Construct used to investigate the functional properties of a DNA fragment from a polytene chromosome interband region. A w+mC reporter is flanked on one side by a HindIII-XhoI fragment from the 3C6/C7 interband (which contains the major part of an insulator) located between loxP recombination sites, and by the gypsy\su(Hw)BR430 insulator on the other side.