摘要:

SummaryEndogenously synthesized trehalose is a stress protectant inEscherichia coli.Externally supplied trehalose does not serve as a stress protectant, but it can be utilized as the sole source of carbon and energy. Mutants defective in trehalose synthesis display an impaired osmotic tolerance in minimal growth media without glycine betaine, and an impaired stationary‐phaseinduced heat tolerance. Mechanisms for stress protection by trehalose are discussed. The genes for trehalose‐6‐phosphate synthase (otsA) and anabolic trehalose‐6‐phosphate phosphatase (otsB) constitute an operon. Their expression is induced both by osmotic stress and by growth into the stationary phase and depend on the sigma factor encoded byrpoS (katF). rpoSis amber‐mutated inE. coliK‐12 and its DNA sequence varies among K‐12 strains. For trehalose catabolism under osmotic stressE. colidepends on the osmoticcally inducible periplasmic trehalase (TreA). In the absence of osmotic stress, trehalose induces the formation of an enzyme IITre(TreB) of the group translocation system, a catabolic trehalose‐6‐phosphate phosphatase (TreE), and an amylotrehalase (TreC) which converts trehalose to free glucose an

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01564.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryTheAspergillus nidulans brlAgene encodes a transcriptional regulator of central importance in controlling conidiophore development. I have determined the effects of mutations in other developmental regulatory genes on expression of abrlA‐lacZfusion gene. Deletion ofbrlAreduced ß;‐galactosidase levels by half and led to delocalization of enzyme accumulation. ThemedA26 andabaA2developmental mutations led to overexpression of the fusion gene without altering spatial specificity. In contrast, thestuA1mutation did not affect the timing or levels ofbrlAexpression during induction, but Instead resulted in spatial derangement of expression. These results and the phenotypes of the mutants suggest a model in which subsets of morphogenetic loci are controlled by differing levels and combinations of regulatory gene products, which are themselves determined by interactions among the regulatory g

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01565.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe expression of the five clustered genes ofListeria monocytogenes: plcA, hly, mpl, actAandplcBis under the control of the positive regulation factor PrfA. Listeriolysin, encoded by thehlygene, is the only prominent PrfA‐controlled gene product observed whenL. monocytogenesstrain NCTC 7973 is cultured in a rich medium at 37°C to the logarithmic growth phase. Stress conditions such as heat‐shock or stationary culture conditions lead to the induction of additional PrfA‐dependent proteins (PdPs): ActA (92 kDa), a 38kDa protein of unknown function and a 34kDa protein which probably represents PlcA. Under nutrient‐stress conditions PdPs are preferentially synthesized and in addition to the already known PdPs at least five new, not yet functionally identified PdPs are detected. All PdPs are either secreted or are localized at the cell surface. Differences in the amount as well as the sizes of the PdPs are observed in differentL. monocytogene

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01566.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryTheSerratia liquefaciensphospholipase (PhIA) is secreted to the medium from its natural host. Here we present results which indicate that, when cloned and expressed inEscherichia coli, secretion can be mediated by a putative host‐encoded pathway, expression of which is controlled by FlhD (formerly FlbB), the master regulator of the flagellar/ chemotaxis regulon. In the absence of this secretion pathway, the synthesized phospholipase accumulates inside the host cell where it forms a complex with the PhlB protein. PhlB, which is encoded from the promoter distal gene of the phospholipase operon, inhibits the phospholipase activity of PhlA. Formation of this enzymatically inactive PhlA/PhlB complex is required for maintenance of cell viabilit

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01567.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryHigh‐resolution SI nuclease mapping of mRNA synthesisedin vivo, in vitrorun‐off transcription with RNA polymerase fromStreptomyces lividansand gene fusions were used to analyse the transcriptional organization of theSallrestriction‐modification system ofStreptomyces albusG. ThesallRandsallMgenes that encode the restriction endonuclease and its cognate methyltransferase constitute an operon which is mainly transcribed from sal‐pR1, a promoter located immediately upstream ofsaIIR, with two possible minor promoters further upstream. Another promoter,sal‐pM, is within the 3′ end of thesaIIRcoding region, and allows expression of the modification gene in the absence of sal‐pR1. Thesal‐pMpromoter might be involved in the establishment of modification prior to restriction endonuclease activity. Sequences upstream of the apparent transcriptional start sites for sat‐pR1 andsal‐pMshow similarity with the −10 region of typical vegetatively expressed eubacterial promoters, but appropriately centered

