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Biomedical subjects

J Schell

Publications and source records attributed to J Schell.

At least 271 records · Page 15Linked to original sources
PubMed1977

Thermosensitive step associated with transfer of the Ti plasmid during conjugation: Possible relation to transformation in crown gall.

It is reported here that transfer by means of a conjugative process of an oncogenic plasmid from a virulent strain of Agrobacterium tumefaciens to a strain of that organism that had been cured of the plasmid is thermosensitive. Since the thermosensitive step found in the conjugative process appears similar in every respect to a thermosensitive step that is involved in the transformation of a normal cell to a tumor cell in the crown gall disease of plants, it is suggested that the observed results may reflect the existence of a thermosensitive step that is common to these two processes.

Journal Article↗
PubMed1976

Octopine and nopaline synthesis and breakdown genetically controlled by a plasmid of Agrobacterium tumefaciens.

Several nopaline degrading strains and one octopine degrading strain are shown to loose oncogenicity as well as the ability to utilize these guanidine compounds when they are cured of their TI plasmid. To investigate whether the specific genes involved in the utilization of one or the other compound are located on the plasmid, plasmid-transfer experiments have been performed. The plasmid from a nopaline degrading strain has been transferred to a naturally non oncogenic Agrobacterium namely A. radiobacter. Furthermore, the plasmid from an octopine degrading strain has been transferred to a plasmid-cured strain which originally had the capacity to utilize nopaline. Both kinds of experiments prove that the TI plasmid determines the strain specificity with regard to the utilization of either octopine or nopaline. They also demonstrate that the synthesis of either octopine or nopaline in crown gall cells is also determined by genes located on the TI plasmid harboured by the transforming A. tumefaciens strains.

Extrachromosomal Inheritance↗
PubMed1976

On the isolation of TI-plasmid from Agrobacterium tumefaciens.

An efficient lysis method for Agrobacterium cells was developed, which allows a reproducible isolation of the tumor inducing (TI)-plasmid. The lysis method is based on the sensitivity of this bacterium to incubation with lysozyme, n-dodecylamine,EDTA, followed by Sarkosyl, after growth in the presence of carbenicillin. We also present a procedure for the isolation of the TI-plasmid on a large scale, that might be used for the mass isolation of other large plasmids which like the TI-plasmid, can not be cleared with earlier described procedures. The purity of the plasmid preparations was determined with DNA renaturation kinetics, which method has the advantage that the plasmid need not to be in the supercoiled or open circular form.

Centrifugation, Density Gradient↗
PubMed1975

Agrocin 84 sensitivity: a plasmid determined property in Agrobacterium tumefaciens.

It was shown for some oncogenic Agrobacterium tumefaciens strains that agrocin 84 sensitivity is determined by the presence of a large closed circular DNA plasmid, called the Ti-plasmid. Whereas wild-type strain C58 is agrocin 84 sensitive, all Ti-plasmid cured derivatives were found to be fully resistant. Moreover all independently isolated agrocin 84 resistant colonies were stably non-oncogenic and plasmid negative. In a growth experiment carried out at 37 degrees C it was shown that the kinetics of appearance of non-oncogenic cells on the one hand and of agrocin 84 resistant cells on the other were identical. The fact that not all oncogenic, plasmid harbouring, Agrobacterium tumefaciens strains are sensitive to agrocin 84, points to the possibility that the genes determining agrocin 84 sensitivity are not essential for tumor-inducing ability.

Adenine Nucleotides↗
PubMed1975

Characterization of different plaque-forming and defective temperate phages in Agrobacterium.

Four Agrobacterium tumefaciens temperate phages (PB2A, PB6(omega), PV-1(LV-1) and PS8), were shown to have the same genome size. Moreover hybridization experiments by the heteroduplex method and electron microscopy showed a 100% homology between these four phage genomes. Indications for lysogeny were found by direct means for the Agrobacterum timefaciens strain 396, Agrobacterium radiobacter strain 8149 and Agrobacterium species 0362 and by the electron microscope negative staining technique for the A.tumefaciens strains b6-806,b6-6,b6s3,b2as,cv-1,4452,11156,11158,396, and 925; for A.radiobacter strains tr-1 and 8149, the latter being bi-lysogenic, and for the A. species 0362. These isolated phage particles, most of which appear to be defective, could be grouped into different classes. No particles could be detected in the lysates of A. tumefaciens RV3, A. radiobacter strains 4718 and S1005, and A. species 0363. Further characterization by genome size was carried out for the defective temperate phages PB6-806, P4452,P8149 and P0362. No evidence for homology between PB6-806 and PB6 omega could be found. The defective phages PB6-806 and P4452 showed the same morphology but a different genome size, whereas the two phages P0362 and P8149 had a very different morphology and genome size.

Bacteriolysis↗