Shifts in nuclear and cytoplasmic nucleic acid content in temperature-synchronized Tetrahymena pyriformis (HSM)

Nuclei were isolated by exposing temperature synchronized Tetrahymena pyriformis (HSM) to Triton‐X‐100. Cell division synchrony was induced with a repetitive 12‐hour temperature cycle (9.5 hours at 13°, 2.5 hours at 29°). Increase in nucleic acid content was biphasic: primarily during the last two hours of the cold period well in advance of the synchronous burst of division and secondarily in the last hour of the warm period. Nuclear RNA content rises almost two hours ahead of cytoplasmic RNA which shows a maximum 0.5 hour before the onset of the warm period. The DNA content reaches a peak 30 minutes later. On the basis of these shifts there appears to be not net synthesis of nucleic acids during cell division. The changes in RNA/DNA of the isolated macronuclei and micronuclei suggest enhanced RNA turnover, loss to the cytoplasm and enhanced ribonuclease activity prior to cell division. Cytoplasmic RNA also appears to be subject to enzymic degradation.