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V Leick

Publications and source records attributed to V Leick.

35 records · Page 2Linked to original sources
PubMed1976

Studies on the amount and location of the tRNA and 5-S rRNA genes in Tetrahymena pyriformis GL.

The amount and location of tRNA and 5-S rRNA genes in the macronucleus of Tetrahymena pyriformis GL was investigated by DNA-RNA hybridization. Hybridization of 32P-labelled tRNA in excess of unlabelled rRNA (25-S + 17-S + 5-S) showed that at saturation 0.021% of the macronuclear DNA was complementary to tRNA. Hybridization of 32P-labelled 5-S rRNA in excess of unlabelled 25-S + 17-S rRNA and tRNA showed a saturation value of 0.017%. In contrast to the 25-S + 17-S rRNA genes, which are found in DNA of high bouyant density, tRNA and 5-S rRNA genes were distributed evenly throughout the main peak observed when bulk macronuclear DNA was fractionated by density centrifugation in CsCl gradients. Sucrose gradient analyses of total macronuclear DNA showed that tRNA and 5-S rRNA genes were found in DNA of all size classes but a significant enrichment in the slowly sedimenting DNA fraction was observed. Saturation hybridization of 5-S rRNA to purified rDNA showed that rDNA did not contain any 5-S rRNA genes.

Animals↗
PubMed1975

Light sensitive chloramphenicol analogues.

Some chloramphenicol analogues have been prepared in order to find reagents which could be used in a photoaffinity labelling study of the peptidayl transferase center of the E. coli ribosome. The compounds were tested for antibiotic activity in vitro in the "fragment reaction" assay, and for their ability to generate very reactive species upon irradiation.

Chloramphenicol↗
PubMed1974

Induction of nucleolar and mitochondrial DNA replication in Tetrahymena pyriformis.

Selective induction of replication of nucleolar and mitochondrial DNA has been demonstrated in starved-refed cultures of Tetrahymena pyriformis by different techniques. Labeling of starved cells with [(3)H]thymidine during a nutritional shift-up and analysis of the DNA in isopycnic CsCl gradients shows that the two initially labeled species of DNA are two species banding on the heavy and light side of the bulk macronuclear DNA. In isolated macronuclei the radioactivity is found only in the high density fraction, which has been shown to be of nucleolar origin. In sucrose gradients the newly replicated mitochondrial and nucleolar DNAs sediment considerably slower than the bulk DNA, as one discrete band corresponding to a molecular weight of about 3 to 4 x 10(7). Electron microscope autoradiography of cells labeled with [(3)H]thymidine as above shows that the peripheral nucleoli of the macronucleus as well as the mitochondria are labeled before any radioactivity is found in the chromatin granules of the macronucleus. The results clearly indicate that nucleolar and mitochondrial DNA replication are under a control independent of that for the replication of bulk DNA.

Animals↗
PubMedDate not supplied

Cilia-mediated oriented chemokinesis in Tetrahymena thermophila.

The role of the cilia in the locomotion ("gliding") of Tetrahymena thermophila in a semi-solid medium has been studied when cells were migrating in gradients of attractant. Video recordings and computer-aided motion analysis of migrating cells and their ciliary activity show that Tetrahymena thermophila migrate by swimming forward in semi-solid methyl cellulose, using their cilia. Ciliary reversals occur at certain intervals and cause a termination ("stop") of cellular migration. Cells with reversed cilia resume forward migration when normal ciliary beating resumes. In gradients of attractants, cells migrating towards the attractant suppress ciliary reversals, which leads to longer runs between stops than in control cells. Cells migrating away from the attractant have a higher frequency of ciliary reversals than the control cells resulting in shorter runs. Stimulated cells adapt to a particular ambient concentration of attractant several times during migration in the gradient. Adaptation is followed by de-adaptation, which occurs during the "stop." In the presence of cycloheximide, a strong inhibitor of chemoattraction, the attractant-induced suppression of ciliary reversal is abolished (cells become desensitized to the attractant). It is concluded that Tetrahymena has a short-term memory during adaptation. This is important for the efficiency of migration towards an attractant.

Animals↗