Heterochromatin heterogeneity in Drosophila chromosomes detected by AluI-banding.

In situ selective digestion of mitotic chromosomes from three Drosophila species (virilis, hydei, and funebris), having a chromosome number 2n = 12, was achieved with AluI restriction endonuclease. The distribution of AluI-bands, revealing a heterogeneity within heterochromatin, was compared with that of quinacrine-bands observed in standard chromosomes. The results confirmed a species-specific AluI-banding pattern, heterochromatin being selectively digested in D. virilis and D. funebris, but unaffected by the enzyme in D. hydei. The overlapping of AluI-bands and Q-bands in D. virilis and in D. funebris is discussed, since these data seem to favour the hypothesis that the induction of AluI-bands does not depend only on the presence of enzyme targets, but also on a suitable conformation of the chromatin.