A destabilized DNA conformation associated with tightly bound nuclear proteins in active genes of rat myoblast

Purified nuclei from tissue cultured myoblasts were disrupted and centrifuged to equilibrium in a sarcosyl-caesium chloride gradient. A small portion (1.3% - 1.9%) of the non histone proteins (NHP) were banded with DNA in a high density region of the gradient. The DNA tightly bound to proteins representing about 0.6% of the total nuclear DNA was degraded after treating cell nuclei with S1 nuclease or DNAse I but resisted to mild micrococcal nuclease digestion. A large portion of the DNA sequences complementary to homologous RNA was concentrated in this DNA-proteins fraction. These finding suggest that a subset of NHP strongly associated to the active DNA regions play a role in the destabilisation of the double helical DNA during transcriptional processes.