摘要:

SummaryPost‐exponentialBacillus thuringiensiscells produce both an endospore and a variety of intracellular inclusions. The latter are comprised of protoxins, each being specific for the larvae of certain species from at least three orders of insects. Following ingestion of spores and inclusions, toxicity results in the spores gaining access to haemolymph, a source of nutrients suitable for germination and growth. MostB. thuringiensissubspecies contain multiple, plasmid‐encoded protoxin genes, often with several on the same plasmid. These genes have been manipulated in order to understand the basis of toxicity and specificity, information which is important to the use of these toxins as biological control agents. Some protoxin genes are in operons, and others are in close proximity, perhaps to enhance the chances of recombination, and some are on unstable plasmids. The arrangement of these genes is probably important for flexibility in the variety of protoxins packaged into inclusions by a particular subspecies and thus the capacity to adapt to changing populations of insects. Protoxins accumulate over a prolonged period during sporulation because of the sequential transcription from two promoters, each being dependent upon a specific sporulation sigma factor, the relative stability of the messenger RNA, and the synthesis of proteins which stabilize protoxins and perhaps facilitate inclusion assembly. During the post‐exponential phase, spore and inclusion formation must be balanced so as to ensure that both are available to contribute to the survival of these ba

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01139.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe expression of an increasing number of genes of both prokaryotic and eukaryotic origin has been shown to be regulated at the translational level by programmed (sequence‐specific) ribosomal frame‐shifting. Among these are the bacterial insertion sequences IS1and two members of the widely distributed IS3‐family, IS150and IS911.Frameshifting provides a means of specifying several proteins with different functions using a minimum of genetic information. In this review, we survey present understanding of the way in which frameshifting is integrated into the overall control of transposition activity in these ele

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01140.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe VR1 and VR2 regions of the class 1 protein have been sequenced from a number of meningococcal strains, including non‐subtypable strains and strains of apparently identical subtype. The amino acid sequences have been used to construct synthetic peptides for mapping subtype‐specific epitopes. The majority of epitopes was found to be located in VR2 at the apex of a predicted surface‐exposed loop. A single amino acid change within an epitope, or an amino acid deletion outside an epitope, were both associated with loss of subtype specificity, resulting from a change in the predicted conformation at the apex of the loop structure. Analysis of the sequence information combined with knowledge of defined epitopes also revealed considerable additional information not demonstrated by current subtyping proce

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01141.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryA molecular karyotype for three differentTrichodermaspecies (T. harzianum, T. viride, andT. reesei) was determined by using two different systems: countour‐clamped electric‐field and rotating‐electrode electrophoresis. Six chromosomal DNA bands were observed inT. harzianumandT. reeseiand five inT. viride.The sizes of these molecules were estimated by their mobility relative to theSchizosaccharomyces pombechromosomes and ranged between 2.2 and 7.4 megabase pairs (mbp). The estimated genome sizes range from 31 to 39 mbp. A number of genes were located in the different chromosomes by means of Southern analysis. The implications of these findings are disc

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01142.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryCurli encoded by thecurlinsubunit gene,csgA, are fibronectin‐ and laminin‐binding fibres expressed by many naturalEscherichia coliandE. coliK‐12 strains in response to low temperature, low osmolarity and stationary‐phase growth conditions. Curli expression is dependent on RpoS, a sigma factor that controls many stationary phase‐inducible genes. Many commonly used K‐12 strains carry an amber mutation inrpoS.Strains able to form Curli carry an amber suppressor whereas curli‐negativeE. coliK‐12 strains, in general, aresup°.Introduction ofsupD, supE, orsupFsuppressors intosup0strains resulted in expression of temperature‐regulated curli. In curli‐deficient, RpoS−E. coliK‐12 strains,csgAis transcriptionally activated by mutations inhns, which encodes the histone‐like protein H‐NS. Curli expression, fibronectin binding, andcsgAtranscription remain temperature‐ and osmoregulated in such double mutants. Our data suggest that RpoS+strains, and hence curli‐proficient strains ofE. coliK‐12, are relieved for the transcriptional repression mediated by the H‐NS protein upon accumulating

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01143.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryBacterial interspersed mosaic elements (BIMEs) constitute a family of highly repetitive sequences containing palindromic units (PUs), also called repetitive extragenic palindromes (REPs). BIMEs were originally described inEscherichia coliandSalmonella typhimurium.We show here, by determining the nucleotide sequence of two intergenic regions ofKlebsiella pneumoniae, by computer searches, and by hybridization, that sequences with similar characteristics are found in the genome of severalKlebsiellaspecies. This reinforces the idea that BIMEs play general and important roles in enterobacteria such as in the organization of the bacterial chromosome.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01144.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryExpression of pyelonephritis‐associated pili (Pap) inEscherichia coliis under a phase‐variation control mechanism in which individual cells alternate between pili+(ON) and pili−(OFF) states through a process involving DNA methylation by deoxyadenosine methylase (Dam). Methylation of two GATC sites (GATC1028and GATC1130) within thepapregulatory region is differentially inhibited in phase ON and phase OFF cells. The GATC1028site of phase ON cells is non‐methylated and the GATC1130site is fully methylated. Conversely, in phase OFF cells the GATC1028site is fully methylated whereas the GATC1130site is non‐methylated. Two transcriptional activators, Papl and Lrp (leucine‐responsive regulatory protein), are required for this specific methylation inhibition. DNA footprint analysis using non‐methylatedpapDNAs indicates that Lrp binds to a region surrounding the GATC1130site, whereas Papl does not appear to bind topapregulatory DNA. However, addition of Lrp and Papl together results in an additional DNasel footprint around the GATC1028site. Moreover, Dam methylation inhibits binding of Lrp/Papl near the GATC1028site and alters binding of Lrp at the GATC1130site. Our results support a model in which Dam and Lrp/Papl compete for binding near the GATC1028site, regulating the methylation state of this GATC site and, consequently, the pap transc

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01145.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryTransformation of plants byAgrobacterium tumefaciensis mediated by a set of virulence (vir) genes that are specifically induced by plant signal molecules through the VirA/VirG two‐component regulatory system. The plant signal is transmitted from VirA to VirG by a cascade of phosphorylation reactions followed by the sequence‐specific DNA binding of the VirG protein to thevirgene promoters which then activates their transcription. In this report, we describe a VirG mutant which is able to activateWr geneexpression independently of the VirA molecule and the two plant signal molecules, acetosyringone and monosaccharides. A strain ofAgrobacteriumcontaining thisvirGgene but lacking a functionalvirAgene was able to induce tumours on all three plants that were tested. A single amino acid change of asparagine (N) to aspartate (D) at position 54, adjacent to the site of VirG phosphorylation, aspartate 52, resulted in this constitutive phenotype.In vitrophosphorylation experiments showed that the mutant protein cannot be phosphorylated by VirA, suggesting that the negative charge resulting from the N to D switch mimics the phosphorylated conformation of the VirG molecule. The same amino acid change in thevirGgene of the supervirulent strain A281 also resulted in a constitutive phenotype. However, thevirgenes were not induced to high levels when compared with the levels of the constitutiveVirgof strain A

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01146.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summarybfp, the structural gene of the major repeating bundle‐forming pilus (BFP) subunit, was cloned from the enteroadherent factor (EAF) plasmid of enteropathogenicEscherichia coli(EPEC) strain B171 (0111:NM). Thebfpopen reading frame encoded a 193‐amlno‐acid protein; comparison of this sequence with the biochemically determinedN‐terminal amino acid sequence showed that the mature pilin protein is comprised of 180 amino acids, that this sequence is similar to other members of the type IV pilin family, and that it is preceded by a 13‐amino‐acid signal peptide. Expression of the clonedbfpstructural gene in an EPEC strain that had been cured of the EAF plasmid yielded a 21000 dalton protein that co‐migrated with the BFP precursor protein. Thus, other genes, probably carried by the EAF plasmid, are required for the maturation of thebfpproduct and for the production of extracellular pilus filaments. Use ofbfpas a hybridization probe showed that homologous sequences are present in all tested EPEC strains and in 13 of 16 testedSalmoneliaserotypes. Fifty per cent of thesebfpprobe‐sensitive salmonellae exhibited the localized‐adherence (LA) phenotype when incubated with tissue culture cell monolayers, a trait previously associated with EAF plasmid‐containing EPEC strains. Scanning electron micrographs of abfpprobe‐positive, LA‐positiveSalmonella dublinstrain showed that it grows as adherent colonies on infected monolayers and that within these colonies, BFP‐like fibres form inter‐bacterial linkages. For EAF plasmid‐containing EPEC strains and for severai Salmonella serotypes, BFP expression may lead to the development of adherent colonies on epithelial surfaces e

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01147.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryInsertion sequence (IS) elements are mobile genetic elements found in prokaryotes. We have identified a repetitive element fromMycoplasma pulmonis, a murine pathogen, that is similar to eubacterial IS elements. By subcloning a single strain ofM. pulmonis, we isolated a variant clone in which the IS element had undergone an apparent transposition event. The nucleotide sequences of the element, designated IS1138, and the target site into which it inserted were determined. IS1138consists of 1288bp with 18bp perfect terminal inverted repeats. Sequence analysis of the target site before and after insertion of IS1138identified a 3bp duplication of target DNA flanking the element. The predicted amino acids encoded by the major open reading frame of IS1138share significant similarity with the transposases of the IS3 family. Southern hybridization analysis indicates that repetitive sequences similar to IS1138are present in most, if not all, strains ofM. pulmonis, but Is1138–like sequences were not detected in other mycoplasmal specie

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01148.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY