摘要:

SummaryImmunophilins are housekeeping proteins present in a wide variety of organisms. Members of two protein superfamilies, cyclophilins (Cyps) and FK506‐binding proteins (FKBPs) belong to this class of immunophilins. Despite the fact that the amino acid sequences of Cyp and FKBPs do not exhibit noticeable homology to each other, proteins of both classes are able to ligate immunosuppressive peptide derivatives. Cyps form complexes with the cyclic undecapeptide cyclosporin A and FKBPs are able to bind FK506 as well as rapamycin, both of which have a pipecolyk bond within their structure. In a ligand‐bound form, immunophilins interfere with signal transduction in T cells. In addition, immunophilins have peptidyl prolylcis‐transisomerase (PPlase) activity and are able to accelerate the rate of conformational events in proline‐containing polypeptides. Microorganisms produce proteins that exhibit extensive sequence homologies to cyclophilins and FKBPs of higher organisms and which have considerable PPlase catalytic activity. While cyclophilins seem to be present in most if not all microbial species investigated, FKBPs are produced by yeasts as well as by a number of pathogenic bacteria, such asLegionella pneumophila, Chlamydia trachomatisandNeisseria meningitidis.The Mip protein ofL. pneumophilais a virulence factor that plays an essential role in the ability of the bacteria to survive and multiply in phagocytic cells. Some results are summarized on the structure and putative functions of immunophilins and place special emphasis on the contribution of these polypeptides to the virulence of pathogenic microor

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00917.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe following characteristics are relevant when replication of chromosomes and plasmids is discussed in relation to the cell cycle: the timing or replication, the selection of molecules for replication, and the coordination of multiple initiation events within a single cell cycle. Several fundamentally different methods have been used to study these processes: Meselson—Stahl density‐shift experiments, experiments with the so‐called‘baby machine', sorting of cells according to size, and flow cytometry. The evidence for precise timing and co‐ordination of chromosome replication inEscherichia coliis overwhelming. Similarly, the high‐copy‐number plasmid ColE1 and the low‐copy‐number plasmids R1/R100 without any doubt replicate randomly throughout the cell cycle. Data about the low‐copy‐number plasmids F and P1 are conflicting. This calls for new types of experiments and for a better understanding of how these plasmids control their replica

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00918.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryMicroorganisms have numerous strategies for coping with environmental changes. In many systems, a single cell has the capacity to generate a seemingly infinite array of phenotypic variants in just a few generations of growth. The resulting heterogeneous population is well equipped for sudden environmental change; even if only a few cells in the population possess a phenotype needed for survival, these cells have the capacity to regenerate a similarly diverse population. Phenotypic switching in these systems usually results from high‐frequency DNA rearrangements which are the subject of this revie

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00919.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe relative abundance of 88 proteins was measured in extracts from three strains ofEscherichia coliK‐12 that are isogenic except for thetopAandgyrBgenes. Mutations in these genes slightly raise or lower, respectively, steady‐state DNA supercoiling levels but have little effect on growth rate. Altered protein abundances were observed in the mutant strains relative to wild type. Many proteins exhibited minimum abundance at wild‐type supercoiling levels, and other proteins exhibited maximal abundance at relaxed levels. A smaller number showed maximal abundance at elevated levels of supercoiling. These data suggest that small, non‐lethal changes in DNA supercoiling can have widespread effects on patterns of gene exp

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00920.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummarySix putative ATP‐binding motifs of SecA protein were altered by oligonucleotide‐directed mutagenesis to try to define the ATP‐binding regions of this multifunctional protein. The effects of the mutations were analysed by genetic and biochemical assays. The results show that SecA contains two essential ATP‐binding domains. One domain is responsible for high‐affinity ATP binding and contains motifs AO and BO, located at amino acid residues 102‐109 and 198‐210, respectively. A second domain is responsible for low‐affinity ATP binding and contains motifs A3 and a predicted B motif located at amino acid residues 503‐511 and 631‐653, respectively. The ATP‐binding properties of both domains were essential for SecA‐dependent translocation ATPase andin vitroprotein translocation activities. The significance of these findings for the mechanism of SecA‐dependent protein t

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00921.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryNeisseria meningitidis(Nm) isolates from disease or during carriage express, on their outer membranes, one or more of a family of closely related proteins designated Opa proteins. In this study, we have examined the potential rotes of Nm Opa proteins in bacterial attachment and invasion of endothelial as well as epithelial cells and compared the influence of Opa proteins with that of Ope protein, which has been previously shown to increase bacterial interactions with eukaryotic cells. Several variants expressing different Opa proteins (A, B, D) or Opc were selected from a culture of capsule‐deficient non‐piliated bacteria of strain C751. Although the Opa proteins increased bacterial attachment and invasion of endothelial cells, Opc was the most effective protein in increasing bacterial interactions with these cells. In contrast, attachment to several human epithelial cells was facilitated at least as much by OpaB as Opc protein. OpaA was largely without effect whereas OpaD conferred intermediate attachment. OpaB also increased invasion of epithelial cells; more bacteria were internalized by Chang conjunctival cells compared with Hep‐2 larynx carcinoma or A549 lung carcinoma cells. Monoclonal antibody reacting with OpaB inhibited bacterial interactions with the host cells. Opa‐mediated interactions were also eliminated or significantly reduced in variants expressing capsule or those with sialylated lipopolysaccharide. These data are consistent with the notion that environmental factors controlling capsule and lipopolysaccharide phenotype may modulate bacterial interactions mediated by these OM proteins. In permissive microenvironments, some Opa proteins may be important in bacterial colonization and translocation in addition to Opc. The data also support the notion that Nm Opa may confer tissue

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00922.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe pheromoneN‐(3‐oxohexanoyl)‐L‐homoserine lactone (OHHL) regulates expression of bioluminescence in the marine bacteriumVibrio fischeri, the production of carbapenem antibiotic inErwinia carotovoraand exoenzymes in bothE. carotovoraandPseudomonas aeruginosa.A characteristic feature of this regulatory mechanism inV. fischeriis that it is cell density‐dependent, reflecting the need to accumulate sufficient pheromone to trigger the induction of gene expression. Using aluxplasmid‐based bioluminescent sensor for OHHL, pheromone production byE. carotovora, Enterobacter agglomerans, Hafnia alvei, Rahnella aquatilisandSerratia marcescenshas been demonstrated and shown also to be cell density‐dependent. Production of OHHL implies the presence in these bacteria of a gene equivalent toluxl.Chromosomal banks from all five enteric bacteria have yielded clones capable of eliciting OHHL production when expressed inEscherichia coli.Theluxlhomologue from bothE. carotovora (carl)andE. agglomerans (eagl)were characterized at the DNA sequence level and the deduced protein sequences have only 25% identity with theV. fischeriLuxl. Despite this,carl, eaglandluxlare shown to be biologically equivalent. An insertion mutant ofeagldemonstrates that this gene is essential for OHHL production inE

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00923.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe recent emergence of indolent and rapidly fatal drug‐resistant strains ofMycobacterium tuberculosishas renewed interest in defining the molecular mechanisms of drug resistance in the tubercle bacilli. In this report, we have examined the mechanism of resistance to streptomycin (Sm) inM. tuberculosisthrough the cloning and nucleotide sequence analysis of the gene encoding the ribosomal SRprotein (rpsLgene) from streptomycin‐resistant strains and their streptomycin‐sensitive parental strains. We have demonstrated that five singly SmRM. tuberculosisstrains and an SmRisolate that has reduced sensitivity to multiple antibiotics have identical point mutations at codon 43 of therpsLgene. Mutations at this same site confer SmRinEscherichia coli.In contrast, two other multiple drug‐resistantM. tuberculosisstrains that are resistant to Sm haverpsLgenes that have the same nucleotide sequence as their drug‐sensitive parent strains, suggesting that different resistance mechanisms are involved in thes

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00924.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryPseudomonas aeruginosastrain K437 is defective in the production of a 90 kDa ferripyoverdine receptor and is unable to grow in an iron‐deficient medium in the presence of the non‐metabolizable iron chelator 2,2′‐dípyrídyl (0.25mM). An attempt to clone the ferripyoverdine receptor gene was made by complementing this growth defect. A number of clones restoring growth of K437 on dipyridyl‐containing medium were obtained and several of these restored moderate expression of the 90 kDa receptor. A 5.5 kbXhol‐HindIIIfragment derived from one of these clones was similarly capable of complementing the dipyridyl growth defect although it failed to restore expression of the 90 kDa ferripyoverdine receptor. Nucleotide sequencing of the 5.5 kb fragment revealed two large open reading frames (ORFs), designated ORFA and ORFB, which appeared to form an operon and were capable of encoding products of 41 kDa and 112 kDa, respectively. Using a phage T7‐based expression system, products of 42 kDa andc.108 kDa were produced from the cloned DNA, confirming that the ORFs were, indeed, expressed. The cloned ORFAB operon was inducible under conditions of iron limitation in both P.aeruginosaandEscherichia coli.In addition, mutants expressing ORFAB constitutively were constitutive for pyoverdine and ferripyoverdine receptor production suggesting that components of the pyoverdine‐mediated iron‐transport system are co‐regulated with ORFAB. The predicted products of ORFA and ORFB showed significant homology to theEscherichia coliEnvC and EnvD polypeptides which are reportedly involved in septum formation. In addition, the ORFB product showed moderate homology to the CzcA polypeptide identified as a component of a membrane‐associated plasmid‐encoded cation efflux system inAlcaligenes eutrophus.Usingin vitromutagenesis and gene replacement, ORFA‐ and ORFB‐deficient mutants of K372, the parent strain of K437, were constructed. These mutants were unable to grow on iron‐deficient minimal medium containing 0.25 mM dipyridyl although they expressed the ferripyoverdine receptor and were proficient in pyoverdine‐mediated iron uptake. Despite the homology of the ORFA and ORFB products to EnvC and EnvD, respectively, the ORFA‐ORFB‐deficient mutants were not defective in septum formation. Introduction of an ORFB mutation into the pyoverdine‐producing strain ML5087 resulted in poor growth of the mutant in an iron‐limited medium. The same mutation in a pyoverdine‐deficient derivative of ML5087 did not adversely affect growth. These data are discussed in the context of a possible role in

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00925.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe genes encoding urease were cloned fromBordetella bronchisepticaand the 5.2 kb of DNA essential for expression analysed in a T7 RNA polymerase transcription‐translation system. At least four poly‐peptides with predicted molecular weights of 69 000, 26 000, 12 200 and 11 000 were found. Partial DNA sequence of the gene encoding the 69 000 Da polypeptide revealed high amino acid identity to the α‐subunit ofProteus mirabilisurease, UreC and jack bean urease. A stable, unmarked deletion was constructed in this gene to create a urease‐negative mutant ofB. bronchiseptica.To assess colonization in a guinea‐pig model, the urease‐negative strain was inoculated with the urease‐positive parental strain in a mixed infection. The urease‐negative strain out competed the urease‐positive strain in the trachea, lungs and caecum. We demonstrate that urease is not essential for B.bronchisepticacolonization of the guinea‐pig respiratory

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb00926.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY