Studies on the radiation-induced dissociation and reassociation of polysomes in Tetrahymena pyriformis

Abstract

(1) A new high yield method for the isolation of polysomes from the ciliated protozoan Tetrahymena pyriformis employs the antibiotic cycloheximide, rapid chilling of the cells, and lysis in the nonionic detergent NP-40. (2) Following dissociation by sublethal doses of γ-radiation, the polysomes recover in a biphasic manner. The first, more rapid phase is complete in 15 min; the second, slower phase, requires an additional 90–120 min. These data suggest that two types of recovery occur. (3) When cycloheximide is present during the irradiation the drug prevents the radiation-induced dissociation of polysomes but does not induce a reaggregation of ribosomes previously dissociated by radiation. (4) Radiation blocks the recovery of polysomes from puromycin-induced dissociation but only during the period of exposure to the radiation. (5) Radiation blocks nearly all amino acid incorporation during the exposure period while 60% of the polysomes still remain intact. We can conclude that while radiation may interfere with initiation of protein synthesis, this cannot be the sole action of radiation on protein synthesis. A further effect on the systematic elongation and termination of polypeptide chains is proposed.