摘要:

SummarySalmonella typhimuriumgrown under oxygen‐limiting conditions were found to enter into, elicit actin filament rearrangement in, and effect morphological changes upon HEp‐2 cells within 15 min after infection. Video microscopy revealed that host cell morphological changes associated with entry began within 1 min of productive adherence. Polarized Caco‐2 cell morphology was affected 40 s after infection with low‐oxygen‐grownS. typhimurium.Stationary‐phaseS. typhimuriumdid not elicit these phenomena within this time‐period even when adherence was enhanced with the afimbrial adhesin, AFA‐I. Thus, environmental cues regulateS. typhimuriuminvasion factors, allowing for immediate entry into host cells. Additionally, actin filament rearrangement and morphological changes in the eukaryotic host cell are essential for entry and occur within minut

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01765.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryTrypanothione reductase belongs to the family of flavoprotein disulphide oxidoreductases that include glutathione reductases, dihydrolipoamide dehydrogenases and mercuric reductases. Trypanothione reductase and its substrate, trypanothione disulphide, are unique to parasitic trypanosomatids responsible for several tropical diseases. The crystal structure of the enzyme fromCrithidia fasciculatais currently under investigation as an aid in the design of selective inhibitors with a view to producing new drugs. We report here the cloning and sequencing of the genes for trypanothione reductase fromC. fasciculataandTrypanosoma brucei.Alignment of the deduced amino acid sequences with 21 other members of this family provides insight into the role of certain amino acid residues with respect to substrate specificity and catalytic mechanism as well as conservation of certain elements of secondary structure.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01766.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe 2μm plasmid encodes a mechanism that ensures the partitioning of the plasmid at cell division. Little is known about the detailed mechanism of this partitioning system; for example, is there equal or unequal distribution of the plasmid molecules at mitosis? The plasmid also encodes a site‐specific recombination system that is thought to be involved in plasmid copy‐number amplification, although to date there has been no direct evidence that the recombination process itself is important for maintenance. We have identified a natural 2μm variant that has acis‐acting mutation in the FLP‐mediated recombination system. We show that this plasmid is unable to amplifyin vivo.Our results demonstrate that the average copy number per cell is not affected for the mutant but there is a large clonal variation. This is a direct demonstration that plasmid partitioning results in an unequal distribution of plasmids and that FLP‐mediated amplification compensates for this and therefore has an important role in

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01767.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThree genes fromPseudomonas aeruginosainvolved in threonine biosynthesis,hom, thrBandthrC, encoding homoserine dehydrogenase (HDH), homoserine kinase (HK) and threonine synthase (TS), respectively, have been cloned and sequenced. ThehomandthrCgenes lie at thethrlocus of theP. aeruginosachromosome map (31 min) and are likely to be organized in a bicistronic operon. The encoded proteins are quite similar to the Hom and TS proteins from other bacterial species. ThethrBgene was located by pulsed‐field gel electrophoresis experiments at 10 min on the chromosome map. The product of this gene does not share any similarity with other known ThrB proteins. No phenotype could be detected when the chromosomalthrBgene was inactivated by an insertion. Therefore the existence of isozymes for this activity is postulated. HDH activity was feedback inhibited by threonine; the expression of all three genes was constitutive. The overall organization of these three genes appears to differ from that in other bacterial specie

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01768.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThealkBFGHJKLandalkSToperons encode enzymes that allowPseudomonas putida (oleovorans)to metabolize alkanes. In this paper we report the nucleotide sequence of a 4592 bp region of thealkBFGHJKLoperon encoding the AlkJ, AlkK and AlkL polypeptides.ThealkJgene encodes a protein of 59 kilodaltons. The predicted amino acid sequence shows significant homology with four flavin proteins: choline dehydrogenase, a glucose dehydrogenase and two oxidases. AlkJ is membrane‐bound and converts aliphatic medium‐chain‐length alcohols into aldehydes. The properties of AlkJ suggest that it is linked to the electron transfer chain. AlkJ is necessary for growth on alkanes only inP. putidaalcohol dehydrogenase (AlcA) mutants.AlkK is homologous to a range of proteins which act by an ATP‐dependent covalent binding of AMP to their substrate. This list includes the acetate, coumarate and long‐chain fatty acid CoA ligases. ThealkKgene complements afadDmutation inEscherichia coli, which shows that it indeed encodes an acyl‐CoA synthetase. AlkK is a 60 kilodalton protein located in the cytoplasm.AlkL is homologous to OmpW, aVibrio choleraeouter membrane protein of unknown function, and a hypothetical polypeptide encoded byytt4inE. coli.AlkL, OmpW and Ytt4 all have a signal peptide and end with a sequence characteristic of outer membrane proteins. ThealkLgene product was found in the outer membrane ofE. coliW3110 containing thealk‐genes.ThealkLgene can be deleted without a clear effect on growth rate. Its function remains unknown.The G+C content of thealkJKLgenes is 45%, identical to that of thealkBFGHgenes, and significantly lower than the G+C content of the OCT‐plasmid and theP. p

