Phosphorylation of Deoxyribonucleosides and DNA Synthesis during Embryogenesis of the Sea Urchin

The phosphorylation of thymidine, deoxycytidine, deoxyadenosine and deoxyguanosine was studied during the embryogenesis of the sea urchin Hemicentrotus pulcherrimus. [3 H]Thymidine was taken up, phosphorylated and accumulated mostly as [3 H]thymidine triphosphate in the early cleavage stage embryos. As the embryos developed, the formation of [3 H]thymidine triphosphate decreased and most of the [3 H]thymidine taken up by the blastulae remained be phosphorylated. When [3 H]deoxycytidine was added to the cleaving embryos, the resultant labeled pool consisted of almost equal amounts of [3 H]deoxycytidine monophosphate and [3 H]deoxycytidine triphosphate. The formation of [3 H]deoxycytidine monophosphate increased up to 10 hr following fertilization and then decreased, while the formation of [3 H]deoxycytidine triphosphate decreased for 10 hr following fertilization and then gradually increased. [3 H]Deoxyadenosine was rapidly phosphorylated to monophosphate derivative in the cleavage stage embryos. The formation of [3 H]deoxyadenosine triphosphate increased rapidly after cleavage stage with a concomitant decrease of [3 H]deoxyadenosine monophosphate. The activity of phosphorylation in [3 H]deoxyguanosine to triphosphate derivative increased rapidly reaching a plateau 10 hr after fertilization. At this point, 80 % of the [3 H]deoxyguanosine was recovered as [3 H]deoxyguanosine triphosphate. Based on the above results, it was concluded that the profile of production of each deoxyribonucleoside triphosphate changed during the embryogenesis of the sea urchin, and the in vivo rate-limiting step of phosphorylation of the individual deoxyribonucleoside was assumed to be different.