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Biomedical subjects

J F Meyer

Publications and source records attributed to J F Meyer.

14 recordsLinked to original sources
PubMed1986

Role of transposition and homologous recombination in the rearrangement of plasmid DNA.

The multi-resistance plasmid pBP16 was used to analyse the variability of R-factors from clinical isolates and the molecular structures and processes involved. The observed rearrangement in pBP16 and its derivatives included inversion, deletion, replicon fusion and dissociation, and transposition. All these events could be traced to the presence and activity of multiple copies of the IS-element IS160 within pBP16. Since IS-elements are common in R-factors, it is likely that they are one of the main reasons for plasmid instability and that they are involved in a major way in plasmid evolution.

DNA Transposable Elements↗
PubMed1986

Insertions of resistance genes into Tn21-like transposons.

The evolution of Tn21 and related multiresistance transposons of natural and artificial origin is described. Variations resulting from insertions and deletions in these transposons indicate the presence of specific recombination sites. There is evidence that these 'hot spots' are flanking several resistance genes. We examined these structures on the basis of the aadA gene, mediating resistance to spectinomycin and streptomycin. Comparison of the DNA sequences of Tn21, Tn7 and pSa indicate the wide spread of these recombination sites.

Base Sequence↗
PubMed1985

R1767, an example of the evolution of resistance plasmids.

The Salmonella R-factor system R1767 undergoes frequent rearrangement of its plasmid components. The flux of genetic material within this plasmid system depends on a combination of illegitimate and homologous recombination. The presence of several copies of IS160 and two multiresistance transposons, Tn2410 and Tn2411, are substantial reasons for the observed variations.

Biological Evolution↗
PubMed1985

Characterization of aminoglycoside 6'-N-acetyltransferases [AAC(6')] from gram-negative bacteria and Streptomyces kanamyceticus.

Aminoglycoside-6'-N-acetyltransferase [AAC(6') enzymes] from several Gram-negative bacteria and Streptomyces kanamyceticus were purified by affinity and ion exchange chromatography. The different enzymes were characterized by their biochemical properties including molecular weights, isoelectric points, substrate ranges, and pH-optima. These biochemical characteristics were compared to the data for 6'-N-acetyltransferases from other Gram-negative and Gram-positive bacteria. All data indicated that the group of AAC(6') enzymes is rather heterogeneous from the biochemical point of view and led us to a new proposal for classification of subgroups.

Acetyltransferases↗
PubMed1985

Evolution of Tn21-related transposons: isolation of Tn2425, which harbours IS161.

The isolation of two multi-resistance transposons, Tn2425 and Tn1831, and their relation to Tn21 and Tn2424, is described. A 1.7 kb segment present in Tn2424 and Tn2425 was identified as an IS element by rec-independent transposition, resulting in a cointegrate structure that carries two direct repeated copies of the IS element. By the isolation of this IS element we demonstrated that transposition is one mechanism leading to sequence variations in Tn21-like structures, especially in the region between the mer operon and the sul gene.

Ampicillin↗
PubMed1985

Evolution of plasmid-coded resistance to broad-spectrum cephalosporins.

A clinical isolate of Klebsiella ozaenae with transferable resistance to broad-spectrum cephalosporins produces a beta-lactamase determined by plasmid pBP60. The beta-lactamase had the same isoelectric point as SHV-1 (7.6). From heteroduplex analysis, an extensive homology between the two bla genes could be deduced; therefore, the new beta-lactamase was designated SHV-2. Enzymatic studies revealed that SHV-2 was able to hydrolyze broad-spectrum cephalosporins due to an increased affinity of these compounds for the enzyme. The assumption that SHV-2 is a natural mutant of SHV-1 was strongly supported by the isolation of a laboratory mutant of SHV-1 that showed activities similar to those of SHV-2.

Cephalosporins↗
PubMed1977

Systolic mitral flutter, an echocardiographic clue to the diagnosis of ruptured chordae tendineae.

A new finding of fine systolic fluttering of the mitral leaflet is described in two patients with ruptured chordae tendinease and severe mitral regurgitation. The flutter is caused by the action of high-velocity blood flow upon the leaflet margin that has lost its support. The jet stream of blood evokes a high-frequency vibratory motion of the tensed leaflet as opposed to the previously described, lower frequency, less specific, diastolic flutter. This finding was not seen in the echocardiograms of 75 patients with other forms of mitral regurgitation. Systolic flutter appears to be specific for ruptured chordae tendineae.

Adult↗
PubMed1975

On the inhibition of elastase by serum. Some distinguishing properties of alpha1-antitrypsin and alpha2-macroglobulin.

1. The influence of serum on the elastolytic and esterolytic activity of elastase has been studied. With both substrates the inhibition curves are linear. 1 ml of normal human serum inhibits the activity of 0.77 mg of pure porcine elastase. 2. Elastase binds faster with alpha2-macroglobulin (k = 3.4-10(6) M-1 S-1) than it does with alpha1-antitrypsin (k = 5-10(5) M-1 S-1). 3. The dissociation constant of the alpha-antitrypsin -elastase complex is much lower than that of the alpha2-macroglobulin-elastase complex but both complexes are very stable (Ki less than 10(-10) M). 4. Protein pi (inter-alpha-inhibitor) does not inhibit elastase.

Animals↗