The sea urchin (Sphaerechinus granularis) codes different H2B histones to assemble sperm and embryo chromatin.

Histones from sperm and gastrula nuclei of the sea urchin Sphaerechinus granularis were analyzed by three different electrophoretic methods, stained with specific color reactions and compared with one another. The histones of the two cell types showed identical properties in none of the three analytical methods employed but the greatest differences involved the H2B type of histones. H2B from embryo chromatin had properties similar to those of the corresponding molecule from calf thymus. In the sperm chromatin no such molecule was observed but two additional ones were found that differed from embryo H2B in size, charge and specific colour reactions. The differences were such that different genes may be postulated for the synthesis of the H2B histones found in sperm and in embryo.