DRASTIC CHANGE IN THE LEVEL OF ACTIN MESSENGER-RNA IN THE COURSE OF SYNCHRONOUS DIVISION IN TETRAHYMENA

Change in actin mRNA level was investigated in the course of synchronous division in Tetrahymena induced by intermittent heat treatment. The level of actin mRNA decreased from just after the end of the heat treatment (EHT) to 45 min after EHT, and then promptly increased before synchronous division at 75 min after EHT. In contrast, levels of the total RNA and mRNAs of Tetrahymena calmodulin and calcium-binding protein of 25 kDa (TCBP-25) increased gradually from EHT to synchronous division. Drastic change in mRNA level before synchronous division seems to be unique to actin mRNA. From the effects of actinomycin D (50-mu-g/ml) on both synchronous division and actin mRNA level, the increase in actin mRNA level starting from 45 min after EHT is speculated to be prerequisite for the oncoming synchronous division. The results of a nuclear run-off experiment supported the above speculation.