in the membrane is proposed for the permease protein. Expression of theFCY2gene product requires a functional secretory pathway and is reduced inmnn9, a mutant strain deficient in outer chain glycosylation. TheFCY2gene was mapped on the right arm of chromosome V close to theHIS1gen

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00627.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryWhen bacterial cells are subjected to a strong selective pressure it often induces specific mutations. Here a model is considered in which errors are introduced at random in one of the strands of the DNA molecule: a nick in one of the strands can initiate strand displacement rendering a region of the chromosome single‐stranded. Upon conversion back to double‐stranded DNA there is a certain probability of introducing errors creating a heteroduplex. If an error results in the production of an mRNA molecule encoding a product which provides a selective advantage, growth will be stimulated and the mutation can be immortalized by chromosomal replication. Otherwise, the error can be corrected by the DNA ‘proofreading’

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00628.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY