Pools of Ribosomal Proteins in Escherichia coli. Studies on the Exchange of Proteins between Pools and Ribosomes

A labelling technique in vivo has been introduced which allows the tritiation of cell components with high specific activity during growth in rich medium. By this technique the pool size of each protein can be measured directly in the supernatant from centrifugation at 150000 times g. A measurable pool was found for the proteins S1, S2, S10, L1, L4, L7, L8/9, L10, L12, L21, and L25. Experiments on migration of ribosomal proteins from the supernatant to ribosomes (i.e. association) and vice versa (dissociation) demonstrate a remarkable constancy in the composition of the ribosome. There is no significant difference between ribosomes engaged or not engaged in poly-(Phe) synthesis.