STUDIES ON SATELLITE DNAS OF DROSOPHILA-NASUTOIDES - THEIR BUOYANT DENSITIES, MELTING TEMPERATURE, REASSOCIATION RATES AND LOCALIZATIONS IN POLYTENE CHROMOSOMES

[摘要] The karyotype of D. nasutoides reveals a very large autosome pair at the metaphase plate. The application of the C-banding technique shows that this chromosome is almost entirely heterochromatic and an isochromosome. Examination of the DNA isolated from purified nuclei of D. nasutoides in neutral CsCl gradients reveals 4 major satellites. As much as 60% of the total DNA appears as satellites in the DNA from larval brains. The buoyant densities of the 4 satellites, designated as I-IV in the order of descending density, are 1.687, 1.682, 1.669 and 1.665 g/cm3, respectively. All 4 satellites show strand separations in alkaline CsCl gradients with the least separation in satellite III. Thermal denaturation studies with purified native satellites show that satellites I and IV consist of repeats of identical sequences, whereas satellites II and III show a large sequence variation between repeating units. As much as 10-24% base-pair mis-matching is observed in the reassociated satellite II. The sequence complexities obtained from DNA reassociation kinetics data are 5, 103, 2.3 .times. 106 and 46 nucleotide pairs for the satellites I, II, III and IV, respectively. The complexity of satellite III is almost as large as that of Escherichia coli, when the reassociation rate is corrected according to the amount of mismatching in this satellite. All 4 satellite sequences are localized in 1 chromosome (dot chromosome) according to in situ hybridizations to polytene chromosomes. The large heterochromatic chromosome seen at the metaphase plate appears as the dot chromosome after polytenization. Therefore, the large heterochromatic chromosome contains all 4 satellite DNA components.