Micronuclear RNA synthesis in Paramecium caudatum.

In a generation time of 8 hr in Paramecium caudatum, the bulk of DNA synthesis detected by thymidine-(3)H incorporation takes place in the latter part of the cell cycle. The micronuclear cycle includes a G(1) of 3 hr followed by an S period of 3-3(1/2) hr. G(2) and division occupies the remaining period of the cycle. Macronuclear RNA synthesis detected by 5'-uridine-(3)H incorporation is continuous throughout the cell cycle. Micronuclear RNA synthesis is restricted to the S period. Ribonuclease removes 80-90% of the incorporated label. Pulse-chase experiments showed that part of the RNA is conserved and released to the cytoplasm during the succeeding G(1) period.