摘要:

SummaryCopper ions are essential for bacteria but can cause a number of toxic cellular effects if levels of free ions are not controlled. Investigations of copper‐resistant bacteria have revealed several mechanisms, mostly plasmid‐determined, that prevent cellular uptake of high levels of free copper ions. However, these studies have also revealed that bacteria apparently have efficient chromosomally encoded systems for uptake and management of trace levels of copper. This review will explore the relationship of copper uptake systems to resistance mechanisms and the possibility that copper resistance has evolved directly through modification of chromosomal copper uptake ge

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01091.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryLegionella pneumophilamutants specifically defective for intracellular replication were isolated using an intracellular thymineless death enrichment strategy. Mutants belonging to two distinct phenotypic classes were unable to grow in macrophage‐like cultured cells. One class of mutants was defective for both inhibition of phagosome–lysosome fusion and association of host cell organelles with bacteria‐containing phagosomes (‘recruitment’). Another class of mutants was defective only for organelle recruitment, suggesting that recruitment may be necessary for intracellular growth. Recombinant clones were identified that complemented the intracellular growth defects of these mutants. A single genetic locus, designateddot(for defect in organelle trafficking), restored wild‐type phenotypes for intracellular growth, organelle recruitment, and inhibition of phagosome–lysosome fusion to mutants belonging to both pheno

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01092.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryWe describe the isolation and characterization of full‐length chromosomes from non‐culturable plant‐pathogenic, mycoplasma‐like organisms (MLOs). MLO chromosomes are circular and their sizes (640 to 1185kbp) are heterogeneous. Divergence in the range of chromosome sizes is apparent between MLOs in the two major MLO disease groups, and chromosome size polymorphism occurs among some related agents. MLO chromosome sizes overlap those of culturable mycoplasmas; consequently, small genome size alone cannot explain MLO non‐culturability. Hybridization with cloned MLO‐specific chromosomal and 16S rRNA probes detected two separate chromosomes in some MLO ‘type’ strains. Large DNA molecules that appear to be MLO megaplasmids were also demonstrated. The ability to characterize full‐length chromosomes from virtually any non‐culturable prokaryote should greatly facilitate the molecular and genetic analysis of these

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01093.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryInEscherichia coli, the binding protein‐dependent transport system for maltose and maltodextrins is composed of five proteins — LamB, MaIE, MaIF, MaIG and MaIK — located in the three layers of the bacterial envelope. Proteins MaIF and MaIG are hydrophobic inner membrane components mediating the energy‐dependent translocation of substrates into the cytoplasm. In this paper, we analyse the topology of the MaIG protein by using methods based on the properties of fusions betweenmaIGand‘phoA, a truncated gene encoding alkaline phosphatase lacking its translation initiation and exportation signals. Fusions were obtained by using either phage λTnphoAor by constructingin vitrofusions located randomly within themaIGgene. The deduced topological model suggests that MaIG spans the membrane six times and has its amino‐ and carboxy‐termini in the cytoplasm. These results will be helpful for the interpretation of the phenotypes of

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01094.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThemaIGgene encodes a hydrophobic cytoplasmic membrane protein which is required for the energy‐dependent transport of maltose and maltodextrins inEscherichia coli.The MalG protein, together with MalF and MalK proteins, forms a multimeric complex in the membrane consisting of two MalK subunits for each MalF and MalG subunit. Fifteen mutations have been isolated inmalGby random linker insertion mutagenesis. Two regions essential for maltose transport have been identified. In particular, a hydro philic region containing the peptidic motif EAA—G———I‐LP, highly conserved among inner membrane proteins from binding protein‐dependent transport systems, is essential for maltose transport.The results also show that several regions of MalG are not essential for function. A region (residues 30–50) encompassing the first predicted transmembrane segment and the first periplasmic loop in MalG may be modified extensively with little effect on maltose transport and no effect on the stability and the localization of the protein. A region located at the middle of the protein (residues 153–157) is not essential for the function of the protein. A region, essential for maltodextrin utilization but not for maltose transport, has been identified near theC‐term

