The molecular organization of the very rapidly renaturing DNA sequences in Drosophila melanogaster: further evidence for a class of non-satellite simple sequence DNA.

Summary The simple sequences of Drosophila melanogaster DNA have been investigated after an extensive fractionation of the genome by actinomycin-CsCl and Ag + - Cs 2 SO 4 preparative gradients. In addition to the simple sequence satellites which occur in lengths with molecular weights greater than 10 million daltons, further evidence is presented for the existence of simple sequences of molecular weight less than 10 million daltons which are associated with less rapidly renaturing DNA. This pattern is a property of only a small number of the DNA fractions at 9.5 million daltons. It is not a generalized feature of the main band DNA sequences which are believed to be genetically active. Thus, the simple sequences investigated here represent a class different from that studied by Wu and Bonner [16, 17] which has slower renaturation kinetics and uniform distribution throughout the genetically active genome as 150 base pair long stretches of middle repetitive DNA spacing unique DNA sequences about 750 base pairs in length. The data presented here are consistent with the existence of a special class of non-satellite simple sequence DNA amounting to more than 10 p. cent of the genome and being associated with less redundant DNA sequences at 10 7 daltons, as proposed by Kram et al. [ 6 ].