Restriction endonuclease analysis and nucleotide composition of satellite III DNA from Drosophila virilis

Satellite III DNA from $\text{Drosophila virilis}$ is composed of a tandemly repeated heptanucleotide containing the sequence which is normally cleaved by EcoRI¹ restriction endonuclease activity. However, we observed only a very limited amount of cleavage of satellite III DNA by this activity. Although methyldeoxyadenosine is known to block EcoRI¹ activity, no modified nucleotides were detected in satellite III DNA subjected to nucleotide composition analysis. Since the proportion of each nucleotide present was consistent with the heptanucleotide sequence, we speculate that the resistance of satellite III DNA to EcoRI¹ cleavage may result from the highly repetitive nature of this DNA.