Figure 1. Testing the enhancer-blocking activity of the gypsy insulator in one copy.

Transgenic lines were grouped into those in which the gypsy insulator displayed (A) weak or (B) strong enhancer-blocking activity. (C) Homozygous transgenic lines in which the gypsy insulator displayed a weak enhancer-blocking activity. In the reductive scheme of the transgenic construct used in the assay, the white gene is shown as white box with an arrow indicating the direction of transcription; the triangle indicates deletion of the Wari insulator located at the 3′ end of the white gene; downward arrows indicate target sites for Flp recombinase (frt) or Cre recombinase (lox); the same sites in construct names are denoted by parentheses; the eye enhancer (E) is shown as white rectangle; the direction of the gypsy insulator (Gy) is indicated by the apex of the pentagon. The numbers of transgenic lines with different levels of white pigmentation in the eyes are indicated. Arrows indicate the excision of an element to produce the derivative transgenic lines. Wild-type white expression determined the bright red eye color (R); in the absence of white expression, the eyes were white (W). Intermediate levels of pigmentation, with the eye color ranging from pale yellow (pY), through yellow (Y), dark yellow (dY), orange (Or), dark orange (dOr), and brown (Br) to brownish red (BrR), reflect the increasing levels of white expression. N is the number of lines in which flies acquired a new eye color phenotype by deletion (Δ) of the specified DNA fragment; T is the total number of lines examined for each particular construct. z^v77h, a null-mutation of the zeste gene.