The sperm nucleus of Aulacomya ater, family Mytilidae, order Mytiloida, contains three proteins (X, Aa5 and Aa6) which are specific of this cell. These proteins have been isolated by CM chromatography and preparative electrophoresis. Electrophoretic analysis, amino acid composition, M r determination and tryptic digestion show that protein X corresponds to a histone-like protein whereas Aa5 and Aa6 are protamine-like proteins.
