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Biomedical subjects

G Cornelis

Publications and source records attributed to G Cornelis.

At least 19 recordsLinked to original sources
PubMed1990

Secretion of Yop proteins by Yersiniae.

Upon incubation at 37 degrees C in the absence of Ca2+ ions, pathogenic strains of the genus Yersinia cease growing and produce large amounts of a series of plasmid-encoded proteins involved in pathogenicity. These proteins, called Yops (for Yersinia outer membrane proteins), are detected in both the outer membrane fraction and the culture supernatant. We present here the nucleotide sequence of genes yop20 and yop25 from Yersinia enterocolitica O:9. Protein Yop25 is very similar to YopE, the corresponding protein from Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica O:8 (A. Forsberg and H. Wolf-Watz, J. Bacteriol. 172:1547-1555, 1990). This is the first report of a yop20 sequence of yersiniae. We present evidences that Yops are not membrane proteins. Their detection in the membrane fraction results either from copurification of large aggregates of extracellular Yops with the membrane fraction or from the adsorption of released proteins to the cell surface. In contrast with Yops, protein P1 has characteristics of a true membrane protein. The release of Yops by Y. enterocolitica occurs by a novel secretion mechanism that does not involve the cleavage of a typical signal sequence or the recognition of a carboxy-terminal domain.

Amino Acid Sequence↗
PubMed1990

Cervical myelopathy: MRI evaluation of cord compression.

In order to assess the consequences of cervical spinal cord compression in cervical myelopathy, MRI measurements of the sagittal diameter of the cervical spinal cord were obtained in 50 normal volunteers and 50 patients suffering from cervical myelopathy. Whatever the degree of stenosis, the values obtained in the latter group are significantly inferior to those of the normal control group (average mean diameter: normal group: 8.2 mm; cervical myelopathy: 6.2 mm).

Adolescent↗
PubMed1989

MRI assessment of unsuspected dural sinus thrombosis.

In three patients with clinically unsuspected diagnosis, MRI has afforded a positive and conspicuous demonstration of dural sinus thrombosis, allowing specific treatment and followed by improvement in the patients' condition. Even in retrospect, CT examinations were nondiagnostic. Presenting symptoms were usual and nonspecific. CT and radionuclide scanning have proved valuable when performed on a clinically oriented basis. Angiography cannot be carried out without clear indications. MRI offers advantages in being a non-invasive technique without ionising radiation, allowing direct visualization and accurate delineation of the thrombus. MRI is definitely the method of choice to assess clinically suspected cerebral venous occlusion. As MRI diagnosis relies on a routine examination protocol, we believe that it will detect other unsuspected cases of dural sinus thrombosis.

Adult↗
PubMed1989

Site-specific recombinations between direct and inverted res sites of Tn2501.

The resolvase gene and the putative res site of Tn2501 are not closely related to any of the previously described resolution functions. In view of this divergence, we designed genetic experiments to confirm the localization of the res site. We analyzed the activity of the Tn2501-encoded resolvase on substrates containing either directly or invertedly repeated res sites. These experiments confirm the localization of the res site that was predicted from nucleotide sequence data and show that the Tn2501 resolvase promotes site-specific inversions in vivo.

Base Sequence↗
PubMed1989

Identification of additional virulence determinants on the pYV plasmid of Yersinia enterocolitica W227.

This paper describes the mutagenesis of the pYV plasmid from Yersinia enterocolitica W22703 (serotype O:9) with Tn2507, a new element generating operon fusions. Analysis of the mutants allowed the identification of an additional Yop protein called Yop20 and the mapping of yop20, yop44, yop48, and lcrV, the gene encoding the V antigen. The last gene appeared to be part of an operon that also may contain yop37 and yop44. At 37 degrees C, mutants affected in this operon grew poorly, irrespective of the presence of Ca2+, or they even died in the presence of Ca2+. This operon is thus involved in the regulation by Ca2+, and we called it car, for Ca2+ regulation. It is presumably the Y. enterocolitica counterpart of the lcrGVH operon of Yersinia pestis. Transcription of yop20 and of the car operon was strongly regulated by temperature and only slightly by calcium. Hence, these genes behaved like the other genes of the yop regulon. Mutants affected in yop20 or in yop48 were markedly less virulent for the desferrioxamine-treated mouse than was the parental strain. Yop20 and Yop48 thus probably are Yersinia virulence factors.

