摘要:

SummaryThe lactose‐controlling elements have been considered to be the simple paradigm of acis‐acting genetic regulatory system, containing a promoter whose activity is modulated by an operator and a catabolite gene activator protein (CAP)‐binding site. The reality is considerably more complex. We now know that transcription is negatively regulated as a result of the repressor binding to three binding sites: the operator, a secondary repressor‐binding site within thelacZgene and a tertiary repressor‐binding site upstream nearlacl.In addition to the promoter, thelac‐controlling elements contain five promoter‐like elements. The physiological role, if any, of these promoter‐like elements is not clear, although three of them can be activated by single base pair changes to give high levels ofin vivoexpression. Finally, the positive activator protein CAP has been found to bind to a secondary site which is coincident with the operator. No role has been identified for this secondary

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01416.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryGenetic approaches can address the question of how integral membrane Sec factors interact with each other and facilitate protein translocation across the cytoplasmic membrane ofE. coli.This review summarizes genetic analyses of SecY, SecE and some other protein translocation factors, utilizing ‘prl’ mutations,‘sec’ mutations, ‘suppressor‐directed inactivation’, ‘Sec titration’, dominant negative mutations and their suppressors. Evidence suggests that coordinate participation of SecY, SecE, SecD, SecF, and probably some other factors, is crucia

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01417.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryPyelonephritis‐associated pilus (Pap) expression is regulated by a phase variation control mechanism involving PapB, Papl, catabolite activator protein (CAP), leucine‐responsive regulatory protein (Lrp) and deoxyadenosine methylase (Dam). Lrp and Papl bind to a specific non‐methylatedpapregulatory DNA region containing the sequence ‘GATC’ and facilitate the formation of an active transcriptional complex. Evidence indicates that binding of Lrp and Papl to this region inhibits methylation of the GATC site by Dam. However, if this GATC site is first methylated by Dam, binding of Lrp and Papl is inhibited. These events lead to the formation of two differentpapmethylation states characteristic of active (ON) and inactive (OFF)paptranscription states. Thefae(K88),daa(F1845) andsfa(S) pilus operons share conserved ‘GATC‐box’ domains withpapand may be subject to a similar regulatory control mechanism involving Lrp and

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01418.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummarySurvival of cells in their natural environment is crucially dependent on their ability to adapt to constantly occurring changes. The ability of cells to respond to extremes of environmental influences is vital to survival. Proteolysis is a central cellular tool in stress response. Proteins of pathways necessary for normal growth, but harmful under stress conditions, as well as proteins damaged by stress have to be eliminated. The yeastSaccharomyces cerevisiae, a model eukaryote, has evolved two different proteolytic systems: (i) a membrane‐enveloped, vacuolar (lysosomal) system, which contains a variety of non‐specific peptidases and (ii) highly specific peptidases residing at different cellular locations. The best characterized peptidase of the specific system is proteinase yscE, the proteasome equivalent found in all eukaryotic cells. Both the vacuolar and the non‐vacuolar systems are vital components of the stress response in

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01419.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryCurli are thin, coiled, temperature‐regulated fibres on fibronectin‐bindingEscherichia coli.The subunit protein of curli was highly homologous at its amino terminus to SEF‐17, the subunit protein of thin, aggregative fimbriae ofSalmonella enteritidis27655 strain 3b, suggesting that these fibres form a novel class of surface organelles on enterobacteria.E. coliHB101 is non‐curliated and unable to bind soluble, iodinated fibronectin. The phenotypically cryptic curlin subunit gene,csgA, in HB101 is transcriptionally activated by expressing the cytoplasmic Crl on a multicopy plasmid. Transcriptional activation ofcsgAby Crl was observed after growth at 26°C but not at 37°C, even thoughcrltranscription was not thermoregulated. A deletion of the 39 carboxy‐terminal residues abolished Crl activity, whereas a deletion of 10 residues at theC‐terminus did not, implying that a region between residue 93 and 122 in the 132‐amino‐acid‐residue large Crl protein is required for activating curli expression inE. coliHB101.crlis a normal housekeeeping gene inE. coliand it is suggested that its gene product may either be a DNA‐binding protein affecting chromatin structure as has been suggested for histone‐like protein H1 or interact with specific regulatory protein(s) controlling transcription of genes required for curli formation

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01420.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe streptomycin‐ and spectinomycin‐resistance gene ofSalmonella choleraesuiswas cloned and its nucleotide sequence determined. The gene is 789 bases long, encoding a protein of a predicted size of 29353 Da. The gene product inactivated streptomycin and spectinomycin by an adenylation modification. It is homologous (c.40% total identity) to streptomycin adenylyltransferase, a 3′ (9)‐O‐nucleotidyltransferase (AAD(3′)(9)), which is encoded by theaadA gene inEscherichia coli, Agrobacterium tumefaciens, Kiebsiella pneumonia, andSerratia marcescens.The AadA protein ofS. choleraesuisdiffers significantly from the other AadA proteins, indicating that it may have diverged from the other members of this family earlier in evolution. Southern hybridization analysis revealed that homologousaadA sequences were also present in other streptomycin‐resistantSalm

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01421.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryResistance to third‐generation cephalosporins in a clinical isolate ofStreptococcus pneumoniaewas shown to be due to the production of altered forms of penicillin‐binding proteins (PBPs) 2X and 1A. The cloned PBP2X gene from the resistant strain was able to transform a susceptible strain to an intermediate level of resistance. The resulting transformant could be transformed to the full level of resistance of the clinical isolate using the cloned PBP1A gene from the latter strain. Chromosomal DNA from the resistant strain (and from other resistant strains) could readily transform a susceptible strain to the full level of resistance to third‐generation cephalosporins (>250‐fold for cefotaxime;>100‐fold for ceftriaxone) in a single step (transformation frequency of about 10‐5). The resistant transformants obtained with chromosomal DNA were shown by gene fingerprinting to have gained both the PBP1A and PBP2X genes from th

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01422.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryBacterial cells possess a subset of genes whose expression correlates with changes in DNA supercoiling brought about by anaerobic growth and by growth at high osmolarity. It has been shown previously that expression of the histidine biosynthetic operon ofSalmonella typhimuriumis derepressed by relaxation of supercoiled DNA. Here, we confirm that ahis:: MudJ operon fusion inS. typhimuriumcan be induced by treatment with the DNA gyrase inhibitor novobiocin in a dose‐dependent manner, and show that the level of derepression is higher in stationary phase than in mid‐exponential phase cultures. Furthermore, expression ofhisis repressed by anaerobiosis and by osmolarity, two environmental parameters which increase the negative supercoiling of bacterial DNA. Novobiocin induction ofhisis also repressed by growing the cells either at high osmolarity or anaerobically. Both environmental repression and novobiocin induction ofhisrequire thehisattenuator. In addition, derepression ofhisexpression by novobiocin and its repression by anaerobiosis or osmolarity are independent of the stringent response gene, r

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01423.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryFollowing treatment with nitrosoguanidine, mutant derivatives ofRhizobium leguminosarumstrain 3841 were isolated which failed to react with AFRC MAC 203. This monoclonal antibody normally recognizes a strain‐specific lipopolysaccharide epitope which is developmentally regulated during legume nodule differentiation. Structural modification of lipopolysaccharide (LPS) was analysed by examining reactivity with a range of monoclonal antibodies with different epitope specificities, and also by analysis of LPS mobility changes after electrophoresis on polyacrylamide gels. One class of these LPS‐defective mutants induced normal nitrogen‐fixing (Fix+) nodules on peas (Pisum sativum), while another two classes of Fix‐mutants were also identified, suggesting that a component of the LPS antigen that is part of the MAC 203 epitope is essential for normal nodule development leading to symbiotic nitrogen fixation. When grown under low‐oxygen or low‐pH culture conditions, one class of Fix‐mutants completely lacked LPS‐1 (the species that carries O antigen) and a second class showed a modified and truncated form of LPS‐1. Mutants with defective LPS structure were also obtained after Tn5mutagenesis of Rleguminosarum3841 and all nine Fix‐mutants were also found to lack the MAC 203 epitope. Three of these transposon‐induced mutants synthesized a truncated form of LPS‐1 that was structurally similar to that of the class of the NTG‐induced mutants described above. These transposon‐induced mutations, and the nitrosoguanidine‐induced Fix‐mutations, were closely linked and could be suppressed by the same cloned fragment of chromosomal DNA. The data presented here suggest that a precondition for normal nodule development ofR. leguminosarum3841 within pea nodules is the ability to synthesize relatively long‐chain LPS–1 macromolecules under the physiological conditions encountered within the nodule. All mutants that lacked the ability to elongate LPS‐1 macromolecules also

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01424.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryTranscription of theEscherichia coli crpgene is negatively regulated by CRP–cAMP that binds to a specific site located downstream of thecrppromoter. A second binding site for CRP–cAMP (CRP site II) exists upstream of thecrppromoter. Using anin vitrotranscription assay, we have demonstrated that CRP‐cAMP activates transcription ofcrpin certain conditions. A promoter which carries an altered CRP‐binding site II is no longer activated by CRP–cAMP, indicating that CRP site II mediates the activation ofcrptranscription. The concentrations of cAMP that are required for positive autoregulation are higher than those for negative autoregulation. Evidence for positive and negative autoregulationin vivois presented by a quantitative S1 nuclease

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01425.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY