Insulator body formation correlates with a reduction in chromatin-bound Su(Hw) that is rapidly restored upon return to isotonicity. (A) A media-treated salivary gland polytene nucleus labeled with CP190 showing the expected band pattern (insets, arrowheads). (B) A polytene nucleus stressed with 250 mM NaCl labeled with CP190 shows bodies in the nuclear periphery and interchromosomal spaces lacking DAPI (insets). (A and B) Boxed regions are enlarged in insets on the right. (C–E) ChIP of Su(Hw) at gypsy (C), 3L:12247800 (D), and homie insulators (E) in media, stressed, and recovery S2 cells. Asterisks mark reductions significantly different from media controls (Student’s paired t test, P = 0.05; error bars represent SEMs). Bars: (A and B, main images) 3 µm; (A and B, insets) 0.5 µm.