Figure 3.

Restricting Split Gal4 expression using the Split Gal4 repressor, KZip⁺. (A) As shown in the Venn diagram (left), the Killer Zipper (KZip⁺) can be used to exclude Split Gal4 activity from cells within an intersection. Where the activity of the enhancer used to drive KZip⁺ expression (Enhancer 3, purple circle) overlaps with that of the enhancers used to drive expression of the Zip⁺-AD (red circle) and Zip⁻-Gal4DBD (blue circle) constructs (see Figure 1B), Split Gal4 activity is repressed and no reporter expression is observed. This is illustrated in bottom-right panels, where the solid lines indicate the expression of all three constructs. Reporter expression is restricted to only that part of the intersection where Zip⁺-AD and Zip⁻ -Gal4DBD alone are expressed (upper right-hand panels; dotted lines). (B) Available Killer Zipper constructs include a basic KZip⁺ that can be expressed under the control of a specific enhancer (left) and several “universal” constructs that express KZip⁺ constructs under the control of LexA drivers. Two of the latter are shown (right), one of which bears a hemagglutinin (HA) tag and the other of which co-expressed a nuclear LacZ molecule. HA and nLacZ permit the detection of KZip⁺ expression in cells by immunostaining.