The effect of distamycin A on heterochromatin condensation of Drosophila chromosomes

Larval neuroblasts of four species of Drosophila (melanogaster, hydei, virilis and funebris) were treated with distamycin A, a DNA ligand which induces distinct undercondensation in AT-rich heterochromatin. For each species the patterns of undercondensation were correlated with distribution of quinacrine-bright regions and of satellite DNAs. An overlapping of distamycin A-sensitive and quinacrine-bright heterochromatic regions was demonstrated for D. melanogaster and D. virilis, but not for D. hydei and D. funebris. Distamycin A undercondensation is thus a further criterion for resolving heterochromatin into different parts and enables identification of the steps of the condensation process within heterochromatic regions.