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Regulation of Ornithine decarboxylase activity in the Growth cycle of Tetrahymena thermophila
Author(s) -
EICHLER WOLFGANG
Publication year - 1990
Publication title -
the journal of protozoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 0022-3921
DOI - 10.1111/j.1550-7408.1990.tb01146.x
Subject(s) - cycloheximide , tetrahymena , ornithine decarboxylase , protein biosynthesis , biology , messenger rna , cell cycle , microbiology and biotechnology , tetrahymena pyriformis , biochemistry , enzyme , cell , gene
Cells of the Ciliated Protozoan Tetrahymena Theermophila, grown in proteose peptone medium to late logarithmic phase, harvested by centrifugation, and resuspended in fresh medium to almost the same cell density, underwent one more divison 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 ODC 1 in Tetrahymena : In late logarithmic phase the cells contained a very low specific activity of ODC of 3 nmol Co 2 .h ‐1 . mg ‐1 in the soluble protein fraction. After growth stimulation the cells the activity was increased up to 100‐fold within 1 h. This high activity was maintained for about 5 h‐ about as long as divison activity—then rapidly declined with a half life time(t 1/2 of about 15 min to the original low level. Inhibition assays with cycloheximide and actionomycin D revealed that: i. the rapid increase of ODC activity was biphasic with one component of translation ofpreexisting mRNA and one component of translation of newly transcribed mRNA; ii. the 1/2 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 t 1/2 of 55 min instead of 15 min. These findings suggest that ODC activity in Tetrahymena is regulated on both leavels: transcriptition and translation and translation and by an inactivating protein factor which is regulated at the level of biosynthesis.