Primary structures of mouse protamine genes and proteins. Schematic representation of the mouse (a) mP1 and (b) mP2 proteins. Numbers denote amino acid residues; the two exons in each protein are shown on bars below the proteins; important residues are indicated as shown in the key (using letters in the single-letter amino acid code, with a subscript number indicating the residue number). And, proposed DNA anchoring domains (regions containing 3 or more consecutive arginine and lysine residues). Proposed phosphorylation sites are amino acid residues identified to be phosphorylated in proteins isolated from sperm or following in vitro incubation of the isolated proteins of five mammalian species with cAMP-dependent protein kinase or protein kinase C.