Tubulin synthesis and heat shock-induced cell synchrony in Tetrahymena

Calcium-dependent mitochondrial extrusion in ciliated protozoa

Here we demonstrate that ciliated protozoa can jettison mitochondria as intact organelles, releasing their contents to the extracellular space either in a soluble form, or in association with membrane vesicles at the cell periphery. The response is triggered by lateral clustering of GPI-anchored surface antigens, or by heat shock. In the first instance, extrusion is accompanied by elevated levels of intracellular calcium and is inhibited by Verapamil and BAPTA-AM arguing strongly for the involvement of calcium in triggering the response. Cells survive mitochondrial discharge raising the interesting possibility that extrusion is an early evolutionary adaptation to cell stress.

Is Cyclin Zeuthen's "division protein"?

Biochemical evidence is presented for the presence of cyclin in Tetrahymena. Zeuthen previously postulated the existence of a heat-labile "division protein" to explain heat-shock-induced division synchrony in Tetrahymena [(1964) Synchrony in Cell Division and Growth (Zeuthen, E., Ed.), pp. 99-158, Interscience, New York]. We show that cyclin is heat-labile in Tetrahymena and suggest that cyclin may be Zeuthen's division protein. Cyclin and cell cycle control is of interest in Tetrahymena because the division mechanism drives macronuclear amitosis, closed and acentric micronuclear mitosis, and cortical differentiation in this cell type.

A thermostable acid alpha-glucosidase from Tetrahymena thermophila: purification and characterization

An acid alpha-glucosidase (EC 3.2.1.20) was purified to homogeneity from the culture medium of Tetrahymena thermophila CU 399. Its general molecular, catalytic and immunological properties were compared to those of the T. pyriformis W enzyme. The enzyme from T. thermophila was a 105-kD monomer and the N-terminus (25 amino acid residues) displayed some homology with that of T. pyriformis enzyme. The purified enzyme was most active at 56 degrees C and showed resistance to thermal inactivation. The acid alpha-glucosidase appears to have alpha-1,6-glucosidase as well as alpha-1,4-glucosidase activity. The Km values determined with p-nitrophenyl-alpha-glucopyranoside, maltose, isomaltose and glycogen were 0.7 mM, 2.5 mM, 28.5 mM and 18.5 mg/ml, respectively. The enzyme was antigenically distinct from T. pyriformis acid alpha-glucosidase.

'Stress-proteins' are induced in Tetrahymena pyriformis by histidinol but not in mammalian (L-929) cells

This study compares the influence of histidinol, a reversible inhibitor of growth and protein synthesis, on patterns of proteins synthesis in Tetrahymena pyriformis and cultured mouse L cells. In Tetrahymena, histidinol (10 mM) reduced total cell protein synthesis by over 60%. Analysis of individual protein bands by SDS-PAGE showed that at least 17 bands became less prominent, while 13 polypeptides became more prominent, during exposure to histidinol. These effects were rapidly reversed by addition of equivalent concentrations of histidine. Actinomycin D (actD) prevented the enhancement of most of the histidinol-'stimulated' bands, suggesting control at the transcriptional level. The majority of the histidinol-'stimulated' polypeptides appeared to be the same as corresponding heat-shock polypeptides, although some polypeptides were 'stimulated' by histidinol and not by heat shock, while others were 'stimulated' by heat shock and not by histidinol. 'Stimulation', both by histidinol and by heat shock, may reflect selective retention rather than induced synthesis of some or all of the relevant polypeptides. In contrast to Tetrahymena, cultured mouse L cells did not alter their normal polypeptide pattern under the influence of histidinol, under conditions in which total protein synthesis was depressed to a similar degree. It is possible that 'stress' proteins might be formed or retained in order to mediate adaptive responses of free-living cells to environmental changes.

A comparison of cortical proteins in Tetrahymena vorax microstomes and macrostomes

Proteins of surface membranes and surface-related cytoskeletons in Tetrahymena vorax microstomes and macrostomes were compared by one-dimensional SDS polyacrylamide gel electrophoresis to see if protein differences could be detected that correlate with the transformation from one phenotype to the other. Some differences were observed. However, these alterations appear to result from the heat-shock procedure used to synchronize the microstome-to-macrostome transition. The apparent lack of transformation-specific changes in cortical proteins is discussed. Similarities and differences between cytoskeletal proteins of T. pyriformis GL-C and T. vorax are also noted and discussed.

The pattern of protein synthesis induced by heat shock of HeLa cells

While incubation of HeLa cells for 5--10 min at 45 degrees C does not affect subsequent cellular growth and DNA synthesis at 37 degrees C, there is an increased synthesis of specific proteins in the molecular weight region of 100 000, 72 000--74 000 and 37 000. The synthesis of these proteins reaches a maximum 2 h after the heat shock and while the protein themselves are stable, their synthesis declines to normal levels 4 h afterwards. The increased synthesis is blocked by actinomycin D but the addition of cycloheximide or NaF during the "induction' period is without effect.