Fig. 7. Iswi associates with Tou, Pnr and Chip and directly regulates ac-sc expression in vivo. (A) Iswi interacts with Tou in yeast. Expression vectors encoding the unfused LexA^DBD or the LexA^DBDIswi were introduced into L40 cells together with the VP16^AD (data not shown) or the VP16^ADTouA. Protein extracts were made from L40 transformants, grown in liquid medium, and assayed for ß-galactosidase activity (expressed as in Fig. 3B). (B) Iswi interacts with Tou in transfected cells. The transfected expression vectors are shown at the top of the panels. The layout is as in Fig. 3C. F-Iswi and B10-TouA are recognized by the M2 antibody and B10 antibody, respectively. (C) Iswi directly interacts with Pnr and Chip in vitro. (C) Autoradiographs of SDS-PAGE gels from representative affinity chromatography experiments performed with GST control beads (lane 2), GST DBD Pnr (lane 3), GST C^T Pnr (lane 4), GST Chip beads (lane 5) and in vitro translated ³⁵S proteins as indicated on the left. One-tenth of the ³⁵S input is shown in lane 1. Luciferase is used as a negative input. (D) Model on how Tou, Iswi and the Brm complex regulate activity of the proneural complex during enhancer-promoter communication at the ac-sc locus. Tou and Iswi positively regulate proneural expression and may belong to a complex with antagonistic activity to that of the Brm complex (Heitzler et al., 2003). The complex containing Tou and Iswi regulates activity of Pnr and Chip during enhancer-promoter communication, possibly through chromatin remodelling.