Data are presented for sequence-specific chromatin-loop organization in histone-depleted nuclei from Drosophila melanogaster Kc cells. We find one loop for each of the tandemly repeated histone gene clusters. The attachment site is localized in the A + T rich H1-H3 spacer on a 657 bp fragment. In the cluster of the hsp70 heat-shock genes, in both control and heat-shocked cells, we find two attachment sites in close proximity upstream of regulatory elements. The transcribed sequences are not associated with the nuclear scaffold in control or in heat-shocked cells. A family of attachment sites related by hybridization to those of the hsp70 genes was discovered.