Characterization of the repetitious human DNA families.

Human DNA isolated from HeLa cells or human placental tissue has been fractionated on hydroxyapatite at COt 1.0. The 25% of total DNA isolated at COt 1.0 is composed of 3% foldback DNA and 22% which renatures by second-order kinetics and can be resolved into five renatured DNA families banding at distinct densities in CsC1 gradients. The individual renatured DNA families were isolated and their physical properties including reassociation kinetics determined. A two-component kinetic analysis was used to resolve kinetic heterogeneity. The three lightest density DNA families possess satellite DNA-like properties. The two heaviest density DNA families were shown to contain reassociated highly repetitious DNA as well as single-stranded, middle-repetitious DNA sequences, suggesting interspersion. The middle repetitious DNA sequences are thought to be related in these two DNA families.