Chromatin superstructure: The next level of structure above the nucleosome has an alternating character. A two-nucleosome based series is generated by probes armed with DNAase-I acting on isolated nuclei

Intact nuclei were probed with DNAase-I-based probes and the resultant single strand pieces indicate that many or all of the nucleosomes exist in structures that cause every second nucleosome in a series to be resistant to attack. The effect is observed with chicken erythrocyte nuclei, rat liver nuclei and is weakly elicited by free DNAase-I. A method is described for the suppression of the intrinsic (CaMg) endonuclease of rat liver nuclei.