No abstract

Chemoattraction of Tetrahymena pyriformis, strain GL, was measured during starvation and under different growth conditions. Log phase cells starved in buffer are attracted by certain amino acids, peptides, and proteins. Cysteine, methionine, and phenylalanine are attractants at 1CT 4 M. The peptides in proteose peptone (PP) and yeast extract (YE) are active at 10~ 6 M. Epidermal growth factor (EOF) is active at >3 X 10~ 5 M. Among the proteins, platelet derived growth factor (PDGF) is the most active (3 X 10 8 M}. Cells growing in denned medium are attracted by PP, YE, and some proteins (PDGF).Swimming speed was measured for starved cells with and without added attractants or repellents. With addition of PP the swimming speed increases from 0.42 to 0.51 mm/s., but for PDGF it is unchanged. The swimming speed of starved cells increases when the cells approach a solidified attractant (PP) as measured by the speed at a given distance. The speed of cells moving towards the attractant is higher than that of cells moving away from it.In conclusion, certain amino acids, peptides, and proteins are chemoattractants for Tetrahymena. Chemokinesis likely plays a considerable role in the case of PP (and YE), since they increase swimming speeds, whereas attraction by PDGF may involve chemotaxis.

In an attempt to establish which RNA polymerase catalyzes the synthesis of the low molecular weight RNA components A, C and D, Ama 1 cells (mutant Chinese hamster cells) were used in experiments with addition of alpha-amanitin. Ama 1 cells contain an altered RNA polymerase II which is 800 times more resistant towards inhibition by alpha-amanitin than the wild type enzyme. Alpha-amanitin (up to 200 microgram/ml) added to these cells does not affect the synthesis of the low molecular weight RNAs A, C and D. These data together with our previous data showing that alpha-amanitin (0.5 - 5.0 microgram/ml) preferentially inhibits the synthesis of A, C and D in normal cells indicate that RNA polymerase II catalyzes the synthesis of the low molecular weight RNA components A, C and D.

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We have previously shown that the cell death of Tetrahymena thermophila in low inocula cultures in a chemically-defined medium is not apoptotic. The death is caused by a cell lysis occurring at the medium-air interface and can be prevented by the addition of insulin or Pluronic F-68. Here, we report that cell death can also be caused by the medium. The specific effects of several medium constituents were tested in the presence and absence of an interface. Four of the 19 amino acids (arginine, aspartic acid, glutamic acid, and histidine in millimolar concentration) as well as Ca2+ (68 microM) and Mg2+ (2 mM) and trace metal ions (micromolar concentrations) are all sufficient to induce the interface-mediated death. The effect of the amino acids and the salt ions Ca2+ and Mg2+ can be abolished by the addition of insulin (10(-6) M) or Pluronic F-68 (0.01% w/v), whereas insulin/Pluronic F-68 only postpones the death induced by trace metal ions. On the basis of our findings, a new recipe for a chemically-defined medium has been formulated. Single cells can grow in this medium in the presence of medium-air interface without any supplements.