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Biomedical subjects

J Hubácek

Publications and source records attributed to J Hubácek.

At least 91 records · Page 5Linked to original sources
PubMed1981

The mechanism of resistance to streptomycin in Escherichia coli. Functional analysis of the permeability barrier of cells harbouring the R1 drd-19Km- plasmid.

The mechanism of phenotypically altered SM resistance in mutants of Escherichia coli JC5455 (Rldrd-19Km-) lrs and JC5455 (pON5300) was compared with that of the standard strain JC5455 (Rldrd-19Km-). On analyzing the membrane polypeptides in polyacrylamide gel both mutants were found to possess a protein spectrum different from that of ths standard strain. Transport of D-xylose and L-arginine was the same in all strains, transport of L-proline was decreased in JC5455 (pON5300) which may indicate a mutational interference with energy metabolism. The basic uptake of dihydrostreptomycin was the same in all strains but there were differences after preincubation of cells with streptomycin or glucose. The increased resistance of JC5455 (Rldrd-19Km-) lrs may be due to observed quantitative differences in membrane polypeptides that might play a role in the binding and functional expression of aminoglycoside-3'adenylyl transferase which modifies streptomycin. The increased sensitivity toward streptomycin in JC5455 (pON5300) can be explained by a mutation due to N-methyl-N'-nitro-N-nitrosoguanidine in the host cell since this change of sensitivity to streptomycin could not be transferred by transformation into a nonmutagenized strain. The coincidence of inducibility of increased transport of streptomycin by this antibiotic and the altered frequency of reversion to high levels of streptomycin resistance in JC5455 (pON5300) and in the transformant JC5455 (pON5302) may indicate that the altered reversibility toward phenotypically high resistance to streptomycin is a property of pON5300 and is transferred by transformation.

Bacterial Proteins↗
PubMed1980

DNA restriction and modification in Escherichia coli: functional analysis of the role of the dnaC(D) gene product.

Escherichia coli strain PC-7 carries two independent temperature-sensitive mutations, one affecting the restriction and modification (R-M) phenotype and the other the DnaC(D) phenotype. The results of complementation and P1 transduction analysis of the mutation affecting the R-M phenotype implicate a fourth gene, designated hsdX, located close to the hsd three-gene complex. The properties of merodiploids constructed between appropriate recipients and F' elements with different mutations in hsdS, hsdR and hsdM genes might indicate that in strain PC-7 the temperature-sensitive products, determined by hsdR and hsdSK cistrons, are synthesized. The role of the temperature-sensitive dnaC(D) gene product in the formation of the restriction endonuclease was studied and no direct relation was found between the DnaC(D) and R-M phenotypes.

DNA Replication↗
PubMed1979

High-level resistance to streptomycin in Escherichia coli with R1 plasmid and the analysis of genetic determinants.

Some properties of streptomycin-resistant mutants of Escherichia coli were analyzed. In a R+ culture, the phenotype under study may be significantly selected at a frequency of 10(-5) on media with higher streptomycin level. The lrs mutation is present in the cells prior to the action of streptomycin and remains in the cells even after curing of the R1 plasmid. The mapping of the lrs gene by conjugation with a concomitant transfer of chromosome and the R1 plasmid in different Hfr strains of E. coli failed to establish the localization of this gene in the tested chromosome regions. The presence of a cryptic plasmid was detected in cells with the lrs mutation after curing of the R1 plasmid. This plasmid codes neither fertility functions nor chloramphenicol-acetyltransferase, streptomycin-adenyltransferase, or ampicillin-beta-lactamase.

Chromosome Mapping↗
PubMed1977

Membrane mutation affecting energy-linked functions in Escherichia coli K 12.

A small-colony forming variant of Escherichia coli with a mutation in the ncf gene was analysed. The alternation of the protein composition in the cytoplasmic membrane and the interaction with K and E group colicins indicated a membrane mutation. The effect of this mutation on some membrane-bound processes, the activity of Mg2+-activated ATPase, the growth on different carbon sources and the active transport of amino acids, is described. This mutation does not exert any effect on the electron transport system.

Adenosine Triphosphatases↗
PubMed1977

[Detection of immunoglobulins in pharyngeal tonsillar tissue by direct immunofluorescence technique (author's transl)].

Using a direct immunofluorescent staining method a qualitative determination of different immunoglobulin fractions in the tissue of hypertropic pharyngeal tonsils of children and youth suffering from repeated infections was performed. It was found that the immunofluorescent staining of IgG was stronger than of IgA. A difference with regard to the frequency of appearance between IgG and IgA could not be seen. On the other hand IgM staining was less frequent and strong. Extracellular IgG was present in germinal centres of the secondary lymphoid follicles, intracellular one was found in the immunocompetent cells. Extra- and intracellular IgG was more often demonstrable in the spaces of the lymphoid tissue, between the surface epithelial cells or around the glands and the blood cappilaries. The results seen here are in correlation with the values of the earlier performed quantitative estimations of the different immunoglobulin classes.

Adolescent↗