1,721,082 research outputs found
Resistance to streptomycin in a producing strain of Streptomyces griseus
No full textStreptomyces griseus S104 was sensitive to streptomycin during exponential growth in a medium which, in the subsequent stationary phase, supported production of the antibiotic in yields above 200 μg/ml. When antibiotic production began cultures developed a tolerance toward their lethal metabolite. This was not due to an increase in pH associated with antibiotic production, since pH effects on streptomycin sensitivity in S. griseus were in the reverse direction.
However, the degree of tolerance was directly related to the amount of cell materia1 present. Streptomycin production caused no change in the proportion of resistant variants in the population, nor did it cause the severe inhibition of protein synthesis observed in non-producing cultures exposed to the antibiotic. The lack of an effect on protein synthesis is attributed to the absence of streptomycin within the cytoplasm since soluble extracts from myceliurn harvested in the
production phase were inactive when bio-assayed immediately after cell disuptionH. however, they developed antibacterial activity rapidly when heated, and more slowly when incubated at 25°C. The addition of phosphatase inhibitors during incubation prevented the appearance of antibiotic activitv, and it was concluded that a small amount of streotomvcin phosphate is present in the rnycelium during antibiotic production. Differences in (14C) streotomvcin uptake suggested
that the myceliurn was appreciably less permeable to the antibiotic in the production phase than during exponential growth. However, a small amount was taken up and much of it was in the soluble fraction of disrupted cells. Bioassays showed that this 14C-labeled antibiotic within the cells had been partially inactivated, suggesting that conversion of streptomycin to an inactive derivative is involved in the mechanism which protects the organism from its metabolite
Action of streptomycin on the growth of Streptomyces griseus
No full textA sterptomycin-producing culture of Streptomyces griseus was sensitive to streptomycin, but inhibition was temporary, and cultures supplemented with the antibiotic up to 100 microgram/ml grew after a lag. Streptomycyn tolerance developed, not by inactivation of the antibiotic but by selection of resistant variants in the natural population. Addition of streptomycin to growing cultures caused a drastic reduction in protein synthesis and an accumulation of "stuck" (70 S) ribosomes within the mycelium. Although the effect on protein synthesis could not be confirmed in vitro because cell extracts fro S. griseus contained an inhibitor of plyuridilic-acid-directed polymerization of L-phenylalanine, it is concluded that streptomycin prevents the growth of this organism by a mechanism similar to that observed with other bacteria and that the tolerance of producing cultures cannot be attributed to the presence of streptomycin-resistant ribosome
Origin of the ribosome factors responsible for peptide chain elongation in yeast
No full textThe data reported in the present paper sugges that in yeast the genetic information for polypetide chain elongation factors is encoded in the nuclear DNA and that such information is translated on the cytoplasmic ribosome
Thymidylate Synthase in plant cells: kinetic and molecular properties of the enzyme from Daucus carota L. cell cultures
No full textUtilization of irradiated carrot cell suspensions as feeder layer for cultured Nicotiana cells and protoplasts.
No full textNon-dividing X-irradiated carrot uspension cells were used as feeder cells to support the division of Nicotiana protoplasts and cells plated at low densities. Pigmented carrot cells have been employed beacuse they are easily recognized when occasional divison and colony formation occurred in the feeder layer. Several parameters wich influenced the plating efficiency have been analyzed. Optimal conditions, which allowed a high final plating efficiency of up to 70%, in the case of Niocotiana tabacum cv Xanthi protoplasts, have been established
Characterization of carrot cell lines resistant to 5MT obtained by irradiating suspension cultures with UV-light.
No full textA mutagenic procedure of carrot cell suspension by means of UV-light has been established. The application of this procedure to the selection of cell lines resistant to 5-methyltryptophan (5MT) increased 11 times the spontaneous mutation rate. Eighteen colonies selected in the course of one experiment have been analyzed for quantitative resistance to the analogue. Four of the most 5MT-resistant lines selected (one spontaneous and three induced) were also tested for their resistance to azetidine-2-carboxylic acid (A2C) to which all of them proved to be resistant even though this was an unselected trait.
The four lines were tested for the intracellular content of some free amino acids. Results of such determination showed that the content of tryptophan and proline was roughly proportional to the degree of resistance of the lines to the two analogues. The fact that all the lines resistant to 5MT over-produced proline suggests that the latter feature may be a direct consequence of the increased pool of free tryptophan. The four cell lines tested showed a rate of tryptophan uptake similar to that of the parental line. On the contrary the rate of proline and A2C by the 5MT-l1 cell line was reduced to 23% and 10% of that of the parental line, respectively
Structure of dihydrofolate reductase-thymidylate synthase gene (Accession No. AJ003139) from Daucus carota. (PGR98-055)
No full textColture di cellule vegetali: metodi ed applicazioni
No full textIl volume descrive lo stato dell'arte nell'ambito della coltura in vitro di cellule vegetali sottolinenafdo le problematiche aperte e le metologie usat
A reliable amplification technique with single-sided specificity for the isolation of 5' gene regulating regions.
No full textA simple and efficient method is described for the isolation of extension fragments of known DNA sequences by polymerase chain reaction (PCR) using a single specific primer. With this method, size-selected genomic DNA fragments are ligated to a plasmid Vector (pGEM-4Z) which contains sequencing primers and the population of chimeric plasmids is used for transforming Escherichia coli. DNA is extracted from an aliquot of the resulting mini-library and PCR performed using a sequence-specific primer and either of the standard sequencing primers of the plasmid vector. This method appears to be more Versatile than inverse PCR (IPCR), since: ii) the DNA sequence needed as the specific primer can be as short as about 20 nucleotides (nt); (ii) the DNA templates to be used in PCR are available in high amount, thus facilitating all manipulations; and (iii) if relinearization of the DNA by restriction enzyme digestion is desired before the PCR reaction, many restriction sites can be chosen from the vector polylinker. Using this method, we have isolated the genomic 5' region of the carrot bifunctional dihydrofolate reductase-thymidylate synthase-encoding gene dhfr-ts using a 21-nt sequence of the 5' region of the dhfr-ts cDNA clone as the specific primer
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