ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00282.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe genetic code, once thought to be rigid, hag been found to be quite fiexible, permitting several different reading alternatives. One of these is translatlonal frameshifting, a process programmed in the mRNA sequence and which enables a +1 or ‐1 shift from the reading frame of the initiation codon. So far, the Involvement of translatlonal frameahifting in gene expression has been described mainly in viruses (particularly retroviruses), retrotransposons, and bacterial insertion elements, in thisMicroReview., we present a survey of the cellular genes, mostly inEscherichia coil, which have been found to be expressed through a transiational frameshifting process, as well as a discussion of the regulatory implications of this proces

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00283.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryRecent evidence from both biochemical and genetic studies indicates that protein targeting to the pro‐karyotic cytoplasmic membrane and the eukaryotic endoplasmic reticulum membrane may have more in common than previously thought. A ribonucleo‐protein particle was identified inEscherichia colithat consists of at least one protein (P48 or Ffh) and one RNA molecule (4.5S RNA), both of which exhibit strong sequence similarity with constituents of the mammalian signal recognition particle (SRP). Like the mammalian SRP, theE. coliSRP binds specifically to the signal sequence of presecretory proteins. Depletion of either P48 or 4.5S RNA affects translation and results in the accumulation of precursors of several secreted proteins. This review discusses these recent studies and speculates on the position of the SRP in the complex network of protein interactions involved in translation and membrane targeting inE. c

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00284.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryExtensive epidemiological analyses of epidemics of meningococcal meningitis have resulted in large, well‐defined strain collections which represent the local diversity and global spread of serogroup A bacteria. Several genes for cell surface proteins are conserved during spread, with a few exceptions: analysis of these exceptions has revealed some of the phenomena which can lead to microevolution. Micro‐evolution is so rapid with serogroup A meningococcal that several independent recombination events have been documented within the last few decades. In a few cases, the recombinant bacteria have become established by clonal replacement plus epidemic spread. Comparison with other bacteria indicates that serogroup A meningococcal provide a number of advantages for analysis of microevolut

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00285.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryEarly genetic analysis of alternate recombination pathways inEscherichia coliidentified the RecE recombination pathway and the required exonuclease VIII encoded by therecEgene. Observations that not ail recombination events promoted by the RecE pathway requirerecAsuggest the existence of an additional homologous pairing protein besides RecA inE. coli.Genetic and biochemical analysis of therecEgene region indicates there are two partially overlapping genes,recEandrecT, encoding at least two proteins: exoVIII and the RecT protein. Biochemical analysis has shown that the RecT protein, in combination with exoVIII, promotes homologous pairing and strand exchange in reactions containing linear duplex DNA and homologous, circular, single‐stranded DNA as substrates. This reaction occurs in the absence of any high‐energy cofactor. These two proteins, RecT and exoVIII, appear to be members of a second class of homologous pairing proteins that are required in genetic recombination and differ from the class of homologous pairing proteins that includes RecA. Members of this second class of proteins appear to include both bacteriophage‐encoded proteins and proteins from eukaryotes and their vi

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00286.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryIntercellular spreading of shigellae Is a prerequisite for shigellosis, although the molecular mechanisms underlying the phenomenon are still largely obscure. To elucidate some of these mechanisms, we performed random TniO insertion mutagenesis inShigella flexneriYSH6000T and found a chromosomal locus in the Notl‐J segment responsible for bacterial spreading. The locus affected in the mutant, designatedvacJ, was neither involved in the invasion of epithelial cells nor in intracellular movement, but was required for intercellular spread. ThevacJmutant was capable of forming bacterium‐containing membranous protrusions within the infected cell, but had diminished ability to move from the protrusions into the cytoplasm of the adjacent epithelial cells. Cloning and sequencing of thevacJregion Indicated that thevacJgene encoded a 28.0 kDa protein possessing a signal peptide at the N‐terminus, which contained the motif characteristic of lipoproteins. The analysis of thevacJproduct indicated that VacJ was exposed on the bacterial surface. ThevacJgene was distributed among shigellae and enteroinvasiveEscherichia coli, and the constructedvacJmutants failed to spread intercellularly, indicating thatvacJis a chromosomal gene essential for the pathogenicity of shig

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00287.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryDiphtheria toxin (DT) is a bacterial protein that crosses the membrane of endosomes of target cells In response to the low endosomal pH. In this paper, we have inserted diphtheria toxin in asolectin vesicles at pH 5.0 and treated the reconstituted system with pronase. The peptides that were protected from digestion were separated by gel electrophoresls, transferred to a membrane and their N‐terminal sequences were determined. All peptides belong to the B fragment of DT and cover residues 194–223, 266–375 and 429–528. The secondary structures of the peptides inserted in the membrane, determined by Fourier‐transformed infrared spectroscopy, were shown to be mostly α‐helices and β‐sheets (44% and 53%, respectively). On the basis of these data and the recently published X‐ray structure of DT, we are proposing a topology for the DTB fragmen

