Thymidylate kinase from Acetabularia. II. Regulation during the life cycle.

The activity of dTMP kinase (EC 2.7.4.9) was estimated during the development of Acetabularia. Enzyme activity was increased at the beginning of the generative phase. Regulation of the dTMP kinase activity was observed even in the absence of the nucleus. More than 30 days after enucleation the enzyme activity increased two- to threefold. The increase in activity was inhibited by puromycin and cycloheximide but not by rifampicin and chloramphenicol. These results indicate that the enzyme is coded by the nuclear genome and translated on 80 S ribosomes. From mixing experiments with low-activity and high-activity cell extracts it is concluded that the regulation is due to de novo synthesis of the enzyme.