Nuclear Transplants between Normal and Mutant Amoebae

Abstract

NITROSAMINES and nitrosamides are recognized as potent carcinogens^1,2 and mutagens³. N-Methyl-N-nitroso urethane has produced viable mutations of Amoeba proteus⁴ 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 X65 strain of A. proteus. Both X65 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 X65 amoebae, and other strains of A. proteus⁵, have many non-birefringent bi-pyramidal crystals which give the cytoplasm its darker granular appearance. Occasionally X65 A. proteus has a few birefringent crystals in the cytoplasm.