A high molecular weight nuclear basic protein from the bivalve mollusc Spisula solidissima.

A basic protein has been isolated from sperm of the bivalve Spisula solidissima. Its characteristics are reminiscent of both histone H1 and of fish protamines. It is unusual in several respects: it contains similar amounts of lysine (24.8%) and arginine (23.1%), plus a residue of tryptophan per molecule. Its size is very large, approximately 297 amino acid residues. It shows a tendency to aggregate, an unusual property given the strongly charged nature of this protein.