Ribonucleic acid synthesis in the cell cycle of L5178Y mouse leukemic cells. Time of replication of the DNA template of rapidly labeled hybridizable RNA

Ribonucleic acid synthesis was studied at different times in the life cycle of a synchronized population of L5178Y mouse leukemic cells. The rate of RNA synthesis, indicated by the specific activity of the isolated RNA after a pulse label with ³H-5-uridine, approximately doubled as cells moved from G1 to S stage; the percent of hybridization of the RNA remained nearly constant. Since the percent of hybridization is the percent of the radioactivity in RNA which binds with DNA over the radioactivity in the RNA added, the rate of synthesis of hybridizable RNA must increase in proportion to that of total cell RNA. Hybridization-competition experiments did not reveal differences in base sequence between the RNA synthesized in G1 and that in S stage. Rapidly-labeled RNA hybridizes to the same extent with DNA synthesized at different times in the DNA synthesis period.