Characteristics of the 'life spanning' phenomenon in Amoeba proteus. Independent nuclear and cytoplasmic ability to impose finite 'life span'.

Amoeba proteus given adequate food grows exponentially and clones of amoebae are normally immortal. After periods of food supply restriction to that necessary for maintenance, or food intake restriction by agitation, cells subsequently given a normal growth diet produce clones of finite life span. Reciprocal nuclear transfer between maintained and normal cells demonstrated that the nucleus and cytoplasm of maintained cells have acquired the independent ability to impose a finite life span on clones developing from cells whose other components are normal. In clones developing from maintained cells, inviable cell production is enhanced and inter-division times are prolonged. Inter-division times and clones mean doubling times do not show normal distribution.