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An analysis of the bovine genome by Cs2SO4-Ag density gradient centrifugation
Authors:J Filipski  J P Thiery  G Bernardi
Affiliation:Laboratoire de Génétique Moléculaire Institute de Biologie Moléculaire Paris 5 °, France
Abstract:Calf DNA preparations having molecular weights of 5 to 7 × 106 have been fractionated by preparative Cs2SO4—Ag+ density gradient centrifugation into a number of components. These may be divided into three groups: (1) the main DNA component (1.697 g/cm3; all densities quoted are those determined in CsCl density gradients), the 1.704 and 1.709 g/cm3 components form about 50, 25 and 10% of the genome, respectively; they are characterized by having symmetrical CsCl bands and melting curves, both of which have standard deviations close to those of bacterial DNAs of comparable molecular weight, and by their G + C contents being equal to 39, 48 and 54%, respectively; after heat-denaturation and reannealing, their buoyant densities in CsCl are greater than native DNA by 12, 10 and 3 mg/cm3, respectively. (2) The 1.705, 1.710, 1.714 and 1.723 g/cm3 components represent 4, 1.5, 7 and 1.5% of the DNA, respectively, and exhibit the properties of “satellite” DNAs; their CsCl bands and melting curves have standard deviations lower than those of bacterial DNAs; after heat-denaturation and reannealing, their buoyant densities are identical to native DNA, except for the 1.705 g/cm3 component, which remains heavier by 5 mg/cm3; in alkaline CsCl, only the 1.714 g/cm3 component shows a strand separation. (3) A number of minor components, forming 1% of the DNA, have been recognized, but they have not been investigated in detail; two of them (1.719 and 1.699 g/cm3) might correspond to ribosomal cistrons and mitochondrial DNA, respectively.
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