An analysis of fish genomes by density gradient centrifugation.

DNA was prepared from 33 species of fishes representing 12 of the 31 orders of Teleostei and one order of Chondrichthyes. DNA samples were investigated to determine modal and mean buoyant densities in CsCl (Rho-0 and <Rho>), main-band asymmetry, intermolecular compositional heterogeneity and base composition. Modal buoyant densities ranged over 1.697-1.704 g/cm3, generally with identical or close values for DNAs from species belonging to the same order. Main bands were practically symmetrical in most cases; when present, asymmetries were on the heavy side of the band and rather modest. In most cases, compositional heterogeneities were equal to, or lower than, those of bacterial DNAs. Both the CsCl band symmetry and the low compositional heterogeneity strikingly distinguish fish DNAs from the DNAs of warm-blooded vertebrates and indicate a major discontinuity in genome organization in the vertebrates. The overall properties of the main bands of fish DNAs are very similar to those exhibited by the light components of DNAs from mammals and birds.