Methylation of nuclear proteins during early embryogenesis in sea urchin.

Isolated sea urchin embryos nuclei incubated in vitro in presence of the methyl donor, S-adenosylmethionine, methylated their own nuclear proteins, following a typical enzymatic reaction pattern. In fact, the methylation activity showed a linear increase in time of incubation and in nuclear proteins concentration. The Km app. was found to be the same in nuclei isolated either from blastula or from gastrula stage; moreover a second value of Km app. was also found at gastrula stage. Otherwise it has been demonstrated that the methylase activity is stage dependent, with a maximal value in nuclei isolated from blastula with primary mesenchyme and that in our conditions the only methylated nuclear proteins are the histones H3 and H4.