摘要:

SummaryAt least 18 aminoacyl‐tRNA synthetase and amino acid biosynthesis genes in several Gram‐positive genera appear to be regulated by a common transcription anti‐termination mechanism. Each gene is induced by limitation for the appropriate amino acid, and not by general amino acid limitation. The mRNA leader regions of these genes exhibit extensive structural conservation. haracterization of theBacillus subtilis tyrSgene revealed that uncharged tyrosyl‐tRNA promotes readthrough of a leader‐region terminator; a conformational switch in the leader mRNA between a terminator structure and an antiterminator structure is postulated to mediate antitermination. Two sites of interaction between the tRNA and the leader have been identified by genetic analysis: the tRNA anti‐codon interacts with a single codon displayed at a precise position in the leader‐region structure, and the acceptor end of the tRNA interacts with a side‐bulge on the

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00432.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummarySwarming is a form of activesurfacemotility that is widespread among flagellated. Gram–negative bacteria. In the laboratory, growth of the bacteria on certain agar surfaces leads to induction of the differentiated swarmer‐cell state. Swarmer cells are generally long and multinucleate, always hyperflagellated, and can move rapidly over the agar surface in a coordinated manner. Some swarm colonies exude large amounts of ‘slime’, which could be essential for promoting intimate cell–cell contacts during swarming. There is evidence that the differentiated swarmer‐cell stage facilitates pathogenic associations with host tissue. Almost nothing is known about the molecular signalling mechanism of surface sensing. Increased viscosity appears to be sensed by several bacteria, but other environmental cues, specific to each bacterium, are also important. In organisms in which swarming motility has been studied in some detail, the chemotaxis system has been shown to play an important rote. The recent discovery of swarming motility in two genetically well‐characterized organisms –Escherichia coliandSalmonella typhimurium– should lead to rapid progress in understan

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00433.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe Gram‐positive bacteriumListeria monocytogenesis a facultative intracellular parasite that invades and multiplies within diverse eukaryotic cell types. An essential pathogenicity determinant is its ability to move in the host cell cytoplasm and to spread within tissues by directly passing from one cell to another. The propulsive force for intracellular movement is thought to be generated by continuous actin assembly at the rear end of the bacterium. Moving bacteria that reach the plasma membrane induce the formation of long membranous protrusions that are internalized by neighbouring cells, thus mediating the spread of infection. The unrelated pathogensShigellaandRickettsiause a similar process of actin‐based motility to disseminate in infected tissues. This review focuses on the bacterial and cellular factors involved in the actin‐based motility of Lmonocyto

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00434.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryPili ofNeisseria gonorrhoeaeare correlated with Increased bacterial attachment to epithelial cells and undergo both phase and antigenic variation. Phase variation of gonococcal pili can be brought about by recombination events in the pilin structural gene,pilE, or by the on/off switch in expression of PilC, a pilus biogenesis protein for which two loci exist. We have studied the binding to epithelial cell lines and to fixed tissue sections ofN. gonorrhoeaeMS11 derivatives and mutants carrying structurally defined PilE and PilC proteins,in situbinding studies ofN. gonorrhoeaeto formalin‐fixed tissue sections resulted in a binding pattern similar to that obtained using viable epithelial cell lines of different origin. Piliated gonococcal clones, containing differentpilEsequences, varied dramatically from one another in their efficiencies at binding to corneal and conjunctival tissue, but bound equally well to cervical and endometrial tissues. Further, the binding data suggested that PJIC expression by itself, i.e. without pili, cannot confer bacterial binding and that expression of either PilC1 or PiiC2 does not confer different binding properties to the bacterial cells. Possible receptors for piliated gonococci were expressed in human tissues, such as cervix, endometrium, cornea, intestine, stomach, mid‐brain and meninges, but not in human kidney. Pretreatment of the target tissues with Proteinase K decreased the gonococcal binding dramatically, whereas pretreatment with neuraminidase and meta‐periodate, which cleave carbon‐carbon linkages between vicinal hydroxyl groups in carbohydrates, did not affect attachment of gonococci. These data argue that pilus‐dependent attachment ofN. gonorrhoeaeto human tissue may be mediated by a eukaryotic receptor having protein characteristics, and that the pilus subunit sequence may play an important role in the interaction with hum

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00435.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummarySporulation inBacillus subtilisdepends on an intact oligopeptide transport system, the Opp system. Mutants inoppsporulate poorly but second‐site revertants can be found that restore sporulation and pep‐tide transport. These second‐site mutations were found in a second oligopeptide transport system,app, in which the peptide‐binding protein, AppA, is mutant owing to a frame‐shift mutation, and the revertants restore the original frame. The AppA mutation is present in the 168 strain of B.subtilis.Theappoperon consists of five genes in the orderappD‐appF‐appA‐appB‐appC, with the locus designations corresponding to their homologue in theoppoperon. Homology between theappandoppproteins ranges from 54% identity for AppF and OppF, to 22% identity for AppA and OppA. Both the App and Opp permease systems can transport tetra‐ and pentapeptides, but tripeptides are not transported by the App system. Strains of the genotypeapp+opp−are resistant to the tripeptide antibiotic bialaphos. The repaired App system can substitute completely for the Opp system in both sporulation and competence for genetic transformation. The pheno‐types raised some speculation about the subunit configur

