Nuclear Transplants between Normal and Mutant Amoebae

NITROSAMINES and nitrosamides are recognized as potent carcinogens 1,2 and mutagens 3 . N -Methyl- N -nitroso urethane has produced viable mutations of Amoeba proteus 4 and we describe a mutant called “Pale”, which is twelve months old and has passed through 70–100 generations. Its cell cycle occupies 5 days compared with 2–2.25 days for the parent X 65 strain of A. proteus . Both X 65 and Pale amoebae are mass cultured using Tetrahymena as a food organism. The Pale mutant, unlike the parent, has few cytoplasmic crystals. These are square thin platelets generally 5–10µ long and strongly birefringent between crossed polaroid filters. Strain X 65 amoebae, and other strains of A. proteus 5 , have many non-birefringent bi-pyramidal crystals which give the cytoplasm its darker granular appearance. Occasionally X 65 A. proteus has a few birefringent crystals in the cytoplasm.