Avian erythrocyte chromatin degradation: the progressive exposure of the dinucleosomal repeat by bovine-pancreatic-DNAase-I-armed probes and free DNAase-I.

Bulky probes composed of glutaraldehyde-cross-linked-complexes of ferritin or bovine serum albumen armed with bovine pancreatic DNAase-I have been used to generate the typical dinucleosome-based series of native or denatured DNA fragments from chicken erythrocytes. Double stranded DNA fragments have shown that the 2N series extends to at least 10N without any clearly defined end-point. The susceptible nucleosomes were observed to be nucleolysed by two major, different methods of attack that generated multiple peaks in the dinucleosomal size class and some characteristics of the digestion patterns have been taken as indications of the presence of another level of structure above that of the alternating structure. The chromatin structure becomes resistant to the probes when the average fragment length falls to approximately 4N but this 'core' is not a single integral multiple of nucleosomes.