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00436.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryStrains ofPseudomonas aeruginosainitially isolated from patients with cystic fibrosis (CF) often express a smooth lipopolysaccharide (LPS) containing many long O side‐chain antigens, but once a chronic infection is established, strains recovered from these patients express little or no LPS O antigen. The genetic basis for this loss of O antigen expression byP. aeruginosaCF isolates is unknown. We report here that 20 CF isoiates ofP. aeruginosa, 13 of which are LPS‐rough, were each capable of expressing serogroup 011 antigen when provided with therfbiocus fromP. aeruginosaserogroup 011 strain PA103 on the recombinant plasmid pLPS2. Eight of the thirteen LPS‐rough isolates co‐expressed another, presumably endogenous, O antigen when they contained pLPS2. Different subcloned regions of pLPS2 complemented distinct strains to restore endogenous O antigen expression. These data suggest that the loss of O antigen expression byP. aeruginosaCF isolates results from alterations specific to therfbregion, and is not due to mutations involving other loci or ancillary LP

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00437.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryTheEscherichia coliregulatory proteins, EnvZ and OmpR, are crucially involved in expression of the outer membrane proteins OmpF/OmpC in response to the medium osmolarity. The EnvZ protein is presumably a membrane‐located osmotic sensor (or signal transducer), which exhibits both kinase and phosphatase activities specific for the OmpR protein. To examine the functional importance of the membrane‐spanning segments (named TM1 and TM2) of EnvZ molecules in transmembrane signalling, a set of EnvZ mutants, each having amino acid substitutions within the membrane‐spanning regions, was characterized in terms of both theirin vivophenotype andin vitrocatalytic activities. One of them, characterized further, has an amino acid change (Pro‐41 to Ser or Leu) In TM1, and appeared to be defective in its phosphatase activity but not in its kinase activity. This EnvZ mutant conferred a phenotype of OmpF−/OmpC‐constitutive. For this EnvZ(P41S or P41L) mutant, a set of intragenic suppressors, each exhibiting a wild‐type phenotype of OmpF+/OmpC+, was isolated. These suppresor mutants were revealed to have an additional amino acid change within either TM1 or TM2. Furthermore, they exhibited restored phosphatase activity (i.e., both kinase+and phosphatase+activities). It was further demonstrated that one of the suppressors, EnvZ(Arg‐180 to Trp in TM2), was able to suppress the defects in both thein vivophenotype and thein vitrocatalytic activities caused by EnvZ(P41S), through intermolecular complementation. These results are best interpreted as meaning that an intimate intermolecular interaction between the membrane–spanning segments of EnvZ is crucial for transmembrane signallingper sein response to an external

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00438.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryEscherichia colimutants,(verA, dilA)specifically resistant to the Ca2+channel inhibitors verapamil and diltiazem, respectively, are hypersensitive to EGTA and BAPTA. We have shown, using 1‐D and 2‐D gel electrophoresis, that the synthesis of at least 25 polypeptides in the mutants was enhanced by treatment with Ca2+chelators and the synthesis of at least 11 polypeptides was repressed. This pattern of induction was not observed in heat‐ or SDS‐treated cells and therefore does not appear to be a general stress response. The majority of the induced proteins are low molecular weight, extremely heat stable and acidic, characteristic properties of calmodulin. Moreover, of the major induced species, three with apparent molecular masses of 12, 18, and 34kDa all cross‐reacted with polyclonal and monoclonal antibodies to eukaryote calmodulins or calerythrin, a heat‐resistant Ca2+‐binding protein fromSaccharo‐polyspora erythraea.TheverA, dilAmutants. In being hypersensitive to EGTA and to the Ca2+ionophore A23187 + Ca2+, may be defective in the regulation of the level of free int

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00439.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe major bacterial histone‐like protein HU is a small, basic, dimeric protein composed of two closely related subunits. HU is involved in several processes in the bacterial cell such as the initiation of replication, transposition, gene inversion and cell division. It has been suggested that HU could introduce structural changes to the DNA which would facilitate or inhibit the binding of regulatory proteins to their specific sites. In this study we investigated the effect of HU on the binding of LexA protein, the regulator of SOS functions, to three of its specific binding sites. We show that HU can displace LexA from its binding sites on the operators of thelexA, recAandsfiAgenes. ThelexAoperator was the most sensitive while the higher affinitysfiAoperator was the least sensitive. Since HU, like its homologue IHF, probably binds DNA in the minor groove we tested the effect of distamycin, a drug which binds to the minor groove, on LexA binding. Like HU, this drug disrupted LexA–operator complexes. These results suggest that distortion of the minor groove of thelexAoperators excludes the binding of the repressor to the major gro

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00440.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryOwing to rapid proteolysis of the coliphage λ‐coded initiator protein, λ O, this protein is considered to carry a rate–limiting step in λ DNA replication. The discovery of ClpXP protease responsible for λ O protein turnover allowed an opportunity to verify this hypothesis. However, neither absence nor excess of this protease significantly affected the transformation efficiency and copy number of λ plasmid, or the Kinetics of the λ phage growth. These results are also incompatible with the hypothesis that the stabilization of λ O plays a role in the switch from early (circle‐to‐circle) to late (rolling‐circle) λ phage DNA replication. Tran‐scriptional activation oforiλprobably assisted by theEscherichia coliDnaA function, remains as the possible rate‐limiting ste

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00441.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY