PT - JOURNAL ARTICLE AU - Tamás Schauer AU - Yad Ghavi-Helm AU - Tom Sexton AU - Christian Albig AU - Catherine Regnard AU - Giacomo Cavalli AU - Eileen E M Furlong AU - Peter B Becker TI - The <em>Drosophila</em> Dosage Compensation Complex activates target genes by chromosome looping within the active compartment AID - 10.1101/101634 DP - 2017 Jan 01 TA - bioRxiv PG - 101634 4099 - http://biorxiv.org/content/early/2017/01/19/101634.short 4100 - http://biorxiv.org/content/early/2017/01/19/101634.full AB - X chromosome dosage compensation in Drosophila requires chromosome-wide coordination of gene activation. The male-specific-lethal dosage compensation complex (DCC) identifies X chromosomal High Affinity Sites (HAS) from which it boosts transcription. A sub-class of HAS, PionX sites, represent first contacts on the X. Here, we explored the chromosomal interactions of representative PionX sites by high-resolution 4C and determined the global chromosome conformation by Hi-C in sex-sorted embryos. Male and female X chromosomes display similar nuclear architecture, concordant with clustered, constitutively active genes. PionX sites, like HAS, are evenly distributed in the active compartment and engage in short- and long-range interactions beyond compartment boundaries. By de novo induction of DCC in female cells, we monitored the extent of activation surrounding PionX sites. This revealed a remarkable range of DCC action not only in linear proximity, but also at megabase distance if close in space, suggesting that DCC profits from pre-existing chromosome folding to activate genes.