Model describing the mechanisms of enhancer blocking by the gypsy insulator.

(A) The chromatin loop formed by the interacting insulators is not sufficient for effective blocking of the enhancer–promoter communication coordinated by Zeste. (B) The gypsy insulators block the eye enhancer by two different mechanisms: the chromatin loop formed by interacting gypsy insulators induces physical constrains on the enhancer–promoter communication; the interaction of Mod(mdg4)-67.2 with Zeste interferes with the enhancer-promoter communication. (C) The gypsy insulators located in opposite orientation block interaction between the eye enhancer located within the loop and white promoter located outside the loop; (D) The gypsy insulators located in the same orientation bring together the eye enhancer located within the loop and the white promoter located outside the loop. (E) The gypsy insulator located on the 3′ side of the white gene interacts with the enhancer and promoter.