摘要:

SummaryMembers of the GTPase superfamily are extremely important in regulating membrane signalling pathways in all cells. This review focuses on membrane‐associated GTPases that have been described in prokaryotes. In bacteria, LepA and NodO are very similar to protein synthesis elongation factors but apparently have membrane‐related functions. The amino acid sequences of FtsY and Ffh are clearly related to eukaryotic factors involved in protein secretion. Obg and Era are not closely related to any GTPase subgroup according to amino acid sequence comparisons, but they are essential for viability. In spite of similarities to well‐studied eukaryotic proteins the signalling pathways of these cellular regulators, with the exception of NodQ, have not yet been eluci

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00845.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryA randomly generated mutation inEscherichia colialanine tRNA synthetase compensates for a mutation in its cognate tRNA. The enzyme's mutation occurs next to a Cys‐X2‐Cys‐X6‐His‐X2‐His metal‐binding motif that is distinct from the zinc finger motif found in some DNA‐binding proteins. Instead, the synthe‐tase's metal binding domain resembles the Cys‐X2‐Cys‐X4‐His‐X4‐Cys metal‐binding domain of the gag gene product of retroviruses. For Ala‐tRNA synthetase, the metal bound at the Cys His motif is important specifically for the tRNA‐dependent step of catalysis, and the enzyme‐tRNA interaction is dependent on the geometry of metal co‐ordiNatlon to the enzyme. These data, and the demonstrated sensitivity of RNA packaging to mutations in the metal‐binding domain of thegaggene product of retroviruses, suggest that an aminoacyl‐tRNA synthetase and retroviruses have adopted a rela

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe SOS response ofEscherichia colihas become a paradigm for the study of inducible DNA repair and recombination processes in many different organisms. While these studies have demonstrated that the components of the SOS response appear to be highly conserved among bacterial species, as with most models, there are some significant variations. Perhaps the best example of this comes from an analysis of the SOS‐like system of the developmental organism.Bacillus subtilis.Accordingly, the most striking difference is the complex developmental regulation of the SOS system as this organism differentiates into its competent state. In this review we have given an overview of the elements that comprise the SOS system ofB. subtilis.Additionally, we have summarized our most recent findings regarding the regulation of this regulon. Using these results along with new findings from other laboratories we have provided provocative molecular models for the regulation of theB. subtilisSOS system in response to DNA damage and during competent cell formatio

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00847.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe effect of variations inNeisseria meningitidispili on bacterial interactions with three epithelial cell lines as well as human umbilical vein endothelial cells was studied using a panel of seven strains expressing Class I or Class II pili. Comparison of adherence of piliated and pilus‐deficient variants of each strain to epithelial cells suggested that Class I pili may mediate bacterial adherence with all three epithelial cell lines. In contrast, Class II pili of the strains used did not increase bacterial adherence to Hep‐2 larynx carcinoma cells, although an increase in adherence to Chang conjunctival and A549 lung carcinoma epithelial cells was observed in the Class II pili‐expressing strains. In addition to these inter‐class functional variations, differences in adherence to epithelial cells were also observed among Class I and Class II strains. Functionally different pilin variants of one Class I strain, MC58, were obtained by single colony isolation. One piliated variant was identified which had concurrently lost the ability to adhere to both Chang and Hep‐2 cells (‘non‐adherent’ phenotype; adherence of<2 bacteria per cell). In addition, several adherent pilin variants were isolated from non‐adherent Pil‐and Pil‐bacteria by selection on Chang cells (adherence of 10–25 bacteria per cell). In contrast to epithelial cells, al) variant pili, whether of Class I or Class II, adhered to endothelial cells in substantially larger numbers (<50 bacteria per cell) and therefore implied the existence of distinct mechanisms in pilus‐facilitated interactions ofN. meningitidiswith endothe

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00848.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryA segment of the exotoxin A gene ofPseudomonas aeruginosa, coding for the N‐terminal end of domain I and domain II of the toxin (ETA), was genetically fused to the diphtheria toxin gene ofCorynebacterium diphtheriae, coding for the N‐terminal end of A fragment of diphtheria toxin (DT). The resulting hybrid protein (termed CED1) was produced in large amounts and exported to the periplasm inEscherichia coli.This chimaeric protein reacted with both anti‐ETA and anti‐DT antisera. Furthermore, the chimaeric protein displayed ADP‐ribosylation activity and exhibited cytotoxicity to mouse 3T6 fibroblasts. These results demonstrated that the chimaeric protein is cytotoxic, and that the toxic potential of DTA can be selectively internalized and translocated via domains I and II of exotoxin A, which are thus sufficient to direct and translocate an enzymatically active heterologous polypeptide segment into the cytosol of sensit

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00849.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryWe have developed a system of transposon mutagenesis for bacteriophage T4. The transposon is a plasmid derivative of Tn5 which contains the essential T4 gene24, permitting a direct selection for transposition events into a gene 24‐deteted phage. The transposition occurred at a frequency of only 10‐7per progeny phage, even though adam‐host was used to increase transposition frequency. Phage strains with a transposon insert were distinguished from most pseudorevertants of the gene24deletion by plaque hybridization using a transposon‐specific probe. Mapping analysis showed that the transposon inserts into a large number of sites in the T4 genome, probably with a preference for certain regions. The transposon insertions in four strains were analysed by DNA sequencing using primers that hybridize to each end of the transposon and read out into the T4 genome. In each case, a 9 bp T4 target sequence had been duplicated and the insertions had occurred exactly at theIS50ends of the transposon, demonstrating that bona fide transposition had occurred. Finally, the transposon insert strains were screened on the TabGEscherichia colistrain, which inhibits the growth of T4motAmutants, and amotAtransposon insert strain wa

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00850.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe expression of several neighbouring genes on plasmid pAD1 that are necessary for conjugation depend on induction with sex pheromone CAD1. Analyses of transcripts by Northern blot hybridization demonstrated that the genesseal(encoding surface exclusion protein) andasa 1(encoding aggregation substance) are transcribed independently. Both genes are organized in different operons together with neighbouring open reading frames of unknown function. Several transcripts could be identified forsealandasa1.Their transcriptional start sites were determined by primer extension experiments, confirming the results of the Northern blot experiments. We also could identifyseal‐andiad‐(encoding an inhibitory peptide counteracting sex pheromone CAD1) specific transcripts which are expressed constitutively, but to a lower extent relative to induced conditions. In addition, we localized theasp1gene coding for aggregation substance of sex pheromone plasmid pPD1 and determined its DNA sequence, which was found to be highly homologous toasa1(aggregation substance gene of pAD1) andprgB(aggregation substance gene of pCFiO). The structural genes were found to be organized more or less identically on the three sex‐pheromone plasmids pAD1, pCF10, and pPD1, and to be highly conserved. Regions supposed to be of crucial importance for regulatory functions, however, were found to differ. We also could identify some conserved DNA motifs which might be potential target sites for transcriptional regulators. In combination these data allowed us to formulate a model for the regulation of sex‐pheromone‐induclble genes of plasmid pAD1. Its main statement is that only in the presence of cAD1 can the genetraE1be transcribed. The positive regulatory factor TraE1 then can trigger expression of the structural genesse

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00851.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe gene for the high‐affinity outer membrane ferrioxamine receptor FoxA ofYersinia enterocoliticawas cloned inEscherichia coliK‐12. AfoxAmutant ofYersiniacould be complemented by the cloned DNA fragment. The FoxA encoding region was sequenced and an open reading frame encoding 710 amino acids, including a signal sequence of 26 amino acids, was deduced. The mature FoxA protein consisted of 684 amino acids and had a molecular mass of 75768 Da. FoxA shared 33% amino acid sequence homology with FhuA, the ferrichrome receptor ofEscherichia coli.Based on the homologies with FhuA and other TonB‐dependent receptors a topological model of FoxA is pres

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00852.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe permeability of bacterial outer membranes was assayed by coupling the influx of highly hydrophobic probes, 3‐oxosteroids, with their subsequent oxidation catalysed by 3‐oxosteroid δ1‐dehydrogenase, expressed from a gene cloned fromPseudomonas testosteroni.InSalmonella typhimuriumproducing wild‐type lipopolysaccharide, the permeability coefficients for uncharged steroids were 0.45 to 1 × 10‐5cm S‐1and the diffusion appeared to occur mainly through the lipid bilayer domains of the outer membrane. These rates are one or two magnitudes lower than that expected for their diffusion through the usual biological membranes. The permeation rates were markedly increased (up to 100 times) when the lipopolysaccharide leaflet was perturbed either by adding deacylpolymyxin or by introducing mutations leading to the production of deep rough lipopolysaccharides. An amphiphilic, negatively charged probe, testosterone hemisuccinate, penetrated much more slowly than the uncharged steroids. Study of various Gram‐negative species revealed thatP. testosteroni, Pseudomonas acidovorans, andAcinetobacter calcoaceticusshowed higher outer membrane permeability to steroid probes and higher susceptibility to hydrophobic agents such as fusidic acid, novobiocin and crystal violet relative to S.typhimuriumandE

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00853.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe nucleotide sequence of a 3.1 kb segment carrying the cytosjne deaminase gene (codA) fromEsctierichia coliwas determined. The sequence revealed the presence of two open reading frames, the first (codB) specifying a highly hydrophobic polypeptide and the second specifying cytosine deaminase. A two‐codon overlap between the two reading frames indicates that they constitute an operon. Transcription of the operon was found to be regulated by exogenous purines. Polypeptides specified by each of the two reading frames were expressed in minicells, and thecodBgene product was found to be highly enriched in the membrane fraction. Uptake experiments showed that the CodB protein is required for cytosine transport into the cell and that the intracellular accumulation of cytosine correlated with thecodBgene dose. A topological model for the cytosine permease in the cytoplasmic membrane is propose

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00854.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY