AbstractA large part of the RNA made in presence of azaguanine is in a state of constant turnover. This RNA resembles pulse‐labeled RNA by its chromatographic properties as well. Polyribosomes do not form or they are very labile, indicating improper interaction between ribosomes and messenger RNA. The synthesis of enzymes,e.g., catalase and penicillinase, is completely inhibited under conditions which allow some polypeptide synthesis. This is not due to long‐lived messenger. No abnormal or modified pencillinase could be detected. During restoration by guanosine after azaguanine inhibition the different proteins are not made at the same pace. This may be due to a selective repression caused by accumulated abnormal RN