RNA SYNTHESIS IN SYNCHRONOUSLY GROWING POPULATIONS OF HELA S3 CELLS .2. RATE OF SYNTHESIS OF INDIVIDUAL RNA FRACTIONS

The rates of synthesis of various species of RNA were examined in synchronously growing HeLa cells as a function of stage in the cell generation cycle. The synthesis of each RNA species examined occurs throughout interphase, but undergoes a two‐fold increase in rate during early S which is dependent on the duplication of DNA; blocking the initiation of DNA synthesis also blocks the acceleration of RNA synthesis. To explain the data, a model is discussed in which the acceleration of RNA synthesis during early S is regulated by the number of active cistrons present; thus, as the genome is duplicated, more template is available for transcription, and the rate of RNA synthesis increases. Some implications of the model, and experimental evidence bearing on them, are also discussed. Copyright © 1968 Wiley‐Liss, Inc.