Animals↗
PubMed1989

Homology between virF, the transcriptional activator of the Yersinia virulence regulon, and AraC, the Escherichia coli arabinose operon regulator.

Virulent yersiniae (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) restrict their growth at 37 degrees C in rich medium deprived of calcium. This property, called calcium dependency, correlates with the secretion of Yersinia outer membrane proteins (Yops) and with pathogenicity. It is mediated by a 70-kilobase plasmid called pYV. The structural genes of the Yops (yop genes), as well as genes involved in the control of their expression (vir genes), have been localized on pYV. In this communication we show that virF encodes a transcriptional activator controlling the yop regulon. This activator is a 30,879-dalton protein related to AraC, the regulator of the Escherichia coli and Salmonella typhimurium arabinose operons. We also show in this paper that transcription of virF is thermodependent and presumably autoregulated. virF is thus responsible for the effect of temperature on the production of the Yops. Finally, we show that virF activates transcription of the yop genes independently of the presence of calcium ions. The role of calcium therefore remains unaccounted for.

Amino Acid Sequence↗
PubMed1989

Contributory aspects of MRI in the evaluation of basal encephaloceles.

Basal encephaloceles are rare pathologies which belong to the now well-defined complex called median cleft face syndrome. This entity includes median craniofacial dysraphism associated to a varying degree with optic tract pathology, dysfunctioning of the hypothalamus-hypophysis axis, agenesis of the corpus callosum and basal encephalocele. The latter is that virtually constant element for which surgery is frequently requested. Owing to the large number of surgical failures (especially in the transsphenoidal type) medical imaging for the evaluation of malformative damages must be very accurate. Until recently, the techniques available, such as standard radiography, conventional tomography, gas encephalography, carotid arteriography and computerized tomography with or without metrizamide cisternography, were either too invasive or too inaccurate. MRI is the technique which provides the best images of prolapsed meninges, brain regions or ventricles, as well as of the anatomical rapport between the hypophysis, the optic tract and the limbic system.

Encephalocele↗
PubMed1988

Nucleotide sequence and transcription analysis of yop51 from Yersinia enterocolitica W22703.

Virulent strains of Yersinia enterocolitica, pseudotuberculosis and pestis secrete large amounts of plasmid-encoded proteins involved in virulence and called Yops. A 2 kb fragment of the pYVe227 plasmid from Yersinia enterocolitica 0:9 encoding Yop51 was sequenced. Gene yop51 was found to encode a 50,882 Da protein consisting of 468 amino acids. This protein shows 99% identity with Yop2b, its counterpart from Y. pseudotuberculosis YPIII (pIB1), confirming that the virulence machinery is highly conserved among Yersinia spp. The homology stops abruptly 240 bp upstream and 175 bp downstream of the structural yop51 gene suggesting that all the sequences involved in the regulation of yop51 are located within the conserved region and confirming that the homology between the plasmids of Yersinia enterocolitica and Yersinia pseudotuberculosis is made up of boxes of high homology. Gene yop51 is only transcribed at 37 degrees C from a VirF-regulated promoter. This promoter was tentatively identified by determining the messenger transcriptional startpoint. The putative yop51 promoter resembles E. coli promoters despite the fact that it is not active in that species in the absence of VirF. A transcription terminator was found at the end of the gene while a second terminator was detected within the structural gene leading to premature termination of some of the messenger molecules.

Amino Acid Sequence↗
PubMed1988

Yersinia enterocolitica O:9 as a potential live oral carrier for protective antigens.

Yersinia enterocolitica has the capacity to invade the intestinal tissue and to resist the primary host resistance. The former is chromosome coded while the second largely depends on the presence of a 70 kb plasmid called pYV. This plasmid directs the conditional synthesis of high amounts of proteins (YOPs) that are secreted and inserted in the outer membrane. In order to evaluate Y. enterocolitica W22703 as a potential live carrier for immunization, three strains expressing beta-galactosidase (GZ), were tested for their ability to induce an antibody response to this antigen in mice. The first strain contained plasmid pGC1256, a mutated pYV plasmid containing lacZ transcribed from a yop gene promoter. This strain produced high amounts of GZ instead of a YOP protein and was shown to be hypovirulent. The other strains tested were W22703 pYV+ and pYV- containing a derepressed lac operon carried on an independent plasmid. Immunoblot analysis of sera of mice having received by oral inoculation, W22703(pGC1256) or the pYV+ GZ producing strain revealed the presence of antibodies to GZ. The response to GZ after inoculation of W22703(pGC1256) was shown by ELISA to be only slightly inferior to that obtained by subcutaneous injection of GZ. No response was obtained after oral inoculation of the pYV-GZ producing strain. This showed that the presence of pYV was necessary to obtain an antibody response in this system.

Administration, Oral↗
PubMed1987

A new method for the physical and genetic mapping of large plasmids: application to the localisation of the virulence determinants on the 90 kb plasmid of Salmonella typhimurium.

A new method based on transposon-promoted deletions was used to generate a set of deletions in the 90 kb virulence plasmid of Salmonella typhimurium. The analysis of 16 deletion mutants allowed: (1) construction of the restriction map of the plasmid for HindIII, BamHI and BglII; (2) localisation of the plasmid region involved in virulence; (3) identification of two functional replicons on the plasmid.

DNA Mutational Analysis↗
PubMed1987

Transcription of the yop regulon from Y. enterocolitica requires trans acting pYV and chromosomal genes.

Virulent Y. enterocolitica strains restrict their growth at 37 degrees C, in rich medium deprived of calcium. This property, called calcium dependency, correlates with pathogenicity. It is conditioned by a 70 kb plasmid called pYV. The analysis of calcium independent (Cl) insertion mutants defined a 20 kb region called the calcium region. This region contains at least three transcription units called virA, B and C. In growth restriction conditions, Y. enterocolitica releases and inserts in its outer-membrane several pYV encoded proteins (POMPs). By transposition mutagenesis using a mini-Mu dlac element, we localized plasmid genes encoding POMPs of 84, 51, 30 and 25 kDa. These genes appear to be scattered on pYV, outside the calcium region and to constitute a regulon. Transcription of these yop genes increased by factors of 3.5 (yop84) to 200 (yop51) when temperature was shifted from 25 to 37 degrees C. On the contrary, calcium had only a moderate effect. Transcription was also dependent on the culture medium and on a trans-acting factor encoded by the calcium region. One Cl double mutant severely affected in transcription of yop51 defined a new locus called virF in the calcium region of pYV. Transcription of the yop genes was very poor in E. coli K12, even in the presence of a fully functional calcium region.

Bacterial Proteins↗
PubMed1987

Tn2501, a component of the lactose transposon Tn951, is an example of a new category of class II transposable elements.

Tn2501 is a cryptic class II transposon found as part of the lactose transposon Tn951. Insertional inactivation and nucleotide sequence analysis of Tn2501 allowed us (i) to localize the transposase (tnpA) and the resolvase (tnpR) genes as well as the resolution site (res) of Tn2501 and (ii) to compare Tn2501 with other well-known elements of the two subgroups of class II transposons (Tn3, gamma delta, Tn951, IS101; and Tn21, Tn501, Tn1721). The genetic organization of Tn2501 is similar to that of Tn3 with divergent transcription of the tnpA and tnpR genes away from the intervening res site. The tnpR gene of Tn2501 shows weak homology with that of Tn3 and even less with those of Tn21 and Tn501. However, the tnpA gene and the inverted repeat sequences of Tn2501 present more homology with those of Tn21 and Tn501 than with those of Tn3. Complementation studies showed that TnpA- mutants of Tn2501 can be complemented, at a low frequency, by the Tn21 transposase. None of the tested transposons complemented TnpR- mutants of Tn2501.

Amino Acid Sequence↗
PubMed1986

Tn951 derivatives designed for high-frequency plasmid-specific transposition and deletion mutagenesis.

We describe the construction of a system allowing high-frequency transposition and deletion mutagenesis with class-II transposons containing a kanamycin or a chloramphenicol-resistance marker. The system utilizes the transposition function of Tn3 and the resolution function of Tn951/Tn2501 which leads to an uncoupling of the resolution and repression functions. It consists of defective transposons inserted into conjugative, replication thermosensitive plasmids. The properties of the system are: easily selectable resistance markers, high transposition frequencies onto plasmids, low transposition frequencies onto the host chromosome, placement of the tnpA gene outside the transposons so that "second-generation" transposition does not occur, possibility to transpose the whole system onto other plasmid vectors with different selection strategies, consecutive use of two transposons for deletion mutagenesis and restriction mapping.

Chromosome Deletion↗
PubMed1986

Genetic analysis of the plasmid region controlling virulence in Yersinia enterocolitica 0:9 by Mini-Mu insertions and lac gene fusions.

Enteropathogenic strains of Yersinia enterocolitica harbor a virulence plasmid (pYVe plasmid) of 70 kilobases (kb) which specifies, at 37 degrees C, a calcium requirement for growth, autoagglutinability, resistance to the bactericidal activity of human serum, and the expression of outer membrane proteins (OMP). Some mutations suppress the calcium requirement for growth while others make the bacteria unable to grow at 37 degrees C, even in the presence of calcium. To analyse the genes involved in these latter phenotypes, the plasmid of a serogroup 0:9 strain was subjected to transposon mutagenesis with a Mini-Mu (Kan, lac) element. The mapping of 15 insertions and the analysis of transcription showed that at least four transcription units, spanning 22 kb, are involved in the phenomenon of calcium dependence. Mutations in two divergent units (virA and virB) suppressed the requirement for calcium at 37 degrees C. When insertions occurred in the other units (virC and virD), the Y. enterocolitica host became thermosensitive for growth. VirA, B and C mutants did no longer express the pYVe dependent OMPs. VirD mutants expressed and released these proteins save two of mol. wt 37,400 and 40,800 daltons. Transcription of the lac genes in the four groups of mutants was dependent on temperature.

Cloning, Molecular↗
PubMed1985

Genetic analysis of virulence plasmid from a serogroup 9 Yersinia enterocolitica strain: role of outer membrane protein P1 in resistance to human serum and autoagglutination.

Enteropathogenic strains of Yersinia enterocolitica harbor a virulence plasmid (70 kilobases) which specifies, at 37 degrees C, a calcium requirement for growth, autoagglutinability, resistance to the bactericidal activity of human serum, and the expression of some outer membrane proteins (OMPs). To map the genes encoding these properties, the virulence plasmid of a serogroup 9 strain (W22708) was subjected to transposon mutagenesis. A set of 68 independent mutations was obtained in Escherichia coli by transposon Tn813 (a tnpR mutant of Tn21)-mediated cointegration with the self-transmissible R388 plasmid. The resulting cointegrates were introduced and studied in Y. enterocolitica W22708. One mutant lost the calcium dependence property. Two other mutants presented a peculiar phenotype: they grew poorly at 37 degrees C, especially in the presence of calcium. Lastly, two mutants were affected in the properties of autoagglutination and resistance to human serum. Analysis of the OMP pattern of these two mutants revealed the absence of the largest OMP, called P1 (I. Bölin, and H. Wolf-Watz, Infect. Immun. 43:72-78, 1984). Complementation of one of these mutations with the cloned structural gene of OMP P1 restored the wild-type phenotype. However, OMP P1 was not sufficient by itself to specify the serum resistance property and a rapid autoagglutination of the host.

Agglutination↗
PubMed1979

Multiple integration sites for the lactose transposon Tn 951 on plasmid RP 1 and establishment of a coordinate system for Tn 951.

Various molecules generated by transposition of the lactose transposon Tn 951 from plasmid pGC1 to plasmid RP1 were examined by DNA heteroduplex and restriction endonuclease analysis. Tn 951 was found to transpose to at least eight different sites on RP 1 in both possible orientations. A coordinate system for the lactose transposon Tn 951 is constructed.

DNA Restriction Enzymes↗