Informational molecules in amoebae: an attempt to follow injected fractions using autoradiography

Cytoplasmic fractions from Amoeba discoides contain informational molecules which, when injected into A. proteus, may influence the characters of resulting clones. An attempt was made to follow and locate these molecules by autoradiography. Using either 3H-uridine or 3H-leucine, radioactive fractions of A. discoides were microinjected into A. proteus and cells examined at varying times after injection. A. discoides were injected with the same preparations to serve as controls. Grain counts were compared for equivalent areas of nucleus and cytoplasm, and results expressed in terms of the ratio between nucleus and cytoplasm. When the light microsomal or the supernatant fractions were injected, the level of labelled molecules was higher in the nucleus than the cytoplasm in over 50% of the cells examined after 6 h, except for those cells injected with 3H-leucine-labelled supernatant material when only 15% cells showed a nuclear/cytoplasmic grain count greater than 1.1. After some purification by sucrose density gradient centrifugation, 'information-containing' peaks '13' from the light microsomal fraction, and '16' from the supernatant fraction were injected. A different pattern of results was obtained. The problems of interpreting these results in the light of known migratory molecules and strain incompatibility are discussed.