Fractionation and characterization of satellite DNAs of the kangaroo rat (Dipodomys ordii)

Abstract

Nuclear DNA from liver cells of the kangaroo rat species Dipodomys ordii was fractionated and characterized with the aid of buoyant density gradients in neutral and alkaline CsCl and in Ag⁺ -CS₂SO₄. More than one-half of the DNA was present in three density satellites, a greater proportion than in any other species yet reported; the purified satellite DNAs were denser than principal DNA. All satellite fractions revealed sharp isopycnic bands and narrow denaturation profiles. Two had identical buoyant densities but differed substantially in T_m, base composition, and reassociation kinetics. In alkaline CsCl all three satellites, as well as a shoulder of intermediate repetitive DNA on the heavy side of the principal band, revealed unique strand densities. The most highly repetitive satellite was unus ually rich in (G + C) and contained 6.7% of 5-methylcytosine. A survey of internal organs and spermatozoa of an adult male revealed no significant differences in distribution of the satellites among tissues.