The phosphorylation of thymidine and the synthesis of histones in ammonia-treated eggs and egg fragments of the sea urchin.

Unfertilized sea urchin eggs may be preloaded with workable amounts of 3H-thymidine. After fertilizing the eggs or treating the eggs with ammonia, the preloaded thymidine is incorporated into DNA in amounts that are proportional to the number of chromosomes that are replicated. The phosphorylation of the internal thymidine is turned on by fertilization and ammonia treatment, but 3H-TTP does not accumulate because it is immediately used for nuclear DNA synthesis. Accumulation of 3H-TTP occurs only in ammonia-treated enucleate fragments in which no nuclear DNA synthesis can occur. Along with the phosphorylation of thymidine, the synthesis of histones occurs in ammonia-treated enucleate egg fragments.