摘要:

SummaryHU and IHF proteins have long been considered the prokaryotic analogues of eukaryotic histones. Their ability to bend DNA, however, is distinctly similar to that of eukaryotic HMG‐box proteins, a recently identified family of chromatin components and transcription factors. In some conditions, HU and HMG1‐like proteins can even be swapped, bothin vitroandin vivo.In spite of this, HU/IHF and HMG‐box proteins are not evolutionarily related, and represent two independent solutions for the same biochemical pr

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01261.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryTheEscherichia coliCadC protein is required for activation ofcadBAtranscription under conditions of low external pH and exogenous lysine.cadBAencodes proteins involved in the decarboxylation of lysine to cadaverine, and cadaverine excretion. Sequence analysis suggested that CadC contains a single transmembrane segment separating a DNA‐binding domain in the amino terminus from a periplasmic domain. Western analysis of subcellular fractions demonstrated that CadC is expressed and concentrated in the cytoplasmic membrane in cells grown either at an inducing pH (pH5.8) or at a non‐inducing pH (pH7.6.). EightcadCmutants were isolated based on their ability to confer expression of acadA‐lacZfusion independent of low external pH or exogenous lysine. Five of these mutants expressed thecadA‐lacZfusion at both pH 5.8 and pH 7.6, but retained the requirement for the lysine signal while the other three mutants displayed pH independence in the presence of lysine, and lysine independence at pH 5.8 but not at pH 7.6. These results support a model in which CadC is a membrane‐bound transcriptional activator of thecadBAoperon capable of sensing (directly or indirectly) signals generated outside the cytoplasmic membrane as a consequence of acidic pH a

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01262.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryCo‐ordinate expression of many virulence genes inVibrio choleraeis under the control of the ToxR and ToxT proteins. These proteins function in a regulatory cascade in which ToxR is required to activatetoxT, and ToxT activates virulence genes. The precise mechanism for ToxR activation oftoxTis unknown, but data presented in this report suggest a direct involvement of ToxR. Primer extension and gene fusion analyses identified a ToxR‐regulated promoter directly upstream of toxT, immediately following a region of inverted repeats capable of terminating transcription. Gel mobility shift studies indicate that ToxR binds DNA within the inverted repeat region, yet preliminary evidence suggests that ToxR binding alone is not sufficient for activation of toxT. Possible mechanisms of ToxR‐dependenttoxTexpression are disc

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01263.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryExpression ofrpsO, the gene encoding the small ribosomal protein S15, is autoregulated at the translational level by S15, which binds to its mRNA in a region overlapping the ribosome‐binding site. By measuring the effect of mutations on the expression of a translationalrpsO‐lacZfusion and the S15 binding affinity for the translational operator, the formation of a pseudoknot in the operator sitein vivois fully demonstrated and appears to be a prerequisite for S15 binding. The mutational analysis suggests also that specific determinants for S15 binding are located in very limited regions of the structure formed by the pseudoknot. It is deduced that a specific pseudoknot conformation is a key element for autoregulat

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01264.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryComputer analysis of the three‐dimensional structure of ADP‐ribosylating toxins showed that in all toxins the NAD‐binding site is located in a cavity. This cavity consists of 16 contiguous amino acids that form ana‐helixbent over β‐strand. The tertiary folding of this structure is strictly conserved despite the differences in the amino acid sequence. Catalysis is supported by two spatially conserved amino acids, each flanking the NAD‐binding site. These are: a glutamic acid that is conserved in all toxins, and a nucleophillc residue, which is a histidine in the diphtheria toxin andPseudomonasexotoxin A, and an arginine in the cholera toxin, the Escherichia coli heat‐labile enterotoxins, the pertussis toxin and the mosquitocidal toxin ofBacillus sphaericus.The latter group of toxins presents an additional histidine that appears important for catalysis. This structure suggests a general mechanism of ADP‐ribosylation evolved to work on different

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01265.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryComputer analysis of the crystallographic structure of the A subunit ofEscherichia coilheat‐labile toxin (LT) was used to predict residues involved in NAD binding, catalysis and toxicity. Following site‐directed mutagenesis, the mutants obtained could be divided into three groups. The first group contained fully assembled, non‐toxic new molecules containing mutations of single amino acids such as Val‐53 → Glu or Asp, Ser‐63 → Lys, Val‐97 → Lys, Tyr‐104 → Lys or Asp, and Ser‐14 → Lys or Glu. This group also included mutations in amino acids such as Arg‐7, Glu‐110 and Glu‐112 that were already known to be important for enzymatic activity. The second group was formed by mutations that caused the collapse or prevented the assembly of the A subunit: Leu‐41 → Phe, Ala‐45 → Tyr or Glu, Val‐53 → Tyr, Val‐60 → Gly, Ser‐68 → Pro, His‐70 → Pro, Val‐97 → Tyr and Ser‐114 → Tyr. The third group contained those molecules that maintained a wild‐type level of toxicity in spite of the mutations introduced: Arg‐54 → Lys or Ala, Tyr‐59 → Met, Ser‐68 → Lys, Ala‐72 → Arg, His or Asp and Arg‐192 → Asn. The results provide a further understanding of the structure–function of the active site and new, non‐tox

