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Rates of Turnover of Deoxythymidine Kinase and of Its Template RNA in Novikoff Hepatoma and Neonatal Liver¹

Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77025

The stability of the messenger RNA responsible for the elaboration of 2'-deoxythymidine (TdR) kinase and the stability of the enzyme itself were determined by the use of actinomycin D and cycloheximide, respectively. The incorporation of uridine-¹⁴C into the RNA of the Novikoff ascites hepatoma cells in vitro was inhibited by more than 90% by actinomycin D at 5 to 50 µg/ml. Under these conditions, no alteration in the activity of TdR kinase was apparent. The template RNA for TdR kinase of liver from 1-day-old rats was also markedly stable to the actinomycin D treatment.

The turnover of TdR kinase in Novikoff ascites cells was determined under conditions in which the incorporation of aspartic acid-¹⁴C into protein was inhibited up to 90% by cycloheximide or puromycin. The half-life under these conditions was 3.5 hr. The half-life of the enzyme in neonatal rat liver was also in this range, i.e., 3.8 hr. This value is similar to that reported previously for the enzyme of control and regenerating rat livers.

¹ This research has been supported by National Science Foundation Grant NSF GB-8010 and Robert A. Welch Foundation Grant Q-198. Manuscript No. 8 from the Cancer Research Center, Baylor College of Medicine, Houston, Texas (Grant CA 10893).

² Lederle Medical Faculty Awardee.

Received 5/20/69. Accepted 9/10/69.