Fig. 1. The L27 domain of DLG-1 is necessary for the AJM-1–DLG-1 physical interaction and for DLG-1 multimerization. (A) Schematic showing the structure of the DLG-1 deletion proteins fused to the LexA DNA-binding domain. Constructs were co-transformed with a Gal4–ajm-1 (encoding amino acids 180-809) fusion. Deletions of the L27 domain abrogated the AJM-1–DLG-1 interaction. DLG-1 multimerization was also assayed by transformation of yeast with LexA–dlg-1 deletion constructs and a Gal4–dlg-1 fusion. Physical interaction was observed in constructs containing the N-terminus and the first two PDZ domains of DLG-1; this interaction was disrupted by removal of the L27 domain. (B) lacZ activity of yeast co-transformed with LexA–dlg-1 deletion constructs and Gal4–ajm-1. Numbers on the streaks correspond to the bait constructs from A. lacZ activity was detected in all streaks except 2 and 3. (C) lacZ activity of DLG-1 multimerization. Yeast were co-transformed with Gal4–dlg-1 and LexA–dlg-1 deletion constructs. lacZ activity was observed in streaks 1, 4, 5 and 6. Both streaks 2 and 3 lacked detectable activity.