Purification and partial characterization of a transcription-inhibitory peptide from Tetrahymena

Signaling in unicellular eukaryotes

Aspects of intercellular and intracellular signaling systems in cell survival, proliferation, differentiation, chemosensory behavior, and programmed cell death in free-living unicellular eukaryotes have been reviewed. Comparisons have been made with both bacteria and metazoa. The central organisms were flagellates (Trypanosoma, Leishmania, and Crithidia), slime molds (Dictyostelium), yeast cells (Saccharomyces cerevisiae), and ciliates (Paramecium, Euplotes, and Tetrahymena). There are two novel aspects in this review. First, cellular responses are viewed in an evolutionary perspective, rather than from the more prevailing one, in which the unicellular eukaryotes are seen by the mammalian organisms. Second, results obtained with cell cultures in minimal, chemically defined nutrient media at low cell densities where intercellular signaling is strongly reduced are discussed. These results shed light on control mechanisms and their cooperation inside the living cell. Intracellular systems have many common features in unicellular and multicellular organisms.

A peptide from Tetrahymena disrupts subunit organization of E. coli RNA polymerase

Incubation of the E. coli RNA polymerase with a polypeptide factor from the protozoan Tetrahymena reduces the affinity of the holoenzyme for DNA. SDS-polyacrylamide gel electrophoresis of the peptide-treated RNA polymerase showed that the band pattern of the polymerase subunits was strongly altered. The three large subunits, beta', beta and sigma, disappear and a high number of rapidly migrating bands appeared. However, a brief heat treatment of the samples almost restored the original RNA polymerase subunit composition, and in addition a high molecular weight protein band approximately 240 kDa appeared. It is suggested that the Tetrahymena peptide specifically binds to the RNA polymerase and changes the structures of the large subunits.

Regulation of ornithine decarboxylase activity in the growth cycle of Tetrahymena thermophila

Cells of the ciliated protozoan Tetrahymena thermophila, grown in proteose peptone medium up to late logarithmic phase, harvested by centrifugation, and resuspended in fresh medium to almost the same cell density, underwent one more division cycle within 5 h after inoculation, thereafter being definitely in full stationary phase. This growth cycle proved to be a useful tool to investigate the activation and deactivation of ornithine decarboxylase ODC1 in Tetrahymena: In late logarithmic phase the cells contained a very low specific activity of ODC of about 3 nmol CO2.h-1.mg-1 in the soluble protein fraction. After growth stimulation the activity was increased up to 100-fold within 1 h. This high activity was maintained for about 5 h-about as long as division activity-then rapidly declined with a half life time (t1/2) of about 15 min to the original low level. Inhibition assays with cycloheximide and actinomycin D revealed that: i. the rapid increase of ODC activity was biphasic with one component of translation of preexisting mRNA and one component of translation of newly transcribed mRNA; ii. the t1/2 of the mRNA of ODC was estimated to be about 2 h; iii. inhibition of protein biosynthesis before ODC inactivation at 5 h caused a decrease of ODC with a t1/2 of 55 min instead of 15 min. These findings suggest that ODC activity in Tetrahymena is regulated on both levels: transcription and translation and by an inactivating protein factor which is regulated at the level of biosynthesis.