POLYRIBOSOME METABOLISM IN ESCHERICHIA COLI TREATED WITH CHLORAMPHENICOL, NEOMYCIN, SPECTINOMYCIN OR TETRACYCLINE

When chloramphenicol, neomycin, spectinomycin or tetracycline is added to growing cells at levels sufficient to block nearly all protein synthesis, polyribosome formation continues: pulse-labeled mRNA still joins to ribosomes at rates comparable to that in untreated cells. The mRNA accumulates in polyribosomes until there is several-fold more than in growing cells. Ribosomes in these polyribosomes seem to be 30 s-50 s ribosome couples, each bearing two or more tRNA molecules. In control studies carried out during and after cell lysis, neither pulse-labeled cellular RNA nor f2 phage RNA joined to ribosomes efficiently in the absence of an added source of energy. Thus, the formation of polyribosomes probably takes place in drug-treated cultures and is not an artifact of lysis. We propose that the antibiotics uncouple polyribosome formation from peptide bond formation. Movement of ribosomes along mRNA could continue to be based on apposition of tRNA molecules to corresponding codons. Each successive aminoacyl-tRNA would transiently reside in the peptidyl-tRNA site of the ribosome. © 1969.