DETACHMENT OF RIBOSOMAL PROTEINS BY SALT .2. SOME PROPERTIES OF PROTEIN-DEFICIENT PARTICLES FORMED BY DETACHMENT OF RIBOSOMAL PROTEINS

We have examined certain properties of protein-deficient particles produced by detaching varying amounts of protein from Escherichia coli ribosomes with 0.5 m-NaCl, 1 m-NaCl or 2 m-LiCl. The particles are highly vulnerable to ribonuclease, and their sedimentation coefficients are very sensitive to changes in the ionic environment and in particle concentration. This behaviour does not seem qualitatively different from that reported for unfolded ribosomes from which no protein was detached, and would appear to be due more to the opening up of the ribosomal structure than to the removal of proteins per se. The removal of relatively small amounts of protein from ribosomes causes marked changes in the sedimentation coefficients; but with the detachment of less than half of the original protein, the coefficients approach a lower limiting value and become virtually insensitive to the further removal of protein, giving particles of different protein content which have the same sedimentation coefficient. The limiting value for particles formed in 0.5 m-NaCl is different from that for particles formed by treatment with 1 m-NaCl or 2 m-LiCl, making it possible in this case to form particles with the same protein content but different sedimentation coefficients. It is concluded that the sedimentation coefficient is not a reliable indicator of the amount or kind of proteins present in particles, and cannot be used as the sole basis for characterizing particles or comparing different particles. Biologically active 30 s ribosomes have been reassembled from inactive NaCl and LiCl particles and the proteins detached from them. © 1969.