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 °C and a minor component with a density of 1.712 g/cm3 and a Tm of 93.5 °C. The complexity of the major component was estimated to be 3.8 × 105 daltons while that of the minor one was 12.9 × 107 daltons. Although cucumber satellite II banded as a single peak at adensity 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 °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 × 105 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 °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 × 105 daltons. Hybridization experiments revealed that the ribosomal DNA was present in satellite II.
Isolation and characterization of native at-rich satellite DNA from nuclei of the orchidCymbidium