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01095.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe universally distributed heat‐shock proteins (HSPs) are divided into classes based on molecular weight and sequence conservation. The members of at least two of these classes, the HSP60s and the HSP70S, have chaperone activity. Most HSP60s and many HSP70s feature a striking motif at or near the carboxyl terminus which consists of a string of repeated glycine and methionine residues. We have altered thegroELgene (encoding the essentialEscherichia coliHSP60 chaperonin) so that the protein produced lacks its 16 final (including ninegly, and fivemet) residues. This truncated product behaves like the intact protein in severalin vitrotests, the only discernible difference between the two proteins being in the rate at which ATP is hydrolysed. GroELtrcan substitute for GroELin vivoalthough cells dependent for survival on the truncated protein survive slightly less well during the stationary phase of growth. Elevated levels of the wild‐type protein can suppress a number of temperature‐sensitive mutations; the truncated protein lacks this ab

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01096.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe invasive phenotype ofShigella flexneriis conferred by a 220 kb virulence plasmid, pWR100, that encodes both the Ipa proteins, which are involved in the entry process, and factors which are required for the export and correct localization of the Ipa proteins. We have characterized the mxiD gene, whose expression, like that of theipaoperon, is regulated by temperature. After inactivation ofmxiD, the mutant strain was unable to invade HeLa cells and to provoke keratoconjunctivitis in guinea‐pigs. Analysis of culture supernatants indicated that wild‐typeS. flexnerisecretes about nine polypeptides and that secretion of several of these, including IpaA, IpaB, and IpaC, is abolished in themxiDmutant. Examination of the membrane proteins of the wild‐type andmxiDstrains suggested that MxiD is an outer membrane protein. Amino acid sequence comparison revealed that MxiD is homologous to the YscC protein ofYersinia enterocoliticaand to theC‐terminal region of the PulD protein ofKlebsiella pneumoniae.Both YscC and PulD are involved in extracellular protein secretion. These results indicate that MxiD is an essential component of the Ipa secretion ap

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01097.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryWe report the characterization of themsbAgene, isolated as a multicopy suppressor of the HtrB temperature‐sensitive phenotype. ThemsbAgene maps to 20.5 min on theEscherichia coligenetic map and encodes a protein with an estimated molecular mass of 64460 Da, with the properties of an integral membrane protein. The amino acid sequence of MsbA is very similar to those of the family of ATP‐dependent translocators, which includes the haemolysin B protein ofE. coliand the mammalian multidrug resistance (MDR) proteins. Mutational analysis ofmsbAindicates that it may form an operon with a downstream gene,orfE, and that both of these genes are essential for bacterial viability under all growth conditions tes

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01098.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryMutations truncating as many as 143C‐terminal residues from the transcriptional activator encoded by theareAgene, mediating nitrogen metabolite repression inAspergillus nidulans, do not significantly reduce the ability of theareAproduct to activate expression of most genes underareAcontrol. Such mutations can even have a gain‐of‐function, derepressed phenotype, consistent with a critical role for this region in modulating the activity of theareAprotein. However, expression of a few genes underareAcontrol is substantially impaired by suchC‐terminal truncations, indicating that regions of an activator protein can play differing roles in the control of different structural genes. This underlines the advantages of being able to monitor effects ofareAmutations on expression of large numbers of structural genes. Additionally, it is shown that truncation of as many as 153C‐terminal residues, virtually all amino acidsC‐terminal to the DNA‐binding region, is compatible with retention of som

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01099.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryOur laboratories have independently identified a gene inSalmonella choleraesuisandSalmonella typhimuriumthat is necessary for efficient adherence and entry of these organisms into cultured epithelial cells. Introduction of a mutated gene into severalSalmonellastrains belonging to different serotypes rendered these organisms deficient for adherence and invasion of cultured cells. This effect was most pronounced in the host‐adapted serotypesSalmonella gallinarum, S. choleraesuis, andSalmonella typhi.The nucleotide sequence of this gene, which we have termedinvH, encodes a predicted 147‐amino‐acid polypeptide containing a signal sequence. The InvH predicted polypeptide is highly conserved inS. typhimuriumandS. choleraesuis, differing at only three residues. TheinvHgene was expressed inEscherichia coliusing a T7 RNA polymerase expression system and a polypeptide of ∼16000 molecular weight was observed, in agreement with the predicted size of its gene product. Upon fractionation, the expressed polypeptide was localized in the bacterial membrane fraction. Southern and colony hybridization analyses indicated that theinvHgene is present in allSalmonellastrains tested (91 strains belonging to 37 serotypes) with the exception of strains ofSalmonella arizonae.No homologous sequences were detected inYersinia, Shigella, Proteus, and several strains of enteroinvasive and enteropathogenicE. coli.Downstream from theS. choleraesuis(but notS. typhimurium) invHgene, a region with extensive homology to the insertion sequence IS3was d

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01100.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY