Histone analysis during the first cell cycle of development of the sea urchin Tetrapygus niger.

To obtain information on the contribution of paternal and maternal histone complement to the assembly of sea urchin chromatin after fertilization, we have compared the complete set of histones of zygotes obtained at the beginning of the first S phase those of sperm and unfertilized eggs of Tetrapygus niger. The electrophoretic pattern on acetic acid-urea polyacrylamide gels and the amino acid composition of the histones is isolated from zygotes are virtually identical with those isolated from unfertilized eggs. These results strongly suggest that sperm histones must be lost before the initiation of the first replication event. The histones of zygotes obtained after the completion of the first S phase have the same electrophoretic pattern as the proteins isolated from zygotes prior to the first S phase; however, differences were found in their amino acid composition. These results suggest that some new proteins may associated with chromatin during the first replication round in Tetrapygus niger development.