EFFECT OF ACTINOMYCIN D AND DL-P-FLUOROPHENYLALANINE ON RIBOSOME FORMATION IN TETRAHYMENA PYRIFORMIS

The effect of actinomycin D and dl‐p‐fluorophenylalanine on ribosome formation has been studied in exponentially growing Tetrahymena cells. Both compounds cause inhibition of ribosome formation. However, ribosome formation is qualitatively very similar in inhibited and uninhibited cells. p‐Fluorophenylalanine is incorporated into ribosomal proteins of completed ribosomal particles when used in inhibitor concentration (1 mg/ml). This demonstrates that limited modifications of ribosomal proteins, due to the presence of the amino acid analogue in the ribosomal polypeptide chains still allow the modified proteins to assemble with ribosomal RNA to give intact ribosomal particles. The p‐fluorophenylalanine containing ribosomes have normal physicalchemical properties with respect to dissociation into sub‐units by dialysis against low Mg++ concentration, sedimentation values in sucrose gradients and buoyant density in isopycnic CsCl gradients. The regulatory aspects of ribosome biosynthesis in the light of the present results are discussed. Copyright © 1969, Wiley Blackwell. All rights reserved