title: Regulation of ribosome synthesis in Tetrahymena pyriformis. 1. Coordination of synthesis of ribosomal proteins and ribosomal RNA during nutritional shift-down.
abstract: When exponentially growing cells of Tetrahymena pyriformis are transferred to a non-nutrient medium the loss of whole cell RNA, 90% of which is ribosomal RNA, exhibits biphasic kinetics, whereas whole cell protein is lost at a constant rate. The ratio RNA/protein declines during the first 5 h of starvation and then remains constant during the subsequent period of starvation. The synthesis of the majority of the ribosomal proteins is coordinately regulated during a nutritional shift-down. Exponentially growing cells devote 17% of their capacity for protein synthesis to the production of ribosomal proteins. Upon starvation this proportion is rapidly reduced 3.5-fold. In long-time-starved cells the absolute rate of ribosomal protein synthesis is only about 4.5% of that of exponentially growing cells. The synthesis of ribosomal RNA and ribosomal proteins appears tightly coupled during the transition from growth to starvation. In long-time-starved cells the synthesis of ribosomal RNA and ribosomal proteins are stoichiometrically balanced with no significant degradation of de novo synthesized ribosomal proteins.
mesh_terms: D000818:Animals; D003470:Culture Media / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D011132:Polyribosomes / Q000378:metabolism; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D012269:Ribosomal Proteins / Q000096:biosynthesis*; D012270:Ribosomes / Q000378:metabolism*; D013769:Tetrahymena pyriformis / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D003470:Culture Media; D012335:RNA, Ribosomal; D012269:Ribosomal Proteins