摘要:

SummaryInBacillusspecies, starvation leads to the activation of a number of processes that affect the ability to survive during periods of nutritional stress. Activities that are induced include the development of genetic competence, sporulation, the synthesis of degradative enzymes, motility, and antibiotic production. The genes that function in these processes are activated during the transition from exponential to stationary phase and are controlled by mechanisms that operate primarily at the level of transcription initiation. One class of genes functions in the synthesis of special metabolites such as the peptide antibiotics tyrocidine and gramicidin S as well as the cyclic lipopeptide surfactin. These genes include thegrsandtycoperons inBacillus brevis, which encode gramicidin S synthetase and tyrocidine synthetase, respectively, and thesrfAoperon ofBacillus subtiliswhich encodes the enzymes of the surfactin synthetase complex. Peptide antibiotic biosynthesis genes are regulated by factors as diverse as the early sporulation gene product Spo0A, the transition‐state regulator AbrB, and gene products (ComA, ComP, and ComQ) required for the initiation of the competence developmental pathwa

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01154.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe virulence genes of the plant pathogenAgrobacterium tumefaciensare induced by more than 40 low‐molecular‐weight phenolic compounds. The prevailing opinion is that (i) wound‐derived phenols produced on breach of the integrity of the cell wall act as the initiating signal in a series of events which results in host cell transformation, and (ii) a classical membrane receptor, putatively VirA, is responsible for the recognition of all such phenolic inducers. Here, we argue that the discovery of the subset of inducers that are relatives of the dehydrodiconiferyl alcohol glucoside (DCG) growth factors redirects our attention to work on the plant wound as a site of cell division, and suggests that we further explore the implications of early work on the relationship between transformation efficiency and the status of the cell cycle of the host. In addition, we argue that the significant structural diversity allowed in the para position of the phenol ring of inducers suggests that a receptor–ligand interaction based solely on structural recognition is insufficient, but that recognition followed by a specific proton transfer event may be sufficient to explainvirinduction activity. Hence, the specificity of the response ofA. tumefaciensmay be a consequence of the features required for a chemical reaction to occur on the receptor surface. Finally, we review affinity labelling studies which exploit this phenol detection mechanism and which provide evidence that the phenol receptor may be other than VirA, the sensory kinase of the two component regulatory system implicated inAgrobacteriumvirulence. Taken together, these hypotheses form a model which has predictive and therefore experimental value, and which may be of broader interest in that it calls attention to the possibility of an intricate co‐evolution of signalling pathways of host and

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01155.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryAn abundant glycoprotein on the surface ofPneumocystis carinii, termed gpA or gp120, is thought to play a role in the interaction of this opportunistic pathogen with its host. Using RNA:RNA hybridization techniques, thein situexpression of gpA mRNA in developmental forms of the organism was investigated in a ferret model ofP. cariniipneumonia. The results suggested that the relative abundance of gpA‐specific mRNA was variable in different developmental stages of ferretP. carinii. P. cariniilocalized along the epithelial lining of alveoli were transcriptionally active. Immunocytochemical detection of gpA and Giemsa staining suggested that many of these organisms were trophic forms ofP. carinii.While no detectable gpA mRNA signal was found in the majority ofP. cariniicysts, a portion of identifiable cysts co‐localized with significant levels of gpA mRNA signal. Differential staining of the cyst wall with Gomori's methenamine silver suggested that the transcriptionally activeP. cariniicysts were the intermediate or precyst forms of the organism, while the cysts with no detectable mRNA signal were either mature or empty (excysted). Alveolar macrophages were observed surrounded by transcriptionally active organisms; however, no gpA‐transcriptional activity was detected within macrophages. Taken together, the results suggest that transcription of gpA occurs in forms ofP. cariniithat are actively replicating, and in close proximity or contact with, alveolar epithelial

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01156.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThePseudomonas aeruginosa ctxgene encoding cytotoxin is carried by a temperate phage φCTX. The genome of φCTX is a 35.5 kb double‐stranded DNA with cohesive ends (cos). It is unique in that thectxgene andattPsite of φCTX exist very close to the respective cohesive ends. In this study, we determined the structure of thisattP–cos–ctxregion. The termini of φCTX are 21‐base 5′ extended‐single‐stranded DNAs. Thectxgene is located 361 bp downstream of the left end (cosL). TheattPcore sequence of 30 bp exists only 647 bp apart from the right end (cosR). TheattP–cos–ctxregion contains six kinds of repeats and integration host factor‐binding sequences and showed sequence‐directed static bends, suggesting its potential to form a highly ordered structure. In addition, φCTX was found to integrate into the serine tRNA gene which was mapped to the 43–45 min region o

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01157.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryTransposon mutagenesis was used to identify genes necessary for the expression ofPseudomonas aeruginosatype 4 fimbriae. In a library of 12 700 mutants, 147 were observed to have lost the spreading colony morphology associated with the presence of functional fimbriae. Of these, 28 had also acquired resistance to the fimbrial‐specific bacteriophage P04. The mutations conferring this phage resistance were found to have occurred at at least six different loci, including the three that had been previously shown to be required for fimbrial biosynthesis or function: the structural subunit (pilA) and adjacent genes (pilB,C,D), the twitching motility gene (pilT), and the Sigma 54 RNA polymerase initiation factor gene (rpoN). One novel group of phage‐resistant mutants was identified in which the transposon had inserted near sequences that cross‐hybridized to an oligonucleotide probe designed against conserved domains in regulators of RpoN‐dependent promoters. These mutants had no detectable transcription ofpilAand did not produce fimbriae. A probe derived from inverse polymerase chain reaction was used to isolate the corresponding wild‐type sequences from aP. aeruginosaPAO cosmid reference library, and two adjacent genes affected by transposon insertions,pilSandpilR, were located and sequenced. These genes were shown to be capable of complementing the corresponding mutants, both at the level of restoring the phenotypes associated with functional fimbriae and by the restoration ofpilAtranscription. ThepilSRoperon was physically mapped toSpelfragment 5 (corresponding to about 72–75/0 min on the genetic map), and shown to be located approximately 25 kb frompilA–D.PilS and PilR clearly belong to the family of two‐component transcriptional regulatory systems which have been described in many bacterial species. PilS is predicted to be a sensor protein which when stimulated by the appropriate environmental signals activates PilR through kinase activity. PilR then activates transcription ofpilA, probably by interacting with RNA polymerase containing RpoN. The identification ofpilSandpilRmakes possible a more thorough examination of the signal transduction systems controlling expression of virulence factors

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01158.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummarySUP35is an omnipotent suppressor gene ofSaccharomyces cerevisiaecoding for a protein consisting of aC‐terminal part similar to the elongation factor EF‐1α and a uniqueN‐terminal sequence of 253 amino acids. Twelve truncated versions of theSUP35gene were generated by the deletion of fragments internal to the coding sequence. Functional studies of these deletion mutants showed that: (i) only the EF‐1α‐likeC‐terminal part of the Sup35 protein is essential for the cell viability; (ii) overexpression of either theN‐terminal part of the Sup35 protein or the full‐length Sup35 protein decreases translational fidelity, resulting in omnipotent suppression and reduced growth of [psi+] strains; (iii) expression of theC‐terminal part of the Sup35 protein generates an antisuppressor phenotype; and (iv) both theN‐ orC‐terminal segments of the Sup35 protein can bind to 80S ribosomes. Thus, the data obtained define two domains within the Sup35 protein which are responsible

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01159.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThecyaAgene ofBordetella pertussisand ofBordetella bronchisepticaencodes a toxin which is a bifunctional protein exhibiting adenylate cyclase and haemolytic activities. InBordetella, virulence factors are synthesized under the control of thebvgregulatory locus, in response to environmental signals. InEscherichia colithecyaAgene is not expressed, nor is it activated bybvgindicating that the activation ofcyabybvgis indirect. To characterizecis‐acting regulatory regions required for the activation of thecyaAgene we constructedcyaA–lacZYfusions containing progressive deletions in the promoter upstream region and isolated promoter mutations by chemical and site‐directed mutagenesis. Deletion analysis shows that a region extending from −569 to −136 bp upstream from the start site of transcription is required for transactivation bybvg, suggesting that multiple binding sites are involved in the activation of thecyaApromoter. No single or double mutations in the promoter upstream region were found which conferred inactive orbvg‐independent Cya phenotype. A double mutation in positions +10 and +13, relative to the transcription start site, rendered the promoterbvg‐independent and functional inE. coli.The constitutive mutations create a new transcription start site, 20 bp downstream from the witd‐type site, by providing new −10 and −35 elements recognized by R

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01160.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryRibosome stalling in the leader region ofermCmRNA results in a 10–15‐fold increase inermCmRNA half‐life inBacillus subtilis.Fusion of theermC5′ regulatory region to severalB. subtiliscoding sequences resulted in induced stability of the fusion RNAs, showing that theermC5′ region acts as a general ‘5′ stabilizer’. RNA products of anermC–lacZtranscriptional fusion were inducibly stable in the complete absence of translation and included a small RNA that is likely to be a decay product arising by blockage of a 3′‐to‐5′ exoribonuclease activity. Insertion of sequences that encode endonucleolytic cleavage sites into theermCcoding sequence resulted in cleavage products whose stability depended on the nature of their 5′ and 3′ ends. It can be concluded from this study that initiation of mRNA decay inB. subtilisgenerally occu

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01161.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe limited host range (LHR)Agrobacterium tumefaciensstrain Ag162 is an isolate with a narrow host range. Introduction of the wide host range (WHR)virAgene is essential for extending the host range toKalanchoë daigremontiana.In this report we show that the region upstream of the ATG start codon is responsible for the LHR phenomenon and that this is probably due to the non‐inducibility of the LHRvirApromoter. By comparing the characteristics of the LHR and WHR VirA receptor proteins, it was found that the LHR VirA protein is able to activate the WHR VirG protein in the presence of acetosyringone and that this acetosyringone‐dependentvir‐induction is enhanced by the presence ofd‐glucose, as in the case of WHR VirA proteins. These results indicate that the domains, acting as receptors for sugars and phenolic signals, must be conserved between the LHR and WHR VirA receptor

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01162.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryWe report the identification and sequence fromEscherichia coliandSalmonella entericastrains of thecldgene, encoding the chain‐length determinant (CLD) which confers a modal distribution of chain length on the O‐antigen component of lipopolysaccharide (LPS). The distribution of chain lengths in the absence of this gene fits a model in which as the chain is extended there is a constant probability of 0.165 of transfer of growing chain to LPS core, with termination of chain extension. The data forE. coli0111 fit a model in which the CLD reduces this probability for short chains and increases it to 0.4 for longer chains, leading to a reduced number of short chain molecules but an increase in numbers of longer molecules and transfer of essentially all molecules by chain length 21. We put forward a model for O‐antigen polymerase which resembles the ribosome and fatty acid synthetase in having two sites, with the growing chain being transferred from a D site onto the new unit at the R site to extend the chain and then back to the D site to repeat the process. It is proposed that the CLD protein and polymerase form a complex which has two states:‘E’facilitating extension and T facilitating transfer to core. The complex is postulated to enter the E state as O‐antigen polymerization starts, and to shift to the T state after a predetermined time, the CLD acting as a molecular clock. The CLD is not O‐antigen or species‐specific but the modal value does depend on the sourc

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01163.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY