Search PubMed⌕ Search

Biomedical subjects

B Kessler

Publications and source records attributed to B Kessler.

6 recordsLinked to original sources
PubMed1992

XylS domain interactions can be deduced from intraallelic dominance in double mutants of Pseudomonas putida.

The XylS protein is the positive regulator of the TOL plasmid-encoded meta-cleavage pathway for the metabolism of alkylbenzoates in Pseudomonas putida. This protein is activated by a variety of benzoate analogues. To elucidate the functional domains of the regulator and their interactions, several fusions of the XylS C-terminus to MS2 polymerase and of the N-terminus to beta-galactosidase were constructed but all are inactive. In addition, 15 double mutant xylS genes were constructed in vitro by fusing parts of various mutant genes to produce mutant regulators exhibiting C-terminal and N-terminal amino acid substitutions. The phenotypic properties of the parental single mutant genes, and those of the double mutant genes, suggest that the C-terminal region is involved in binding to DNA sequences at the promoter of the meta-cleavage pathway operon, and that the benzoate effector binding pocket includes critical residues present at both the N-terminal and C-terminal ends of the protein. The intraallelic dominance of the Ile229 (Ser229-->Ile) and Val274 (Asp274-->Val) substitutions over the N-terminal His41 (Arg41-->His) substitution, and the intraallelic dominance of Thr45 (Arg45-->Thr) over Ile229 and Val274, support the proposal that these two regions of the regulator interact functionally. Combination of the Leu88 (Trp88-->Leu) and Arg256 (Pro256-->Arg) substitutions did not suppress the semiconstitutive phenotype conferred by Leu88, but resulted in a protein with altered ability to recognize benzoates. In contrast, the Leu88 semiconstitutive phenotype was suppressed by Val288 (Asp288-->Val), and the double mutant was susceptible to activation by benzoates.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1992

A general system to integrate lacZ fusions into the chromosomes of gram-negative eubacteria: regulation of the Pm promoter of the TOL plasmid studied with all controlling elements in monocopy.

A new procedure is described to recombine plasmid-borne lacZ fusions into the chromosome of gram-negative eubacteria in order to study promoter activity in monocopy. The procedure is based upon the insertion into the chromosome of a target bacterium of a recombinant transposon that carries DNA sequence homology to the regions flanking lacZ fusions present in multicopy promotor-probe vectors, which can be mobilized via RP4-mediated transfer but are unable to replicate in non-enteric bacteria. Double recombination between the promoter-probe vectors and the chromosomal homology region of the transposon is genetically selected by reconstruction and expression of wild-type sequences from truncated lacZ and aadA (streptomycin/spectinomycin) resistance genes in the homology fragment and from an amber mutation carrying lacZ and aadA genes present in the plasmid vectors. The structure of desired clones is confirmed by screening for loss of the transposon-encoded kanamycin resistance marker. We have used this procedure to assemble in monocopy in Pseudomonas putida the regulatory elements controlling expression of the XylS-activated Pm promoter of the TOL catabolic plasmid pWWO. We show here that the Pm promoter undergoes a XylS-independent, strictly growth-phase-controlled activation by benzoate but not meta-toluate. In the presence of XylS, however, activation by both effectors involves a combination of growth phase-dependent and -independent controls.

Blotting, Southern↗
PubMed1979

[Clinical experience with acute mesenteric vascular occlusion (author's transl)].

Between 1964 and 1978 twenty patients suffering from acute mesenteric vascular occlusion were treated in the surgical department (University of Münster). The average duration of the anamnesis until their hospitalization was 3.1 days and the actual operation was performed 11.35 hours later on the average. In only 15% of the cases had a correct preoperative diagnosis been given. As regards the frequency of causation, 60% of the mesenteric vascular occlusions were caused by a mesenteric arterioembolism, 20% by a mesenteric venous embolism, 10% by a mesenteric arterial thrombosis and 10% by a non-obstructive occlusion. In a post cardiac infarction condition was the predisposing factor in 50% of all cases, valvular defect in 33.5% and tachyarrhythmia in 16.6%. The causes found for the mesenteric venous tbrombosis were insufficiency of the right heart, absolute bradyarrhythmia, recurrent venous thrombosis of the leg, and myeloproliferative syndromes.

Adolescent↗