Analysis of plant genomes. IV. Isolation and characterization of satellite DNA components from two dicotyledons cucumber (Cucumis sativus) and radish (Raphanus sativus).

Satellite DNA fractions from cucumber and radish, two plants having low DNA contents and relatively small chromosomes, were isolated and characterized. Reassociation studies of satellite and total nuclear DNA showed that the satellite fractions in these two plants contain most of the rapidly reassociating DNA. Cucumber satellite I was found to contain one major component (70% of the total satellite) having a density of 1.706 g/cm3 and a Tm of 90.5 degrees C and a minor component with a density of 1.712 g/cm3 and a Tm of 93.5 degrees C. The complexity of the major component was estimated to be 3.8 X 10(5) daltons while that of the minor one was 12.9 X 10(7) daltons. Although cucumber satellite II banded as a single peak at a density of 1.700 g/cm3 in neutral CsCl gradients, it was observed to have a rather broad denaturation profile with a Tm of 86.5 degrees C. Its Cot curve was also broader than that of satellite I and one of its components (40% of the total) had a complexity of 5.8 X 10(5) daltons. Two satellite fractions were also observed in the case of radish DNA but only satellite I was isolated in a pure form and characterized. This radish satellite formed a sharp, symmetrical peak at a density of 1.698 g/cm3 in neutral CsCl gradients and underwent denaturation in a narrow temperature range of 6 to 7 degrees C. An analysis of the optical reassociation kinetics showed that this satellite contained a major and a minor component. The major component, which comprised 80% of the satellite, had a complexity of 12.9 X 10(5) daltons. Hybridization experiments revealed that the ribosomal DNA was present in satellite II.