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Biomedical subjects

M Tal

Publications and source records attributed to M Tal.

At least 73 records · Page 4Linked to original sources
PubMed1982

lac Transcription in Escherichia coli cells treated with chloramphenicol.

When protein synthesis was blocked by chloramphenicol in vivo, transcription initiation of lac mRNA was severely inhibited. In a promoter mutant (L8-UV5) or in wild-type cells supplemented with adenosine 3',5'-phosphate (greater than or equal to 5 mM), nearly normal initiation could be achieved, and when the mRNA chains formed were extracted, they coded for the 5'-terminal alpha-peptide of the lacZ gene in vitro. However, even under such conditions, only a fraction of RNA polymerases proceeded to the end of the Z gene in the presence of chloramphenicol; as a consequence, a wide range of sizes of mRNA was produced, and very few transcripts were formed all the way to the natural termination site of the operon. In other words, premature transcription termination occurred in chloramphenicol-treated cells, as current models predict, but terminations occurred to variable extents at several intragenic sites and apparently at least one intergenic site. Termination at intragenic sites occurred far less in cells bearing a mutation in the transcription termination factor rho.

Chloramphenicol↗
PubMed1979

Relief of polarity in E. coli depleted of 30S ribosomal subunits.

Escherichia coli was depleted of ribosomes by a thermal shock at 47 degrees C which quantitatively destroyed the 30S ribosomal subunits. During recovery in minimal medium at 30 degrees C RNA is synthesized while protein synthesis resumes only after about 90 min. It is shown that lac mRNA is synthesized in the complete absence of ribosomal activity and hence RNA synthesis is not coupled to protein synthesis. Lac mRNA from a series of lac nonsense mutants was examined in both heated and untreated cells. It was found that the polar effect of nonsense mutation is relieved in the absence of ribosomes and that this relief is due to the synthesis of larger mRNA molecules. Since Rho remained active in thermally treated cells, premature termination at secondary signals within the lac operon must also depend on the presence of active ribosomes.

Escherichia coli↗
PubMed1979

Synthesis and degradation of lac mRNA in E. coli depleted of 30S ribosomal subunits.

Escherichia coli was depleted of active ribosomes by a thermal shock at 47 degrees C which quantitatively destroyed the 30S ribosomal subunits. During recovery, RNA is synthesized while protein synthesis resumes only after about 90 minutes. It is shown that lac mRNA is synthesized in the complete absence of ribosomal activity and hence RNA synthesis is not coupled to protein synthesis. Transcription time and average transcript length were slightly less than in untreated cells. lac mRNA was degraded much more slowly in bacteria depleted of ribosomes. In E. coli W both functional half life (T 1/2 = 28 min vs. 2.25 in untreated cells) and chemical stability. The analysis of rna and pnp mutants showed that polynucleotide phosphorylase is involved in lac mRNA degradation in heat treated cells but that RNase I is not. The functional T 1/2 was increased in pnp mutants and was 95 min during the recovery period. The rate of chemical decay is so slow that the half-life cannot be accurately determined.

Bacterial Proteins↗
PubMed1979

Physiology of polyploids.

Polyploidy, a multiplication of the whole chromosomal complement, is a very widespread phenomenon in higher plants. Natural polyploids have been suggested to be more successful than their diploid progenitors under certain conditions. This success may be due to "balance hybridity," i.e., the combination of the advantage of hybridity together with the balancing of excessive segregation and sterility by chromosome doubling, and possibly also to the effect of genome multiplication per se. The latter effect can be studied independently of the effect of other genetic changes only in autopolyploid newly derived from single ancestral strains. The existing knowledge on the effect of genome multiplication on the physiology of the plant is fragmentary and based on too narrow a representation of plant types; much of the information available on the effect of genome multiplication pertains to the tomato. Various aspects of polyploidy are discussed according to levels of function and organization: gene action, cell characteristics, growth substance, water balance, ion balance, stability of phenotypic expression and the response of polyploid plants to stress. Future work on the physiology of autopolyploid plants should be directed towards: (1) the investigation of more representative experimental systems that should include genetically homogeneous and heterogeneous species of both wild and cultivated plants; and (2) diploid-polyploid comparisons on the level of isolated tissues and cells, in addition to the whole plant.

Cell Cycle↗
PubMed1979

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: V. Effect of Abscisic Acid on Indoleacetic Acid Metabolism and Ethylene Evolution.

The wilty tomato mutant flacca, the normal cultivar Lycopersicon esculentum Mill. Rheinlands Ruhm, and abscisic acid-induced phenotypic revertants were compared with respect to ethylene evolution, activity of tryptophan aminotransferase, and [1-(14)C]indoleacetic acid decarboxylation.The level of ethylene evolution was higher in flacca plants than in the normal cultivar. Ethylene evolution was reduced to the wild type level in abscisic acid-induced phenotypic revertants and to a lesser extent in mutant plants grown under humid conditions. Leaf epinasty, which characterized flacca plants in the present experiments, did not appear in absciscic acid-treated mutant plants, but did appear under high humidity. Tryptophan aminotransferase activity, similar to ethylene evolution, was higher in flacca plants and was reduced to the normal level by abscisic acid treatment. Indoleacetic acid decarboxylation was similar in mutant and normal plants, but was increased by abscisic acid treatment. The relationships among ethylene, auxin, and the morphological symptoms which characterize the mutant are discussed.

Journal Article↗
PubMed1979

A study of the contour and external surface of class V composite resin fillings.

Twenty-five Class V Composite-resin, Adaptic fillings were prepared on extracted human teeth under five different matrices. White stones and flame diamonds were used as polishing devices. The smoothest surface was obtained with celluloid strip and the most acceptable contour obtained with preformed matrix.

Composite Resins↗
PubMed1978

New chemotherapeutic agent for root canal treatment. A preliminary electron microscopic study on an in vivo and in vitro endodontically treated tooth.

A preliminary in vivo and in vitro electron microscopic study of root canals treated endodontically with EDTA-C and Salvizol proved the latter to be superior as a chemomechanical and irrigation solution, especially in the apical third of the roots. A further virtue of Salvizol, as has been demonstrated, is its capability to dissolve the organic matrix of dentin, thus exposing the mineralizing front and the patent tubules even in the apical third of the canal. The combined properties of Salvizol which introduce it as a chemotherapeutic agent for endodontics are: (1) broad spectrum of bactericidal activity, (2) ability to dissolve calcium, (3) neutral pH, (4) cleansing potency, and (5) biologic compatibility.

Dental Pulp Cavity↗
PubMed1977

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: IV. Effect of Abscisic Acid and Water Content on RNase Activity and RNA.

Plants of the wilty tomato (Lycopersicum esculentum) mutant, flacca, and of the normal cultivar Rheinlands Ruhm growing under either "normal" or high humidity were used in this research. Under normal humidity, RNase activity was much higher in mutant plants in which abscisic acid (ABA) and water content were lower than in the normal plant. The mutant also contained less RNA and protein per cell and less soluble RNA relative to ribosomal RNA as compared with the normal genotype. In ABA-treated mutant plants, RNase activity decreased while RNA, protein, the ratio of soluble to ribosomal RNA and water content increased.Under high humidity, RNase activity in mutant plants was decreased, but was still somewhat higher than that in the normal plant, although water saturation deficit was equal in both plant types. Abscisic acid increased RNase activity in the mutant plants. The content of RNA and protein per cell was similar in both types, but the ratio of soluble to ribosomal RNA remained lower in the mutant. In ABA-treated mutant plants, although the content of DNA and RNA per fresh weight was similar to that of control mutant plants, the ratio of RNA to DNA decreased significantly. In addition, ABA caused an increase of the soluble to ribosomal RNA ratio toward the normal value in mutant plants.Contrary to ABA, kinetin increased RNase activity in the mutant under normal humidity and decreased it under high humidity.A similar incorporation of labeled uridine into RNA in normal, mutant, and ABA-treated mutant plants under normal humidity suggests that the difference between mutant and normal plants in respect to total, soluble, and ribosomal RNA results not from a different rate of RNA synthesis but from a different rate of RNA degradation, i.e. RNase activity.

Journal Article↗