Cytoplasmic and nuclear basic protein synthesis during early sea urchin development

Abstract

Nuclear and cytoplasmic basic proteins were isolated from three early developmental stages of Strongylocentrotus purpuratus following a 1-h incubation in 14C-amino acids. The absorbance profiles of electrophoretically separated basic nuclear proteins from zygote and 32–64-cell stages are very similar. Both stages have three peaks of 14C-incorporation. One peak coincides with the F3 bands of carrier blastula histone and the other two peaks directly precede it. Very little absorbancy or radioactivity are associated with the other fractions of carrier histone. Blastulae raised in the continuous presence of actinomycin D contain nearly the same histone pattern as controls raised without the drug. This demonstrates that histones are translated during early development using stored maternal messages. Acid extracts of the crude microsomal fraction from 32–64-cell and blastula stages contain several very radioactive basic protein bands. These active proteins are extracted with the non-labeled ribosomal basic proteins and have the same electrophoretic mobilities as histones. Since similar migrating fractions are found in nuclei of blastulae but not the 32–64-cell stage, it is suggested that histones are made during early cleavage, but only a small portion immediately become an integral part of chromatin. The remaining fractions may be held in the cytoplasm for several cell divisions before becoming incorporated into chromatin at the onset of blastulation.