摘要:

The production of insecticidal crystal proteins (ICPs) inBacillus thuringiensisnormally coincides with sporulation, resulting in the appearance of parasporal crystalline inclusions within the mother cell. In most instances, the temporal and spatial regulation of ICP gene expression is determined at the transcriptional level by mother‐cell‐specific sigma factors that share homology with σEand σKfromBacillus subtilis. ThecrylllICP genes are a notable exception; these genes are transcribed from σA‐like promoters during vegetative growth, are induced or derepressed at the onset of stationary phase, and are overexpressed in sporulation mutants ofB. thuringiensisblocked in the phosphorylation of Spo0A, a key regulator of sporulation initiation. Transcription alone, however, cannot account for the impressive ability of this bacterium to accumulate insecticidal proteins. A variety of post‐transcriptional and post‐translational mechanisms also contribute to the efficient production of ICPs inB. thuringiensis, thus making this bacterium a cost‐effective biological

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010001.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

We have mutatedAcinetobacter calcoaceticusNCIB8250 to growth deficiency on phenol as sole carbon source and isolated genes with similarity to phenol hydroxylase and catechol 1,2‐dioxygenase by complementation. Sequence analysis reveals the presence of six open reading frames (ORFs) with similarities to aPseudomonasmulticomponent phenol hydroxylase which are followed by an ORF with similarity tocatAfromA. calcoaceticusADP1. Transformation of these genes to ADP1 confers the ability to grow at the expense of phenol as sole carbon source. Primer extension analysis indicates phenol‐inducible transcription from an RpoN‐dependent promoter sharing sequence similarity with the σ54consensus promoter sequence, except that the −12 box is GG instead of GC. AcatA::lacZtranscriptional fusion shows the same induction profile for β‐galactosidase expression as transcription from the σ54‐dependent promoter. This result suggests thatcatAis cotranscribed in the same operon with the phenol hydroxylase‐encoding genes and is consistent with the fact that no apparent additional promoter is found forcatAby sequence analysis or primer extension. Catechol 1,2‐dioxygenase activity is induced in NCIB8250 by benzoate, whereas β‐galactosidase expression from thecatA::lacZfusion is not. This observation leads to the hypothesis that two differentially regulatedcatAgenes should be p

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010013.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

The actinomyceteAmycolatopsis methanolicacontains a 13.3 kb plasmid (pMEA300), capable of enhancing the spontaneous mutation frequency of its host. Depending on the growth medium pMEA300 is not only maintained as an integrated element but can additionally be present as a multicopy, autonomously replicating plasmid. The minimal replicon of pMEA300 was identified. Two unlinked DNA fragments of 2.6 kb and 0.8 kb were required for pMEA300 maintenance. Sequence analysis of the 2.6 kb fragment revealed at least two open reading frames,orfAandorfB, encoding putative proteins of 170 amino acids (18 373 Da) and 416 amino acids (45 260 Da), respectively. No clear similarities were found between the deduced amino acid sequences of the putativeorfAandorfBproducts of pMEA300 and replication proteins identified for variousStreptomycesplasmids. The pMEA300 proteins ofA. methanolicathus may represent unfamiliar types. The 0.8 kb fragment contained a single complete open reading frame (korA), encoding a protein of 118 amino acids (12 917 Da). The putative KorA protein of pMEA300 shows sequence similarity with various otherStreptomycesplasmid‐encoded Kor proteins which may belong to the GntR family of transcriptional repressor proteins. The data provide preliminary evidence for the possible involvement of akil—korsystem in autonomous replication of pMEA

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010021.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

In plantaexpression of a high‐affinity iron‐uptake system involving the siderophore chrysobactin inErwinia chrysanthemi3937 contributes greatly to invasive growth of this pathogen on its natural host, African violets. A previous study reported that global regulation by iron in this strain was mediated at the transcriptional level via thecbrlocus which, when inactivated by insertional mutation, prevents the chrysobactin system from being tightly repressed by FeCl3‐ Herein, we report the nucleotide sequence of this locus and the functional analysis of its encoded products. Sequence analysis of a 4.8 kb genomic segment of a plasmid encompassing thecbrlocus and characterization of the cognate translated products made it possible to uncover a system exhibiting similarity with prokaryotic transporters implicated in the transport of iron complexes. Accordingly, the CbrA product was shown to be the periplasmic component of a permease complex also including two integral membrane proteins, CbrB and CbrC, and the ATP‐binding unit CbrD. This system allowed internalization of Fe(III) when supplied to bacterial cells as59FeCl3or59Fe dicitrate, via complexation to a second siderophore recently detected in strain 3937. Most notably, we demonstrate that this second siderophore‐mediated iron‐acquisition system is operational in bacterial cells grown in the presence of FeCl3. The regulatory effect ofcbrwas further assessed on alacZchrysobactin operon fusion indicating that the transcriptional control exerted bycbron expression of the chrysobactin system is of homeostatic nature. In conclusion,E. chrysanthemiprovides an interesting model in which iron acquisition involves an inductive process resulting in differential expression of two siderophore‐mediated pathways in relation to external iron

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010033.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

To investigate the co‐ordination between DNA replication and cell division, we have disrupted the DNA replication cycle ofEscherichia coliby inserting invertedTersites into the terminus region to delay completion of the chromosome. The invertedTersites (designated InvTer::spcr) were initially inserted into the chromosome of a Δtusstrain to allow unrestrained chromosomal replication. We then introduced a functionaltusgene by transforming the InvTer::spcrstrain with a plasmid carrying thetusgene under control of an arabinose‐inducible promoter. In the presence of 0.2% arabinose, the cells formed long filaments, suggesting that activation of the invertedTersites by Tus arrested DNA replication and delayed the onset of cell division. Induction ofsfiA, a gene in the SOS regulon, was observed following arrest of DNA replication; however, when asfiB114allele was introduced into InvTer::spcrstrain, long filaments were still formed, suggesting that thesfi‐independent pathway also caused filamentation. EitherrecA::camrorlexA3alleles suppressed filamentation when introduced in the InvTerstrain. Interestingly, in both therecA::camrandlexA3mutants, virtually all cells had a nucleoid, suggesting that cell division was proceeding even though DNA replication was not complete. These results suggest that DNA replication and cell division are uncoupled whenrecAis inactivated or when genes repressed by LexA cannot be i

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010045.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

Since the discovery ofShigellaas the aetiologic agent of acute dysentery almost 100 years ago, this organism has been described as a non‐motile and non‐flagellated organism that invades the human colonic mucosa. In this study, the production of flagella by prototypic strains of all fourShigellaspecies and, moreover, by fresh clinical isolates was demonstrated by electron microscopy. Theflagellum ofShigella(flash) is ∼10 µm long and 12–14 nm in diameter and is typically seen emanating from one pole of the bacterium. Flash is composed of a putative structural polypeptide subunit of 33–38 kDa that shares immunological similarities withEscherichia coli,Salmonellaspp., andProteus mirabilisflagellins, and with the recently described recombinantShigella flagellins(FliCSSand FliCSF) expressed inE. coliK‐12. AfliCSS‐specific oligo probe hybridized with all fourShigellaspecies, while afliCSFprobe hybridized with allShigella flexneriandShigella dysenteriaestrains, but not with allShigella sonneiorShigella boydiistrains, indicating genetic divergence among their flagellin genes.Shigellaexhibits motility in low‐concentration motility agar under physiological growth conditions. The expression of flash and motility appears to be strictly regulated by unidentified genetic and environmental factors. These heretofore undescribed features may allow the bacteria to circumvent the natural intestinal mucosal defences leading to bacterial colonization and disease. The motility of shigellae may represent an evolutionary adaptation important for ba

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010063.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

When yeast cells growing on a poor nitrogen source are supplied with NH4+ions, several nitrogen permeases including the general amino acid permease (Gap1p) are rapidly and completely inactivated. This report shows that inactivation by NH4+of the Gap1 permease is accompanied by its degradation. A functionalNPI1gene product is required for both inactivation and degradation of Gap1p. Molecular analysis of theNPI1gene showed that it is identical toRSP5. TheRSP5product is a ubiquitin—protein ligase (E3 enzyme) whose physiological function was, however, unknown. Its C‐terminal region is very similar to that of other members of the E6‐AP‐like family of ubiquitin‐protein ligases. Its N‐terminal region contains a single C2domain that may be a Ca2+‐dependent phospholipid interaction motif, followed by several copies of a recently identified domain called WW(P). The Npi1/Rsp5 protein has a homologue both in humans and in mice, the latter being involved in brain development. Stress‐induced degradation of the uracil permease (Fur4p), a process in which ubiquitin is probably involved, was also found to require a functionalNPI1/RSP5product. Chromosomal deletion ofNPI1/RSP5showed that this gene is essential for cell viability. In the viablenp1/rsp5strain, expression ofNPI1/RSP5is reduced as a result of insertion of a Ty1 element in its 5′ region. Our results show that the Npi1/Rsp5 ubiquitin‐protein ligase participates in induced degradation of at least two permeases, Gap1p and Fur4p, and probably

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010077.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

In the overtly differentiated colonies ofStreptomyces coelicolorA3(2), discrete phases of glycogen synthesis are found at the vegetative/aerial mycelium boundary (phase I) and in the immature spore chains at aerial hyphal tips (phase II). We have characterized twoS. coelicolor glgBgenes encoding glycogen branching enzyme, which are well separated in the genome. Disruption ofglgBI led to the formation of abnormal polyglucan deposits at phase I, with phase II remaining normal, whereas disruption ofglgBII interfered specifically with phase II deposits, and not with those of phase I. Thus, each branching enzyme isoform is involved in a different phase of glycogen synthesis. This situation contrasts with that in simple bacteria, which typically have a single set of enzymes for glycogen metabolism, and more closely resembles that in plants.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010089.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

The H‐NS protein of enteric bacteria is one of the major proteins of the bacterial nucleoid and seems to play an important role in nucleoid structure. Transcription of thehnsgene encoding the H‐NS protein appears to be negatively regulated by H‐NS itself bothin vitroandin vivo. We have examined the role of this mode of regulation in wild‐type cellsin vivo. We find thathnstranscription is down‐regulated when DNA synthesis is blocked in growing cells, in a manner that is dependent upon continuing H‐NS protein synthesis. These data suggest thathnsautoregulation serves to matchde novoH‐NS synthesis to the demands of DNA synthesis and may maintain a relatively constant H‐NS:DNA ratio. It has previously been suggested thathnstranscription is activated as cells enter stationary phase, which would require a complete relaxation of autoregulatory control given that DNA synthesis decreases at this time. However, we show here that levels ofhnsmRNA in fact decline at the onset of stationary phase in a manner fully consistent with the autoregulation model. We also fail to detect any significant accumulation of the H‐NS protein in

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010101.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY

摘要:

Analysis of the DNA sequence directly upstream of the chemotaxis operon ofRhodobacter sphaeroidesidentified a single gene whose product has strong similarity to the methyl‐accepting chemotaxis proteins (MCPs) found in enteric bacteria. The deduced protein had a highly conserved signalling sequence and only one very hydrophobic region at the N‐terminus, in contrast to enteric MCPs. A possible cytoplasmic location of the majority of the protein was supported by Western blotting. ThemcpAgene was insertionally inactivated and the resulting phenotype examined using swarm plate assays. The mutant lacking McpA lost chemotaxis to a wide range of attractant stimuli but only under aerobic conditions; it retained almost normal chemotaxis under anaerobic/photosynthetic conditions. The identification of a sensory protein which is active only under one set of growth conditions suggests thatR. sphaeroidesprobably has several MCPs, which co‐ordinately respond to changes in environmental conditions. Southern hybridization at relaxed stringency to the conserved sequence of theR. sphaeroidesandCaulobacter crescentus mcpgenes identified three possible additionalmcp

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.mmi_18010115.x

出版商:Blackwell Science Ltd    

年代:1995

数据来源: WILEY