Regulation of ribosomal and transfer RNA synthesis

Chloramphenicol (CM) initially accelerates the synthesis of transfer as well as ribosomal RNA when cells are growing in minimal medium. This effect is absent in an amino acid medium. High concentrations of CM, which inhibit most protein synthesis, relieve the need for an external supply of a required amino acid for RNA synthesis. However, a lag precedes the resumption of RNA synthesis when CM is added to amino-acid-starved cells. These results suggest that the rate of RNA synthesis is determined by the internal amino acid concentration. This may be accomplished by a repressor mechanism in which the transfer RNA acts as repressor and amino acid adenylate as inducer. At high CM concentration, the rate of RNA synthesis decreases progressively with time. At intermediate CM concentrations the amount of protein synthesized is paralleled by an increase in RNA synthesis, over and above the fixed amount produced at CM concentrations which completely block protein synthesis; i.e. concentrations exceeding 50 μg/ml. In 110 min at 25°C this fixed value amounts to half the normal RNA production. Under these conditions the synthesis of ribosomal RNA decreases steadily whereas transfer RNA is synthesized at a constant rate. The data suggest that a protein present in log phase cells is necessary for and consumed during the synthesis of ribosomal RNA. This protein is probably the protein component of the CM-particles.