Comparative analysis of proteins selectively released from cell nuclei of different eukaryotic species under conditions of mild hydrolysis by nucleases.

Nuclei of cultured Chinese hamster fibroblasts, dechoryonized eggs of Drosophila melanogaster, calf thymocytes and mouse spleen were digested with micrococcal nuclease or DNAse I under conditions when about 15-20% of nuclear DNA is hydrolyzed. Proteins released from the nuclei with this DNA were analyzed by electrophoresis in polyacrylamide gels in the presence of SDS and the most prominent components were purified in each case. It is shown that these components derived from different species have different electrophoretic mobilities but are very similar in the amino acid composition characterized by high glycine content and a low lysine/arginine ratio. Molecular weights of two of those components, from mouse spleen and thymocytes, were estimated and are shown to be 25,500 and 23,000, respectively. Notwithstanding their different molecular weights they have the same N-terminal amino acid--arginine.