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01568.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe expression of theRhizobium melilotiC4‐dicarboxytic acid permease gene (dctA) is controlled by the sensor DctB and the transcriptional regulator, DctD. TheR. melilotiDct system has been reconstituted inEscherichia coli.Expression of thedctApromoter is DctBD dependent and is induced in the presence of C4‐dicarboxyrtc acids (dCA). Other carbon sources also influencedctAexpression. We demonstrate that the cAMP receptor protein (CRP) has a repressive effect on thedctApromoter. A mutated CRP molecule (CRP‐H159L), unable to activate catabolic promoters (but still proficient in ONA binding), gives similar results. This suggests that the CRP‐cAMP complex represses thedctApromoter activity by direct interaction with the DNA. Direct binding of the CRP‐cAMP complex to thedctApromoter was confirmedin vitroby gel mobility‐shift assays. Sequence analysis of thedctApromoter indicates that the most likely binding sites for CRP are the two confirmed DctD‐binding sites. It is proposed that the CRP‐cAMP complex competes with DctD for occupancy of these sites. Since in the presence of CRP‐cAMP complex the uninduced levels ofdctAexpression are reduced, whereas induced levels are largely unaffected, such competition appears to be an essential regulatory feature

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01569.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryEscherichia colipossesses two energy‐coupled import systems through which substances of low concentration and of a size too large to permit diffusion through the porins are translocated across the outer membrane. Group B colicins, ferric siderophores and vitamin B12are taken up via the TonB‐ExbB‐ExbD, group A colicins via the TolA‐TolQ‐TolR system. Cross‐complementation between the two systems was demonstrated in thattolQ tolRmutants transformed with plasmids carryingexbB exbDbecame sensitive to group A colicins, andexbB exbDmutants transformed with plasmid‐encodedtolQ tolRbecame sensitive to group B colicins. TolQ‐TolR interacted through TonB, and ExbB‐ExbD interacted through TolA with the outer membrane receptors and colicins. Activity of ExbB ExbD via TolA was higher in cells laciting TonB, and activity of TolQ TolR via TonB was increased when TolA was missing. The very distinct TolA and TonB proteins mediate exclusive interaction with group A and group B receptors, respectively. ExbB‐TolR and ExbD‐TolQ mixtures showed little if any complementation ofexbB exbDandtolQ tolRmutants indicating coevolution of ExbB with ExbD and TolQ with ToIR. Sequence homology and mutual functional substitution of ExbB‐ExbD and TolQ‐TolR suggest the evolution of the two import systems fr

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01570.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe PhoR protein ofEscherichia coliK‐12 belongs to a family of structurally related sensor‐kinases that regulate responses to environmental stimuli. These proteins are often located in the inner membrane with two membrane‐spanning segments that are separated by a periplasmic domain, which is supposed to sense the environmental stimuli. However, the hydrophobicity plot of PhoR suggests a somewhat different topology in which a large periplasmic domain is lacking and an extended cytoplasmic domain is present besides the kinase domain. In protease‐accessibility experiments and by usingphoR‐phoAgene fusions, the topology of PhoR was investigated and the absence of a large periplasmic domain was confirmed. Furthermore, the function of the extended cytoptasmic domain was studied by creating internal deletions. The mutations in this domain resulted in a constitutive expression of thephoregulon, indicating that the mutant PhoR proteins are locked in their kinase function. We propose that this extended cytoplasmic domain functions by sensing an internal signal that represses the kinase function of the Pho

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01571.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryWe have isolated RNA polymerase fromMycobacterium smegmatisand established conditions for specific transcription initiationin vitro.TheM. smegmatisenzyme has a strong dependence on supercoiling of the DNA substrate for transcription from mycobacterial promoters. We also show that RNA polymerase is the target for rifampicin, and that this antibiotic specifically inhibits the transition from synthesis of short oligoribonucleotides to full‐length transcripts. RNA polymerase isolated from a rifampicin‐resistant mutant ofM. smegmatisis less sensitive to rifampicinin vitro, confirming that one mechanism of rifampicin resistance in mycobacteria is through alteration of RNA polymerase. Thisin vitrotranscription system provides a simple method for the characterization of gene expression in mycobacteria including the pathogensMycobacterium tuberculosis, Mycobacterium aviumandMycobacterium leprae.It also provides a system for evaluating potential anti‐mycobacterial

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01572.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe Sigma subunit of bacterial RNA polymerase Is necessary for the specific binding of RNA polymerase holoenzyme to promoter DNA. Promoter complexes which form with holoenzyme containing σ;54remain as closed complexes unless they are activated by one class of enhancer binding protein. The σ;54transcription factor can bind specifically to certain promoter sites in the absence of the core RNA polymerase subunits. This property has allowed demonstration of a new role for core polymerase in transcription, namely that it assists the binding of σ;54to promoter DNA, An altered form of σ;54with a deletion within the amino‐terminal region showed increased affinity for specific DNA‐binding sites. Although able to complex with core RNA polymerase the mutant σ;54failed to respond to core polymerase in the manner characteristic of the wild‐type σ;54by altering its footprint. This result indicates that σ;54has a latent DNA‐binding activity which is revealed by core RNA polymerase, and possibly involves a change in σ;54conformation. Promoter complexes which formed with σ;54‐holoenzyme appeared to be qualitatively different, depending upon the target promoter sequence, suggesting that different activatable complexes form at different

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01573.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY