title: Ribosome biosynthesis in Tetrahymena thermophila. III. Regulation of ribosomal RNA degradation in growing and growth arrested cells.
abstract: We have measured the turnover rate of ribosomal RNA in exponentially growing Tetrahymena thermophila cells, cells entering the plateau phase of growth, and nutrient-deprived (starved) cells. Ribosomal RNA is stable in cells in early log phase growth but it begins to turnover as the cells begin a deceleratory growth phase prior to entering a plateau state. Likewise, rRNA in cells transferred from early log phase growth to a starvation medium begins to be degraded immediately upon starvation. In both cases the degradation of rRNA exhibits biphasic kinetics. A rapid initial exponential degradation with a half time of nine and one-half hours lasting for six hours is followed by a slower exponential degradation with a half-life of 35 hours. When starved cells are transferred to fresh growth medium turnover of rRNA ceases. The evidence presented suggests that the alteration in degradation rate is a regulated process which is most likely independent of the cell cycle.
mesh_terms: D000818:Animals; D002455:Cell Division; D003470:Culture Media; D012335:RNA, Ribosomal / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D013768:Tetrahymena / Q000378:metabolism*
chemical_list: D003470:Culture Media; D012335:RNA, Ribosomal