Renaturation properties and localization in heterochromatin of human satellite DNA's

Human DNA has been fractionated by centrifugation in an Ag+-Cs2SO4 preparative density gradient. Besides satellite DNA I and II, previously demonstrated and characterized, a newly identified satellite DNA III has been isolated, having a CsCl density of 1.696 g/ml and accounting for 1.5 % of the total genome. The renaturation properties of human satellite DNA III, estimated by determining its CsCl densities and melting curves after denaturation and renaturation, indicate that it is fast renaturing and therefore highly repeated, as are the other human satellite DNAs. The nuclei obtained from human placenta and leukemic leucocytes have been fractionated into heterochromatin and euchromatin. Satellite DNAs are enriched in heterochromatin, while they are no longer detectable in the DNA extracted from euchromatin, centrifuged in Ag+-Cs2SO4.