Mammalian chromatin substructure studies with the calcium-magnesium endonuclease and two-dimensional polyacrylamide-gel electrophoresis

The basic regularity of chromatin substructure that has been reported in rat liver chromatin (Hewish and Burgoyne) was also detected in mouse chromatin. The regular series of DNA fragments produced by the action of Ca Mg endonuclease on rat chromatin were studied further. The smallest single stranded class has a molecular weight of approx. 45,000 to 63,000 and the smallest double stranded class has a molecular weight of approx. 120,000 to 150,000. Studies of the substructure of the DNA fragments produced by the Ca Mg endonuclease have shown that the regular series of double stranded fragments have regular series of single stranded fragments within them. It was concluded that the regular series of double stranded fragments was probably a consequence of the regular series of single stranded fragments. Digestion time courses are presented for mouse and rat nuclear DNA.