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01769.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryWe studied the symbiotic behaviour of 20 independent Tn5 mutants ofRhizobium tropicistrain CIAT899 that were deficient in exopolysaccharide (EPS) production. The mutants produced non‐mucoid colonies, were motile, grew in broth cultures at rates similar to those of the parent, and produced significantly less EPS than did CIAT899 in broth culture. A genomic library of strain CIAT899, constructed in pLA2917, was mobilized into all of the mutants, and cosmids that restored EPS production were identified. EcoRI restriction digests of the cosmids revealed nine unique inserts. Mutant complementation and hybridization analysis showed that the mutations affecting EPS production fell into six functional and physical linkage groups. On bean, the mutants were as efficient in nodulation and as effective in acetylene reduction as strain CIAT899, induced a severe interveinal chlorosis, and all but one were less competitive than CIAT899. On siratro, CIAT899 induced nodules that were ineffective in acetylene reduction, whereas the EPS‐deficient mutants induced effective nodules. Microscopic examination of thin sections showed that nodules from both siratro and bean plants inoculated with either CIAT899 or an EPS‐deficient mutant contained infected cells. These data indicate that EPS is not required for normal nodulation of bean byR tropici, that it may contribute to competitiveness ofR. tropicion bean, and that the loss of EPS production is accompanied by acquisition of the ability to reduce acetylene on si

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01770.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryWe have studied the molecular mechanism of the negative regulation byflgMof the late operons of the flagellar regulon ofSalmonella typhimurium.A 7.8 kDa protein that was identified as theflgMgene product was purified to homogeneity; its amino‐terminal sequence was identical to the deduced sequence except for the lack of the initiating methionine. The purified FlgM repressed transcription from thefliCpromoter, one that is activated by the sigma factor, FliA (σF). No DNA‐binding activity was detected in FlgM. Chemical cross‐linking experiments showed that the purified FlgM bound to σFand disturbed Its ability to form a complex with RNA polymerase core enzyme. These results indicate that FlgM is a novel type of negative regulator that probably inactivates the flagellum‐specific sigma factor through direct interaction, i.e. it is an anti‐s

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01771.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryA mutant ofRhodobacter sphaeroides, N1, has been isolated which is incapable of photosynthetic growth and, instead of synthesizing bacteriochlorophyll, N1 excretes coproporphyrin III into the growth medium. Using conjugative gene transfer, several clones were isolated from aR. sphaeroidesgene library which restored normal pigment synthesis and photosynthetic growth to N1. Using transposon Tn5 mutagenesis, the gene was located to a 1.05 kbEcoRI fragment. Sequence and transcription analysis defined the position and expression of an open reading frame of approximately 920 bp, which is proposed as the anaerobic coproporphyrinogen III oxidase dedicated to bacteriochlorophyll biosynthesis.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01772.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThepucoperon ofRhodobacter sphaeroidesencoding polypeptides of the major light‐harvesting complex, LH2, has been found to be linked tohemF, a gene encoding a putative anaerobic coproporphyrinogen III oxidase. Thepuc‐hemFregion of theR. sphaeroidesgenome has been investigated by insertional mutagenesis, complementation analysis of these insertional mutants and DNA sequencing. A third gene, designatedpucC, has been found immediately downstream ofpucAand has been shown to be essential for LH2 expression.pucCis cotranscribed withpucBandpucA; however,hemFand thepucBACoperon were found not to be transcriptionally linked. Ultrastructural studies indicated that the morphology of the intracytoplasmic membrane may depend upon expression ofpucCas well aspu

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01773.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe response of non‐differentiating bacteria to nutrient starvation is complex and includes the sequential synthesis of starvation‐inducible proteins. Although starvation for different individual nutrients generally provokes unique and individual patterns of protein expression, some starvation stimulons share member proteins. Two‐dimensional polyacrylamide gel electrophoresis revealed that the synthesis of a small (13.5 kDa) cytoplasmic protein inEscherichia coliwas greatly increased during growth inhibition caused by the exhaustion of any of a variety of nutrients (carbon, nitrogen, phosphate, sulphate, required amino acid) or by the presence of a variety of toxic agents including heavy metals, oxidants, acids and antibiotics. To determine further the mode of regulation of the protein designated UspA (üniversal stress pUrotein A) we cloned the gene encoding the protein by the technique of reverse genetics. We isolated the protein from a preparative two‐dimensional polyacrylamide gel, determined itsN‐terminal amino acid sequence, and used this sequence to construct a degenerate oligonucleotide probe. Two phages of the Kohara library were found to contain the gene which then was subcloned from the DNA in the overlapping region of these two clones. The amino acid sequence, deduced from the nucleotide sequence of theuspAgene, shows no significant homology with any other known protein. TheuspAgene maps at 77 min on theE. coliW3110 chromosome, and is transcribed in a clockwise direction. The increase in the level of UspA during growth arrest was found to be primarily a result of transcriptional activation of the corresponding gene. The induction was independent of the RelA/SpoT, RpoH, KatF, OmpR, AppY, Lrp, PhoB and H‐NS proteins during stress conditions that are known to induce or activate these global regulators. The ‐10 and ‐35 regions upstream of the transcriptional start site of theuspAgene are characteristic of a σ70

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01774.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY