摘要:

SummaryIn recent years considerable advances have been made in the understanding of the molecular basis of iron‐mediated regulation of diphtheria toxin expression. Thetoxgene has been shown to be regulated by the heavy metal ion‐activated regulatory element DtxR. In the presence of divalent heavy metal ions, DtxR becomes activated and binds to a 9 bp interrupted palindromic sequence. The consensus‐binding site has been determined by both the sequence analysis of DtxR‐responsive operators cloned from genomic libraries ofCorynebacterium diphtheriaeas well as byin vitrogenetic methods using cyclic amplification of selected targets (CAST‐ing). it is now clear that DtxR functions as a global iron‐sensitive regulatory element in the control of gene expression inC. diphtheriae.In addition, the metal ion‐activation domain of DtxR is being characterized by both mutational analysis and determination of the X‐ray structure at 3

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01280.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryDisulphides are often vital for the folding and stability of proteins. Dedicated enzymatic systems have been discovered that catalyse the formation of disulphides in the periplasm of prokaryotes. These discoveries provide compelling evidence for the actual catalysis of protein foldingin vivo.Disulphide bond formation inEscherichia coliis catalysed by at least three ‘Dsb’ proteins; DsbA, ‐B and ‐C. The DsbA protein has an extremely reactive, oxidizing disulphide which it simply donates directly to other proteins. DsbB is required for the reoxidation of DsbA. DsbC is active in disulphide rearrangements and appears to work synergistically with DsbA. The relative rarity of disulphides in cytoplasmic proteins appears to be dependent upon a disulphide‐destruction machine. One pivotal cog in this machine is thioredoxin

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01281.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe involvement of the RTX haemolysins (Apxl and ApxII) of the swine pathogenActinobacillus pleuropneumoniae in virulencewas investigated using haemolysin‐deficient mutants constructed by a mini‐Tn10mutagenesis procedure. Two types of haemolysin mutant with single insertions of the transposon were obtained from a serotype 1 strain producing both ApxI and ApxII. One presented a complete loss of haemolytic activity because of the absence of ApxI and ApxII production. The other displayed weaker haemolysis than the wild type and produced only ApxII. The chromosomal regions flanking mini‐Tn10were cloned and sequenced. In the non‐haemolytic mutant, the transposon had inserted inapxIB, a gene involved in the exportation of ApxI and ApxII toxins. The weakly haemolytic mutant resulted from the disruption of the structural gene for ApxI. Both mutations In theapxIoperon were associated with a significant loss of virulence for mice and pigs, demonstrating that haemolysins are involved inA. pleuropneumoniaepathogenicity. The non‐haemolytic mutant was apathogenic and the weakly haemolytic mutant retained some virulence for pigs, suggesting that both ApxI and ApxII are needed for full

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01282.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryHaemophilus influenzaerepresents a common cause of human disease and an important source of morbidity and mortality. Disease caused by this organism begins with colonization of the upper respiratory tract. Several studies indicate thatH. influenzaeis capable of binding to and entering cultured human cells, properties which are potentially of relevance to the process of colonization. In the present study, we isolated anH. influenzaegene designatedhap, which is associated with the capacity forIn vitroattachment and entry. Analysis of the derived amino acid sequence ofhapdemonstrated significant homology with the serine‐type lgA1 proteases expressed byH. influenzaeandNeisseria gonorrhoeae.It is notable that thehapproduct shares the catalytic domain of the lgA1 proteases and appears to be processed and secreted in an analogous manner. We speculate that thehapgene product is an important determinant of colonization, perhaps enabling the organism to evade the local immune response and thereby persist within the respiratory trac

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01283.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryCampylobacterjejuniis a significant cause of bacterial enteritis in humans. Three of sevenC. jejuniisolates examined were found to contain fragmented 23S rRNA. The occurrence of fragmented 23S rRNA correlated with the presence of an intervening sequence (IVS) within the 23S rRNA genes. The IVS is 157 nucleotides in length and replaces an eight nucleotide sequence in the 23S rRNA genes ofC. jejuniisolates that contain intact 23S rRNA. The two ends of the IVS share 31 bases of complementarity that could form a stem‐loop structure. Fragmentation of the 23S ribosomal RNA results from the excision of the IVS from the transcribed RNA; the 3’ cleavage site maps within the putative stem‐loop formed by the IVS. Southern hybridization analysis revealed that the IVS is not present in the genomes of isolates that contain intact 23S rRNA, suggesting that the IVS is not derived fromCampylobacterchromosomal sequences. TheC. jejuniIVS is located at a position analogous to that of the IVSs found in bothSalmonellaandYersin

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01284.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryA homologue of the bacterial cell division geneftsZwas cloned from the filamentous bacteriumStreptomyces coelicolor.The gene was located on the physical map of the chromosome at about ‘11 o'clock’ (in the vicinity ofglkA, hisAandtrpB).Surprisingly, a null mutant in which the 399‐codonftsZopen reading frame was largely deleted was viable, even though the mutant was blocked in septum formation. This indicates that cell division may not be essential for the growth and viability ofS. coelicolor.TheftsZmutant was able to produce aerial hyphae but was unable to produce spores, a finding consistent with the idea thatftsZis required in order for aerial hyphae to undergo septation into the uninucleoid cells that differentiate into s

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01285.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe LuxR regulatory protein ofVibrio harveyias well as the autoinducer molecule, N‐(3‐hydroxybutanoyl) homoserine lactone, are known to be required for expression of luminescence. Although LuxR has been implicated in the activation of the promoter of theluxoperon ofV. harveyi, and can bind to two distinct sites upstream of the transcription initiation start site, its mode of action is unknown, in the present experiments, mobility shift assays were used to demonstrate that LuxR bound to the distal and proximal sites in an independent rather than co‐operative interaction with a much tighter binding to the distal site. Deletion and mutation analyses of DNA upstream of theluxpromoter followed by transconjugation IntoV. harveyi in transusing the chloramphenicol acetyl‐transferase (cat) gene as a reporter demonstrated, however, that the proximal site for LuxR was absolutely critical for promoter activation while the distal LuxR site was only necessary for maximum activation. This result was confirmed by mutation of the proximal site which blocked activation of theluxpromoter and binding of LuxR to this site, but did not prevent LuxR binding to the dist

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01286.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryWe have studied the formation of spontaneous mutations on plasmids present In the monomeric and dimeric states in arecFstrain ofEscherichia coli.Two test systems were employed: (i) the precise excision of Tn5 from thetetAgene of the plasmid pBR322 and (ii) operator constitutive (Oc) mutations on the pBR322‐derived plasmid pPY97. The rate of Ocmutations was increased by a factor of three when this plasmid was present in the dimeric state compared to the monomeric state and the Ocphenotype was caused by small deletions in the operator sequence. No apparent mutational hot‐spot was found. The rate of Tn5 excision was increased on dimeric compared to monomeric plasmids. Excision from a dimeric plasmid usually resulted in two types of mutant plasmids; a dimeric plasmid, where the Tn5 had excised from one of the plasmid units, and a monomeric parental pBR322. A mechanism to account for this is suggested. Complementation tests revealed that the increased mutation rate on dimeric plasmids is the result of dimers being mutaphilicper se, rather than the result of a general, trans‐acting increase in mutation rates of the host, induced by the presence of the dimeric plasmid. Furthermore, it was found that the rate of Tn5 excision from plasmids in the monomeric state was increased when the region carrying the inserted Tn5 was dupli

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01287.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryTrimethoprim and sulphisoxazole were used as selective agents in culture to isolate, by a stepwise procedure, a series ofChlamydia trachomatisL2 populations resistant to the cytotoxic effects of the drugs. Two trimethoprim‐resistant populations. L2TriR‐60 and L2TriR‐100, and one sulphonamide‐resistant population. L2SulfR‐100, were characterized in more detail. In addition to being resistant to trimethoprim, L2TriR‐100 was cross‐resistant to metho‐trexate, sensitive to sulphisoxazole and displayed a ribonucleotide auxotrophy similar to that of its parental wild type,C. trachomatisL2. Surprisingly, L2TriR‐100andL2SulfR‐100appeared phenotypicallyidentical. Both mutants were highly resistant to trimethoprim, sulphisoxazole, and methotrexate. In contrast to wild‐typeC. trachomatisL2, these populations were sensitive to 5‐fluorouracil L2TriR‐100 and L2SulfR‐100 were incapable of taking pyrimidine ribonucleotides from the host cell and no longer synthesized thymidine nucleotidesde novo.The pyrimidine requirement of these mutants was met by salvaging host‐cell uracil and thymidine, a property which can account for their drug‐resistance characteristics. L2TriR‐100 and L2Sulfn‐100 could also salvage adenine and guanine. Using L2TriR‐100 as a starting stock, a mutant population resistant to the cytotoxic effects of trimethoprim and 5‐fluorouracil (L2Tri/5‐FU) was selected. L2TFi/5‐FU was resistant to 5‐fluoro‐uracil because it had regained the capacity to tak

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01288.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe cell wail ofMycobacterium smegmatisme2155 was shown to be an effective permeability barrier to hydrophilic compounds. Permeability coefficients to β‐lactams ranged from 10 × 10−7to 0.5 × 10−7cm s−1. Cell wall proteins were solubilized with EDTA and Genapol and were tested for channel‐forming activity by reconstitution into lipid bilayers. Proteins were able to induce a voltage‐gated cation‐selective channel. The mycobacterial porin channel appeared to be water‐filled since the single‐channel conductance followed the mobility sequence of hydrated ions in the aqueous phase. On the basis of the Renkin equation and the single‐channel conductance, the channel diameter was estimated to be around 3 nm. Model calculations showed that cation selectivity may be caused by four negative point‐charges at the channel mouth. The permeability properties of the cell wall of intact cells were in good agreement with those of the reconstituted channel. Negatively charged cephalosporins, cefamandole and cephalothin, diffused at a 10‐ to 20‐fold lower rate than the zwitterionic cephaloridine. The mycobacterial porin represents a major hydrophilic pathway of

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01289.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY