Satellite DNA in calf heterochromatin

Analysis of nuclear DNA from calf liver by Cs₂SO₄-Ag⁺ density gradient centrifugation revealed a minor heavy peak (7% of the total DNA) at a density of 1.57 g/cm³, a main peak at a density of 1.51 g/cm³ and a minor light peak (3% of the total DNA) at a density of 1.44 g/cm³. Upon fractionation of total chromatin into constitutive heterochromatin and euchromatin, DNA from the heterochromatin fraction showed the same three peaks but was enriched in the two satellite DNAs, while DNA from the euchromatin fraction showed essentially no satellite DNA. The complementary strands of the light satellite DNA were inseparable upon gradient centrifugation in alkaline CsCl, while those of the heavy satellite DNA separated to some extent. In neutral CsCl, the heavy and light satellite DNAs sedimented at densities 1.713 and 1.706 g/cm³, respectively, on the heavy side of the main peak (density = 1.699 g/cm³). Base analysis on the three DNA fractions indicated that the satellite DNAs are high in GC content in comparison to main DNA.