Macromolecular synthesis, differentiation and cell division in Tetrahymena pyriformis mating type I variety 1

Abstract In Tetrahymena pyriformis , mating type I, variety 1, cycloheximide rapidly and completely inhibited incorporation of 14 C‐L‐leucine into protein. Actinomycin D (25 μg per ml) inhibited incorporation of 14 C‐uracil into cold‐TCA‐insoluble material, after a 5–10 minute lag. Frequently a subsequent decline in the amount of radioactivity was observed. Protein synthesis continued in actinomycintreated cultures for a variable time after cessation of RNA synthesis. Oral development was affected by cycloheximide virtually immediately, and by actinomycin D after a 10–15 minute lag. Cells affected by either drug before the onset of oral membranelle formation were permanently arrested in the stomatogenic field phase. Cells affected in the early and middle stages of membranelle formation completed development of membranelles, but did not invariably complete cell division. Cycloheximide, when added at the beginning of membranelle formation, brought about arrest or resorption of membranelles after they were completed. Actinomycin did not elicit resorption, but sometimes brought about blockage during cell division. Cells affected by either drug after membranelles were fully formed (and cell division was just beginning) completed oral development, nuclear divisions, and cell division. These results suggest that concurrent RNA and protein synthesis are essential for the initiation but not for the completion of membranelle differentiation. The results also suggest that a specific messenger RNA(s) with a very short half‐life is required for the synthesis of proteins involved in the initiation of membranelle differentiation.