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00288.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe alternative sigma factor, RpoN (σ54) is responsible for recruiting core RNA polymerase to the promoters of genes required for diverse physiological functions In a variety of eubacterial species. The RpoN protein InRhodobacter capsulatusis a putative sigma factor specific for nitrogen fixation(nif)genes. Insertional mutagenesis was used to define regions important for the function of theR. capsulatusRpoN protein. Insertions of four amino acids in the predicted helix‐turn‐helix or in the highly conserved C‐terminal eight amino acid residues (previously termed the RpoN box), and an in‐frame deletion of the glutamine‐rich M‐terminus completely inactivated theR. capsulatusRpoN protein. Two separate insertions in the second hydrophobic heptad repeat, a putative leucine zipper, resulted in a partially functional RpoN protein. Eight other linkers in therpoNopen reading frame (ORF) resulted in a completeiy or partially functional RpoN protein. TherpoNgene inR capsulatusis downstream from thenifHDKU2genes, in anifU2‐rpoNoperon. Results of genetic experiments on thenifU2‐rpoNlocus show that therpoNgene is organized in anifU2‐rpoNsuperoperon. A primary promoter directly upstream of therpoNORF is responsible for the initial expression ofrpoN.Deletion analysis and insertional mutagenesis were used to define the primary promoter to 50 bp, between 37 and 87 nucleotides upstream of the predictedrpoNtranslational start site. This primary promoter is expressed constitutively with respect to nitrogen, and it is necessary and sufficient for growth under nitrogen‐limiting conditions typically used in the laboratory. A secondary promoter upstream ofnifU2is autoactivated by RpoN and NifA to increase the expression ofrpoN, which ultimately results in higher expression of RpoN dependent genes. Moreover. rpoN expression from this secondary promoter is physiologically beneficial under certain stressful conditions, such as nitrogen‐limiting environments that contain high salt (>50mM NaCl) or l

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00289.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe pathways of pectin and galacturonate catabolism InErwinia chrysanthemlconverge to form a common intermediate, 2‐keto‐3‐deoxygluconate, which is phosphorylated to form 2‐keto‐3‐deoxy‐6‐phospho‐giuconate (KDGP) and then cleaved by the aldolase encoded by thekdgAgene. We cloned thekdgAgene of theE. chrysanthemistrain 3937 by complementing anEscherichia coli kdgAmutation, using an RP4‐derivative plasm id. Restriction mapping of thekdgAregion and isolation ofkdgA‐lacfusions allowed the more precise localization of thekdgAgene and determination of its transcriptional direction. The nucleotide sequence of thekdgAregion indicated that thekdgAreading frame is 639 bases long, corresponding to a protein of 213 amino acids with a molecular mass of 22187 Da. Comparison of the deduced primary amino acid sequences of theE. chrysanthemiKDGP‐aldolase to theE. coli, Zymomonas mobilisandPseudomonas putidaenzymes showed that they are highly conserved. TheE. chrysanthemi kdgAstructural gene begins 153 bases downstream of an open reading frame that has a high homology with thezwf E. coligene encoding giucose‐6‐phosphate dehydrogenase. Thezwfgene is also linked toeda (kdgA)inE. coliandP. putidabut genetic organization is different. Regulation ofzwfandkdgAexpression inE. chrysanthemi wasanalysed usinglacZfusions. The expression ofzwfis independent of the growth rate, but is repressed in the presence of glucose. Induction ofkdgAby pectin‐degradation products is mediatedin vivoby the negative regulatory genekdgR, which also controls all the steps of pectin degradation. However, the KdgR repressor is unable to bindin vitroto the 5′

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00290.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryYmoA and Hha are highly similar bacterial proteins downregulating gene expression InYersinia entero‐colitlcaandEscherichia coli.respectively. The pheno‐type ofymoAmutants evokes that of mutants affected in some histone‐like proteins. This paper describes complementation of aymoAmutation inY. enterocoliticaby thehhagene fromE. coli.We show that YmoA and Hha are not only very similar proteins but that they are functionally Interchangeable. Genetic experiments indicate that Hha can also stimulate transposition eventsin vivo.By Southern Biol analysis we detectedhha‐homologous genes at least inCitrobacter diversus, Shigella flexneri, Shigella dysenteriae, Klebsiella pneumoniaeandSalmonella typhimurium.We suggest that both YmoA and Hha belong to a new family of proteins down regulating gene expression in different enterob

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00291.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY