The Amino‐Acid Sequence of Histone H2A from Cuttlefish Sepia officinalis

The amino acid sequence of cuttlefish testis histone H2A (124 residues) was establijhed from structural data obtained by automated sequencing of large peptides generated by the cleavage of the protein with V8 staphylococcal protease or by limited chymotryptic hydrolysis. Compared to the calf thymus homologous histone, cuttlefish H2A shows 14 substirutions (most of them conservative) and 5 deletions. Extensive evolutionary changes were mainly observed in the basic amino‐terminal and carboxy‐terminal regions of the molecule, which are the primary DNA‐binding sites. Few punctual changes are observed in the central region (residues 18‐ 118), which interacts strongly with histone H2B to form the dimer H2A‐H2B.