ORIGIN OF CHLORAMPHENICOL PARTICLE PROTEIN

These experiments show that the majority of the protein found associated with the RNA synthesized in the presence of chloramphenicol is nonribosomal protein existing in the cells at the time of addition of the drug and hence that chloramphenicol particles are not incomplete ribosomes. The experiments are the following: 1. (a) The pool of free ribosomal protein as measured kinetically in normally growing cells is too small to provide the protein found on chloramphenicol particles, showing the chloramphenicol particle protein cannot derive solely from a pool of free ribosomal protein. 2. (b) The specific activity of chloramphenicol particle protein is independent of the time between a pulse labeling of cellular protein and the addition of the drug, showing that the protein found on chloramphenicol particles is not normally incorporated into some cellular structure from which it is unavailable to form the particles. 3. (c) The amount of protein which is synthesized in 90 minutes of chloramphenicol treatment is less than 3% of the protein found on chloramphenicol particles, showing that nearly all of the protein of the particles must have been synthesized before the drug was added. 4. (d) The specific activity of chloramphenicol particle protein parallels the specific activity of soluble protein and not ribosomal protein when the particles are prepared in cultures with different relative specific activities of ribosomal and non-ribosomal protein. 5. (e) Upon removal of chloramphenicol, the RNA of the chloramphenicol particles is matured to ribosomes while the protein previously sedimenting with this RNA is not found on mature ribosomes. © 1968.