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01266.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryGilding is the directed movement of cells across surfaces which occurs in the absence of external organelles such as flagella. Gliding of the complex prokaryote,Myxococcus xanthus, results from the action of two independent sets of genes known as the A (adventurous motility) and S (social motility) genes. Strains with mutations in both systems (A−S−) do not spread on agar surfaces because both individual and group movement is abolished. To generate regulated, transcriptional fusions with operons including A and S genes, we introduced TN5‐lacinto A−and S−strains to obtain non‐motile A−S::Tn5‐lacand A::Tn5‐lacS−double mutants. These insertions identify five separate clusters of A genes and three separate clusters of S genes on theM. xanthusgenome. Some Tn5‐lacinsertions map near two of the five previously identified motility gene clusters, but at least five new clusters were identified in this search. Single mutations at only one locus, mgIA, block motility; the mgIA locus is epistatic to A and S motility genes. A‐and S‐Tn5‐lacinsertions were transduced into mgl+and δmglstrains. The levels of β‐galactosidase activity produced from each A‐or S‐Tn5‐lacinsertion are similar in otherwise isogenic mgl+and δmgl strains, showing that MgIA does not regulate t

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01267.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryRecent findings suggest that axial flagellar proteins and virulence proteins of Gram‐negative bacteria are exported from the cytoplasm via conserved trans‐location systems. To identify residues essential for secretion of flagellar axial proteins we examined the 591‐residueCaulobacter crescentusflagellar hook protein. Western blot assays of the culture media of strains producing mutant hook proteins show that only residues 38–58 are essential for its secretion to the cell surface. We discuss the observation that this unprocessed 21‐residue sequence is not conserved in other axial proteins and does not correspond to the SGL‐, ANN LAN‐ and heptad repeat motifs that are located Just upstream of the essential secretion information in the hook protein and are conserved near theN‐termini of other axial proteins. These motifs, for which an essential role in export or assembly has been proposed, are required for motility. However, we also demonstrate that hook protein can only be secreted when the flagellar basal body is present in the cell envelope. The cell‐cycle regulation of hook protein secretion confirms the specificity of the assay used in these studies and suggests that the basal body itself may serve as a secretion channel for

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01268.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe opportunistic fungal pathogenCandida albicansproduces secretory aspartyl proteinases, which are believed to be virulence factors in infection. We have studied thein vitroexpression of seven known members of the SAP gene family in a range of strains and serotypes by Northern analysis.SAP1andSAP3were regulated during phenotypic switching between the white and opaque forms of the organism. TheSAP2mRNA, which was the dominant transcript in the yeast form, was found to be autoinduced by peptide products of Sap2 activity and to be repressed by amino acids. The expression of the closely relatedSAP4‐SAP6genes was observed only at neutral pH during serum‐induced yeast to hyphal transition. NoSAP7mRNA was detected under any of the conditions or in any of the strains tested. Our data suggest that the various members of theSAPgene family may have distinct roles in the colonization and invasion of the h

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01269.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummarySummary The FeSII protein ofAzotobacter vinelandiihas been proposed to mediate the ‘conformational protection’ of the molybdenum‐dependent nitrogenase components against oxygen inactivation. We have cloned and characterized the structural gene for the FeSII protein (thefesIIIocus). Hybridization studies did not reveal the presence offesII‐like genes in a number of diverse species of well‐studied nitrogen‐fixing bacteria, with the exception ofAzotobacter chroococcum.Thefeslllocus is transcriptionally expressed during both nitrogen fixing and non‐nitrogen fixing conditions, although the level of its message is up‐regulated by approximately 2.5‐fold during nitrogen fixation. The promoter region was identified by primer extension analysis, and is similar to other σ70‐type promoters. Mutants devoid of the FeSII protein were constructed. These mutants possessed growth characteristics on a variety of carbon substrates during non‐diazotrophic as well as diazotrophic growth that were essentially indistinguishable from the wild‐type strain. Nevertheless, the nitrogenase activity in cell‐free extracts is significantly more sensitive to irreversible oxygen inactivation in the mutants as compared with the wild type. When treated with 250 mM NaCI (a condition known to dissociate FeSII from nitrogenase components), the wild‐type and mutant extracts were equally hypersensitive to oxygen Inactivation. Upon energy starvation, conditions in which ‘respiratory protection’ is inoperable, the MoFe and Fe proteins of nitrogenase are degraded much more rapidlyin vivoin the deletion mutants, compared to the wild type. Strains relying on either the vanadium or the ‘iron‐only’ alternative nitrogenases exhibited similar growth rates irrespective of the presence of absence of the FeSII protein, and thein vitroinactivation of the vanadium nitrogenase components was not affected by the lack of the FeSII protein. All in all, these results are consistent with a model whereby ‘respiratory protection’ is the major physiological mechanism responsible for the protection of all three nitrogenases during energy supplemented growth. Upon energy starvation, however, ‘conformational protection’ mediated by the FeSII protein is capable of temporarily protecting the conventional molybdenum nitrogenase component

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb01270.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY