Bacterial polyribosomes and their participation in protein synthesis in vivo

Abstract

In several species of bacteria, polyribosomes are demonstrable in lysates prepared by osmotic lysis of protoplasts or by breakage of whole cells in a French cell. These components have a broad distribution of sedimentation coefficients ranging from 120 s to 400 s in Bacillus megaterium and from 120 s to 300 s in Salmonella typhimurium . They constitute about half of the total ribosomal material in B. megaterium and about one-third in S. typhimurium . They can be partially resolved into individual components by zone centrifugation through density gradients. These structures are converted to 70 s ribosomes by the action of ribonuclease. Labeling of growing cells with amino acids for short times leads to greater incorporation of radioactive material into polyribosomes than into single ribosomes. The subsequent addition of unlabeled amino acids results in faster removal of radioactive material from polyribosomes than from single ribosomes. This is taken as an indication of in vivo involvement of polyribosomes in protein synthesis.