Histone patterns during early embryogenesis in the euchiuroid Urechis caupo.

Histones were isolated from nuclei of Urechis caupo unfertilized eggs and embryos from early cleavage through gastrula. Polyacrylamide gel electrophoresis showed the presence of a slow migrating H1s fraction in the egg which was replaced by a faster migrating H1 during development. Radioactive labelling showed no synthesis of H1s from fertilization up to gastrula and a high rate of synthesis of H1 relative to the other histones during cleavage and blastula stages.