Rat liver chromatin digested in situ with endogeneous Mg(2+)-dependent deoxyribonuclease exhibits two distinct DNA repeats.

Incubation of rat liver nuclei in the presence of 1.0-5.0 mM Mg2+ at 37 degrees C releases oligonucleosomes containing at least two distinct chromatin-DNA repeat elements. The 'short' repeat is derived from the dimer to pentamer series, while the 'long' repeat is found in the monomer and hexamer to decanucleosomes. Both repeat lengths decrease during enzymatic hydrolysis but in 5.0 mM Mg2+, which is optimal concentration, the 'long' repeat is degraded faster.