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Fig. 3. So binds to the pros enhancer and activates transcription.
(A) The three putative So-binding motifs are highlighted in red within
the core-enhancer. These are also present in the mini-enhancer. (B)
Alignment of a consensus So-binding site and the three putative So-binding
sites. Essential residues are colored red; conserved residues are colored
blue. (C) A mobility-shift gel showing a complex that contains So
protein and labeled SoAE DNA. SoAE is a So-binding site identified in the
so gene autoregulatory element. Each reaction also contained a
50-fold molar excess of an unlabeled competitor DNA as indicated, except for
the reaction loaded into the leftmost lane, which did not contain competitor.
The SoAE(mut) competitor has a mutated So-binding site; the Lozenge competitor
contains a So-target sequence identified in the lz enhancer. The Pros
competitors contain the three putative So-binding sites from the pros
enhancer. (D,E) Transgenic core-enhancer-β-gal reporter expression
(green) in eye discs counterstained for Pros (purple). (D-D'') The
wild-type core-enhancer induces β-gal expression in the same cells that
express Pros. (E-E'') The core-enhancer with mutant So sites does
not induce β-gal expression. (F) Schematic of the approach to make
so(ey) and eya(ey) mutant eye discs. The
expression patterns of So/Eya in wild-type (left), so/eya
mutant (middle) and so(ey)/eya(ey) (right)
mutant eye discs are shown in red. In so(ey) or
eya(ey) eye discs, So/Eya expression is limited to cells
anterior to the MF (black line). (G-J) Expression of neural-specific Elav
(purple) and Pros protein (green) in a wild-type eye disc (G-G''),
an eya(ey) disc (H-H''), a
so(ey) disc (I-I''), and an
Lz-GAL4/+; UAS-soDN/+ disc
(J-J'').